I’ve mentioned in some other posts that our optical tools can do a lot more than just test a lens’ MTF. For most of the last two years, though, testing MTF is what we’ve been doing. We may not seem all that busy, but we’ve assembled what is probably the world’s largest database of current camera lenses; approximately 1,500,000 measurements on 1750 copies of 330 different lenses from 15 manufacturers.
Recently, though, we’ve started exploring some of the other testing available to us. Partly that’s because we’re geeks and like doing this stuff, and partly because we’re looking for more and better ways to test lenses. One of the things we’ve been doing a lot lately is looking at field-of-focus curves. There is a LOT of information in field-of-focus MTF testing, enough that makes it worth doing them even though each takes a lot longer than a standard MTF test.
This is an introductory article – one where we’re showing you what we’re finding out as we’re finding it out. If you already understand all about field vs focus graphs you won’t get much here. But if you don’t, this should be a nice, painless introduction to some of the new testing we’re doing.
So What Are Those Amazingly Gorgeous Graphs, Anyway?
Officially, they’re called an MTF vs Field vs Focus graph and gorgeous part comes from software written by uber interns Markus and Brandon. They’re fairly intuitive, but also have a lot more information in them than you might realize so let’s talk about what they are and how they are made.
Let’s start with a regular MTF graph. Many of you have seen them. Many of you don’t really understand them, but that’s OK. The MTF vs Field vs Focus graph are actually simpler in many ways and you don’t really need to speak MTF to appreciate them. So read along for a second.
Notice the regular MTF graph above goes from 0mm of image height to 20mm along the horizontal axis. Image height isn’t a good word for us photographers. It really should read ‘distance from center toward the side of the sensor’. The center is “0”, one edge is “20”.
The raw data the optical bench gives us actually goes from -20mm to +20mm, that is from one side of the sensor to the other, like the graph below. To make that graph above, we actually average all the measurements from both sides of center and and plot them as though it was showing one side (from center to edge). The actual information that comes from the optical bench puts the center in the middle and shows both sides, like this.
So, the takeaway here is “Field” is from one side of the camera sensor to the other. The field is also called ‘Image Height’ by Geeks who measure stuff in labs, so in the graphs ‘field’ or ‘image height’ both mean distance away from the center of the image.
When we make an MTF curve like those above, we set the lens to infinity focus and lock the focus ring in that position. (Locked is a technical term meaning ‘stuck some gaffer tape on the focus ring’.) The Optical bench then fine-tunes focus, determining the exact focus position at which the MTF is highest at the center of the lens. It’s very accurate, measuring focus in 5 micron increments. (In case you don’t know, the infinity mark on a photo lens means ‘around infinity’. On a Cinema lens it should be accurate, but still might not be 5 microns of focus accurate.) Once the optical bench has determined the best focus, it measures the MTF from one side of the lens to the other, remaining at that ‘best for the center of the lens’ focus position.
In photographic terms, if you used center-point autofocus on a fence at right angles to you, the MTF curve would show you how sharp that fence would be from one side of the image to the other. People might look at that photograph, though, and say “Halfway from center, the grass in front of the fence is in better focus than the fence, and at the edges the grass behind the fence is in better focus.” That’s commonly called field curvature, but probably better described as plane-of-focus curvature.
Another related comment is “If I used the left sided autofocus point, wouldn’t the MTF (OK, they’d say sharpness, but I’m being all technical here) be better for that part of the fence? The answer is probably yes. But if you do that, probably the center would not be as sharp. Because the best focus at that part of the fence may well not be the best focus for the center of the fence.
When we do a Field vs Focus the optical bench is set differently. At each point, it measures and records the MTF over-and-over as the focus is slowly changed through an 60 micron range. (These graphs are labeled from 0.6 to -0.6, which is incorrect, but I’m not going to remake all the graphs since it’s not really important for this article.) At each focus point the MTF is recorded. So the vertical axis of the graph of MTF vs focus position. The 0,0 point in the center of the graph is best center focus. As you go from left to right across the image, you can see that the best focus can be in front of, or behind, where the best focus point at the center of the image.
This is why MTF vs. Field vs. Focus is in many ways a better test than just MTF. For every point across the image, it shows you where the best focus is located and what the best possible MTF is at that location.
We’re measuring our curves at f/5.6 so the focus range is rather thick. This is mostly because it smooths out the graphs and shows the shape of the field well. Wide open, many lenses get so soft off axis that it’s harder to see the shape of the field. And f/5.6 gives us a ‘common aperture’ that all lenses can reach so the graphs will be similar.
The MTF Part
In these graphs, MTF is represented as a color, with red as the highest (sharpest) and blue as the lowest. There’s a key on the right side and some outlines around each area on the graph showing you the MTF to the nearest 0.1. So you know the red area in the graph above is an MTF of > 0.8 for example, orange is 0.7 to 0.8, etc.
We lose some MTF information, though, compared to a standard MTF graph. It’s a fair trade for the new information we get, but still there is some loss. One thing you may have noticed in the graph above, the curves are done at 30 lp/mm. The standard MTF graph shows us MTF at multiple frequencies, but for this graph we have to chose one of those. The curves are very, very similar at all frequencies, though, so this isn’t too much of a loss.
One other thing some of you probably noticed; the graph above was for just the sagittal component of the MTF. We can’t plot both the sagittal and tangential curves on this graph like we can a regular MTF graph. (If you don’t understand sagittal, tangential, and astigmatism very well, I recommend this excellent article by Paul van Walree). So we have to make two graphs for each lens; one sagittal and one tangential.
The example above is for an individual copy of the Canon 35mm f/1.4 Mk II lens and it shows a couple of important things. First, the curvature of the sagittal and tangential planes are different: the sagittal plane has a wide M-shaped curve, while the tangential is (overall) rather flat. So there is some astigmatism in this lens, although not much. Second, the tangential curve isn’t quite symmetrical, it’s a little different on the left than the right. This is a copy variation effect. This copy is a bit decentered, although not enough that you can tell it on anything other than an optical bench.
So How is This Useful?
Actually, I’m going to take up several blog posts talking about we might use these. But lets start with one: knowing a lens’ field of focus curve can be helpful when ‘choosing’ or ‘using’. Let’s say I’m considering buying a 50mm wide-aperture prime lens. Or let’s say I already have one and want to get the very most out of it.
Knowing what the field of focus looks like can help me choose the best 50mm for the kind of photography we do. If I already have one, it can help us frame a shot for the strength of my lens. Not many of you have considered it, because you don’t have a handy reference for field-of-focus curves. (Some of the best photographers figure it out when they add a new lens to their bag, though.)
One important thing to note: When our field of focus curve is moving towards the top of the graph, the focus curve of your image is moving towards the camera. Think of the camera as sitting a couple of inches above the graph and focused down toward the center of the graph. The field of best focus in the graph would then look like the field of focus would from the camera. I’ll give you an example later.
Let’s look at the field curvatures for some 50mm lenses. I’ll make a few comments as we go and then some overall comments after.
One thing that should be apparent is the tangential field for this lens is generally not as sharp as the sagittal field, even stopped down to f/5.6. Another is that the fields are entirely different shapes (they are for most lenses). It should be intuitive that out near the edges this lens will be astigmatic. Well, maybe not at f/16, but did you actually buy a wide-aperture prime to shoot at f/16? The field curve is a good demonstration of why the MTF curve has marked astigmatism at the edges.
The inexpensive 50mm Canon has a more extreme sagittal “M” than the f/1.2 lens did, but the tangential field is quite flat. We would expect this lens to have some astigmatism in the 10mm to 15mm off axis area (the middle third of the image) even stopped down, but that it would have less astigmatism near the edge. Also you can see that the tangential and sagittal fields are more evenly sharp in this lens.
And I guess this is a good example of why you don’t spend an extra thousand dollars for f/1.2 if you plan to shoot at f/5.6.
The Sigma has a very slight M curve in the sagittal field, and a fair U curve in the tangential field. The designer has actually used this effect to cross the astigmatisms back-and-forth so there’s never a lot of astigmatism, as you can see on the standard MTF curve.
Also notice how the sharpness (at f/5.6 remember) stays good out to the very edge of the image. One point that is apparent here, and useful to know if you’re shooting landscapes and architecture: in the middle third of the image (from about 10mm to 15mm from the center of the sensor) both fields are curving in the same direction. So a two dimensional subject, like the fence I talked about above, or the test chart you’re shooting in the basement is going to focus in a slightly different plane than the center.
When the Sony Planar T 50mm f/1.4 ZA was first released, people commented that it had a different look than other 50mm lenses they were shooting with. The field curvature shows part of the reason why (and also why this is not just a Zeiss remake). The sagittal plane of the Sony is extremely flat; the most supine of any 50mm lens. The tangential plane has a different curve than the others (and like the Canon 50mm f/1.2 is not quite as sharp as the sagittal plane). This is part of the different ‘look’ of the lens. It also tends to make the field of focus flatter than the other 50mm lenses.
The Zeiss Makro Planar f/2 has a more accentuated curve, with pronounced sagittal “M” and tangential “U” curves. You’ll see in subsequent posts that this sort of a Zeiss look; a lot of their primes have similar curves. Actually if you overlay the two curves in your mind, you realize that out to 15mm (3/4 of the way from center to edge), the curves are almost identical, meaning there’s very little asigmatism until you get in the outer 1/4 of the image.
For those who can’t overlay the curves in their mind, I’ll do it for you. Here’s a simple image where I put the two field curves over each other, then used the Photoshop difference filter. That dark area in the center is where there is virtually no astigmatism.
On the other hand, the curve of that dark area shows how the field of focus curves in your shot, too. Remember, though, this is the field of focus at infinity. This is a Makro lens so it has a much flatter field at close distances. Non-macro lenses usually don’t change their field of focus all that much at closer range.
The Otus is a unique lens and I think the field of focus curves show another way that it’s special that the standard MTF chart doesn’t show. Although not exactly the same, it should be readily apparent that the sagittal and tangential fields for this lens have very similar curves. It’s the only 50mm we’ve seen that is this way, although the Sony and Sigma lenses were to some degree.
You will probably notice the very slight tilt in the copy of the Nikkor 50mm. Please ignore it, it’s not significant for today’s discussion. This lens has a fairly typical sagittal plane curve, similar to the Canon or Zeiss 50mm lenses, and a tangential field that has a bit of a U curve. You should be recognizing this pattern as fairly typical for 50mm lenses. That isn’t surprising since almost all of 50mm lenses have a double-gauss core design; we’d expect most of them to be somewhat similar.
So Why Do We Care?
Well, for several reasons, I think, only some of which are apparent from this introductory post. I’ll be doing several posts about this over the next week showing you some other things we’re using field curvatures to look at.
Knowing the field vs focus curve of a lens can sometimes help you as you frame a shot, or even choose a focus point. You can certainly see how using an outer focus point for several of these lenses will put the center off focus, or how if you focus-recompose you may get some unexpected change in focus. Having an idea of how the field of focus of your lens is shaped can be quite useful.
Let’s do that example I promised earlier. Here’s a repeat of the summary graph I made of the two fields for the Milvus 50mm f/2 lens.
In theory, for a shot at distance we would expect the field of best focus to curve towards the photographer a bit as you go from center towards the edge, then get kind of astigmatic and softer at the very edge. Our lab graph, because it’s magnified, is going to curve more than a photograph would, but the pattern should be similar. So I took a Milvus out to a hill behind our office and lined up shots from a position nearly parallel to the slope.
Then I took f/2 shots at a couple of different focused distances on the slope (the tall grass was almost at infinity focus), and ran Photoshop’s find edges filter to find the areas of sharpest focus (grass is nice for this because it becomes just a dark area when you downsize the image).
Focused a few feet back
Focused on the tall grass at the top of the hill.
The curvature of the field of focus seems pretty obvious and agrees with what I expected from the lab results. Depending on what you’re going to shoot, knowing this might be useful when choosing a lens. (You can quickly correct for distortion in post processing, but it’s harder to correct for out-of-focus areas.)
Oh, and remember I mentioned that the 50mm Makro has less field curvature when close, and almost none at macro distances? Here’s the same treatment on a shot of some mulch at about 2 meters distance. There are some other variables here, but I think the field looks flatter, although not as flat as it would at true macro range.
If you’re in the market for a 50mm lens and want to shoot a lot of architecture, than a curved field like the Zeiss 50mm Makro might not be your best choice (yes, I know it wouldn’t be your best option for lots of reasons other than this). It should also be pretty obvious, though, that you can take your lenses out and do just what I did above to get a good idea of what the field of focus curve looks like for any of the. All you really need is a grassy field, or a mulch bed, and Photoshop.
That might not give you as clear a picture of astigmatism as the lab graphs do, though. Astigmatism has quite an effect on bokeh, so knowing where areas of inevitable astigmatism are might help you frame or crop your shots.
Of course, you might not care a bit. Our next post will simply be putting up the field curvatures for a number of prime lenses of different focal lengths, giving you a resource for that. If people find them useful, we’ll start posting more of them. If nobody cares, we’ll just make framed prints of them to decorate the office.
There are other interesting things we are trying to do with field curvature, though, and I’ll get to those in later posts. First among these is adding field curvature to our screening tests. The curves I showed you today are hand picked to be nice and fairly level. In a later post I’ll show you how sample variation causes tilts of the field. It’s an interesting explanation for what many people call decentering. Once you see it, you’ll be able to test for it at home, BTW. But be patient for a bit. Doing this stuff takes time.
Roger Cicala, Aaron Closz, Markus Rothaker, and Brandon Dube
Each year in Cologne, Germany, over 150,000 people travel from all over the world to attend Photokina – the world’s largest photography trade show. This is also where various photography brands work to announce their newest flagship products, which will be used by millions for years to come. With Photokina coming to a close this weekend, we decided we should look through all of the new product announcements, and highlight our favorite announcements from this year’s giant trade show.
Perhaps the largest announcement for price conscious videographers came with the Panasonic GH5. The GH series has been respected in the videographer industry for a number of years, bringing pro-level features to a small, and budget friendly system. Panasonic decided to continue their GH series and announced the development of the GH5 at Photokina this year. With 4K/60fps, the GH5 looks to be a promising new system, and the most interesting feature comes in its 6K Photo mode, allowing you to pull ~18MP images from video footage. The downside? No release date was set (aside from early 2017), nor was any price mentioned in the press announcement.
Olympus E-M1 II
Olympus also showed up and announced a continuation to their beloved E-M1, with the Olympus E-M1 Mark II. In short, the E-M1 II has speed in mind, pulling 60 frames per second (in jpeg) and an incredible 18fps with 20.4MP RAW files. It also has High Res mode, allowing for 50MP photos, as well as 4K video functionality at 30fps, and Image Stabilization built into the body. No price point or release date set, though it’s planned to hit shelves within the next 6 months.
To use with that new Olympus E-M1 II announced above is a new lens for their Micro Four Thirds systems, with the Olympus 25mm f/1.2 Pro Lens. At f/1.2, this lens is incredibly fast, and at a 50mm equivalent focal range with a 35mm sensor. Weather-sealed, and packed with high-quality glass, the 25mm f/1.2 is expected to give exceptional image quality to those who are shooting with Olympus systems. The Olympus 25mm f/1.2 Pro series is expected to arrive sometime in the next month.
Sony also showed the loyalists to the Sony A-mount system a bit of respect, with the Sony A99 Mark II. In short, the A99II has a 42.4 full frame CMOS sensor, 4K at 30fps, 12fps shooting, 5-axis image stabilization, and wifi and NFC built in. In short, it’s essentially a Sony a7R Mark II in an a99 body. So if you’re sticking to the A-mount systems and were hoping for a refresh to the camera line Sony has been seemingly neglecting, your new flagship system is here.
Panasonic Lumix G85
Panasonic wasn’t done with their announcement of the GH5 this year either, they also offered up their Lumix G85 system. With 4K at 30fps/24fps, and weather sealing packed into a micro four thirds mirrorless system, the G85 looks to be an excellent system for those who are wanted all the features found in the high-end systems but want a smaller form factor along with a smaller price tag to boot.
From the moment that Sigma unveiled their Art series lenses back in 2012, with the much beloved Sigma 35mm f/1.4 Art, everyone has been asking Sigma the same question – when is the 85mm Art series coming? Those who have been eagerly waiting for this announcement can finally get some rest, as the Sigma 85mm f/1.4 Art series is finally here. Available soon for Canon, Nikon, and Sigma systems, the 85 Art is expected to wow critics everywhere, and I know Roger and Aaron are eagerly waiting to get one to take apart. We’re expected to have these in stock in October.
Sigma also announced an ultra-wide angle zoom hoping to compete with the well-respected Canon 11-24mm f/4 and the Nikon 14-24mm f/2.8G. Available in October for Canon, Nikon, and Sigma mounts, the Sigma 12-24mm f/4 is expected to be a monster for those landscape photographers who need something wide.
Sigma 500mm f/4 Sports Series Lens
Sigma also announced a monster of a telephoto lens, with their Sigma 500mm f/4 DG OS HSM Sports Lens. With the build quality you’ve seen from Sigma over the last few years, the 500mm f/4 Sports is a weather sealed telephoto with built-in Optical Stabilization. However, unlike Sigma’s usual pricing at $800-1600, the Sigma 500mm f/4 Sports is expected to arrive for Canon, Nikon and Sigma in late October for $6,000.
With seemingly millions of other sports action cameras coming out over the last few years, GoPro has sort of shifted from the spotlight. But they’re hoping to regain some of their old momentum with the announced of the Hero5 Black edition. Ditching the clear plastic casing found on previous models, the Hero5 is sleek and comes with a plethora of new features. For one, Voice Control and a built-in Touch Screen are now standard, along with built-in image stabilization and ofcourse waterproofing. And with 4K at 30fps, the new GoPro Hero5 looks to be a promising upgrade to GoPro’s system, and will be available Oct 2nd.
Profoto also came guns blazing, and showed off the new Profoto D2 studio strobe. With incredible speed, the Profoto D2 has a flash duration as low as 1/63,000th of a second and allows up to 20 flashes per second at lower power. And with 10 full stops of power, the D2 is a nice upgrade to their previous monolights, the Profoto D1. The Profoto D2s are available now.
Profoto TTL-S Trigger System
Also announced by Profoto this year was the newest trigger allowing for HSS and TTL with the Profoto B1, Profoto B2 and Profoto D2 lights on Sony systems. The TTL-S is much like the Canon TTL-C and Nikon TTL-N that came before it, but for the Sony alpha series of cameras. Allowing for complete control and pairing of Profoto lights on Sony systems, this is exciting, as Sony is finally getting some attention from third party product manufacturers.
It wouldn’t be a Photokina without a groundbreaking announcement and surprise, and Fuji were the big winners with their announcement of the Fuji GFX 50S. In short, the GFX is a monster, packing a 51.4mp Medium Format sensor into a (fairly) small mirrorless system. Using a Bayer Array sensor, the Fuji GFX is hoping to steal some of the attention away from Phase One and Hasselblad in the medium format race, showing that exceptional digital medium format image quality can be found for under $10K. The new system uses the new G Mount from Fuji, with 6 lenses to be used with the system – 63mm f/2.8 (50mm Equiv in 35mm terms), 32-64mm f/4 (25-51mm Equiv), 120mm f/4 (95mm Equiv), 110mm f/2 (87mm Equiv), 23mm f/4 (18mm Equiv), and 45mm f/2.8 (35mm Equiv). Sadly, though, no release date has been set, aside from 2017.
While it wasn’t officially announced at Photokina, for all purposes, the Canon 5d Mark IV was an announcement for Photokina. The latest in Canon’s most popular line of cameras packs a 30mp full frame sensor into the system, capable of shooting at 7fps and 4K at 30fps (yeah yeah, we know it’s crop sensor for 4K video…we’ll have that information soon). It also includes a 3’2″ touch screen, and dual pixel RAW – allowing you to apply micro focus adjustments after the photo is taken. With GPS and Wifi, the Canon 5d Mark IV appears to be a nice little upgrade to the 5d Mark III.
Is there something that you’re excited about that we missed? Feel free to mentioned them, along with your favorite announcements in the comments below.
Great sports photography is not about recording moments that happen on the field of play, rather great sports photography is a medium that connects the viewer with the athlete and sport in an intimate way not possible in any other way. Most viewers of sports watch the game or an athlete on TV or in person were all the moments are fleeting. With sports photography, the action is slowed down and moments are frozen and presented to the viewer in 1/1000 of a second in such a way where they can study and process it in a unique way. With this, the audience is allowed to digest an image as long as it’s presented by the photographer in a compelling way.
SANTA CLARA, CA – JUNE 17: Michael Phelps warms up in the practice pool during day 2 of the Santa Clara International Grand Prix at George F. Haines International Swim Center on June 17, 2011 in Santa Clara, California. (Photo by Jed Jacobsohn)
To capture great sports photography you have to follow five basic rules that can apply to any form of photography but are especially important for sports photography. They are 1) Composition 2) Light 3) Background 4) Subject/Content 5) Practice.
Proper composition is essential to great sports photography. It can be challenging in today’s marketplace when a lot of images are displayed on social media, and thus you are at the mercy of whatever the viewer is digesting the material on, and that’s usually a small phone. Furthermore, you’re subject to the constraints of whatever platform you’re publishing on, be it Facebook, Instagram, or Twitter and you should be conscious of the composition with each platform in mind. However, with that in mind, you should stay true to proper composition despite these constraints.
Lolo Jones prepares to run in the 100m hurdles during track and field at the Olympic Stadium during day 11 of the London Olympic Games in London, England, United Kingdom on August 7, 2012. (Jed Jacobsohn/for The New York Times)
Great light is key to an extraordinary photograph. When in comes to sports photography, finding different angles and knowing what the light may do in a particular situation can be very helpful. It is essential to do your homework and research before going to a particular venue or assignment. For example, if you know that the sunset will happen at 6 PM and there is a great view from the top of a stadium it might be great to scout beforehand to see where you can capture both the environment and the action on the field. Or perhaps there will be shadows of athletes from above that can make for nice graphic elements. Knowing what the light is going to do can help with this point.
NEW YORK – AUGUST 30: the Baltimore Orioles and the New York Yankees on August 30, 2013 at Yankee Stadium in New York. (Photo by Jed Jacobsohn for Nike)
Another aspect of great light can also be created with artificial lighting as well. Having a knowledge of the proper use of a strobe or continuous artificial lighting is also key to have in your arsenal as a complete sports photographer and often relevant when working with athletes, especially in portrait situations.
Having a clean background or a background that doesn’t distract the viewer from the subject of the photograph is especially challenging and important in sports photography. We’re often at the mercy of the photo positions available to us, so it’s especially important to choose wisely on where you place yourself when possible. Again, proper research and planning can help with this point. For example, if you know that shooting on the south side of a stadium at 4 pm into the sun will produce a backlit image and this produce a black background that this is something to look for and choose a position to shoot from accordingly. Another technical aspect of cleaning up the backgrounds can be achieved by shooting with the fastest possible lenses with the largest aperture possible. Shooting action with messy backgrounds it’s essential to be shooting at least at f2.8 to blow out the backgrounds. One of my favorite lenses for portraits is the Canon 50mm 1.2L because you can us it in almost any situation and make the background blow out.
The USA vs Japan during the Women’s World Cup final on July 5, 2015, in Vancouver, Canada. (Photo by Jed Jacobsohn/The Players Tribune)
But shooting lenses at f/1.2-f/1.8 isn’t the only thing that comes into play when working to get a clean background. Background compression comes into play when using longer lenses, and because of that, focal ranges will provide different effects to depth of field. So many sports photographers love the use of longer lenses, Like the 400mm f/2.8 because not only does it allow them to get great close ups while staying out of the action, it also will give them a nice depth of field, bringing the attention to the subject.
During the Rio Olympic Games in Rio on August 18, 2016. (Copyright Jed Jacobsohn/Players’ Tribune)
But the background isn’t the only thing that can come into play when choosing the lens for your subject, minimum focus distance can also have some effects as well. For example, say you’re shooting your son’s little league game, and you have a fence separating you and the players playing. By using something like the 70-200mm f/2.8, you’re able to take advantage of the ~3.9ft focusing distance, and photograph the game with the fence between you, without the fence becoming a distraction in the photos or through focusing issues.
Having a compelling subject matter is important to grab the attention of the viewer. In this day an age where imagery is everywhere, it is especially important to offer your audience something they are interested in. Along these same lines, it is important to know your audience or client and cater to them. Always provide the images that are expected of you, and then give more.
Hunter Pence of the San Francisco Giants, on February 3, 2015, in San Francisco. (Photo by Jed Jacobsohn/The Players Tribune)
Paul Pierce of the Washington Wizards, on August 29, 2014, in Los Angeles, Ca. (Photo by Jed Jacobsohn/The Players Tribune)
One doesn’t need to photograph a famous athlete to accomplish this. Great sports stories are everywhere if we take the time to find them. If you can find the last point and apply the first three rules to it, then you are destined to great sports photography.
The biggest piece of advice I can offer is the most obvious among photography. In order to become a better sports photographer, you need to practice. However, practice doesn’t need to involve going to your local sports arena to photograph the LA Lakers each week from the stands. Practice can happen at your niece’s soccer game, our son’s basketball tournament and even tracking can be practice by throwing a tennis ball around a park with your dog chasing it back and forth. Becoming a sports photographer for a major publication takes thousands of hours of experience, and years of knowledge – and great sports photography can be captured at all levels – from professional to amateur.
As a staff photographer with the Players’ Tribune, all these elements of sports photography come into play with my job. One day I may be asked to cover the Olympics or the Super Bowl and another day I would spend a couple of days with an athlete for training and portraits, so it’s important to be well rounded.
In the repair department, there are things we hate. Salt water for cameras and lenses, salt water and sand for tripods and lenses. Sand in legs of the zoom mechanism of lenses ruins threads, they’ll never be smooth again.
Right behind those two is dust. Dust doesn’t always destroy equipment, but dust in equipment ruins pictures and can ruin circuit boards. So we hate Burning Man. The fine alkali dust that gets in everything at Burning Man isn’t as bad as sand and salt water – but it’s up there. Every year we tell people to take cheap or disposable equipment to Burning Man. It’s probably going to be ruined, and you aren’t going to like the charges. And every year people say, “It’s just dust.”
Side note for future renters. If you don’t want to take your own equipment into an area where you know it will be ruined, don’t rent our equipment and assume the Lenscap policy will cover you. It does not cover gross negligence, reckless, or intentional damage. Lenscap is designed as coverage for any accidents you may encounter, not as a way to avoid having to take common sense precautions when using our equipment in inhospitable conditions.
Since we’ve been doing a lot of Burning Man cleanup, we thought we’d share what a typical item goes through. Maybe some of you will pick up some cleaning pointers. Others may get some logical respect for dust. And some others will enjoy a peak inside the Nikon D810 that is the subject of this little post. I’ll warn you on the front end: this isn’t a teardown with great pictures. These are quick captures while we were working so there may be some motion blur and bad lighting.
So here’s a couple of views of our weary traveler as we received it.
The viewfinder cups are removed. There was a lot of dust under them and while you can’t tell here, inside the viewfinder. Lensrentals.com, 2016
This is a poor shot, but the flash is open here, showing how much dust got into the flash tray. Lensrentals.com, 2016
Before we did anything else, particularly opening the port covers, we spent 15 minutes blowing and brushing the easily removed dust off. Pardon the blur, but it gives you a general idea of what’s left.
It’s not looking great yet; that’s for sure. But we felt like we could open the ports and look at the connections. There’s still lots of caked on dust, but it’s not loose enough to fall into things. We could have used some wet cloths and things at this point and gotten off some more dust, but we didn’t want to add moisture to the equation yet.
I’m not saying that’s not an entirely acceptable option, but our primary goal at this point will be getting dust out of the inside and for that we wanted things as dry as possible.
The battery compartment, memory card slots, and the area around all the I/O ports had plenty of dust inside, so we knew further disassembly would be required.
We have kind of a love-hate relationship with disassembling Nikon cameras. The good part is they are very logically laid out and assembled, with each panel coming off by itself which makes disassembly a joy. The bad part is Nikon has a policy of using as many different sized screws as is humanly possible, making it necessary to keep incredibly organized.
For example, there are nine screws of 5 different sizes holding on the bottom plate. This may be because they’ve carefully engineered the best possible screw at each location to provide the most strength. It may just be because they hate us. I’ll never know.
As each panel was removed, we saw the same thing; the rubber weather resistant seals stopped the majority of the dust. In most of the pictures below you can see beige areas along the rubber seals that are caked dust. Beyond the seals, inside the camera, there are loose dust particles that got through, but the vast majority was kept out.
Overall, I’m impressed with how much dust did NOT get inside the camera. But there was still way more inside than was acceptable. One thing I should note is around every port and opening there was more dust close, and less dust further away from the opening. If there had been relatively even distribution, we might consider that it all came in through the mirror box or viewfinder or something. But I’m comfortable some dust got in from every possible access.
It doesn’t show well in pictures of this size, but while there was a little dust on the PCBs underneath all those covers, it wasn’t an enormous amount. We blew it off, of course, but it wasn’t bad. Each of the plates and seals that we removed were cleaned inside and out after removal.
Here are a couple of crops from the main PCB and internal back cover to give you an idea of what I describe as ‘light dust’ inside. It’s more than acceptable but probably wouldn’t cause any damage.
I haven’t mentioned it, but all of the rubber grip material was removed, too. There was no way to try to clean it well in place. At this point were pretty happy with what we’d seen. There was a lot of dust in the viewfinder assembly, but not too much had gotten into the rest of the camera. We were expecting worse, though. When you see this kind of dust under the lens cap…
…and in the mirror box, you figure the front of the camera is going to be worse than the back.
That makes sense since it’s the most exposed. It’s also the bigger problem since it’s in the optical path. On to the quick picture, just to thank Nikon for the ease with which the front and top cover assemblies come off in their cameras.
The front assembly itself and the lower (base plate side) of the front of the camera weren’t horribly dusty, although worse than the back.
But the area above the lens mount and under the flash was badly caked with dust. This isn’t surprising since this area is open to the viewfinder, the lens mount, and the flash assembly, so there’re lots of ways for the dust to get in.
This is especially a problem because there are lots of mechanicals in here that don’t like dust: springs, mirror, and shutter motor gears, etc.
When we took the top off, the same thing was apparent. Lots of dust got in the top center area and seemed thickest in the parts we didn’t want it in: motors, gears, the optical prism, and electro-mechanical dials and switches.
One thing we did notice at the top; there wasn’t a lot of dust right around the rubber seals, and the distribution was more even, which makes me think most of this came in from the front panel and around the viewfinder assembly rather than directly through the top seals.
Well, I won’t bore you with 762 eight-by-ten color glossies of what we did there at the Group B bench. But there was much Rocket blowing, many Q-tips were sacrificed, the sensor, AF sensor, and mirror box were wet-and-dry-and-wet-and-dry cleaned. Toothpicks cleaned gears and springs. And much time (about 2 hours) passed. After which everything inside looked shiny clean and new.
Here’s the camera reassembled, but still missing the rubber grips which are more difficult to clean than the insides.
To give you an idea of how difficult, here’re two pieces as they sit currently. Both have been washed with soap and water. The larger part has also had a vinegar-water wash (that works with alkali dust) and toothbrush scrubbing. We’ll try one a few more things but at this point, I think we may lose this part of the battle and have to replace the rubber. But the camera itself is working fine.
Because someone will ask what we do know, the camera will go into service as a testing camera here for at least a few weeks (probably 8,000 shots) to let any remaining dust work its way into the mirror box and/or viewfinder and get cleaned again.
So now you see part of the reason why I’m so cynical when people tell me their camera was caked with dust and dirt but they cleaned it off, and it’s fine. The outside of this camera could have been cleaned (well, maybe not the rubber grips). But it wouldn’t have for all that long – those dust encased springs, gears, and switches would have started misfunctioning sooner rather than later.
Protect your gear, my friends. Plastic bags, rubber bands, and tape are your friends. Dust, water, and sand are your enemies.
“But you must not eat from the tree of the knowledge of good and evil, for when you eat from it you will certainly die.” Genesis 2:17.
I have enjoyed, for some years now, the process of learning about lenses and optics. This blog shares a lot of what I’m in the process of learning. A lot of you like reading about what we’re doing and finding out what we’re finding out about what is. A lot of others don’t like it because it upsets their preconceived notions of what should be.
This post is going to be more polarizing than most. I’m going to talk about the very real phenomenon that people are describing on the internet; that they’re seeing more lenses with optical problems. If you aren’t interested in that, or are comfortable just saying they’re all bad photographers, this will be a long, boring article you want to skip.
One of the more common responses on various internet forums seems to be “this manufacturer or that needs to up their quality control.” There’s a bit of truth to that. A slightly less common response has been “your manufacturer, but not mine, can’t make their lenses without a lot of variation.” There’s a bit of truth there sometimes, but not very much. The broader truth is we’re observing an industry-wide issue. It’s not happening because lenses are worse. Lenses are actually better than they’ve ever been overall. There are some exceptions, of course.
For those of who don’t want to read further, here’s the summary:
The optics of new lenses are designed to take advantage of high resolution sensors. They are sharper than they were a decade ago.
An optically misaligned lens is just as soft in the bad area no matter how good the design. But the difference between the good and bad areas may be greater.
Opto-mechanical design and sample variation isn’t really much different than it was when the best cameras were 16 megapixels. (Some manufacturers have made improvements, but not most.)
Cameras resolve far more than they did a few years ago. They can demonstrate lens flaws you might not have seen with your last camera.
Metrology (optical testing and measurement of lenses) is the same as it was decades ago (There are some exceptions, particularly Sigma). In many cases you may see defects in your pictures that the service center can’t see with their testing.
In a nutshell, you can now take a picture with a high-resolution camera and see defects in the lens that might not have been apparent on your last camera. The manufacturer or service center often still use crude optical tests that don’t show the defect.
Why Higher Resolution Makes a Difference
Yes, I know this is obvious, sort of. But still, it’s worth discussing.
First, let me say that optical physics guys can do all kinds of math and show that, particularly if you involve vague terms like ‘depth of field’ and ‘resolution’ any statement about resolution is either right or wrong. I’m going to stay out of that and try to limit this discussion to words, pictures, and common sense. We’ll start with a simple, common-sense analogy. Things are way more complex than this, but it gives an idea of the overall picture.
Looking at Points
We all understand that a lens resolves a point in the world around you into a point on the sensor. If we look at a 5 micron point projected through a good lens mounted on our Olaf Bench, the point looks like a point, at least in the center of the image.
5 micron point source seen through the center of a really good lens.
Out towards the edges, where aberrations are warping the light rays around, that point of light looks somewhat different.
The same point source, seen near the edge through an excellent lens.
Now remember, that’s a magnified view of that point source I’m showing you; we’re basically looking at the image the lens makes magnified by a microscope. Let’s pretend that the white box in the image below represents a 6.25 micron pixel from a Canon 5D Mk III (22.3 megapixel full-frame sensor). Despite the fact that the dots look different on the microscope of my optical bench, they may look like perfect dots to your camera . . . . or nearly perfect. (And again, I’m leaving out details about AA filters, Bayer arrays, etc. but the analogy holds if we made this a 4 or 16 pixel array instead of a single pixel.)
This little analogy should explain why I often say, “Yes, there’s a difference in the optical bench tests, but I doubt you’ll see it on your camera.” Those dots are clearly different and the MTF taken at those two points will be different. But basically either one was going to fill up 1 pixel on my camera, with maybe just a tiny bit of bleed over from that lateral point on the right. The optical bench might see the difference, but your camera sensor probably wouldn’t.
But now many of us have a 40- or 50-megapixel cameras. Which means our pixel pitch is now 4 microns instead of 6.25. What the lens rendered as a 1 pixel dot now is bigger than a pixel. Still, even that edge pixel looks pretty good, with just a little spill into adjacent pixels (or array of pixels, whatever your pleasure).
But that was a really great edge pixel from a $5,000 prime lens. What about one from a more standard looking lens? Well, this edge pixel from this zoom lens is smearier and has a more noticeable chromatic aberration. And you should get the idea that it might be more apparent on a camera with smaller pixel pitch, as represented on the left below.
My analogy might be a little clearer if I average each of my pretend pixels from above, since my allegorical camera would only be reporting one value for each pixel. (Yes, I’ve invented color sensing pixels and eliminated the Bayer filter for this allegory, but if you prefer, consider each box to be a 4-pixel array complete with Bayer filter). But the point is simple: higher resolution means you’re going to get better detail about how smeary that dot is. In this case, either camera would show you this lens has lateral chromatic aberration, but the higher density pixels (on the left) also show the complex coma-type aberrations a bit more too.
Yes, I have mad Photoshop skills
Depth of Field
Depth of Field is one of those interesting phenomenon that’s both very scientific and very arbitrary. It’s determined by a complex mathematical formula, so it’s seems uber scientific. The key definition in determining depth of field (and some other concepts) is the Circle of Confusion (CoC). The definition of the circle of confusion (in words) is the width where the point blurs enough that it is larger than some maximum allowable diameter.
Depending upon your purpose, ‘maximum allowable diameter’ can have different definitions, and therefore depth of field calculations that come out of the formula can be very different. For an SQF calculation you might want to make it larger than some point size on a final print of a certain size. When we’re working with camera sensors, reasonable definitions might be the width of a pixel, or a 4 pixel square, or a 16 pixel square. Whatever formula you want to use, though, a smaller pixel means a smaller circle of confusion, which means a narrower depth of field.
Now, you may ask, why does that matter? Well, one thing people are seeing more frequently is a tilt in their lens. (In forums people call every lens defect “decentering”, but optical decentering often isn’t involved. Tilt and spacing errors are at least as common as optical decentering.)
Let me show you the effect of depth of field in two field-curvature graphs of the same lens, which has a small tilt. With a larger depth of field (on the right) there’s no way you’d notice it on any type of test chart testing; focus on the center and the left and right sides are going to be equally sharp. With a narrower depth of field (on the left), you might start to notice one edge is softer than the other if you were testing on a chart, brick wall, or other flat surface.
For this purpose, imagine the black line is your test chart, carefully focused in the center of your lens. The colors (and numbers) show the actual MTF measurement you would see at all focus points even if you had focused past or in front of the actual chart.
The drawing is a bit exaggerated since I basically doubled the depth of field by stopping the lens down (which is why the MTF is higher on the left). With the wider depth of field, though, the left edge MTF is 0.82 and the right 0.77. Those numbers aren’t very different and most of us would agree that was normal. With the narrowed depth of field, however, the MTF on the left edge is about 0.84 but on the right edge it’s 0.57. If I give you those numbers for your lens you’ll understandably scream that it’s awful and decentered. (Of course, it’s actually tilted, but people on the forums always scream ‘decentered’. It’s like playing Lens Bingo.)
This was probably pretty obvious without the illustrations, but the bottom line is if you move from 20-ish megapixels to 40- or 50-ish megapixels, you’re more likely to see flaws in your lens if you look for them. This has happened to some excellent photographers I know. They have noticed a lens here or there that was fine on their 5D Mk III or A7 that has a weak side or corner on their 5Dsr or A7rII.
So Why Doesn’t the Service Center See This?
This section is not going to name names. I’m under nondisclosure agreements with any company we help with testing so I’m ethically and legally unable to share names. You can take it on faith that I’m sharing facts or feel free to think I made it all up. I would point out, though, that for 10 years I’ve only made stuff up on April 1 and this is September.
The summary is almost all of you greatly overestimate the type and amount of optical testing that lenses get, whether it’s at the factory after assembly or in the repair center when it has a problem.
A lot of repair locations literally do resolution testing on an 8 X 11 or 13 X 19 ink jet printed chart. One used pictures of a bookshelf across the office to do optical adjustments on very expensive lenses (I know because they left their memory card in the camera they insisted we send in with the lens). AF 1951 charts are still commonly used (and remember, the ‘1951’ is the year the chart was developed, which means it was designed for film). Some use large, high-resolution ISO 12233 charts, but not many.
Factory Service Centers and Factory Authorized repair facilities generally use a factory-specified graph, again often printed at ink-jet resolution. It’s shot with a camera hooked up to adjustment software that gives pass-fail readings. This isn’t necessarily bad, although it’s not great. And depending on the factory, that chart may actually not be as good as an AF1951 or ISO12233 chart.
Some service centers use Lens Test Projectors and a center-only collimator to do testing and adjustments. If you ask a manufacturer’s engineer what the gold standard of testing is, with few exceptions that’s what they’ll say: a center-only collimator and a lens test projector. (Trust me on this one, I’ve had several say just that until we showed them why it wasn’t). If you ask them how long has that been the standard, though, they’ll tell you since the 1960s. That means since film.
Cooke Lens Test Projector, courtesy Cook Optics
Don’t get me wrong, a lens test projector and centering collimator is really good testing; generally better than test charts. We’ve used them in the past. They’re still the gold standard for Cine lenses everywhere. But Cine lenses are resolving 4K (just under 9 megapixels) or perhaps 6k (about 19 megapixels), not the 40- or 50-megapixels of a high resolution SLR. (BTW — I’ve got a couple of lens test projectors and centering collimators sitting on shelves in the back gathering dust if anybody wants to buy one.)
Things may actually be a little worse than what I’ve described so far. Remember, the ‘spec’ of ‘in spec’ is whatever the manufacturer says it is. A wide-angle lenses has a field of view of over 50 degrees to each side, for example, but I know of two manufacturers that don’t test wider than 30 degrees. They feel that anything significant will show up by that angle. That’s not my experience, but that’s what they say. Another does all of their testing at f/4 because that’s the standard for their automated testing software. And yes, a whole lot of problems that show up at f/1.4 disappear at f/4.
For example, scroll back up and look at the introductory picture, the crop from the center of a test chart. That lens was sent back from a factory service center twice, the last time with a note that said it met manufacturer’s specifications, no they couldn’t share those specifications, and there was nothing else they could do. It’s fixed now, but not by them.
My point here is not to get you all gathered together with pitchforks and torches to go storm the castle. This wasn’t a plot, in my opinion, it’s simply a lot of inertia. Metrology isn’t sexy and doesn’t make money. Until recently complaints about lenses weren’t any more frequent than they were back in 1990, so there was no real motivation for change. And I do want to repeat, the reason I know some of this stuff is because a number of manufacturers and service centers are suddenly and rapidly trying to improve their testing because they realize it now is a problem.
Better Metrology is the Answer, Right?
Well, yes, of course, but there’s another problem with better metrology: it’s too much better. I’m going to pull back the curtain a bit and show you things you don’t want to see. For years now, you’ve been seeing my summary MTFs, the average of 10 lenses, each tested at 4 rotations. So the MTF you see shows either the average or the range of 40 measurements at each point. It’s sometimes more accurate than the computer generated MTFs you see listed with a lot of lenses, but it’s still a summary.
Olaf Optical Testing, 2016
We do 10 or more copies and come out with an ‘expected range’ for a given lens. Then we can plot a particular lens (the lines in the graph below) against that range and find out if it’s acceptable. The one below, for example, shows as about average or maybe a little better.
Olaf Optical Testing, 2016
That’s good, but remember, even the line above is the average of the 4 rotations and two sides of the tested lens lumped together. What I don’t show you very often is what a single lens looks like at 4 rotations because you’ll get upset.
Let’s look at the raw measurements for that went into making the lines for the lens above: this is the full MTF at each of 4 rotations; “0 degrees” is side-to-side as mounted on a camera, “90 degrees” is top-to-bottom, and the other two are diagonals.
That’s not quite as smooth and beautiful, is it? That’s reality, my friends, for basically ever lens we test (and while I’m not identifying the lens, this is a really good prime lens). I expect you’re now wondering, after looking at the 90 and 135 degree rotations above if one corner of the lens is significantly softer than the rest. Obviously it is on the MTF bench. But will you see it on your camera?
Just to give you an idea below are 4 more copies of that lens, hand selected to be among the best from 20 copies or so. Even with these hand-selected best copies of prime lenses there is, if you look, always one corner that’s a little softer or more astigmatic than the others. But none are quite as weak as the one above. But most of the 20 looked about like the one above?
Unlike chart testing or even lens test projectors, optical bench testing shows us MORE resolution than your camera can see. At this degree of examination, no lens we’ve ever tested is perfectly identical in all 4 rotations. That’s many thousands of lenses tested. And none that were perfect. Ever. The fact is, those 4 lenses in the graph above are as close to perfect as we ever see.
This is why, when people suggest I cherry pick them a perfect copy, I tell them I’ve never seen one. With better lenses, mainly primes, we expect ‘so good that it looks perfect on your camera’. For most lenses we are looking for ‘within the expected range we see for this lens after eliminating bad copies’.
Let’s go back to the examples above. That lens on top, you may have noticed, is indeed a bit worse than the 4 ‘best possible’ copies out of 20 I picked out for the second image. The worst copy, the one on top, was an ‘average’ copy of this lens. Was it acceptable? Actually it was. It rented 20 times and no one ever had the slightest complaints about it. After every rental it was tested on a high-resolution, oversized chart and it looked fine.
Even when we made a point of looking for the weakest area on test charts or in photos, it looked fine on a 5D III. If we put it on a 5Dsr, though, we did agree we could see a little weakness on test charts. We thought.
My point here is that when we have a ‘too good’ test, so within that test we have to decide ‘where is the cutoff.’ In other words, we still have to decide ‘what is in spec.’
I’ll pause now for 476 of you to say “well, for that kind of money they should all be perfect.” Because I know you want to. Even those of you who know it’s not possible. And then I’ll say like I always do, “that was just a $1,5oo prime.” Because you can’t get perfect with $15,000 primes. The goal is not perfect. The goal is close enough so you can’t see any different in the picture you take.
So What’s the Bottom Line?
It’s pretty simple, actually. New cameras are showing defects in lenses that manufacturer’s weren’t quite ready to deal with. They (and we) are regrouping to put more adequate testing in place. We had a bit of a head start because we have been doing higher level testing for a while. We’re still, for example, the only place on the planet (as best I know) that can test electromagnetic focus lenses on an optical bench, for example, although at least one manufacturer will be doing it in a few months.
But we still don’t know exactly where the cut-off should be. We test lenses that go into satellites and stuff. Those aren’t perfect either, but in those cases the engineers who designed the cameras know exactly what resolution the camera can resolve and tell us so we can say a given lens is OK or not OK. The manufacturers, if they want to, can do that same thing. And at least in some cases they are starting to. But we’re all going to have to live through a transition period while those changes are made.
And I want to make it clear that we’re struggling with this, too. Months ago I tested a lens for Fred Miranda. I correspond with Fred regularly and I know he is an exceptionally careful photographer and will notice any (and I do mean any) flaw in a lens. I sent him a lens that passed with flying colors. Sure it had a slight abberation in one corner, but it was well within ‘my spec’. Fred sent it back after one day’s shooting for a soft corner — and absolutely identified that same corner I had passed as ‘good enough, you’ll never notice it on a camera’. My ‘in spec’ standard for that lens was developed when a 5D III was high resolution. He had put the lens on a much higher resolution camera and was noticing something that wouldn’t be noticeable on a lesser camera. (To be honest, it probably wouldn’t be noticed by most photographers, either. But Fred has bionic MTF eyes, I think.)
When high-resolution SLRs came out all of us, myself included, were wondering which lenses would let us maximize all that resolution. Few of us; not me, not you, and not the manufacturer, worried that that high resolution would let us see the weaknesses in a lens. Crowd-sourced complaints, legitimate complaints, have gotten their attention (and mine).
Things will get better in a couple of years, because changes are being made, but it’s not better right now. I know you want instantaneous changes, but they aren’t possible. For example, we took the decision a few months ago to improve our standard testing – the optical bench is excellent, but it takes 10 or 15 minutes to test a lens. We can’t run 800 lenses a day through it. But even our custom-made, high-definition test charts are barely adequate for testing the best lenses on the best cameras. We’re having to develop, in conjunction with a metrology company, new equipment that can be as accurate as an MTF bench but fast. That equipment isn’t cheap (think small house or maybe a Bentley) but more importantly you can’t just order one from Amazon. They’re built to order and it will be months before it’s up and running.
And remember, we’re a small company that responds to change quickly. Big companies have 12 layers of management approval and budgets made out a year or two in advance. The testing department is managed by an optical engineer who is human, and humans are often a bit resistant to change. There’s accountants who are going to want to know why everything is costing so much, especially because this wasn’t in next years budget. The companies are aware of the problem, they’re addressing it, but it’s going to take them some time to make changes.
And, as best I know, everyone is still figuring out the best ways to test lenses to make sure we catch every defect that might be visible on a photograph without all the ‘noise’, if you will, of false-positive results. Remember, we’ve never seen a perfect MTF curve on any lens, but we’ve seen lots of lenses that are photographically perfect on the best cameras. Some experimenting is needed to figure out exactly which things are significant and which aren’t. (If you’ve read this far and still think ‘they should all be perfect’, I don’t know what else to say except reality sucks, doesn’t it?)
For example, we’ve just started doing field-of-focus testing on lenses. It may well be that this is going to correlate better with the defects you can see in a photograph than actual MTF tests do. We’re still deciding what frequency of MTF test is most appropriate for newer cameras. Historically, 20 line pairs / mm correlated most closely to what you see when you take a picture. In higher pixel-density cameras we know 30 lp/mm is better and we’ve moved to that. But we aren’t sure if 40- or 50 lp/mm might be necessary. Those have a lot more false positive results, though, which makes things more difficult.
In the meantime, those of you out there who have been saying, “just go take some pictures and see if they’re OK.” Well, right at the moment, you have the correct answer, at least for people shooting the highest resolution cameras for a photo. A lot of photos of different subjects looked at carefully are probably going to identify things we’d be arguing about in the lab.
And this is coming from a guy who spends all day, every day, testing things optically in a lab. Right at the moment, ‘take more pictures’ is correct and I am, well, less right. But give me a few months to experiment and few hundred thousand dollars worth of new testing equipment and I’ll be righter.