Lenses and Optics

Overcoming My f / Entekaphobia

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Published March 4, 2013

Entekaphobia – fear of the number 11

Or. . . How I Learned to Appreciate Small Aperture Photography

If you read my blog much, you know I’m a resolution fanatic. I test every new lens for resolution. For personal use, I’ll choose the lens with higher resolution over the one with creamy bokeh every time. When choosing a camera, I have a (yes, I’m ashamed to admit it, but it’s true) strong tendency to want the most megapixels. I’m a resoholic.

Being a resoholic, I’ve always been somewhat fanatical about apertures. Whenever possible I shoot with the lens stopped down at least one stop to wring the maximum sharpness out of my lens. But I’m always careful not to stop down too far because I was taught, soon after I picked up a camera, that if you stopped down too far the dreaded diffraction softening would kick in.

With today’s high-pixel density cameras, that meant f/8 was as far as I would ever stop down. My mental map of aperture sharpness was like the ancient maps of the world – past f/8 there was nothing but the notation Here Thar Be Monsters. Or the equivalent label in Latin or Olde English, just because that makes it seem much cooler.

 

Detail from The Carta Marina by Olaus Magnus (1490-1557).

 

Go to f/11 and the diffraction monster would come and eat the resolution right out of your photographs. The diffraction monster loves to snack on some tasty resolution. When testing I really never checked past f/5.6 or f/8. That’s where the maximum resolution would be. Any further, and, well, you get it by now.

But I knew there were excellent photographers who shot their landscapes and macros at f/11 or even f/16 because they needed the depth of field. I heard rumors of photographers in far off lands who even actually took photographs at f/22. I considered them sort of like those guys who jump off cliffs in batsuits and fly around for a while before pulling their parachute rip cords. It was fascinating to know people did that, but made me a bit queasy. I was certain the survivors would eventually learn the error of their ways.

But lately, some people like Tim Parkin at Onlandscape.com started opening my eyes (by repeatedly beating on my head). They claimed to be shooting at f/16 and even f/22 with high-pixel-density SLRs, carefully postprocessing their images, and getting very nice detailed results. I shook my head sadly at first, hoping they would come to see the light (pun intended). But then I looked at Tim’s recent article The Diffraction Limit and had to admit, their f/22 images didn’t look bad at all.

So I decided it was time to open the closet door and see just how bad the diffraction monster really was.

Preliminaries

Before we get into all of this, let’s remember we’re looking at two simultaneous events when we stop a lens down. I am not going to get into lengthy discussions of Airy Discs, Raleigh Criteria, and other arguments here. You can read about them elsewhere. This is the simple overview of what’s going on.

  • 1) As we narrow the aperture (higher f/number) diffraction occurs which causes some loss of resolution.
    • 1a) Smaller pixels are affected more than larger pixels since diffraction causes a spread of the point into a disc. A disc of small size might still fit nicely on a large pixel, but might cover two small pixels. The math is mildly complex, it’s not linear, and I’m not going into it more than that.
  • 2) As we narrow the aperture, the lens resolution increases.
    • 2a) The increase is different for different lenses.
    • 2b) The increase may occur at different rates for the center, middle, and corners of a lens.
  • 3) Decreasing aperture is sort of a race between these two effects. When we first stop down, the lens sharpening is greater than the diffraction softening. As we stop down further, lens sharpening slows or stops, but diffraction softening continues.

 

Some Resolution Testing

I’m not one to really believe what I see in online exampless; given enough postprocessing an online jpg can look pretty sharp if the lens was the bottom of a beer bottle. I want at least a side dish of numbers or some comparative crops with my reviews, thank you.

I decided our current Nikon lineup gave me a great opportunity to look at diffraction effects. By shooting the same lenses on a D700, D3x, and D800 I can look at full-frame sensors with 12, 24.5, and 36 megapixel sensors. That gives linear pixel densities of 118, 168, and 204 pixels per mm, respectively.

I decided to use 50mm lenses because we have 3 choices that are quite different in how they behave at various apertures.  The Zeiss 50mm f/1.4 (the schizoid fiftoid) is very soft and dreamy looking wide open, but becomes razor sharp once stopped down to f/5.6 – it’s like two lenses in one. The Zeiss 50mm f/2 Makro planar is quite sharp even wide open, but seems to maximize it’s center resolution by f/4. The Nikon 50mm f/1.4 G is reasonably sharp wide open, but seems to keep getting sharper the more you stop it down.

So I tested all 3 lenses on all 3 bodies at apertures from wide open to completely stopped down in our Imatest lab.

The Effect of Stopping Down on MTF 50

I started right in the middle of my selections: the Nikon D3x with the very predictable Nikon 50mm f/1.4 G lens. Here are the MTF 50 values in line pairs / image height for the center point, weighted average of 13 points, and average of the 4 corner points. Please note that the plotted average is NOT just the average of center and corners, so if the ‘average’ value is near the center, you know the lens stays fairly sharp in the middle regions, while if it’s nearly as low as the corners the lens falls off rapidly away from the center point.

 

Nikon 50mm f/1.4 on D3x at various apertures

I have to admit I was a bit shocked. Just as expected, the resolution starts to decrease after f/8, but it doesn’t decrease all that much. Even at f/16 the resolution is still quite a bit higher than it was at f/1.4.

The next step was to see how things look with lower and higher pixel density cameras. So I shot the same lens on a D700 and D800.

 

Nikon 50mm f/1.4 on D700 at various apertures

 

I was a bit surprised here, too. I had expected the lower pixel density of the D700 would shift the peak resolution a bit, perhaps to f/11, but that wasn’t the case, although the drop after f/8 did seem less severe.

 

Nikon 50mm f/1.4 on D800 at various apertures

 

Things weren’t as different as I expected on the D800, either. The center does seem to peak around f/5.6 with the corners peaking at about f/8, which isn’t surprising. The other cameras show only a slight increase in resolution at the center between f/5.6 and f/8 so it makes sense there would be a bit stronger diffraction effect on the D800. I had really expected more than this. The lens still improves in the corners strongly between f/5.6 and f/8 and the improvement is greater than the diffraction softening.

The message I took away, though, is that diffraction softening is real, it occurs where it is supposed to, but it’s really not as severe as I had thought. Even on the D800 resolution is as high, or higher, at f/16 than it was at f/2.8. At f/11 the resolution is as good, or better, than at f/4. And at both f/11 and f/16 resolution is clearly higher than it was wide open. Perhaps the diffraction monster’s teeth aren’t as long and wicked as I thought.

Some Different Lenses

Diffraction softening is fairly constant, but lens sharpening as the aperture decreases is not. Different lenses behave differently. I compared the Zeiss 50mm f/1.4 and 50mm f/2.0 Makro Planar lenses to the Nikon 50mm f/1.4 G we tested above on all three cameras. In the interest of brevity we’ll just show the graphs for the D3x. The variations for the D800 and D700 were similar to these.

 

ZF 50mm f/1.4 on D3x

 

ZF 50mm f/2 Makro on D3x

 

Let’s start with wide open performance. At f/1.4 the ZF f/1.4 lens isn’t as sharp as the Nikon 50mm was, while the ZF 50mm f/2 Makro is sharper at f/2 than either of the other lenses at that aperture. The f/2 Makro has reached maximum center sharpness by f/4 and then slowly loses resolution. The lens doesn’t reach maximum corner sharpness until f/8. The ZF 50mm f/1.4 gets maximum center sharpness at f/5.6 and corners again at f/8 on the D3x. (In the graph above, you can see the Nikon reached maximal sharpness at f/8 for both centers and corners.

The pattern was unchanged on the D800, but on the D700 the two Zeiss lenses center sharpness shifted just a bit to the right – moving to f/5.6 for the 50mm f/2 Makro, with corner sharpness remaining peaked at f/8.

So there is some difference in stopped down behavior with different lenses. Before you ask me to go test this or that, the work has largely been done already at sites like SLRgear.com and Photozone – they show center, corner and edge sharpness at various apertures in their lens reviews.

Yes, I Took Pictures

OK, the numbers surprised me a lot, so I went and did what had to be done. I actually took photographs stopped down to f/16 and even f/22.

Here’s one picture I shot at various apertures (this was on a Canon 6D).

 

 

What I saw mirrored what the numbers said I would see. Below are some 100% crops of the white gazebo just off center and some tree trunks near the left edge. I also tried something I was told was possible, but hadn’t really believed. I took the obviously diffraction softened f/22 image and did my best to sharpen it in Photoshop. (By best, I mean about 45 minutes testing different combinations of sharpness and contrast enhancement in 3 layers before getting the results shown below as ‘f/22 sharpened’.)

 

 

I haven’t tried this kind of sharpening before and was feeling my way along. I’m sure it would be better with practice (I blacked out the large tree-trunk for example and the image is about 1/3 stop darker than when I started) but still I found the results surprisingly acceptable.

One thing I found very interesting is that I could perform what was basically postprocess abuse on the f/22 image to a degree that would have been impossible with one of the other shots. Below, for example, is the f/2.8 image above processed with exactly the same settings I used on the f/22 image. The center crop, particularly, looks like a ‘find edges’ special effect filter.

 

 

I don’t mean to suggest that the postprocessed f/22 image is going to be as good as a nice f/5.6 or f/8 image at all. Rather I’m suggesting it can be improved to a larger degree than they can, making up some of the out-of-camera difference between them.

Does this mean f/16 is my new f/5.6? No, not at all. But I think I may become a lot more aggressive about using f/8 and f/11 when I’m trying for a larger depth of field. I even might use f/16 if absolutely needed. I don’t think I’ll be shooting f/22, though. That’s just a step too far for me.

 

Roger Cicala

Lensrentals.com

March, 2013

 

An aside: I’ll be going on vacation for 10 days at the end of this week, shooting with my new camera at my new-found apertures. I don’t expect there will be any more blog posts until late March.

Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

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  • Mad Hungarian

    Yeah, my own informal tests on my Canon 6d and 60d show the full-frame 6d showing minor diffraction effects at f/16 and more severe at f/22. The 1.6x cropframe 60d shows the same effects at f/11 and f/16 respectively. But it’s not like they fall off the edge of the world or anything.

    I think Bryan Peterson refers to the “sweet spot” as the “don’t care range” or somesuch. You use it for those shots where you don’t care about depth-of-field. For the other shots, depth-of-field concerns are much more important than the resolution/diffraction effects.

    But related to this, a curious thing happened to me on the way to the astro-forum. I’d been vexed for some time that my DSLR shots of planets/moon were a lot softer than my visual observations of same. Originally i thought it might be field curvature, and that did probably have some effect too. But now i think diffraction is probably the culprit. My Schmidt-Cassegrain telescope is f/10, and then i hang a 2x or 4x teleconverter onto it, which i think raises it to f/20 or f/40. And then i hook up my crop-frame DSLR which i know starts showing diffraction softness at f/11. So is it any wonder than that my shots therein seem to be showing extreme diffraction softness?

  • Roger, thanks for the review and affirming my real world results.

    However, I suggest a different way of looking at the problem, one that focuses on photography, which is about communicating the experience as true as possible, as opposed to trying to show every microscopic detail, which you rarely notice anyway. Here’s what I mean:

    I’ve been shooting at f/32 with my Pentax 645NII camera for years and, last year, moved over to a Nikon D800E with a 14-24mm lens. My typical shot is at the focal length of 14mm at f/22, focused at the hyperfocal distance of 24 inches (nearest subject is 12 inches away). That’s my solution to shooting the prairie landscape, very immersive. There’s no other way of getting everything sharp or, should I say “acceptably sharp.”

    Granted, at f/8 or f/11, some parts of the image show incredible detail, but the rest of the picture looks like crap. So, there’s no real choice. Focus stacking is impossible with real world landscapes of the prairie.

    For many years, my secret, if it is a secret, is to use certain Photoshop techniques, along with the sharpening software called FocalBlade, to bring back the sharpness with great results, being able to make 42×56″ prints with medium format film and 30×40″ prints with the D800E. I haven’t pushed the threshold with the Nikon, yet.

    But, I think we have to think about the idea a little differently. It’s all about how we perceive the world and how we take pictures to match that perception. For instance, the reason we want everything sharp in a landscape image is that it’s printed on a 2-dimensional piece of paper and the world is 3-dimensional. To emulate the real world perception of focusing your eyes at a multitude of distances, the only way to do it is to have everything sharp. That’s because, you’re essentially focus stacking with your eyes and brain. The same goes for HDR, where your pupil gets bigger and smaller depending on the brightness of whatever you’re looking at.

    Now, if you lean in to see a flower or a bug and want to best replicate that experience in similar wonder and detail, that’s what a macro lens is for. The reason that blurring backgrounds are preferred in macro shots is because that emulates the real world. When you focus on something, that’s where you put your attention. Everything else you ignore, even if everything else is intensely distracting. It’s as if you are cutting out, say, the flower with no background at all. But, of course, our pictures are rectangular and include the background, so in order to emulate reality, it must be as unintrusive as possible.

    But, when you’re “taking in” the landscape, you’re viewing the scene as a whole. So, if the landscape shot is missing on some fine flower details, you probably never saw them in the first place. Therefore, the shot, though lacking the finest information, emulates the real world experience.

    So, from a perspective of communicating the human experience, f/22 plus some Photoshop magic is the most realistic way of doing the job.

  • Jane Wiens

    All I have right now is a D90. Is it this camera a lost cause when considering the use of a 50mm f1.4G. I don’t see any discussion on that particular one. My photography language is a bit limited but I understand more than basic. I want to shoot outdoor portrait with depth of field. Is the 50mm f1.4G a good choice. Any suggestions?
    I can’t buy another camera right now, it will have to do for now. I want a soft picture background but quality resolution for the portrait. Am I making sense?

  • Actually, I should qualify my last comment. There IS a limit…the limit would be when pixel size gets smaller than the wavelengths of light it is supposed to be sensitive to. If the light itself can’t fit through what would effectively be the “aperture” of the pixel itself, the results would probably be fairly odd. I’m not exactly sure what the results would be, and it is possible to do things at subwavelength scales, but I think it could be considered the practical limit of sensor resolution. That, in explicit terms, would be around 700nm (wavelength of red light), or 0.7µm pixels. We have a LONG way to go before we have pixels that small, and there are other factors to consider with pixels that small (i.e. noise, although again noise is often misunderstood, especially in the context of ultra high resolution sensors.)

    Second, apologies Ralf, I misspelled your name in my last post! 😮

  • @Raf: Regarding diffraction and its effects on smaller pixels. You are making the classic mistake in understanding about diffraction that most photographers make. The DLA (diffraction limited aperture) is not this turnaround point where smaller pixels produce worse quality than larger pixels. The DLA is simply the point at which THE LENS creates an Airy Disc (blur circle) that is as large as the pixel size, and thus marking the point of diminishing returns.

    Quick thought experiment. If you have two cameras, one with an 8µm pixel and one with a 4µm pixel. When the 4 micron pixel becomes diffraction limited, the size of the lens’ blur circle is just over 4 microns (not really, this is VASTLY simplified, and is usually about twice as large when using bayer sensors, but for discussion sake). The 8 micron pixel is not diffraction limited…and (according to the classic misunderstanding) should still be resolving more resolution than the now diffraction limited 4 micron pixel sensor, right? Wrong. The 8 micron pixel sensor is still resolving less…the minimum blur circle size it can resolve is 8 microns. It is literally INCAPABLE of resolving enough detail to even be as sharp as the lower resolution sensor…despite not being diffraction limited!

    Lets say the lens is now producing a 6 micron blur circle. The 4 micron sensor is now producing worse quality than the 8 micron sensor, right? Nope, it is still resolving more detail. If we assume a single point of light is being resolved at the center of the lens, the 4 micron sensor’s smaller pixels, though “diffraction limited”, are actually resolving something akin (-ish) to a round circular point of moderately bright light. The 8 micron sensor? It’s still resolving a dim square…it is still resolution limited relative to the 4 micron sensor, and is still incapable of resolving the point of light at all…outside of allowing that single pixel to be a bit brighter than the surrounding pixels. At 8 microns, the sensor with the larger pixels is now finally diffraction limited. The 4 micron sensor? It’s now able to resolve even more roundish definition to that nice round point of diffracted light…while the 8 micron sensor is still just resolving an 8 micron sized square.

    Diffraction does not mean a sensor with smaller pixels resolves less. It just means that the benefit of it’s higher resolving power diminishes, and *approaches* the LESSER resolving power of a sensor with larger pixels. From a physical standpoint, a higher resolution sensor can never resolve less detail than a lower resolution sensor.

    Total resolution, what you actually get out of a camera (lens + sensor in combination) is easy to roughly compute with a root mean squares formula. This formula is not entirely accurate, but its approximation is good, and it is ideal for demonstrating the REAL effects of diffraction. The formula below is for computing total system resolution in terms of spatial resolution (lp/mm). This is a good unit, as lens resolution is usually described in terms of lp/mm or cycles/mm. The formula is (in case you would like to verify with more than just the D800 and D700…note that this applies to all cameras and any lens, and APS-C sensors tend to have even smaller pixels, and are thus capable of outresolving even a D800 at the same distance with the same lens):

    TSR = (1l / (sqrt(LR^2µm + SR^2µm) / 1000µm/mm)) / 2l/lp

    Where TSR is total system resolution, LR is the lens blur circle size at a given aperture, and SR is sensor pixel pitch (fixed for a given sensor, say 4.9µm for the D800). Blur circle size for an f/4 lens is 5.7µm, f/8 is 11.6µm, and f/16 is 23.3µm. If we compare system resolution of the D800 and D700, at f/4, f/8 and f/16, according to the above formula:

    D800 f/4 = 65.983
    D700 f/4 = 48.642
    D800 f/8 = 39.625
    D700 f/8 = 34.714
    D800 f/16 = 21.038
    D700 f/16 = 20.193

    At every aperture, even thoroughly diffraction-limited ones, a higher resolution sensor will produce better results than a lower resolution sensor. As you can see, you have diminishing returns. At f/4 the D800 is 35% better than the D700, where as by f/16, the D800’s benefit has shrunk to a mere 4.2%. By f/22, the lead shrinks to 2.2%…however the D800 is still capable of producing a higher resolution result (technically speaking…you probably wouldn’t be able to see the difference with the naked eye in a print.) (Keep in mind, I’ve simplified things for this post, with a bayer sensor things are a little more complicated and the final numbers would be a bit different, giving a further edge to the D800.)

    So, to answer your question “where is the limit”…for all intents and purposes, there is none. A higher resolution sensor will always outperform a lower resolution sensor, for any lens, at any aperture.

  • Hello Roger,
    thank you for your continued efforts informing photographers, and this article is particularly insightful!
    What strikes me is that you get higher resolution at f/16 on a D800 than with a D700 at ANY aperture! Strictly following the assumption in your Preliminary 1a) this shouldn’t be: The larger pixels of the D700 should be less affected by the effects of diffraction than the smaller pixels of the D800 and therefore the D700 should have an advantage (meaning: lower diffraction) over the D800 at higher f-stops. At some f-stop (maybe f/22 or f/32) it finally shouldn’t matter if you shoot a D700 or D800, the image is (or ought to be) so blurred by diffraction that a high resolution body doesn’t give you any more detail. But instead – according to your graphs – you always have a resolution advantage with the D800, at least up to a ‘blurry’ f/16. That leaves me with the question, where is the limit: will an even higher resolution DSLR (e.g. 56MP) still perform better at f/16 than a D800 at f/16, possibly even better than a D800 at f/8? I guess we’ll find out soon enough…

  • Nicolas Woollaston

    The psychology of it may be related to your spending time with m43. From a diffraction point of view I think f/16 on your D800 is roughly equivalent to f/8 on m43 for a lens with the same angle of view. So your uneasiness about f/11 and f/16 is valid in the m43 world, but not so much now you are using a D800. I would be very interested to see a comparison test with an m43 body and good 25mm lens or an APS-C body and a good 35mm lens if you have the time and inclination. Thanks for a great blog.

  • Tim Ball

    Thanks Roger, good article.
    I find lenses vary a lot in their handling of diffraction. For instance my Zeiss ZA 25/2.8 seems to handle F16-22 really well, however my Zeiss ZE 100/2 really, really doesn’t like F16 at all and F22 would kill it!.

  • This is going to be very useful for me thank you very much for posting

  • Frank Kolwicz

    Michael C said: “Exporting the corrected RAW file from DPP as a TIFF often increases the size of a 22MP RAW file to over 100MB!”

    That’s what happens every time a RAW file is converted to Tiff at 16 bits, no matter what program you use. I don’t think DPP does anything special. If you’d like to show me that it’s better than Lightroom and does hold more detail, I’d like to see it.

  • mike

    Very interesting article and something that has been missing from most photography websites. I first came across the issue of different behaviour of lenses when stopped down beyond f11 with the Tamron 90mm macro (version before current one). It is fine up to f11 but by f16 performance falls off a cliff and is totally unusable at f22. It is particularly surprising for a macro lens to have this characteristic. I have taken many thousands of macro pictures with a range of canon and sigma macro lenses but the tamron stands out as being completely different from them in the way performance suddenly falls away rather than having a gentle tail off, I think I have seen this reported elsewhere too. Had I known this then of course I would have never purchased the lens as a macro lens is very frequently used at these small apertures.

  • Marek

    The crucial thing which most people miss in the whole discussion about diffraction is that it is relevant only in the context of achieving the *absolute maximum* resolution your camera + lens combination can deliver, under the critical assumption that *one is photographing a perfectly flat object which rests exactly on the focal plane* of the camera + lens optical system.

    This assumption has rather little relevance to practical photography, because “real life” photographic subjects, in contrast to test charts, most often are *not* flat and are *not* resting exactly on the focal plane when the picture is taken.

    In practical photographic situations, the benefit of increased depth of field outweighs decrease in resolution connected with diffraction as one moves away from the focal plane. What constitutes the visual impact of a landscape photo with detail in both *very nearby* foreground and *very far* background is the great DOF achieved by choosing a very small aperture. The fact that *if* there was a flat subject in the scene *exactly* on the focal plane *then* a better resolution could be achieved by choosing a larger aperture is simply not relevant. What we need in the photo in question is front-to-back sharpness. We don’t care that it’s not the *absolute maximum* that our system can deliver in an artificial laboratory condition.

    An appropriate test would involve an *out-of-focus* test chart and aim to determine beyond what distance below and behind the focal plane, fretting about diffraction does not matter anymore.

  • Hi Roger,

    have lots of fun on your vacation.

    Interesting writeup as usual, and interesting to see how little the difference between the lenses appears to be once they are stopped down to f8. F8 and be there, as the old saying goes.

    I assume that pictures from less sharp lenses will profit by the stronger sharpening as well – may be you can lift the veil and do another article on sharpening after your time off.

    Thanks and greets

    Ralf C.

  • Hans vanDriest

    Photoshop sharpening is one solution, Topaz detail is another one, with considerable more options.
    Another point is that not all lenses behave the same when stopped down. Some lenses handle f16 much better than other ones, so it seems to be not only diffraction limiting sopped down resolution.

  • Nqina Dlamini

    Great write up and comparisons. I was disappointed with the ZF 50mm f/2 results, I assumed it would seriously kick the Nikon’s behind.

    Enjoy your holiday, we will miss the blogs.

  • >Digital Lens Optimizer

    At first glance it looks kind of convoluted to use. Why all these sliders if they have the lens data? Would be interesting to compare to good sharpening and Lightroom lens corrections.

  • Michael C

    Canon has introduced a tool called Digital Lens Optimizer to their Digital Photo Professional (DPP) software beginning with version 3.11.10 that was released about the same time as the 5D mark III last year. It applies Canon’s knowledge of the lens and camera sensor combination’s design and performance, as well as their proprietary demosaicing algorithms to provide lens correction that is very effective at minimizing the effects of diffraction. It does this at the RAW file level. Once the correction is applied, the size of the RAW file doubles! Unfortunately, other programs such as Lightroom only read the original, uncorrected data in the modified RAW file. Exporting the corrected RAW file from DPP as a TIFF often increases the size of a 22MP RAW file to over 100MB!

  • c.d.embrey

    For some of us the limiting factor is the printing press, not RAW vs JPEG, not bit depth nor defraction. It is very possible to shoot JPEGs at F/16 and get print ads that even advanced pixel pepeeprs can’t complain about.

    Glad to see you do these tests, maybe it will help with people understanding the real world.

  • Matt

    Hi Roger,
    Thanks for the good info. And thanks for the clever title of the article. “My f/Triskaidekaphobia” isn’t nearly as fun.
    Matt

  • A

    Roger: If possible please could you add f5.6 and f8 crops into the Canon 100% crops? Your graphs show that the optimum sharpness is probably achieved at f5.6, but your 100% crops jump from f2.8 to f11, neatly avoiding the aperture that should offer the best results.

    Other than that, another interesting article; thank you.

    Now go and enjoy your holiday!

  • Chris K

    I’ve got a ton of macro shots with tiny apertures. I started at f/11 with my 5D1 and 100/2.8 and quickly stopped down to f/16 if the shot needed more DOF. I had a fair number of shots at f/22, even. f/32 was a bridge too far, where the virtue of more depth of field was ruined by the blurring of all details in the image.

    Today, with my EM5 and 45/2.8 I’ve found f/16 is workable, even. That gives me about the same DOF I got from my 5D and 100/2.8 at f/32, and the overall sharpness is much better (to say nothing of the flash and ISO advantages). M43 seems to punch above its weight when it comes to diffraction, and it’s a great advantage when it comes to macro.

    Also, ask some Canon MPE shooters how they feel about diffraction. At 5x if you’re not deep into diffraction limits you’ve got almost no DOF, so unless you’re shooting apparently flat subjects it’ll be hard to make a photo anyone cares about.

    Equipment aside, in my experience I’ve had many more macro photos ruined due to insufficient DOF (often compounded by slightly missed focus) than I have by diffraction softness. IMHO macro photography lives and dies by getting the right amount of DOF, and technical merits always (or rather, should always) take a back seat to artistic merits. I’m not going to turn my nose up at f/16 or even f/22 if the added DOF makes the photo better. I might not be able to print at 20×30, but at least the photo will be more interesting.

    Check out John Shaw’s Closeups In Nature for excellent examples of great photos with tiny apertures. The MTF charts may show his photos to be suboptimal, but the PHOTOS paint a different story.

    This is kind of in the same vein (IMHO) as ruining a shot with insufficient shutter speed because you were trying to keep the ISO low. I used to do this all the time, but after looking at too many blurry photos with no noise, I decided I would always aim high on ISO rather than living on the shutter speed margins. This decision seems smarter every year, as noise reduction gets better and better.

  • tjshot

    @ Hervan
    Stopping down is an effective way to perform AA-filtering.
    After proper sharpening, the loss in MTF50% performance (compared to a hardware AA filter at wider apertures) is negligible.

  • Hervan

    Great article. Reading it made me come up with the following hypothesis: could smaller apertures be used as a last resort anti-aliasing filter? In cameras without AA filters, that is. I know it wouldn’t be as useful as a proper AA filter in front of a sensor, but I’m just curious. 🙂

  • Still waiting for your Leica APO-Summicron-M 50 mm f/2 ASPH review and test. Would be very curious to see how it stacks up to the lenses you’ve tested here.

  • Roger, thanks for the great article. I now makes sense to me. Lower contrast will measure as lower detail. But as long as the real detail is still there sharpening can improve the situation.

    What is the main difference between original sharpness from the lens (e.g. with low diffraction blur) vs. a software sharpened result? The final prints can come very close but all sharpening will at some point introduce sharpening artifacts. How much you can see in the final print depends on the print size and print process. Long live f/8-f/11 :-).

  • tjshot

    Nice article.
    Results are in line with theoretical findings, as per resolution tables I provided for Tim’s article.
    The importance of resolution and proper sharpening (appropriate amount/radius for each F-stop) is even greater if we consider oversampling requirements for ink-jet color printing; it’s often overlooked but best performance from printers require a high dpi input.

    I ran a few simulation scenarios in a full study I did out of curiosity when current generation of high res full frame bodies were announced.

    Links below:
    Part 1:
    http://www.canonrumors.com/forum/index.php?topic=1902.0
    Part 2:
    http://www.canonrumors.com/forum/index.php?topic=2412.msg51441#msg51441

    Part 2 is the complete document, which integrates also the analysis of different inkjet-print performance from simulated sensors.
    I linked Part 1 because I believe some of the forum follow-ups may be interesting.

    The development is a bit long and math-oriented, but results are discussed also in a qualitative way.

    The simulations show how sharpening can recover high frequency details, even for diffraction limited scenarios; a higher pixel count sensor does better in this respect, but this factor is often underestimated or ignored.

    People often think of diffraction as something that “happens abruptly” from a given F-stop; however for an imaging system (lens + sensor) diffraction only starts to affect performance at a given F-stop, related to photosites pitch of the sensor itself, but its effect can be quite subtle and recoverable with proper sharpening.

    A denser sensor pixel pitch, after proper sharpening, can squeeze more information out of the same lens than a larger pitch one, even when the lens is performing below the Nyquist limit of both sensors (for example stopped down to F16 or smaller).
    In other words the same lense stopped down to F16 would deliver better sharpness and resolution on a 50 Mpxls sensor than on a 36 or 21 Mpxls one, after proper sharpening is applied.

    This is mainly due to the fact that a denser pitch generally allows to push sharpening further, for a similar SNR (Signal to Noise) ratio; moreover the higher Nyquist limit will allow to recover and sharpen even the high frequency information that a lower Nyquist limit would cut off.

    The concept of a sensor “outresolving” a lense is thus prone to many caveats: the whole imaging chain, i.e. lens + sensor, should be considered when evaluating performance: considering the lens only, then assuming a sensor would be “outresolving” it due to its higher Nyquist limit, is simply uncorrect.

    I’d like to enphasize a few more points I already pointed out elsewere.

    Of course contrast drops significantly with smaller apertures but it’s well recoverable up to F22 for sensor pitch in the 4-5 microns range; smaller stops will involve a serious, mostly unrecoverable, degradation.
    An important thing to keep in mind when considering the effects of diffraction is the difference between shooting a real-life object or a standardized MTF target.
    MTF testing is performed imaging a uniformly-lit sine-wave pattern of given contrast ratio, which may produce a lower contrast transfer than a finite object with hard edges and dishomogeneous illumination: for example a tree against a light background in a landscape shot or a textured object with strong stray light in a close-up shot may retain more contrast than a standard MTF plot of lens/sensor combo would suggest.
    The effect on resolution (MTF 10% values in my simulation) is often negligible, but perception of sharpness (in rough approximation MTF 50% for 35mm sensors) is greatly enhanced.
    On the other side, a dimly lit subject, even with distinct edges and textures, will probably result in lower perceived sharpness than the standard MTF plot of lens/sensor combo would suggest.
    For my simulation I relied on the standard MTF testing parameters (a uniform rolloff for lens MTF) which don’t take into account the increased/decreased contrast resulting from real scenarios.
    In other words, for real subjects the use of a small aperture like F22 + sharpening will probably result in better performance than my theoretical analysis suggests; more so for landscape photography, where high contrast details are common.

  • James Scholz

    Thanks, Roger, I loved seeing the comparisons. I shoot these kind of comparison shots of architecture all the time as architectural photography is my business. But I don’t have the numbers, and like you, I like to see those as well looking at grass and bricks. Hopefully you will do more articles like this in the months to come.

    Happy shooting in the coming days.

  • richard

    I recently did a DOF v. diffraction test and posted at http://forums.dpreview.com/forums/thread/3387836?page=7#forum-post-50933740 Hover cursor over each image to see EXIF data.

    Improved DOF far outweighed softening from diffraction, at least in my simple test. I didn’t do any post-processing beyond importing to LR4.3 and exporting as jpeg.

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