One of the most common examples of anti-logic we see at LensRentals is the statement The lens is soft/frontfocuses/backfocuses. Now don’t get me wrong, there are bad copies of lenses out there, as best we can tell ranging from 3% to 7% of lenses. And we know, despite our checkout procedures, that 1 of 400 lenses or so will be damaged in shipping and arrive not functioning. Sometimes there’s actual damage or misalignment of an element in the lens, although the vast majority of the time that’s not the case. Usually the subject of the photograph is soft because the lens is not focusing precisely.
Three to 4 times a week we have the following conversation:
“The lens you sent me frontfocuses, its not good.”
“OK, we’ll overnight you a replacement.”
Then the first lens comes back and its perfectly fine when we check it out. But the customer is very happy with the replacement lens, it worked great even thought the first one didn’t. So what has happened? Its rather simple, actually, and like most examples of anti-logic it stems from a wrong assumption: the customer knows his/her camera is ‘fine’ because it works with fine with their other lenses—none of them front focus or back focus.
The key to the puzzle is the definition of ‘fine’. Most people assume that ‘fine’ means ‘perfectly calibrated’. In reality cameras are like any other manufactured item, calibration is within a given tolerance range. We don’t have privvy to what the actual tolerance range Canon, Nikon, or the other manufacturers (except Zeiss and Leica) consider acceptable, so lets arbitrarily say the manufacturer will consider a camera or lens to be ‘in specifications’ if its + or – 3 ‘focus units’ from perfect. We can assume they reached this number because anything within + or – 3 focus units will be within the depth of field of a wide aperture (probably f/2.8) lens.
Lets consider that I have a camera body that is -2 focus units from perfect, and a lens that is +2 focus units from perfect. Both are considered ‘fine’ according to the manufacturers definition, although they certainly aren’t perfect. However, the combination of a +2 lens on my -2 camera will be absolutely perfect, I’ll love the lens on my camera . After my experience with this one lens on one camera, I will write Sonnets on the various online forums about how great it is, and will tell anyone who doesn’t like it that they must be a bad photographer. I will have become the most dreaded online lifeform, a FLAO (Fanboy with Loss of All Objectivity).
But what if the lens was -2 focus units from the theoretical perfect and I put it on my -2 focus units from perfect camera? Well it depends. If the lens is say an f/4 maximum aperture, probably not much: the depth of field from an f/4 aperture lens may well mask a bit of front focusing or back focusing. You might notice the lens frontocuses 3 feet in front of the subject at 20 feet if you pixel peep, but since the depth of field is 10 feet the subject is still in focus and the lens seems fine. I will probably describe the lens as very good, but not descend to complete FLAOdom.
But if its an f/1.4 lens with a very shallow depth of field, the front focusing will be noticeable: the subject will be out of focus and soft. If I know how to do a front/backfocus test I may have figured out the problem, but here’s the kicker: if I sent the lens in to the manufacturer to fix the problem they would check the lens out, say it was fine (because it is fine, its within specifications) and send it back. Ony if I send the camera and lens together to be calibrated would the fact that the two together are out of focus be apparent, and then the manufacturer would be able to fix the calibration.
Ah, but there’s no free lunch. If the camera calibration was adjusted as part of the fix, I might find that another lens in my kit that used to be great, now backfocuses a bit. In the past, many full time pros who were aware of these issues, would send their entire collection of cameras and lenses to the manufacturer to be calibrated together. This was one of the original reasons Canon and Nikon formed their Professional Services groups. Most of the rest of us just made do, or sent copy after copy of a given lens back until we got one that was sharp ON OUR CAMERA.
The bad thing is many, many people who did this then hopped on their online camera forum and made blanket statements like “I had to try 3 copies before I found one that was calibrated right”. In reality what they should have said was “I had to try 3 copies before I found one that was calibrated right FOR MY CAMERA”. Those other two copies might well have been fine on someone else’s camera.
When you have a few dozen copies of each lens and each camera like we do, you quickly find out this is just a fact of camera reality. And the funny part of all this is the more expensive wide aperture lenses are the ones most likely to show the problem, because their depth of field is so narrow and the in-focus portion of the picture is so sharp compared to the out of focus portion. That $200 f/5.6 zoom is not going to show a minor front focus problem because the depth of field is about half a mile. The $2,000 f/1.4 prime has a depth of field of a few inches and any problems are immediately evident (and the owner 10 times more invested in wanting a perfect lens).
The good news is newer cameras have taken all this into account and the fix is right at your fingertips. The following cameras all have a “lens microcalibration” feature: Canon 1DMkIII, 1DsMkIII, 5DMkII, 50D; Nikon D3, D3x, D300, D700; the Pentax K20D, the Olympus E-30 and E-620, and the Sony A900. I’m surprised at how many people don’t take advantage of this feature – its a bit time consuming to do, but once done each of your lenses is locked in the camera’s memory and it will automatically compensate so that each lens is at a nearly perfect focusing plane whenever you mount it on the camera. I find the feature makes such a huge difference for most of my better lenses that I consider this feature alone makes the upgrade to one of the above bodies worthwhile.
Bad lenses (and cameras) will still exist, but the vast majority of front and backfocus issues will be a thing of the past. And for those of you who don’t have this feature, we will continue, as we always have, to do our best to get you a lens that works great on your camera, even when it means sending a replacement.
Roger Cicala
Lensrentals.com
More Lensrentals Articles
Addendum I recently saw the greatest real life example of this ever, in an online forum where the poster states ’Canon’s New XX camera sucks’ (I’m eliminating names so the bots don’t pick this up and repeat it.) He goes on to say he had a body for several years, and a hand picked collection of lenses that he knew were perfect because he’d gone through several copies of each to get the sharpest one. Now he bought a new body and all his lenses sucked, and he’d now exchanged bodies twice and they still all sucked. So here is the perfect example of a person starting with a camera at the edge of tolerance, choosing through multiple selection a set of edge-of-tolerance lenses, and now generalizing that all the new bodies suck. The sad part is the new body has microfocus adjustment and he never even tried it. Just sent copy after copy back to the store.
Great write up. Very helpful and right on. This is the best article on the net, dealing with the lens to body match up.
Thank You
Ken
love this article. i had a hard time deciding on buying EF24-70/2.8 due to many say of this softness issue. now i say what the heck, i wish to capture nice family moments instead of perfectly clinical sharp pictures..
thanks for the great explanation.
Kudos for having the patience to say “We’ll overnight you a replacement” rather than saying “Tough luck buddy, you get what you get”. You guys have great customer service.
And thanks for the explanation. I didn’t realize body and lens could be mismatched like that. And thankfully since I’ve got a 50D I can compensate. Thanks!
It’s also worth noting that lenses, mainly faster ones, have aperture-related focus shift. For optical reasons a typical DSLR focusing screen may ‘see’ the lens as if it is at f/2.8 or even f/4, despite it being an f/1.4. The same thing applies to AF modules. Pro and advanced DSLRs from Canon and Sony (not Nikon) have f/2.8 AF sensors which kick in only when using lenses of f/2.8 or faster, but with anything slower they use sensors which only make use of f/5.6 ‘worth’ of the lens. Sony’s amateur model sensors actually work at a very small aperture, f/7.1.
These factors – focus shift as aperture is changed, typically from wide open to f/8 with little further visible effect; focusing screen ‘effective aperture’ for manually checking; AF sensor working aperture; switching between wide aperture (f/2.8) and normal (f/5.6 etc) sensors – can all change your perception of how well a given lens performs for AF or indeed manual focus accuracy.
Combine it further with the fairly complex field flatness (or lack of) in fast and wide range zoom lenses, and the increasing use of wide area focusing arrays, and results can be unexpected. The good news is that the increasing provision of Contrast Detection direct focusing (AF, assisted or manual magnified) Live View can assure absolutely precise focus especially if combined with stopping down to working aperture. Live View focus checking now provides a very reliable quick way to set micro-focus adjustments on cameras like the 5D MkII though with models like Sony’s A900 and A850, which have no LV, it’s necessary to make repeated exposures, review them at maximum magnification and fine tune the results.
sort of like a car that isn’t pulling until new tires are put on or maybe the tires are rotated. the vehicle is out of alignment causing a pull to the left, the tires on the front have a radial pull to the right so the vehicle drives straight, rotate the back tires (no pull) to the front or install new tires (no pull) and now the car pulls left and the customer will swear the shop screwed up as “i didn’t have this problem before”
great article.
Love the article! Thank you very much! I purchased a canon 50mm F.1.8 a few months ago and i havent really touched it as it always seems to be soft, but i assumed it was just as it is just cheap glass. But now you have given me hope! But im currently trying to work out how to use my lens microcalibration function on my Canon 5D Mark II. I have found the option on my menu, but im unsure how to create the correct calibration for each of my lens’s. Please can you help me with how to follow out the process to get it right?
Thanks for the article, very useful. Although in my experience with a Nikon D7000 and AF-D 80-200mm (double ring) lens is that the distance of the subject and zoom range are also factors of focus calibration. I use the micro autofocus adjustment on the camera, but one setting is not enough. If the subject is far away at 200mm, I have to use -5, if middle range then -10, if very close then -20. At 80mm the difference is much less. At the local NIkon shop I was told that it can not be calibrated, I have to use a full frame body to be sharp at all ranges. What do you think of this?
I was considering buying one of your used Canon 7D’s and in doing the research I learned that the 7D also has a lens micro-calibration feature. Thought you might like to know that since you didn’t mention it in this article or in the specs.
Awesome article; I will bookmark it for forever.
Makes me want to know what to do with my problem. My camera doesn’t have the micro adjust feature. It is a Sony a580. I noticed severe backfocusing with my 90mm Sigma 2.8 macro but forgot about it after awhile and used the same lens fine for macro work. I splurged for a Zeiss 85mm 1.4 and it had worse backfocusing issues than the 90mm. I didn’t have any discernible issues on any of my other lenses, but I am not a rich man and I can’t live with a $1500 lens that I can’t count on to AF correctly. Right now it is in Sony Service and they said they will adjust the camera to the 85 1.4, but I am concerned that all my other lenses will then be unacceptable. What do you think they should do?
Eric,
Sony should be able to make that adjustment without affecting how your camera works with your other lenses. It’s such a great lens that I think it would be worth the trouble to let them fix it.
Roger
Luckily, some cameras, such as the Pentax K-5, have the option of saving the AF Adjustment setting globally (for all lenses) or specifically to one lens! I
agree that AF Adjustment is a very worthwhile exercise if one wants optimal image sharpness, but it begs the question of why other systems without this functionality seem to be able to deliver “sharp” images regardless of lens used; for example, the Panasonic m4/3 system.
Thanks, Steve
Hi Steve,
Panasonic m4/3 is doing AF using information gathered from the main (and only) sensor. During AF it “continuously” adjust the lens until the image on the sensor is in focus. It’s working the same way you make manual focus using live view.
The same is true for all systems using contrast detect AF with information from the main sensor: all almost all mirrorless, compacts.
One exception in mirrorless camp, Nikon 1 when using phase detection autofocus. Even if phase detection is integrated onto the main sensor, so body calibration is near perfect, lens calibration is still counting.
Marius
@Steve Solomon: m4/3 like all current mirrorless systems uses contrast detection AF, so it’s not subject to these problems, with the tradeoff of somewhat slower focusing speed. Read this other just-as-excellent article as to why: http://www.lensrentals.com/blog/2010/07/how-autofocus-often-works
I have one thing to add to the article. From my experience lenses behave differently at various distances. For example my 80-200mm f2.8 AF-D has stellar performance throughout its range anywhere from 3 to 10 meters but often underperforms at the long end when shooting distant objects.
Just my 2c worth. ;^)
Thanks for this. In the past I have been able to take all of my equipment in to Canon USA when I was having focusing issues and have them adjust them so they would all work together. I would bring in my camera bodies, and my main 4 fast prime lenses.
When I independently checked the focus accuracy with my SpyderLensCal, everything was spot on. Since the bodies I shoot with don’t have micro focus adjustment I was pleased as punch.
But it got me to thinking- if the tech at Canon really cares and knows what they are doing, they should be able to get bodies to adjust to a “zero” point and lenses as well. So there is reason for hope.
My advice to anyone who might be frustrated with spotty focusing is to take your gear in – ALL of it- to Canon and have the cameras serviced and adjusted. It is so worth it.
Great article. I love being able to microadjust all my fast primes on my Canon 5DII bodies and know the autofocus is going to get it spot on, at least most of the time.
Hi, great site! I also have sharpness issues but since I have a zoom lens (24-105mm L), how could I possibly get adjustments on different focal length? Also, how much difference does proper caibration make? No matter what I do, the images are always coming out less sharp when 100%. My old Nikon d70 gets sharper images than this! How come Canon website does not even address this or offer help, I mean it would be nice if they do if there really is nothing wrong with the SLRs. Thanks
Frankie,
The autofocus calibration can make your focus more accurate but it can’t make a soft lens sharp. With a zoom you usually can’t perfectly calibrate the entire range so most of us lock in the focal length we shoot at most of the time.
Roger
Well, about 3 years ago when I bought my camera and lenses (kit ones), I noticed that all of them front-focused more or less. I didn’t quite know much about bad focusing back then. Still I suspected it might have been a camera issue. So I addressed various specialized sites and forums, hopefully, to get an answer. Unfortunatelly, the few who tired to answer a noob like me, told me that there’s no such thing as camera bad focus, only lens bad focus. So I accepted the idea that all my online acquired lenses were bad and I had to deal with that. Time passed and I learnt that cameras can focus bad also, I wish I’d remember those a$$hole$…