Canon EF 50mm F1.2 L Lens’ Dynamic Back-Focus

Test Chart shot with the Canon EF 50mm F1.2 L Lens

12 Aug 2009 Canon EF 50mm F1.2 L Lens’ Dynamic Back-Focus

On August 1st, I bought a Canon EF 50mm F1.2 L USM Lens. I’d been thinking of getting this lens for a long time, though had held off because I heard that it back focused when trying to focus on things close to the lens. For much of my current work though, if I’m working close up, I often use LiveView and manual focus anyway, so I thought I’d go for it. After all, I usually put claims of back-focusing down to bad technique. I’ve not had a single lens that back focuses myself, and I’ve been through some glass.

Anyway, I’d been pretty busy over the last 10 days, but as I was coming towards the end of my two weeks grace period to take the lens back if there were problems, I figured I’d do a few tests. I set up my tripod and grabbed the Focus Test Chart that Tim Jackson kindly made available a few years ago, and shot a few tests. To cut to the chase, I took the lens back and got a refund.

I have to admit I thought it was going to be a bit sharper wide open than it is. My 85mm F1.2 is much sharper wide open. Still, this is not the reason for my disappointment. Read on to see what happened…

First, here’s an animation of a cropped and of course re-sized image, showing most of the test chart page. This is really to let you see the big picture (pardon the pun). To see the 100% crop, you’ll need to scroll down a little more. First though, note that I used the 5D Mark II’s Autofocus Micro-adjustment feature to set the camera to bring the focus forward by 2 steps, and that was enough to make it possible to auto-focus on the black line that runs through the middle of the Test Chart. From this point, there was no more back-focusing, which is a good start, I’d hoped. Note, the 2 steps in the micro-adjustment does not necessarily equal 2mm, though it seemed to in my case today. Apparently the distance that a step adjust the focus depends on the maximum aperture of the lens (according to the 5D2 manual).

Test Chart shot with the Canon EF 50mm F1.2 L Lens

Test Chart shot with the Canon EF 50mm F1.2 L Lens

Now that you have an idea of what the entire chart looks like, take a look at a 100% crop of the right side of the chart (below). As we reel through apertures 1.2, 1.4, 2.0, 2.8, 4.0, 5.6 and 8.0, although it’s very soft to start with, you can see that the focus starts with the 2mm text both above and below the line of small text pretty much the same. They are both blurred, but to roughly the same degree. That’s because I did the micro-adjustment, and I used LiveView to ensure that the focus was set on the thick black line on the chart before starting to shoot. As I said, I didn’t start back-focused.

I didn’t adjust the focus again at all as I shot through apertures 1.2, 1.4, 2.0, 2.8, 4.0, 5.6 and 8.0. I actually shot F11 and F16 as well, there wasn’t much point in including these apertures here. Take a look, and see what you think of these results before reading on below.

100% Crop of right side of Test Chart

100% Crop of right side of Test Chart

As you can see, despite the fact that I focused as closely as possible on the thick black line on the chart, which is the same distance from the camera as the text that says “This text should be perfectly in focus” in this crop, the text starts to sharpen up from the back “2mm” text. Then the depth-of-field continues to increase backwards, and doesn’t really come forward to sharpen up the front “2mm” until we get to around F8.

Here’s what’s happening; as the aperture closes, the point of focus is slipping slowly backwards. By the time the lens starts to sharpen up at F2.0, the focus is already back as far as the back 2mm text, and because the focus continues to move backwards, it takes an aperture of F8 to give us enough depth-of-field to encompass the front 2mm text.

Of course, the depth-of-field should be distributed by around 1/3 in front and 2/3 behind the point on which we set the focus. But that’s not what we’re seeing here.

Because of this “dynamic” shift backwards, the only way to manually correct the focus while shooting is to hit the depth-of-field preview button near the lens mount on the camera body, and focus with the button depressed. I tested this at F2.0, F4.0 and F5.6, and it is possible to focus correctly, but when you look through the lens or check with live view without the DoF preview button pressed, and therefore the lens automatically set to wide open at F1.2, the focus runs off.

I was prepared to live with having to manually focus this lens when shooting things close to the camera, but I am not prepared to do all of my focus adjustments with the depth-of-field preview button pressed. That to me is just bad design.

I do just want to reiterate, that this problem only seems to happen when focusing at around 50cms, as in my tests. If you do not intend to work this closely, the lens is probably fine. There are many people getting great results with this lens at longer shooting distances. I might buy another copy at some point, and just forget about using it close up.

I am not prepared to put up with this at the moment though. I threw my test shots onto my laptop and took it to show the folks at the camera shop. Even though I’ve heard that Canon advises manual focus adjustment at close distances with this lens (though I can’t find a link to this statement anywhere), I was hoping that the the people at the camera store would tell me that the focus should not dynamically shift backwards, and suggest that I might have a dud lens. It would have been the my first dud lens from Canon, but I was hoping that would be their response. They didn’t say that though, and they couldn’t say that replacing the lens would make it any better, so I asked for my money back.

Boy am I glad that I checked this lens before my two week grace period ran out. I have to admit, I’m sad about this. I wanted to love this lens. I like the focal length, and I wanted that insane bokeh for some work that’s coming up, as well as some of my flowerscapes, but I just couldn’t bring myself to try another copy today. Maybe I’ll buy another copy later. For now, I’ve got a little space in my lens cabinet that looks awfully sad.

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32 Comments
  • kel
    Posted at 02:08h, 15 December Reply

    Did you send the lens to Canon with your camera body or just the lens? if just the lens, did you tell canon what type of camera you use the 50mm for?

    • Martin Bailey
      Posted at 23:51h, 15 December Reply

      I took the lens to Canon without a camera, as I use the lens with three different ones. I did tell them which cameras I used though. Either way, the lens doesn’t focus properly up close unless you manually tweak it.

  • Tom K.
    Posted at 07:48h, 28 June Reply

    I don’t know. You should have tried this lens in the real world for a while. This guy shoots it at f/1.2 all the time and his results are superb: http://www.flickr.com/photos/petezelewski/

    • Martin Bailey
      Posted at 10:10h, 28 June Reply

      I couldn’t resist it and actually bought another copy of this lens a few years ago, and have been very happy with it. BUT, the focus runs out a lot in certain circumstances. I had Canon adjust it so that it focuses to the front a little more than it should, and it’s doing fine.

      • Tom K.
        Posted at 10:29h, 28 June Reply

        I just bought one and received it today. I have to take it out, hopefully tomorrow. I did take a few shots with it indoors and using f/1.2 is going to take some skill on my part. I have a 5D mark 2 which has micro-adjust. I have never done that to a lens before. Never had to. I hope this lens works out for me. I love the 50mm focal length and I love fast lenses. This lens has a very controversial reputation. Some love it. Some despise it. If it is not flawless I will send it to Canon for calibration.

        • Martin Bailey
          Posted at 11:44h, 28 June Reply

          Tom, if you want flawless, you might as well send it back right now. Really, the lens is flawed from the design up. That’s why I send my first one back.

          BUT, as you say, and I already knew, many people love and get great results from this lens. Fact is, my best shots with this lens wide open have the focus tweaked manually as I shoot. Well, that was before I had Canon adjust it. I also have micro-adjustment, but I use a number of cameras and can’t be bothered to test and change them all. I prefer the base products to just work.

          This is the only Canon lens that I’ve ever had to have adjusted like this, but it’s worth it. It’s a great little lens, once you learn how to get the best out of it.

          • Tom K.
            Posted at 15:04h, 28 June Reply

            I have been testing it some inside this evening and after some testing it required no micro-adjustment. The shots I did take we’re all in my house with nothing but conventional indoor lighting such as lamps. I have to say the focus has been dead perfect except for one that just barely missed. That could have been user error. I can’t wait to get this thing outside.

            I am incredible grateful for your feedback Martin. It has been extremely helpful.

            • Martin Bailey
              Posted at 16:13h, 28 June Reply

              If you were shooting at f/1.2 and got those results, then you might just have a copy without the usual problems. Congratulations!

              Cheers,
              Martin.

        • Martin Bailey
          Posted at 11:51h, 28 June Reply

          By the way, Canon can’t calibrate it, because as I said in this post, the back-focusing isn’t constant. It shifts dynamically as the subject gets further away from the camera. The only thing you can do is try to optimize it for your own shooting style. As depth-of-field increases as the subject gets further away though, the Depth-of-Field increases, so increasing accuracy for object nearby is best. That’s when the lens runs out most too.

          • Tom K.
            Posted at 15:15h, 28 June Reply

            Martin,
            I see that you shot with a 5D mark 3 and the 50 f/1.2. Does the improved autofocus on the 5D Mark 3 improve the autofocus on the 50L?

            • Martin Bailey
              Posted at 16:09h, 28 June Reply

              Hi Tom,

              I’ve not noticed any problems at all, but as I said, I had Canon adjust the lens, so it’s no longer performing like one straight out of the box.

              Cheers,
              Martin.

  • 50mm Lens
    Posted at 12:50h, 25 March Reply

    There a lot of really good and affordable 50mm lenses out there, it really just comes down to which brand your prefer. They are all quite good.

  • Michael
    Posted at 07:33h, 09 December Reply

    Yeah, to me the 50mm 1.2 L lens was a huge let down. Much of what I attempted to use it for was close up available light portraits. The back focus issue is too significant to ignore or compensate for in post production as someone suggested. Now my assistant uses it as he’s ofter further away and I use the 50mm 1.4.

    For me I just add it to the list of misfit products that Canon has released while leaving their professional clientele hangin’. Others on the list would be the:

    1D MKIII and focusing and AI servo focusing shortcomings. Replaced sub mirror and still not as good as 1D MKII. Focus point selection (not being able to select it in a linear fashion as with previous models) was a huge step backward.

    1D MKIV – major short comings with focus and shooting in low light (as with the MKIII this could be with a percent of bodies built – many of the reviews that point to the flaws on popular retail sites have been removed – mine included). High level noise is almost unacceptable when compared to Nikon D3S. It could have been a great camera and perhaps several of us just received bogus copies…I’ll never know b/c I’m not going to sail that ship again.

    580EXII – too many flawed units built. Still shooting with 580EX’s as a result.

    Will the list go on? I may just finally make the switch to Nikon and I’m tired of waiting to see if Canon will get back on track. They were once the leaders not too long ago…

    Michael

  • Martin Bailey
    Posted at 10:53h, 09 March Reply

    Igor,

    Thanks for the comment, but I think you missed the point somewhat.

    What you say is correct, and as I mention above, I may even buy this lens again at some point, accepting it’s shortcomings. I know that it’s a great lens when used at a reasonable working distance. You don’t need to convince me of this. But, I also wanted to use it at minimal focus distance with wide open apertures, and this lens with it’s current design will not enable me to do that. This is why I took mine back.

    At some point, I will probably pick up another copy, and just rule out the possibility of shooting close with it. I have plenty of other Canon lenses that will allow me to do that, without a trade-off in image quality.

    Cheers,
    Martin.

  • Igor
    Posted at 18:01h, 07 March Reply

    Hi,

    I did my own review of this lens on the link above and found that I could not replicate the back focus issue or that it was so slight that in real world use it won’t matter.

    Let’s assume all 50mm f1.2 L’s have back focus as described above. Is it that much of a problem really? Some of Leica’s most expensive glass (35mm Summilux ASPH and pre-ASPH) back focus but this is slight and something that if you know about it it can be easy to compensate. The overall qualities of lens can often make up for minor technical problems.

    For instance, this 50 also exhibits strong CA at large apertures in fringes of scenes with high contrast which could also be seen as a problem but again you can compensate for it in post processing.

    To finish off, there is a compromise in everything we do and I don’t think you will ever find a perfect lens no matter what the money is you pay for it (Noctilux is a prime example of this). It is important to know what the issues are so that you can work the compensating for them in your photography workflow and then just get on with the shooting.

    Cheers, I

  • Will
    Posted at 18:20h, 11 October Reply

    Casual location portraiture is nice, I like to photograph people outside if I can, it’s so much better than in a studio.

    I had a look through your gallery, your wildlife photography is pretty awe inspiring. It’s something I’ve never done, but have a lot of respect for. You need a lot of patience and have to be able to endure the cold…I’m from Scotland and I guess I can naturally do the latter.

    If you are ever exhibiting in Tokyo let me know.

    Will

    • Martin Bailey
      Posted at 11:01h, 13 October Reply

      For sure, you need patience to get some of the wildlife work that I do. Much of it also is about knowing where to go at what time of year. I run tours in Hokkaido, and Nagano from next year, helping others to get similar images.

      Thanks for looking at the gallery too! I’ll definitely be shouting about an exhibition when I finally get around to planning it. I was hoping to at least get a plan in place this year, but there’s so much other stuff going on, it might end up being carried over to 2010 now.

  • Martin Bailey
    Posted at 14:00h, 11 October Reply

    I’m not going to be shooting coming of age or 7-5-3 etc Will. I have no interest in that sort of photography. I’m trying to cultivate a market for more casual location portraiture. I don’t want to own a studio and do the family Kimono shots. :-)

  • Will
    Posted at 13:42h, 11 October Reply

    Everyone I know with the 85 1.2 loves it. Glad you are putting it to good use with the family shoots your doing. It’s a good market to be in here, hope you manage to get a lot of work with coming-of-age etc.

    Cheers

    Will

  • Will
    Posted at 17:58h, 10 October Reply

    Hi Martin,

    Glad I came across your blog. I too was thinking of buying a canon 50mm F 1.2 L lens from Fujiyacamera in Nakano, but I have been doing some research on it and I was beginning to think it was a bad idea (even though I really wanted to get one and love using it). Reading your blog has made my decision for me, I’m not getting it. I got a 24-70 f 2.8L last year and I have got so much good work out of it I think it’s a waste to invest in a 50 mm f 1.2L as the performance doesn’t really match the price. Maybe in time a better one will come out.

    Ah well, will have to think of another new toy to play with.

    Cheers

    Will

    p.s. Did I talk to you at a shoot during fashion week this Spring? You look familiar.

    • Martin Bailey
      Posted at 12:39h, 11 October Reply

      Hi Will,

      I’m pleased the review helped. I too am hoping that a model II of this lens comes out, fixing the near focusing issues.

      I should stress that if you don’t want to focus on things pretty close to the camera, this is still a good lens. You just have to use it at 3 feet or more distance, or you’ll see the focusing issues.

      Not to confuse matters, but for work more than three feet, I would still like this lens. I just find it hard to justify paying for such a lens that has an inherent problem that Canon cannot bring themselves to fix.

      The 24-70/2.8 is a great lens. I did four family shoots yesterday, and although I took a bunch of lenses, I used only the 85mm/1.2 and the 24-70/2.8. Great lens!

      Unfortunately it wasn’t me at Fashion Week. I wasn’t there. :-)

  • Martin Bailey
    Posted at 21:14h, 01 September Reply

    Hi Brian,

    Thanks for the comments.

    Yes, our findings seem to be pretty much the same. I originally called it “dynamic back focus”, which you could also call “focus creep” or “focus shift”.

    When I used auto-focus originally, it back-focused by around 2mm, which I did fix with the in camera calibration, but the focus creeps backwards as the aperture closes for the actual shot. This happens when you manually focus as well as auto-focus, and as you reiterate, cannot be fixed with calibration.

    I realize that this is predictable and therefore can be worked around, but I personally am not interested in paying this much for an L lens only to have to use workarounds to make it do what it should do by design. The fact is, it’s badly designed.

    I really wanted this lens to be workable for me, but with the close work that I also wanted to use it for, I don’t feel it’s practical. I might revisit it at some point, and just resign myself to the fact that I would not realistically be able to use it close up. I know that it’s a cracking lens when used for subjects of further than three feet or so away.

  • Brian
    Posted at 20:11h, 01 September Reply

    Hi Martin – your tests accurately reflected the nature of this lens. See this explanation below taken from dpreview:

    “Basically, the focus shifts back slightly when the shutter is released creating a photo that’s not perfectly in focus when taking a picture at between f2 to around f4 at a distance of less than three to five feet while the subject appears to be manually or auto in focus.

    This isn’t a back focus issue. The slight “focus shift” is caused by the lens design, not the auto focus mechanism in the camera or lens, so it can’t be corrected with calibration and you can’t get around it by focusing manually. It is very minor and predictable though, and there are several “work arounds” out there.

    As I mentioned in an earlier post this has never been an issue in my real world photo efforts since I purchased my 50 1.2 L in December of 2006.

    Here are a few threads that discuss the 50L’s focus shift:

    http://forums.dpreview.com/…forums/read.asp?forum=1029&message=32534282

    http://forums.dpreview.com/…forums/read.asp?forum=1029&message=32365163

    http://forums.dpreview.com/…forums/read.asp?forum=1029&message=32165069

    I hope this tells you everything you wanted to know.
    Brian.

  • Martin Bailey
    Posted at 14:05h, 18 August Reply

    Great test shots Holly, as usual. 😀

    I do enjoy my 50mm F1.4 as well, but have to admit that I haven’t taken it out much at all lately. I too will stick it on the camera soon and put it through its paces again.

    The 85mm is as you say though, just so much better, as one would expect from the price. I’d rather pay another few hundred dollars for a usable 50mm F1.2 L if it could get close to the 85mm.

  • Holly Sisson
    Posted at 00:19h, 14 August Reply

    I have the 50 1.4 and rarely shoot with it. If it is winter, and I am shooting inside a clients home, I’ll throw it in my kit in case there isn’t enough room to make the 85 1.2L work, but the 85 is so superior (as to be expected) that it is difficult to shoot with the 50 unless it is absolutely necessary. When I first bought the 50 1.4 I tested it out shooting old antique toy vehicles (seen in this blog post: http://hollysissonphotography.com/blog/2008/06/02/to-the-distillery-district-and-the-beach/ ), and was pretty satisfied that I had a sharp copy of the lens. Some of the images were shot wide open, some slightly stopped down. I bought it at the same time as the 85 1.2L which is on the CPS list, the 50 is not (as it’s not a professional lens), but the camera store gave it to me for a discounted price, so it doesn’t hurt to have it on hand I guess.

    Actually, going out for an outing and lunch with my daughter next week, think I’ll try and travel a bit lighter (I’ll be carrying home 10 lbs of coffee beans!), so think I’ll bring the 5D (much lighter compared to the 1D MkIII) with the 50 1.4 attached…and see how I make out.

  • Martin Bailey
    Posted at 00:17h, 14 August Reply

    Holly,

    I also wrote this in the forum earlier, but I’m wondering if Canon limited the 85mm F1.2 to three feet (95cm) for this very reason. If they new that their design caused problems when focusing closely, they could theoretically just stop it from being able to do so, right?

    I’d rather they did just that with the 50mm F1.2, because from what we hear, it certainly does perform exactly from three feet or more away.

    With the 50mm F1.2 only having been out a few years, I doubt that they’ll redesign it as a II in the near future. I guess my only option is to forget about using it close up, and get another copy, or just forget about it, period.

    Cheers,
    Martin.

  • Holly Sisson
    Posted at 00:07h, 14 August Reply

    Absolutely Martin, I can see why you’d want that close up ability with the 50 since the 85 can’t focus that close. It is a real shame that the 50 doesn’t perform as well as the 85. I often wonder why photographers have the 50 over the 85, I think they possibly haven’t done their research, for if they had they should know that the 85 has a stellar rep compared the to 50. For those who use it for portraits (i.e. Becker) perhaps it works as well as the 85 in those instances (further back)…but I often focus as closely as I can with the 85 1.2L and achieve fabulous results. Ah well, what can we do?

  • Martin Bailey
    Posted at 10:14h, 13 August Reply

    Thanks for the comments folks! I really appreciate it.

    Eric, I was wondering that myself. I’ll try the 50mm F1.4 again and let you know. It is very soft wide open, but that’s to be expected. I personally expected this 50mm F1.2 L to be much sharper wide open than we can see it is above.

    Also Eric, as we noted recently, the 100-400mm is an L lens, but definitely not the sharpest pencil in the box. All L lenses were not create equal, that’s for sure.

    Whythe, I agree that the back two might look a hair sharper than the front two, but bear in mind that I calibrated the focus in single steps in the Autofocus Micro-adjustment, and one step further forward was obviously too much. Also, when I’m focused on that thick black line, the back 2mm should be slightly sharper, because DoF should extend 1/3 forwards and 2/3 back from the line.

    More importantly, as you can see from the animation, the depth-of-field only ever extends backwards. If there was no backwards creep in the focus, the front 2mm should be totally in focus before the 6mm mark at the back, but that isn’t the case. As you can see, the 14mm mark is sharp before the front two. 😀

    Landon, I heard The Becker talking about the 50mm F1.2 recently as well. I think I listened early last week, a few days after I picked mine up. The thing is, from what I hear, this lens performs badly close up. I even read somewhere that Canon made a statement that it has to be focused manually when you get close to the nearest focusing distance. That was what had put me off it for a long time, but I figured because I was shooting with LiveView most of the time anyway, when doing the sort of close work that I’d use the 50mm for, that I could live with the manual focus adjustments. What I wasn’t ready for was having to focus with the DoF Preview button pressed, which is just silly.

    I’m sure that once you step back a few feet, this lens performs much, much better. I didn’t even test it though, as I knew that the problems at close range would bug me to much to put up with it in a $1,400 lens. 😀

  • Eric Vogt
    Posted at 09:03h, 13 August Reply

    How does the 1.2L compare to the f1.4 lens. I know the L lens should be better (I LOVE my 70-200mm L), but does this stay true for the 50mm lenses?

  • Holly Sisson
    Posted at 01:46h, 13 August Reply

    I’ve heard that the 50 1.2L isn’t as sharp as the 85 1.2L (which is known to be tack sharp wide open, if you nail the focus, mine certainly is). I wish the 50 had a better rep, as like you I’d love to add it to my collection, alas this review seems to make it more clear that it’s not a good beat. Wish Canon would reengineer it. If the 85 would allow for a smaller min. focus distance it would be perfect. (What the heck, add IS to the mix and it WOULD be perfect!)

  • Wythe Whiting
    Posted at 00:37h, 13 August Reply

    Hi Martin,

    To my eye at f1.2 the lens seems to be a bit back-focused. Though it’s hard to tell b/c both the front and back 2mm marks are blurred, the 2mm in the back seems a hair sharper to my eye. If this is true, then the back focus may not be “dynamic”, but static. Have you tried adjusting the backfocus in-camera a bit more (one more click) to see if the problem clears?

  • Landon
    Posted at 00:31h, 13 August Reply

    Boy howdy, that certainly does creep backwards. Good thing you tested it fully.
    Drifting backfocus is not something you are going to be able to correct for in a lens settings preference menu either.
    Interesting too that The Becker uses this exact lens 90% of the time. So it is a specimen or batch problem?

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