Lou_Meluso Posted May 31, 2012 Share Posted May 31, 2012 <p>When I got my 7D, I checked the focus accuracy of my EF primes and zooms and all were pretty close to spot on with a couple needing a point or two of front/back adjustment. No big deal and all are focusing well with this body. I recently purchased a 5DMK2 body and discovered the same situation with the lenses. Most fall in right on or need very minor tweak to get dialed in sweetly....except my EF 50mm f/1.4.<br> On the new body it needs a full -14 to pull proper focus yet on the 7D it needs no adjustment at all! The other lenses seem fine, it's just this one that is far off. Why is this? Is it the lens or the body that is a problem. It works quite well with the extreme adjustment so no point sending it in for repair. I'm just curious as to why there is this big difference, with this lens.</p> Link to comment Share on other sites More sharing options...
hjoseph7 Posted May 31, 2012 Share Posted May 31, 2012 <p>Full frame vs Crop ?</p> Link to comment Share on other sites More sharing options...
Lou_Meluso Posted May 31, 2012 Author Share Posted May 31, 2012 <p>Thanks Harry. I thought of that but I don't see how that should make a difference. The flange distance is the same. Why only one lens? I cleaned the contacts on the lens and still got the same result. Oddly, the focus speed was OK and the focus confirmation light came on. I first noticed it as I was testing it by shooting a house flat about 90 feet away. I stepped through the apertures and I could not believe how, even at that distance, even stopped down, how poorly the Canon lens performed. That led me to pull out the focus charts and test further on sample subjects near and far. That's where it became clear that it was seriously back focusing as a matter of course. After fussing with the focus adjustment for while I arrived at my current setting and I'm getting the performance I expected. Very Odd. Especially since the other lenses all work fine.</p> Link to comment Share on other sites More sharing options...
Marcus Ian Posted May 31, 2012 Share Posted May 31, 2012 <p>Harry's got a good point, the DOF is deeper, so it's simply possible you don't see the same necessity for fine adjustment. But also, there is variance from body to body.</p> <p>I know it is kind of counter intuitive, but since each lens varies optically, mechanically, and electrically in <em>how</em> it achieves the same thing, adjustments are not always predictable. </p> Link to comment Share on other sites More sharing options...
scott_ferris Posted May 31, 2012 Share Posted May 31, 2012 <p>Micro AF adjustments are dealing with incredibly small distance changes. One speck of sand on a mounting flange can take you all the way from one extreme to the other of adjustment.</p> <p>Also adjustment if focus distance specific, if you calibrated them at different distances it is quite common for the adjustments to be different. One recommendation is to check your focus distances in EXIF and calibrate your lenses to that distance, for instance if you shoot at 8 feet with your 85 f1.2 and use it wide open all the time then that is where you should set it up. But that is getting way too anal for the majority of people.</p> <p>I have found that good technique gets me better results than Micro AF adjustments for all but the lenses that need the most extreme adjustments.</p> Link to comment Share on other sites More sharing options...
alan_bryant1 Posted May 31, 2012 Share Posted May 31, 2012 <p>I'm dealing with the same thing on my new 5D3. I'd previously used a 5D mk 1 and 30D; neither of these cameras has AF adjustment, and neither needed it, since they both worked well with all of my lenses.</p> <p>Now I've got a new 5D mk 3. Most lenses work very well, but my first time out with the 70-200/2.8, I found the AF is pretty far off. Over a distance of 50 feet, it consistently front focuses by around 6 or 7 feet at 200mm. That's enough to miss basically every shot, but not enough that it's obviously wrong in the viewfinder. I don't have the gear with me now, but as I recall the correction I worked out was +10 at 200mm and +14 at 70mm.</p> <p>I am mystified as to how this one lens is so far off, when it's fine on the other cameras, and the other lenses are fine on all the cameras....?</p> <p>Scott, how does good technique help? If AF is consistently wrong, it's consistently wrong. Technique doesn't help that.</p> Link to comment Share on other sites More sharing options...
matthias_meixner2 Posted May 31, 2012 Share Posted May 31, 2012 <p>Just an idea: The elements in the lens do not stop moving immediately. Now if the camera thinks that things are in focus it tells the lens to stop focusing and triggers the shutter. Now if the lens elements continue moving slightly between the AF stop and taking the picture, the picture will be slightly out of focus. Microadusting would help in this case if AF always moves the lens elements in the same direction before stopping AF. It would anticipate the movement of the lens elements that happen just after the camera has sent the command to stop AF.</p> Link to comment Share on other sites More sharing options...
scott_ferris Posted May 31, 2012 Share Posted May 31, 2012 <p>Alan,</p> <p>You are right, if it consistently wrong, it is consistently wrong. But far too often micro AF adjustment is thrown out as a fix for bad technique or just missed focus on shots. I currently have seven AF lenses and none needed dramatic adjustments on my micro AF adjustable bodies, I see no noticeable differences between groups of shots with it on or off, there are always miss focused images during a session. I realise I am lucky but was just pointing out that often micro af is thrown out as a fix for that when it isn't.</p> <p>Your experiences with your 70-200 are a particular sort of problem, again Canon recommends either using the longest focal length, or, the one that you use the most, to set up micro AF settings, which doesn't help much if you bought your zoom to zoom! But if you send it to Canon and it has big variations across the zoom range then they can use multi-point remapping of the AF. Trouble with that is that it throws if off for your other bodies. I don't know the technical reasons for the variations you are seeing and can't help.</p> Link to comment Share on other sites More sharing options...
alan_bryant1 Posted May 31, 2012 Share Posted May 31, 2012 <p>FYI Scott, the 5D mk 3 allows setting different microadjustments for the long and short ends of the zoom range. I assume it interpolates the in-between focal lengths. I guess this is how future cameras will work.</p> <p>Perhaps the next generation will allow different corrections for different focus distances.</p> Link to comment Share on other sites More sharing options...
scott_ferris Posted May 31, 2012 Share Posted May 31, 2012 <p>I didn't know that Alan, it is an interesting advance that I hadn't noticed in the specs. Thanks.</p> Link to comment Share on other sites More sharing options...
curt wiler Posted June 1, 2012 Share Posted June 1, 2012 <p>Assuming you are dealing with phase detection autofocus here, the problem is not the lens mount distance but rather the distortion of wavefronts when they arrive at the sensors (which are not the image sensor, by the way). The lens optics may be slightly out of alignment, and the detectors in this particular body may be especially sensitive to it. That's why individual bodies and lenses may need to be calibrated to each other. Have you tried live view, which uses contrast detection for focus? This should be independent of these effects. Disclaimer: I do not use this camera, being a 50-year Nikon person, but the effects will be the same if the capabilities are comparable. See <a href="http://en.wikipedia.org/wiki/Autofocus">here</a> for a brief introduction to the subject.</p> Link to comment Share on other sites More sharing options...
matthias_meixner2 Posted June 1, 2012 Share Posted June 1, 2012 <p>A wrong AF sensor calibration would result in focus problems with all lenses and not just a very selected set of lenses.</p> Link to comment Share on other sites More sharing options...
Lou_Meluso Posted June 2, 2012 Author Share Posted June 2, 2012 <p>Thank you all for your thoughts. I tested my EF 50mm f/2.5 Macro lens on both bodies with no problems on focus. I suspect the f/1.4 lens is the problem here and I'll keep an eye on it for any drift. </p> Link to comment Share on other sites More sharing options...
Robin Smith Posted June 2, 2012 Share Posted June 2, 2012 My 50/1.4 is perfect as is on my 5dII. Curious. I generally share Scott's view of AF adjustment, but sometimes clearly something needs fixing. Robin Smith Link to comment Share on other sites More sharing options...
tpurvis Posted June 2, 2012 Share Posted June 2, 2012 I found this to be the case last weekend. I was shooting a wedding with 2 7Ds. One was mine, the other my sons. I have had an issue with my camera and my 85 1.8. The focus is off and I have yet to get it adjusted on this body. I almost left this lens at home, which would have been a shame. I mounted the lens on my sons body and was blown away by how sharp it is. I will be buying some sort of lens adjustment tool and registering all my lenses on both bodies. Link to comment Share on other sites More sharing options...
scott_ferris Posted June 2, 2012 Share Posted June 2, 2012 <p>Tom,</p> <p>Don't buy anything, far and away the most accurate way of doing it is free. <a href="http://www.northlight-images.co.uk/article_pages/cameras/1ds3_af_micoadjustment.html">Here is a very good article</a> on how to do it.</p> Link to comment Share on other sites More sharing options...
tpurvis Posted June 2, 2012 Share Posted June 2, 2012 Thanks Scott. I had seen this and am glad to hear that someone of your experience recommends this process. Link to comment Share on other sites More sharing options...
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