Sigma 35mm f/1.4 Micro Adjustment?

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  ziggy53 Super Moderators Posts: 23,851 moderator

  September 19, 2013 edited September 19, 2013

  Many, if not most, of the Canon microfocus adjust (MFA) information on the Internet is not helpful, and some of it will just cause you more problems than doing nothing.
  
  Before you decide if you need the MFA, do some testing yourself:
  
  Please do the following tests in order:
  
  The first thing that I do is to check a new (or new to me) lens for autofocus accuracy and speed. While the speed thing is more subjective, as in "Is the speed sufficient for my intended use?", focus accuracy can decide whether you keep the lens or return the lens (or sell the lens if you don't have return privileges).
  
  When I test a new lens I often choose a few different subjects for comparison:
  
  1) A brick wall, shot straight on and squared with, using a tripod. This is a pretty good test for front-focus, back-focus, field curvature and vignetting issues. If a camera/lens combination does not focus accurately in this test, something needs to be serviced. Make sure to test at least twice MFD from the wall.
  
  2) A fence line or similar, shot at an angle to the subject. Put a singular strong-contrast target on the top of the middle post and use a single focus point in the camera to focus against the target. This shows focus accuracy and/or how easily distracting for/aft objects influence AF accuracy (compared to the above wall shot). It also shows bokeh tendencies at different aperture settings.
  
  3) A focus target/chart like in the following:
  
  http://regex.info/blog/photo-tech/focus-chart
  
  I do recommend testing these charts at twice minimum focus distance or greater. Most lenses, especially most zoom lenses, do not do their best at MFD. True macro lenses are the major exception.
  
  4) A US stop sign, or similar very high contrast signage, both centered and off center and to the side and/or corner. This can show chromatic errors and off-axis errors.
  
  5) A spectral highlight at night. (Point source ideally, but a street light at some distance will do.) Try to avoid "blooming" of the source but allow some white clipping. This shows internal reflections and dispersion problems. Again, test both in the center and with the subject at the sides or corners.
  
  6) Now just shoot "typical" subjects for your use of the lens(es). It's important that the lens perform correctly for your intended uses.

  ziggy53
  Moderator of the Cameras and Accessories forums

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  Matthew Saville Registered Users, Retired Mod Posts: 3,352 Major grins

  September 19, 2013 edited September 19, 2013

  LoganH wrote: »

  Edit: I just found a youtube video showing how to micro adjust. But could not find the micro adjust within the menu system of the T3i. After looking at the usb dock more closely and a comment left by a buyer, it appears the T3i does not have this micro adjustment feature in the camera.....so it seems I have to buy this usb dock to get my focus exactly right......................not happy.

  
  Yep, I'm very used to doing AF microadjustment with all my pro cameras for the work I do, but I just bought a Nikon D5200 the other day as a small, lightweight camera and I found that it too does not have any form of AF adjustment. I was dumbfounded by this, but luckily the camera seems to focus perfectly with all my lenses.
  
  Aside from the fact that your camera simply cannot calibrate your lenses, it would still be nice to know whether or not you can count on this lens to function without any calibration. I especially like Ziggy's #2 test method, though I usually just go up on my apartment balcony and take pictures at a shallow angle of the grassy area below. Again the trick is to focus on something that more than fills your selected focus point, so that there is no room for error, yet you can still see a clean transition from foreground to background.
  
  I would add another tip to the mix- turn your in-camera sharpening all the way up to it's max, and use one of the more vibrant picture styles overall. This will allow you to check your focus on the back of your camera effortlessly, without using a computer or software to do any silly calculations.
  
  Of course if you shoot JPG or video, be sure to turn your sharpening and picture styles back to whatever you usually prefer, because while this is great for RAW shooters who like to determine sharpness easily, this will ruin your images otherwise.
  
  Honestly, I think charts and graphs and software are for people who have more money than they know what to do with. A simple test focusing on a tree trunk in the park will be perfectly accurate, as long as you understand simple geometry and get the angle correct.
  
  Either way, if you set up your test right you should be able to clearly see where focus is, in relation to where it should be.
  
  As with any test, be sure to eliminate any variables for error, and click multiple test shots. I use a solid tripod and a cable release that can perform autofocus. I perform my tests in bright sun and then also in dim light, but bright sun should be a priority of course for the best accuracy.
  
  And there's a very good chance that, even without any focus adjustment, your Sigma will shoot perfectly on your T3i. As it is a big chunk of glass, of course, you will want to keep in mind that no super-fast prime can nail every single shot every single time, when used on anything less than a flagship camera. (And even then your keeper rate at f/1.4 and close distances may not be 100%) So, in other words, even when you're on the job and you know your lens is focusing perfectly, you should be clicking 2-3-4 shots depending on the overall reliability of your camera's autofocus. I have seen many people get angry at their lenses for not focusing accurately, when it is the body's overall consistency that is the problem. ;-)
  
  Good luck!
  
  =Matt=

  “My first thought is always of light.” – Galen Rowell
  My SmugMug Portfolio • My Astro-Landscape Photo Blog • Dgrin Weddings Forum

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  LoganH Registered Users Posts: 113 Major grins

  September 21, 2013 edited September 21, 2013

  Wow. Thanks for all of this information! I will try many of these tests tomorrow!!!

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  Email: loganhickle91@gmail.com

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