Microadjusting lenses - example

I just got a Micro Lens Cal device which you use to make microadjusting your lenses a simple operation. To use it you simply ensure your camera and the MLC are on the same plane - I mounted each on tripods and leveled and checked height of lens and DLC. Then you simply follow the Canon owners manual on microadjustment - set center focus spot, single focus, lens wide open and make sure you're at least 50 times the focal length distance from the DLC (in this example I was using the 85L lens so I was about 15 feet away). I next took 3 photos each with 0 ma, -5, -10, +5 and +10. I then loaded all the photos into Lightroom to better view the results (my bodies don't have the latest hi-res screens). In my case the widest settings were -5 and +10 (typically I was hovering about +/- 5. You can vividly see where the best setting is for a given lens/body combo. In the attached photos the left is the 85L standard - no ma. The right is with only -5 ma. I tweaked the settings a bit thereafter but you can see the change. When using f1.2 just a hair off really shows. Besides the ruler, notice the text in the upper left corner. (The photos don't show this clearly but the top of the ruler is about 3 inches behind the target and the bottom is 3 inches in front, with 0 being on plane. Also my apologies for the crop size of the two photos not being equal, but you see the difference). I wasn't having any focus issues but I read an article about this device so I got myself an early Christmas gift. Well worth the $50 to make sure your equipment is working properly.

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Holy chromatic aberrations!

Anyways, glad it works for you.

It looks like it's still back focusing...

why do the 85s have such bad CA.

Try it at both minimum and maximum zoom (not with the prime obviously but in general), and both close to the target and distant. You'll probably find there's no one MA value that works for everything. Canon lenses generally need calibration to get the lens right at all zoom/distance combinations, even then it can take Canon a few tried to get it working properly.

I am still wondering how you can align correctly with such target ..
Lensalign pro has got holes with 10cm deep red pins to get a perfect alignment. Actually, I wouldn't trust your results without being sure your sensor is at exactly parallel from the target.

newworld666 wrote in post #11421589
I am still wondering how you can align correctly with such target ..

The target you focus on is right next to the measurement point. Unless you've got the calibration device almost perpendicular to the camera, it's not going to be off by more than a fraction of a mm, and certainly well within the depth of field of any lens you're likely to be working with.

Actually there is clearly "a type" of back focusing, but I wouldn't trust it, till I am not sure the sensor is parallel to the target.

Frugal wrote in post #11418707
It looks like it's still back focusing...

That's been dialed out (-3ma). Per the Canon owners manual they say adjust in large steps (I was using increments of 5). It was amazing how in just an adjustment of 5 units could take the ruler from fully blurred to pretty sharp. I got my lenses so the ruler was clear typically from +2 to -2. No single adjustment would give just a clear 0 and all else blurred. Each numbered increment is less than an inch so even at 1.2 you still have a couple inches of DOF (you aren't supposed to calibrate at the minimum focus distance - depending on my lens I was shooting at between 6 feet and 60 feet). Also when using this device you are shooting at the distance where the center focus spot aligns with the large black/white square. When looking though the viewfinder the focus spot will cover a good part of that area. I then assure that I'm square and level to the device but in actual use you don't have to split hairs - just set-up fairly resonable and shoot. Surprisingly in my case the "infamous" 50L took the least amount of adjustment (0 on one body and 3 on the other) where the 135 took the most (8 and 10 ma) on the two bodies. But as I said in my original post I wasn't having any issues, but simply wanted to confirm all was working within limits (particularly while some equipment is still under warranty). All in all a helpful tool if you have the ability to micro-adjust your camera/lens combinations.