7D Micro-Focus Adjustment - done for all (my) lenses

Started Apr 17, 2010 | Discussions thread
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kidmike
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7D Micro-Focus Adjustment - done for all (my) lenses
Apr 17, 2010

Today, I did my best to avoid doing real work, so I set up my 7D on a tripod, set up a bunch of lights, hung op a focus test chart, and tested each of my lenses with various micro-focus adjustments to find the sweet spot for each of my camera-lens combos. Some surprises.. and some as expected.

First, let me link to the original article that inspired me today, where "Hollis_F" posted a good step-by-step process.
http://photography-on-the.net/forum/showthread.php?t=795126&page=2
He also linked to the standard ISO 12233 chart in PDF format.
http://www.graphics.cornell.edu/~westin/misc/res-chart.html

I opened this PDF in Photoshop, and printed it at high res on Canon 13x19" glossy paper at 100% size (almost as large as the 13x19" paper it's on).

I set up a couple modeling lights I have, and later augmented with some more random lights when I needed to test the longer lenses and wanted more light. I hooked the 7D camera up to my computer via USB, and used the EOS Utility to capture direct to my HD. I set Lightroom to Auto-Import these pics as they appeared on my HD, as LR makes it very easy to compare closeups and resolution. I set up a separate directory for each of my lenses. I shot each zoom at the largets focal length, assuming that's where the narrowest Depth of Field is. Finally, I set the camera settings to Neutral to avoid any contrast changes or such.

To begin, I started with the low end of the MFA range, which goes from -20 to +20. Starting at -20, I took a picture every 5 intervals, so I ended up with 9 photos (-20, -15, -10, -5, 0, 5, 10, 15, 20). I took care to snap them in this order, and I immediately update the keywords for each with the setting, since there's no EXIF information to display the MFA amount.

Then, using Lightroom, I zoomed into the very center of the picture, and I just scrolled back and forth through all 9 files. A trend becomes very obvious, and after a couple trips through, you have an idea that the sweet spot is around a certain point. I then usually shot 3 more pics, one at that guess, and the others at +2 and -2. Repeated the viewing process. This got me close enough for me to be happy.

OK, OK, so I'm sure you want to know some results, right? OK, here goes:

Canon 50mm 1.8: +14
Canon 60mm 2.8 macro: -2
Canon 85mm 1.8: -15
Canon EF-S 17-55/2.8: -2
Canon 70-200/F4L: -5
Canon 100-400L: 0

OK, so conclusions? Well, the only big surprise to me was the 85mm/1.8, which I consider to be extremely sharp. It registered -15, and it was a big difference. The 50mm/1.8 is a very cheap lens, and I tested it just for giggles, and I will happily ignore that result.

And finally, someone will ask for samples, so I'll post just one example (not all 80+ RAWs, for obvious reasons). These samples are from the EF-S 17-55/2.8IS. Here is the worst case scenario, a +20 on the MFA scale: (NOTE: LARGE FILES!)
http://www.michaellandry.com/photos/839567823_wLivB-O.jpg
And here is the same lens, adjusted to the sweet spot of -2:
http://www.michaellandry.com/photos/839567823_wLivB-O.jpg

I'm sure someone will have some criticism of the steps I took, and that's more than welcome, but I'm not going through this again. It was, however, a nice way to waste my afternoon... now, to get out there and shoot something!

Mike

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Michael Landry Photography
http://www.michaellandry.com
Proud owner of a new Seven-D!

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