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Old 09-14-2012, 02:57 PM   #1
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Join Date: Mar 2006
Location: NW Burbs of Chicago
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Have You Micro-Focus Adjusted Your Camera?

Some of the newer dSLR cameras allow you to calibrate the focus of your camera/lens combo if you find that it consistently front or back focuses.

Have anyone tried this feature? Do you really notice a difference?

I was suspicious that my 7d and 50mm f/1.4 had some focus issues so I printed out a focus chart and took a picture on my tripod with MLU and timer with my MFA at 0 and one at +15 and I could not notice any difference at 100% crop.

I am wondering what I did wrong with my test or if they call it MICRO for a reason, and the impact is too small to notice in some cases.

Any success stories with this feature or is it just marketing hype?

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Old 09-14-2012, 04:01 PM   #2
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Usually if you suspect back or front focus issues with a lens, the best way to test for it would be to use a focus chart, or some highly detailed subject to shoot that has a linear pattern, laying it flat face-up on a flat surface, and take the shot with your lens at a roughly 40-45 degree angle to the sheet (this helps reveal the depth very clearly, as you have lines/detail close to you and extending all the way through the center focus and rearward...helping you determine EXACTLY where your focus is trying to aim). How you photograph the focus chart is pretty vital to the test - just make sure you were shooting it in that manner. And yes, micro focus pretty much means what it says...it's pretty fine differences. I've seen lenses that test out to have backfocus issues needing 6-10 correction, but in normal use with smaller apertures you would never notice it 99% of the time. It really only rears its ugly head when you're wide open aperture, and shooting a subject with killer-thin depth of field...the kind where the iris of the eye is in focus, but the eyelashes are already out of the focus area!

If you hadn't already, use a wide open aperture - this also helps to narrow your depth of field on that lens to help demonstrate small focus differences. Then use the central spot focus point aimed at a predetermined or marked centerpoint on the chart/sheet (some folks use AA batteries lined up all in a row spaced evenly apart, some use a ruler, etc). Take the photo (shutter length is not really relevant - just as long as you're eliminating motion or camera shake blur from the equation). With a fast lens like that, the focus should be on a very small, narrow section of the focus chart or sheet, and foreground & background hashlines or detail should be blurred. If you mark the sheet at a precise spot you are aiming at, you should easily be able to tell if the focus nailed it spot-on, or was a little behind or in front of that spot. Then you can do the microAF adjust if needed.

I have been lucky - I've had 3 DSLRs in a row and 8 lenses that have required no micro AF adjustment. My most recent camera did prove to have a slight backfocus on its focus plate (not the lenses...the focus was backfocusing on all lenses the same amount), so a quick adjustment to the focus plate screws solved that issue on the second day I owned it, and it's been perfect since.

Sometimes you get lucky, and a camera & lens are nicely in line and need no adjustment. Sometimes, the camera's focus plate is out of alignment, and all lenses will have the same amount of front or back focus. And sometimes a particular lens will be slightly off, and the microAF adjust lets you fine tune it to match the camera body, to correct for slight differences.
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Old 09-14-2012, 04:53 PM   #3
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Join Date: Jan 2005
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I have and am glad I did.

Here is a link that is a good read, and also includes a method to focus test your lens / camera, as well as a downloadable focus chart. It's an old link made for an older camera, but the principles and chart still apply.
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