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01-31-2013, 03:21 PM   #1
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AF Adjustment

I am trying to do some focus adjustment for the first time and had a couple questions.

The first questions is which direction to adjust for FF and which direction to adjust for BF.
The second is whether I should adjust this or not? it looks fine at f 2.8 but then seems to be FF wider than that.

2.8
Attachment 157758
2.0
Attachment 157759
1.8
Attachment 157760
1.6
Attachment 157761
1.4
Attachment 157762

Thanks in advance!


Last edited by mikemike; 01-31-2014 at 12:35 AM.
01-31-2013, 03:40 PM   #2
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Yes it looks like you should. This page explains things fairly well:
Fixing Front and Back Focus - The Remedy - PentaxForums.com

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01-31-2013, 03:48 PM   #3
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Your 2.8 shot appears front focused on the right. That's because the camera is off center.
You should redo your tests because the camera must be lined up with the centre of the chart.
I'm guessing all of these shots are front focused.

Last edited by chromo; 01-31-2013 at 03:55 PM.
02-01-2013, 08:04 AM   #4
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That's definitely not a good chart for getting any sort of consistency. There's too many possible targets near the black line, which is also too ambiguous with a front and back edge.
The best ones are here....AF Charts

02-01-2013, 12:53 PM   #5
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QuoteOriginally posted by Adam Quote
Yes it looks like you should. This page explains things fairly well:
Fixing Front and Back Focus - The Remedy - PentaxForums.com
What a superb article - just what Im looking for to test a lens I have just bought for when my K30 arrives - thx for the effort - appreciated.

Now for a feature request :-) Please find a way that we can subscribe to articles like this so we can find them easily later for future reference?
02-01-2013, 01:40 PM   #6
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I usually use live view to adjust my auto focus. AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D, 1D X
02-01-2013, 01:42 PM - 1 Like   #7
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QuoteQuote:
That's definitely not a good chart for getting any sort of consistency. There's too many possible targets...
I use a cement sidewalk with one crack full of short grass :-)
02-08-2013, 01:36 PM   #8
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QuoteOriginally posted by SpecialK Quote
I use a cement sidewalk with one crack full of short grass :-)
I use an angled 3 foot high brick wall and focus on the label of a soda can sitting on top.

These focus checking kits are good but some not worth their ridiculous price for a piece of cardboard with a bit of print on it. Total ripoff !


Last edited by chromo; 02-08-2013 at 04:03 PM.
02-08-2013, 04:48 PM   #9
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Honestly, I used to obsess over things like this. I went to University to study engineering and now I'm a software architect, so I'm a little on the technical side - and when you do stuff like that for a living you tend to develop habits of trying to understand and perfect things. I got to the point where I was even adjusting my aftermarket focus screen to an accuracy beyond the shim sizes that came with it - they weren't thin enough to provide the accuracy I needed.

Did I end up with a super accurate system? Yes. Did I really need it? No.

What I've learned over the years is that close is good enough. If your lens is so affected as to need any significant adjustment, you will see that in your photos.

Now that I've said that, I'll let the engineer in me talk.

Your focus chart and the technique you're trying to use are worthless. You'd be better served walking around taking candids wide open and adjusting as you go until you're pleased with the results.

If you want any meaningful result, you'd best do at least 5 things. Trust me on this, I've learned from my own experiences:

-First, scrap that focus chart, it's useless. Your camera is capable of accurately focusing on an all-white plastic jug. Don't believe me? Try it. The contrast of those grey areas against the white is slapping your camera's AF system in the face, saying 'focus on me!', making the entire test far too dependant on your aim, and that's assuming the AF sensor is in that little red area in your viewfinder. Unlikely at best.

-Provide adequate non-tungsten, bright lighting. Natural lighting preferred.

-Fix your camera in one position on a tripod.

-Provide a flat standing target (perpendicular to ground) with many random contrasty areas to focus on. Be sure that your camera is as close to square with this as possible.

-Angle a long meter stick or some other long, straight object alongside the focal plane of your target. Be sure it has an equally distanced scale printed on it.

Assuming you've done the 5 things above, start testing. Repeat the tests, being sure to always 'un-focus' your lens between tests. Try from close, medium, and far distances. Distance is relative depending on the lens being calibrated. I've had repeatable, excellent results using this technique.

If you're having trouble visualizing the setup I'm talking about, have a look at this. It's easy to make one of these out of junk lying around. It's really the only way to do it.
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