Lens af microadjustment

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Archive 2008 · Lens af microadjustment

Hotspur
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p.2 #1 · Lens af microadjustment

The method here did not work for me:

http://blog.willshootphotography.com/2008/10/canon-50d-af-mi.html

So I downloaded and printed out the test chart here:

http://focustestchart.com/chart.html

The link for downloading the chart is at the bottom of the page.

My methodology:

Position chart, taped down to a flat board, at 45 degrees (short spirit level assures this). Set up camera on tripod at same level as center of chart so that chart just fills screen. Set lens wide open (I've found that the back focus in my most severe example, the 50 f/1.4, went away at f/11).

Take a series of 9 shots with settings at intervals of 5 (-20, -15, etc.), noting carefully which frame number is which, and leave camera on tripod.

Import into Lightroom and immediately note in the keywords what the setting was for each (as far as I can tell, this info is not stored in EXIF data). Examine images one at a time at a magnification where I can see the entire chart. It quickly becomes apparent where the focus changes from front focus to back focus. If that happens between, say, -10 and -5, I put the card back in camera and shoot 4 more (-9, -8, -7, -6) and examine again. I'm looking for the shot where a back number (say, 40) is just as clear (or fuzzy) as the front 40.

Here were my settings using LiveView per http://blog.willshootphotography.com:/2008/10/canon-50d-af-mi.html
50 f/1.4: -10
100 f/2.8: -2
70-200 f.2.8: -2
24-105 f/4: -20

And here were the settings using the chart from focustestchart.com:
50 f/1.4: +4
100 f/2.8: -6
70-200 f.2.8: 0
24-105 f/4: -15

I can't see a pattern in all this. Went out just now with the 100 macro and shot flowers. Spot on. And I'm happy with performance of the 50. Now on to the 24-105.

Open questions to explore: 1) On the zooms, should I do this at both maximum and minimum zoom? 2) I'm setting focus for wide open aperture; what happens when I stop down? To use example from above, now that I've corrected focus on the 50 at f/1.4, is it still good at f/11?

Nov 01, 2008 at 06:55 PM

BennyR
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p.2 #2 · Lens af microadjustment

Will Swetnam wrote:
Here is the test that I used - I found that a combination a target I found on the web, and one that I created myself did the trick.

http://blog.willshootphotography.com/2008/10/canon-50d-af-mi.html

I ended up testing only at the near end of the focusable distance for the lens thinking that the narrower DoF closer to the lens would require more precise positioning of the elements to get tack sharp focus - if I focus on something 100 yards away, the DoF is more and should prob allow for slight variations in the focus ring position that will still yield tack sharp focus.

Thoughts?

- Will

http://blog.WillShootPhotos.com

Dude, that's well written, nice to see. I'll get around to trying it some time.

Nov 01, 2008 at 07:57 PM

SoundHound
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p.2 #3 · Lens af microadjustment

The only thing that you can be sure of is if you MA you AF at one distance that it will be sharp(est) there.

Nov 02, 2008 at 06:13 PM

Randy Wright
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p.2 #4 · Lens af microadjustment

Hi Hotspur,

Regarding your quote below, I use Canon's ZoomBrowser EX program to read the M/A adjustment amount # and check focus spot. Pretty easy to use...

"Import into Lightroom and immediately note in the keywords what the setting was for each (as far as I can tell, this info is not stored in EXIF data)."

Also, I get much better M/A results since I started using Canon's Ec-B focus screen, you can actually see letters and lines bend until they line up correctly when manual and M/A focusing, especially useful on my 600 and 1.4/2.0 tc's.

Randy

Nov 02, 2008 at 07:17 PM

Hotspur
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p.2 #5 · Lens af microadjustment

I got an aftermarket Ec-B focus screen, probably not a good idea as it's not quite square with the camera. The bigger problem, though, is that not all my glass is real fast, so it's difficult to see things at, say, f/5.6.

After posting I noticed that the MA amount shows up on some screen (Func? Info?). Very handy.

Nov 05, 2008 at 09:55 PM

Tom_W
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p.2 #6 · Lens af microadjustment

Polansky wrote:
Here you can find a very accurate method, which works great and is also easy to use: Perfect AF Microadjustment method

For the benefit of more recent owners of the 1-series, 5D2, and 50D, I'm showing your link again. This method is pretty easy. Interestingly, I found my fisheye was backfocusing about 8 marks which surprised me since I've never noticed any issues with it (the benefit of stopping down with a very short lens). The 16-35, 24/1.4 and 35/1.4 were both front focusing just a bit (-3 adjustment each). My longer lenses were all right on the money. The 24-70 was right on as well.

Mar 28, 2009 at 04:20 PM

retrofocus
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p.2 #7 · Lens af microadjustment

I found the microadjustment tool quite useful on my 5D MkII camera. This method worked quite well for me and it is fairly easy to set it up if you have a larger monitor screen:

http://www.northlight-images.co.uk/article_pages/cameras/1ds3_af_micoadjustment.html

I adjusted my zoom lenses for the most often used focal length, e. g. at 17 mm of the 17-40 lens and and an average number out of different focal lengths with the 24-70. There was a small improvement after microadjustment, visible in a bit larger RAW file size:

17-40 f4 L lens: -3 microadjustment (17 mm)
24-70 f2.8 L lens: -5

All my primes didn't need any adjustment.

Mar 28, 2009 at 04:49 PM

abam
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p.2 #8 · Lens af microadjustment

+10 on my 35L
+12 on my 50L
+5 on my 85 1.8
+7 on my 135L

Mar 28, 2009 at 05:44 PM


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