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05-21-2016, 02:57 AM   #1
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DFA 24-70 FF and FB other problems

Hi,
I bought DFA 24-70 for K1. I choose from two copies. But still I have some issues.

first: I have FF @ >30mm. If I set proper setting for it then ofc lens is BF @24mm :/
I think that one corner is smuch softer that others.
I next week I have Film Music Festiwal but after that I think I will send lens and body to calibration.
If you had/have similar problems please post your thoughts.
Best!

05-21-2016, 05:13 AM   #2
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AF adjust is really most effective for primes, in that once set nothing should change.

AF adjust is a compromise for zooms, as, like you've found, focus accuracy can vary through the lens's zoom range.

You should (a) determine what adjustment is needed at the short, middle and long end of the zoom, average the adjustments and use that figure, accepting the fact that the level of focus accuracy will vary slightly but should be ok at higher f numbers, or (b) note the adjustments in (a) and be prepared to make adjustments as required when you're shooting and know what fl you'll be using, or (c) adjust for your 'favourite' focal length and accept that focus might not be spot on at other focal lengths, again accepting the fact that the level of focus accuracy will vary slightly but should be ok at higher f numbers.

Notwithstanding the above which will apply to any zoom lens however perfect, if you think that one corner is softer than the others, and you determined this by testing with the camera on a tripod vertically and horizontally square to a target - a wall? - , then you might have a faulty lens.
05-21-2016, 05:50 AM   #3
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I bought 24 70 from b&h last month and had a same issue. I ended up sending it back for another copy. Right side was soft. Second copy has focusing problem. But I decided to keep it. My 15 30 is also set at +2. Maybe these lenses are tamron lenses, and have some issues?
DFa 70 200 is dead on accurate.
I wish Pentax develop its own 24-70 * lens, matching build quality and optic of dfa 70 200. but I guess Pentax has more other ff lenses to worry about before they get to 24 70 star lens.
05-21-2016, 06:59 AM   #4
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Sound like the lens might be decentered (one or more of the elements is not seated properly in the lens barrel). Decentered lens cannot be calibrated with the camera's fine focus adjustment. The lens must be repaired by a qualified technician. Therefore, would recommend that you return the lens.

05-21-2016, 05:44 PM   #5
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QuoteOriginally posted by fwbigd Quote
Sound like the lens might be decentered
Yup, agreed.

If you switch into live-view, zoom in all the way, and manually-focus on a flat target, can you get everything sharp? If so: AF problem. If everything is always soft (or some areas of the image are soft), you've got an optical problem with the lens (the most common is decentering). This has nothing to do with the AF system.

Either way, I'd either exchange it, or send it in under warranty.

AF tuning is a cute trick that I use on old AF primes and lenses that aren't under warranty anymore; however, if I buy a $1000+ brand new lens from an authorized dealer, and it doesn't work perfectly, it's going back.
05-22-2016, 11:24 AM   #6
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Original Poster
yeap have to make test shots with flat big wall
thanks for comments and ideas!
05-22-2016, 04:29 PM   #7
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Just my experience, I had two K1s to test before buying, I tried FA 50 and FA 43 because I knew older AF lenses tend to have some focus errors. Anyway, one of the K1 focuses well (no need for fine focus adjustment for both lenses) with only few misfocuses - but the other K1 needed +3 focus adjustment for FA50, and never focused well with FA43 no matter how I adjusted the fine focus adjustment. I kept the good one. I haven't tried 24-70 yet. My DFA 28-105 though, are very accurate on both K1s.
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