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03-29-2013, 06:14 AM   #1
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DA15 limited AF issue

Hey!

I have owned DA15 over one year. When my K5 came back from service three months ago, lens does not AF accurate or it does not do the same at variable apertures.

Let me explain little more. I have done some test with tripod at different apertures and at different distance. I used center point focus. Here are results.

At 1 meter, it requires AF adjustment +3 (f4 and f5.6), but it is ok at f8.
At 2 meters, f4 ok, but f5.6 and f8 needs -6/-8
At 3 meters, f4 ok, but f5.6 and f8 needs -7/-8
At 5-6 meters, f4 ok, but f5.6 and f8 needs -5/-8
At 15-20 meters, f4 ok/-3, but f5.6 and f8 needs -5
At 30-50 meters, f4 ok/-3, but f5.6 and f8 needs again -5

I was wondering is this normal behavior for wide angle lens. I usually use this lens between f5.6 and f11 (f16). Then its not problem, i can dial -5/-7 and be happy. But when I need f4, it is annoying to dial AF adjustment back. Or is it just the camera.

What do you think about?

Thanks !

-Sami-

03-29-2013, 07:00 AM   #2
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AF set the aperture wide open so aperture should not make a difference in focus at all because the apeture is only closed when actually taking a photo and not during focusing.
The focus distance could make a difference though.


You are saying that the aperture need so much adjusting ect, but how do you measure it.
Focus field actually shift more to the back the future away you focus at macro the focus field should be equal divided.
03-29-2013, 07:40 AM   #3
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Step away from the focus charts. Set your camera to 0 correction and go take pictures.

The DOF of a 15mm lens is measured in meters, even up close at f/4 (actually, 0.8meters at one meter distance). At 30 meters and f/5.6 it is effectively infinite. I don't think there's anyway to accurately test and calibrate a lens like this.

Pete
03-29-2013, 07:51 AM   #4
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QuoteOriginally posted by Anvh Quote
AF set the aperture wide open so aperture should not make a difference in focus at all because the apeture is only closed when actually taking a photo
In this case that is likely true; however focus shift (focus changing with aperture) is a known phenomenon.

03-29-2013, 08:25 AM   #5
s76
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Here are some 100% crops. All taken at 2 meters with center point focus. Focus at phone and bag.
1. f4 adjustment 0
2. f4 adjustment -8
3. f5.6 adjustment 0
4. f5.6 adjustment -8

What do you think?

-Sami-

Last edited by s76; 09-20-2013 at 04:24 AM.
03-29-2013, 09:38 AM - 1 Like   #6
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The zero adjustments look spot on to me. I would expect the background to be blurred given the aperture, the relative closeness of the subject and the significant distance between the subject and background.

I would suggest some research on Depth of Field.
03-29-2013, 12:50 PM   #7
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QuoteOriginally posted by Parallax Quote
In this case that is likely true; however focus shift (focus changing with aperture) is a known phenomenon.
read it quickly, maybe I've read some things wrong but there seems to be some mistakes in it, this one is better in mine eyes Spherical aberration

it could be but from the reviews this lens is well corrected and f/4 is not what I called fast
03-29-2013, 01:01 PM   #8
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QuoteOriginally posted by Anvh Quote
it could be but from the reviews this lens is well corrected and f/4 is not what I called fast
Unlikely that it is happening here, particularly with an f4 lens.

03-29-2013, 01:08 PM   #9
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QuoteOriginally posted by Parallax Quote
The zero adjustments look spot on to me. I would expect the background to be blurred given the aperture, the relative closeness of the subject and the significant distance between the subject and background.

I would suggest some research on Depth of Field.
+1 your copy is absolutely okay.
03-29-2013, 11:01 PM   #10
s76
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Thanks to all!

Maybe I was worried for no reason. Have to go out and enjoy this little lens.

-Sami-
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