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01-17-2011, 06:13 AM   #1
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am I doing something wrong?

fist thing first, a little context
I had a K20D with a kit lens for a while and have been pretty satisfied with the results ... mostly I use the combo for documenting my climbing trips
recently I bought a DA* 16-50. This is its second outing. First one was a mixed bag, but I couldn't really deduce anything since I was shooting and indoor competition without flash and under bad lightning.
Anyhow, I shot a lot of pics on this trip and I am VERY unsatisfied with the results (actually sharpness).

I've posted 8 pics that show the "problem" and would like to hear your input on the matter... I plan to do some further testing, including a tripod
So, am I doing something wrong or is the lens the problem?

since PentaxForums doesn't allow uploading zip files larger than 3 Mb, I uploaded the zip file (26 Mb) so you can download them HERE.


Last edited by dankoBanana; 01-17-2011 at 02:21 PM.
01-17-2011, 09:51 AM   #2
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I think if you post one typical shot, in perhaps 800 x 600 resolution, with a 100% crop of one section at full resolution to show the issue you are having, you will get more responses.

Not many people will download 26mB to look at the issue
01-17-2011, 10:22 AM   #3
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QuoteOriginally posted by Lowell Goudge Quote
Not many people will download 26mB to look at the issue
Particularly a zipped file... too much bad stuff floating around out there.
01-17-2011, 10:27 AM   #4
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I agree, I just hit your link and shut you down. Nothing personal, but my download folder has way to much stuff in it and sorting through it to see what I wan to keep is a chore I dislike already, without adding other peoples picture files to it.

01-17-2011, 10:32 AM   #5
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I did down load and look at all the files. In the different photos I see different things. Some are a little back focused. Some have some subject blur. The sweet spot on this lens for best MTF as around f4. Most of the photos you use ISO 400 and then when you have a faster lens you donít make use of it. ISO 400 will loose a little detail. One photo you can see his eyes are in focus but because you are so close his nose and everything behind is out of the DOF.

Most of what I see is just the little things adding up. Maybe if you had a particular point of a photo I could be more precise.

DAZ
01-17-2011, 12:51 PM   #6
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the sweet spot of the lens is between f5.6 and f8 so unless I needed more DOF, I used f8 or f5.6

I didn't wanted to post 800x600 re-sized pics because you can't really judge sharpness on them ... as for trusting the source, DAZ downloaded the file and he can attest its all good

from the pictures, it seems to me that @16mm things are OK, but @50mm the lens front focuses
note that I did use auto focus on all of them and I plan on doing a manual focus / tripod test ... but I would really love to hear am I seeing thing correctly here

on picture 1, the sharpest part of the rock is on the left and there its sharp ... also the rock was sharper above the center ... since I've focused on the middle and all the sharp parts are further away, I'd say the lens is front focusing?

picture 2 ... don't really know what is going on... back focus maybe? or just miss focus?

picture 3 is of a persons head @16 mm and everything seems ok .. facial hair seem sharp (@iso 400 and without noise reduction)

picture 4 was taken as a test ... @50mm and f5.6 the camera seems to have front focused ... I concluded this because the center seems to be the least sharp part of the tree

picture 5 was a another test ... @50mm I focused on the closes leaf and on the picture it's out of focus while the back leaves and the branch are rather sharp ... front focus again?

picture 6 .... head out of focus, the shirt in focus ... front focus again?

picture 7 ... nothing really in focus @ 16mm ... maybe user error

picture 8 ... considering it's ISO 400 with no cleaning done, this one seems to be in focus @16 mm .... everything seems to be reasonably sharp?
01-17-2011, 02:10 PM   #7
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As for down loading some just donít do ZIP files. I can scan before opening so I will at least look, some will not. To each their own risk level.

Now that I know what it was you intended to focus on I can say more. Most of the photos that I can see the focal points are behind the subject. This would include #4 the tree, at the back edge (on the sides) looks like they are coming into focus. # 7 look like the trees are in focus but are getting into the mist so I canít tell. #2 looks like it is just past his head and some subject blur but only on his hand/rope. This would be back focus and can be adjusted in the camera.

As for the sweet spot for aperture that depends if you want center f/4 or edge f/8. I can see that you wanted more DOF so you used a smaller aperture. DOF is also dependent the distance to the subject. The closer you are the narrower the DOF will be. Also the closer you are the more the focal plain will be spherical and look less like a flat plain. This means if you are shooting a wall and you are close you may only get the center or the edges but not the entire wall.

#8 looks the best but could use some PP. I know we are talking about just the lens but with some PP most of them would look better (and even if not sharper be preserved that way).

Any other specific questions?

DAZ
01-17-2011, 02:21 PM   #8
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tnx I know I need to work on my technique, but I just wanted to get a confirmation on the back/front focus issue
I'll have to do some adjusting then or if I am unable to do so with satisfying results, ship the lens/camera combo to Pentax Croatia to adjust the combo for me

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