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12-29-2010, 09:49 AM   #1
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Faulty DA 15mm Limited?

Hi,

I bought recently the highly regarded DA 15 limited, but I think that it is optically faulty.
The problem is that when it is manually focused to infinity the photo is soft across the frame (specially at f4.0). If I manually focus to 2 meters the centre of the photo (the background) is much sharper, but on the other hand the borders and corners seem softer when they should be sharper.
Even when I get a sharp photo, if I compare it with another taken with my DA 12-24, the latter seems to be sharper at all f-stops (I expected both to be of the same quality).

What do you think? Should I send the lens to be serviced?

I attach some crops. Thanks!

Rescaled photo.



CENTER CROP

F4.0 focus to infinity



F4.0 focus to 2 meters



F8.0 focus to infinity



F8.0 focus to 2 meters



BORDER CROP

F4.0 focus to infinity



F4.0 focus to 2 meters



F8.0 focus to infinity



F8.0 focus to 2 meters




Last edited by Turo; 12-29-2010 at 09:50 AM. Reason: Correction
12-29-2010, 09:54 AM   #2
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Probably you should wait for someone who owns the lens to answer, but with some lenses infinity focus is achieved before you turn the ring all the way...

If you don't have the same problem with AF, then maybe this is the issue.
12-29-2010, 10:25 AM   #3
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QuoteOriginally posted by Turo Quote
If I manually focus to 2 meters the centre of the photo (the background) is much sharper, but on the other hand the borders and corners seem softer when they should be sharper.
If you don' have a problem with autofocus you should be OK, it's hard to manually focus a wide-angle (I find my 28mm hard enough).

The corners will very likely be soft at f4 because they will not be in the plane of focus.
12-29-2010, 10:47 AM   #4
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Ultra wides such as the 15mm always gives the impression of being soft but in fact you need to manage your expectations. The fact is that they usually squeeze so much into a frame that when you zoom in to to say a person in the image, you may have forgotten how many times the magnification is. Longer lenses usually will not have such issues - we'll be happy to see say defined strands of hair. But to get the same image with a wide lens, you'll have to move so close to your subject such that its beyond its typical use.

12-29-2010, 10:56 AM   #5
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To add on, I do own the lens and what you have shown is about normal for this lens. My advice is - don't pixel peep for this lens. <;
12-29-2010, 11:53 AM   #6
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My DA14 exhibits similar behavior where the centre might be sharp but everything else are blurry with focus toward infinity. The puzzling part is that sometimes the image would be sharp across the frame. I have yet to test my theory but I believe my K-m is rather hopeless to AF ultra wide and often BF as the target gets smaller and toward infinity. I briefly observed the distance scale on the lens as it AF and my assumption seems to be correct, but I will need more test after winter to be certain. At close distance, AF is always accurate and images are very sharp even for the newspaper test. In the meantime, I will just use hyperfocal.
12-29-2010, 12:13 PM   #7
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I own the da15 and rented the da12-24 to compare. From my tests, if you cannot get AT LEAST the same quality shot from the da15 as the da12-24 @15mm then (IMHO) you should return the da15 for another copy. My shots so far look way better than yours but I always use AF with it and usually f8 shooting a K20D or K5. I picked the da15 over the zoom because of size and its about as perfect at 15mm as any lens I ever touched.
12-29-2010, 12:49 PM   #8
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My DA 15 is absurdly sharp at close focus distances. At long focus distances, I find softness is an issue unless you really stop the thing down, where diffraction will get you anyways, because your DOF needs to be absolutely huge. Also, are you using a UV filter? They tend to soften things up.

However you can only see these sort of details at pixel-peeping levels. At normal viewing sizes, these details are so small they are insignificant, IMHO.

The biggest problem with the DA 15 is keeping everything in focus. That problem will be similar with the 12-24. Other than flare resistance though, I doubt you should expect much of an IQ differential between the two. It's much more about size and flare resistance in this case.

12-29-2010, 01:29 PM   #9
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Those pictures are simply out of focus. I have the 15 ltd, and for mine at least I can tell you straight off that infinity focus is not where the lens says it is. Do not trust the infinity mark on the focus ring. Turning the focus ring all the way to the end will always put it out of focus (I've ruined night sky photos like that when AF was unusable and I had to MF).

AF on infinity always distinctly puts it somewhere between the infinity mark and the 1m/3ft mark, and the photos are dead on. I have verified this many times on both my K-5 and K-x.

The extreme corners do suffer noticably in terms of CA and sharpness under close examination, but the center rivals that of my 35 ltd macro.

Last edited by Cannikin; 12-29-2010 at 01:43 PM.
12-30-2010, 11:30 AM   #10
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Thanks for the replies!

I normally use AF with this (and other) lens. The problem is that I noticed that the photos taken with this lens were way softer than other photos taken with the rest of my wide angles DA 12-24, DA* 16-50 at 16mm and the DA 21 Limited that I sold to acquire the DA15mm. The typical city views like the one I posted, that have a background and a foreground were quite blurry when I auto-focused to the background.
When I shot something near, the pics are normally sharp, just a tad less sharp than my DA 12-24, but nothing to worry about.
If I had not the problem with AF on I would probably not noticed it.

I think I will send the lens to be serviced or exchanged for a better copy.

Regards.
Turo.
12-30-2010, 12:07 PM   #11
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Let us know if the new copy is better! Thank you.
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