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05-12-2012, 04:03 AM   #1
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da 15 ltd soft corners ??

I would like some advice regarding my recently purchased DA 15. I understand that it is known to be soft in the corners wide open but shouldn't the softness disappear when it is stopped down. The gas meters were taken at F8 1/400s The brick wall f9 1/500. These images appear to be soft in the corners. Acceptable?

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05-12-2012, 05:04 AM   #2
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IMHO the sharpness is not just acceptable but very good. Especially the brick wall seems to be very sharp. I think if you correct the CA, the corners might appear a little bit sharper.

Before I bought this lens a few weeks ago, I read a a lot of reviews on the web complaining about the weak corners of these lens. After some testing I can say that this issue is not field relevant at all. This lens has an amazing FOV, produces contrasty images which show only very little distortion. Overall I think sharpness is an overrated concept - most of the images get resized anyway. And even if you want to get a large print, it's very unlikely that you view it from such a short distance that you get a similar impression like you get with 100 % crops on your monitor.

The DA 15 mm is a really amazing lens. Have fun with it!
05-12-2012, 05:47 AM   #3
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Thanks for your reply. I just want to be sure this is normal for this lens . I have read on this forum and other forums how sharp and how littlle ca it has particularly when stopped down. I am finding that even stopped down the lens has soft corners and produces ca. If this is unusual for this lens then I will take it to pentax and have it checked. The gas meter shot is sharp in the center but the top right hand corner is awfully soft. My other lenses if stopped down 4 stops do not show ca and are sharp corner to corner but they are not wide angle lenses so maybe it is unfair to make the comparison.
05-12-2012, 07:44 AM   #4
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I'd say my da 15 produces a similar level of sharpness and CA. CA is pretty normal for a lot of lenses and quite easy to fix in PP. When you compare this lens to others, you have to keep in mind that it is an UWA lens.

05-12-2012, 07:55 AM   #5
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I was also frustrated with this but then I tried various positions of focus within the infinity symbol on a tripod with RC and then compared the pics in PC (don`t forget to mark the positions for different pics on a sheet of paper), and simply use manual focus (easy with quickshift) at the position where corners came out sharpest (with my K5 this position is near the inner edge of the right part of the infinity symbol (the right "circle")...I am now basically able to use the 15`s field curvature to work for me not against me
just give it a try
some examples
https://picasaweb.google.com/lh/photo/hbA-FCHFmQa4rYdagitfXdMTjNZETYmyPJy0li...eat=directlink
https://picasaweb.google.com/112897657322031504958/TestovaciaJazda#5688539827134151890
05-12-2012, 09:26 AM   #6
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Looks good.

While the corners do get better when stopped down, they never approach the sharpness of the center of the frame. This is pretty typical of UWA lenses.

The CA looks pretty good, too. The CA is low in this lens, but not non-existent.

Compared to the Pentax DA 14mm & Nikon 14mm, the DA 15 actually is significantly better in the corners.
05-12-2012, 11:23 AM   #7
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The focus field is not flat for most lenses, and that is perhaps more true of the DA15 than some other lenses. Meaning that if you focus on something like the center of a flat wall, the corners will be behind the focus "plane". You'd need to focus on a wall that is curving toward you at just the right rate in order to see the corners in focus.
05-12-2012, 02:47 PM   #8
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Thanks for the replies. I understand that I will get distortion but it's just that I thought the depth of field at these f stops would mean that the image would be in focus in all parts.

05-12-2012, 02:54 PM   #9
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It's bad imho, but I am comparing it against my EF-S 10-22. At f8, one would think the DOF should mask the weak edge/corner sharpness somehow but not with the DA14/15. The DA14 has severe field curvature which is a design flaw imho, and I suspect the same to the DA15 but not as severe (but still not good as a modern prime). Unfortunately, Pentax has lagged behind with their wides, IMHO anyway.
05-12-2012, 03:03 PM   #10
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You dont get an evenly sharp image until f11..
05-12-2012, 03:04 PM   #11
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QuoteOriginally posted by wlachan Quote
It's bad imho, but I am comparing it against my EF-S 10-22. At f8, one would think the DOF should mask the weak edge/corner sharpness somehow but not with the DA14/15. The DA14 has severe field curvature which is a design flaw imho, and I suspect the same to the DA15 but not as severe (but still not good as a modern prime). Unfortunately, Pentax has lagged behind with their wides, IMHO anyway.
Photozone disagrees with you.
05-12-2012, 03:16 PM   #12
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Photozone tests different points of the image projection manually and this method avoids field curvature problem. But if you check out their DA14/15 samples, they are quite bad toward the edge/corners. You can workaround the problem somewhat by focusing farther but this method can only go so far. For scenery, these lenses are just poor performers. For close snaps, they may be fine.

Last edited by wlachan; 05-12-2012 at 03:37 PM.
05-13-2012, 02:06 PM   #13
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QuoteOriginally posted by everydaylife Quote
Thanks for the replies. I understand that I will get distortion but it's just that I thought the depth of field at these f stops would mean that the image would be in focus in all parts.
It doesn't work that way. Common DOF formulas assume a typical print viewed from a typical distance; they don't account for pixel peeping. The DOF is considerable shallower if you judge by how a 10MP+ image looks blown up to 100%,
05-13-2012, 02:09 PM   #14
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QuoteOriginally posted by wlachan Quote
For scenery, these lenses are just poor performers.
Completely false. Most scenery is not flat, so the curvature of the focus plane is not relevant. And most shots of scenery are taken at aperture like f/8 or f/11 where there simply *is no corner softness*. The DA15 is *fantastic* for landscape. Sharper than virtually anything else ever made, practically immune to flare, virtually distortion and CA-free - you aren't going to come close to those specs.
05-13-2012, 03:42 PM   #15
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QuoteOriginally posted by Marc Sabatella Quote
Completely false. Most scenery is not flat, so the curvature of the focus plane is not relevant. And most shots of scenery are taken at aperture like f/8 or f/11 where there simply *is no corner softness*. The DA15 is *fantastic* for landscape. Sharper than virtually anything else ever made, practically immune to flare, virtually distortion and CA-free - you aren't going to come close to those specs.
Actually, the 15 is somewhat soft in the corners, even taking field curvature into account. It doesn't mean I love it any less, it is just a characteristic of the lens.
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