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06-21-2012, 11:02 AM   #106
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QuoteOriginally posted by audiobomber Quote
The measurement may be taken at 5%, but the actual blur covers a lot more of the frame than 5%, as shown in the test photos I've posted several times.
Perhaps true of your copy; I haven't seen your test photos or read how you controlled for field curvature (did you specially construct a flexible test surface and then painstakingly experiment to reproduce the exact field curvature to match the DA15?)

Anyhow, on my copy, I can say that when the corners are in focus while shooting wide open - which is virtually never true in any real world shot - the noticeable softness is only around 5% of the frame, tops. And I'd guess those corners wouldn't even be present in the 16mm frame - that is, if you cropped the 15mm image to match the 16mm (especially after correctly for the distortion in the latter), what was left of the 15mm image would have practically no softness left in the corners.

QuoteQuote:
You have claimed that the prime sharper in the center, but I can't see it.
Well, I don't have your copy of the 15, nor any copy of the 16-45 to compare with. All I can do is appeal to photozone numbers, which confirm the higher center resolution for the 15 at all apertures. Indeed, the *amount* of the difference may not be statistically significant. but I think that should be the bottom line: both lenses are plenty sharp. The decision between them should not be based on sharpness, but other facts. Much greater flexibility for the 16-45, small size and better IQ in ways other than sharpness for the DA15.

QuoteQuote:
I'm not trying to say the 16-45 is the better lens, it is not. But the way people carry on about the 15mm is a little out there IMO, and the 16-45 deserves more respect than it gets.
Seems the 1645 gets plenty of respect, but maybe a few nay-sayers exist who exaggerate whatever deficiencies the lens might have, and you are trying to put those criticisms into perspective? Anyhow, I'd just observe the same is true for the 15 - lots of people praise it, a few naysayers, and I am trying to put those criticisms into perspective. Whatever small flaws these two lenses might have, their critics tend to blow them *way* out of proportion, and both are excellent lenses. Which is better for a given person depends on his/her needs.

06-21-2012, 11:04 AM   #107
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My first DA 15mm consistently front-focussed. I had it replaced and the new one works. I'm not saying that's causing Laurentiu's AF issue, but BF/FF can lead to unreliable focus. I haven't had any trouble at all focussing with my DA 15 on a K-x or K20D.
06-21-2012, 11:17 AM   #108
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QuoteOriginally posted by audiobomber Quote
I would also say that my 16-45 is sharper and has much better CA performance than the one tested by PZ. You can view these at 100% to see for yourself. The difference in CA between my DA 15 and my 16-45 is very subtle.
https://picasaweb.google.com/bonhommed/Comparo?authkey=Gv1sRgCLOD9LjmoOKTlAE...99863119344722
https://picasaweb.google.com/bonhommed/Comparo?authkey=Gv1sRgCLOD9LjmoOKTlAE...18589306741906
FWIW, it appears there is either a pretty significant different in focus point between these two shots, or else the 16-45 *is* noticeably softer in the center than the DA15. Because when I compare the house at the center of the frame, and the background around it, between the shots, the DA15 is very clearly a lot sharper. The 15 remains noticeably sharper coming forward, looking at the houses and driveways along the left side of the street (also compare the pile of trash). It looks like the 16-45 image is probably focused somewhere near the fire hydrant on the left side of the street, whereas the 15 is probably focused on that distant house. if so, that would easily explain differences in their performance in those bottom (near) corners.
06-21-2012, 11:45 AM   #109
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QuoteOriginally posted by Marc Sabatella Quote
Perhaps true of your copy; I haven't seen your test photos or read how you controlled for field curvature (did you specially construct a flexible test surface and then painstakingly experiment to reproduce the exact field curvature to match the DA15?)
I did nothing fancy, just a couple of test shots from my front balcony. They were linked above and you have commented on them before. They are posted at full resolution:
https://picasaweb.google.com/bonhommed/Comparo?authkey=Gv1sRgCLOD9LjmoOKTlAE...99863119344722

https://picasaweb.google.com/bonhommed/Comparo?authkey=Gv1sRgCLOD9LjmoOKTlAE...18589306741906

QuoteOriginally posted by Marc Sabatella Quote

Well, I don't have your copy of the 15, nor any copy of the 16-45 to compare with. All I can do is appeal to photozone numbers, which confirm the higher center resolution for the 15 at all apertures. Indeed, the *amount* of the difference may not be statistically significant. but I think that should be the bottom line: both lenses are plenty sharp. The decision between them should not be based on sharpness, but other facts. Much greater flexibility for the 16-45, small size and better IQ in ways other than sharpness for the DA15.
Totally agree. They are different lenses, each with its own strengths and limitations.

06-22-2012, 12:48 AM   #110
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QuoteOriginally posted by Marc Sabatella Quote
assuming I even believe it is possible for a lens to misfocuson a Pentax DSLR, which I am still very much in doubt about.
Why write so much, when you could have just said this from the beginning?
06-23-2012, 10:16 PM   #111
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??? Because the subject of thread had nothing to do with whether or not there exists any technical fault that could cause a lens to misfocus. Only when in some very tangential aspect of the discussion that became relevant was there a reason to bring it up.
06-25-2012, 12:51 PM   #112
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QuoteOriginally posted by Marc Sabatella Quote
??? Because the subject of thread had nothing to do with whether or not there exists any technical fault that could cause a lens to misfocus.
I think focusing reliability falls very well under the scope of the OP inquiry:

QuoteOriginally posted by normhead Quote
Just wondering though.. is there something else I should be looking at?
QuoteOriginally posted by normhead Quote
( PS.. my eyesight means going MF isn't really a possibility.)
It is pretty clear the OP will have to rely on AF, so the question that comes up is if he can.

Of course, if you believe AF is perfect and infallible, you will deny any possible impact or relevance to the subject.
06-25-2012, 07:44 PM   #113
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DA 15 (any wide angle) is really hard to properly manually focus on that little viewfinder, better to use the distance scale.

Never had a real problem with the DA 15 and autofocus.

I will say this: the lens is excellent but, IMHO, a one trick pony for a very simple reason: no zoom! (duh!) It is tonnes of fun and I could not ask more from it... but too often I find myself unable to move to the correct location to take the shot (and with a 15mm lens, location makes ALL the difference). I can zoom with my feet for most primes... but the 15 is really hard to use because often, zooming with your feet ACTUALLY means running 20 meters!.. so it gets tricky when you are shooting things that aren't dead/stationary.

It is for this reason that I am strongly considering the 16-45 or 12-24 as a replacement (i've been getting along pretty well with my 18-55 lately, even...). Even though I hate zooms.... with wide angles it really just seems more practical to suck it up. In wide angle land, focal length is more important than any other optical quality. Good luck with your decision.

07-01-2012, 09:41 PM   #114
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QuoteOriginally posted by Laurentiu Cristofor Quote
Of course, if you believe AF is perfect and infallible, you will deny any possible impact or relevance to the subject.
Of course it isn't perfect or infallible. But it's not a variable here that could possibly influence a rational person to choose one lens model over another. Even if one were to choose to believe in the possibility that a lens was capable of inducing misfocus, there would be no valid reason to believe that one particular lens model was more prone to that as-yet-unproven possibility than any other lens. The fact that one person in the world had a problem with one particular copy of one model that he attributed to a lens defect in no proves that it was in fact a defect, nor does it prove that defect is more common to that model.
07-02-2012, 05:31 AM - 1 Like   #115
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QuoteOriginally posted by br.davidson Quote
though I wouldn't say the DA15 has "nice" bokeh
Riiiiight...



Granted it isn't exactly easy to get good Bokeh out of the DA15 - but it is still capable of producing some good bokeh if you are aware of the quirks of this particular lens. Just stop the DA15 Limited ASPH down to f/11 and you can get away with just about anything without having to worry all that much about IQ. With such a Wide FOV camera shake really isn't much of an issue and neither is DOF.
07-02-2012, 12:06 PM   #116
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QuoteOriginally posted by Marc Sabatella Quote
Even if one were to choose to believe in the possibility that a lens was capable of inducing misfocus, there would be no valid reason to believe that one particular lens model was more prone to that as-yet-unproven possibility than any other lens.
Of course there are valid reasons for one lens model to focus more reliably than another in certain scenarios. Performance of AF in low light depends on the maximum aperture of the lens. Slower lenses will fare worse than faster ones in low light conditions, even in the absence of any calibration issues.
07-08-2012, 05:28 PM   #117
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Finally got an opportunity to try the DA15 for landscape scenarios. It works pretty well, although resolution drops in extreme borders even when stopping down beyond f/8. But this lens works great for panorama stitching, because of its low distortion. I finally reviewed it here.

It is not trivial to get both the foreground and the background to look in focus, even when stopping down to f/11. Here is one of the better results at St Helens:



A 6 shot panorama at f/11:



And 5 shot panorama of the Olympic range at f/16:

07-10-2012, 11:32 AM   #118
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Those are some great shots..., I have to get some pano software.
07-10-2012, 12:33 PM   #119
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If you are on Windows try MS I.C.E. which is free. Works great and has some nice features especially considering the price.
Here's a two image DA15 stitch I did with it a while back. (the da15 is great for these because you don't need so many individual shots).

07-10-2012, 12:40 PM   #120
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I'm on a MAC.... sometimes that sucks...
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