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01-20-2012, 12:36 AM - 1 Like   #16
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QuoteOriginally posted by Emacs Quote
Smaller sensor and still it's not excellent: only just good when stopped down to f8
Nonsense. Even wide open, 90% or more of the field of view - the only part normally in focus when shooting an ultra wide at f/4 - is sharper than anything else out there, including the 16-45 that has erroneously been claimed to be better. Plus of course, there is the remarkable lack of distortion and CA, plus legendary the flare resistance. The *only* respect in which any other lens beats the DA15 is in the *extreme* corners at f/4 or f/5.6, and this is a part of the image that will virtually never be in focus in any real world images taken at that aperture and focal length. In *all* other respects - all of which are *far* more important in the real world - the DA15 beats all comers.

Bottom line: don't be misled by the numbers. The reality is that in practice, this lens is every bit as good as those of us who own it and shoot with it regularly say it is. We know that unbeatable sharpness in 90%+ of the frame plus low distortion and CA and flare resistance trumps whatever softness might exist at large apertures in the extreme corners that are likely to be out of focus anyhow. Situations in which sharpness in the extreme corners wide open is more important than sharpness in 90%+ of the frame, more important than low distortion and CA, and more important than flare resistance are practically non-existent. There are essentially no real world situations in which other lenses will outperform the DA15.

01-20-2012, 01:41 AM - 1 Like   #17
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QuoteOriginally posted by wlachan Quote
I am afraid the proof is in the pictures. I have yet to see any DA15 pics which are sharp corner to corner due to field curvature (and please no more downsized samples).
I am happy with this lens

https://picasaweb.google.com/112897657322031504958/TestovaciaJazda#5650074475651883026

https://picasaweb.google.com/112897657322031504958/TestovaciaJazda#5688539827134151890
01-20-2012, 01:46 AM   #18
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Not bad & appreciated.
01-20-2012, 01:50 AM   #19
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thanks
feel free to browse through the Testovacia jazda (test drive) album for more DA 15 shots, though most of pics are resized just like in other albums

01-20-2012, 04:50 AM - 1 Like   #20
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I'll echo what others are saying, the center sharpness is excellent,and the corner sharpness is good, and corner sharpness is very good at F/8. At phorozone.de, the DA15mm bests the DA14 at all apertures in the center and the corner of the image. At F/8, the DA15 bests all of the zooms, the DA12-24mm, the DA16-45mm, and the DA16-50mm, in the center and the corners. Plus, I've personally observed that much of the DA15 corner softness at F/4 is due to field curvature, (the focus plane isn't flat) which doesn't affect real images. Back to my original question, which is how did Pentax get a 3.5x-4x retrofocus magnification (reverse magnifying out to 15mm) in two stages, vs four stages for FF designs, with good quality, in a compact package? I guess its the combination of aspherical optics and low dispersion glass, and the reduced image circle which allows for less thick glass, which makes for a more compact design, but I don't know anything about optics.
- Sheldon



Last edited by sheld; 01-20-2012 at 05:52 AM.
01-20-2012, 09:04 AM - 1 Like   #21
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QuoteOriginally posted by sheld Quote
At photozone.de, the DA15mm bests the DA14 at all apertures in the center and the corner of the image. At F/8, the DA15 bests all of the zooms, the DA12-24mm, the DA16-45mm, and the DA16-50mm, in the center and the corners
I have taken thousands of pictures with the DA 12-24, and hundreds with the DA 15 and the DA 16-45, and I can find no issues with the DA 15's corners compared to those other lens, even at wider apertures. In real world use, the DA 15 produces images with slightly more clarity at large print sizes than the zooms; at smaller print sizes (10" by 15'' or smaller), it would, howevre, take a very practiced eye to notice any real differences in the output of these lenses.

I suspect as well that the photozone results test only at a single distance, rather than multiple distances. Just because a lens is sharp corner to corner at 10 feet doesn't mean it will retain that corner to corner sharpness at longer distances, especially if we're talking about a zoom lens that involves the inevitable optical compromises that come with that sort of lens. At longer distances, the impressive corner to corner sharpness of the DA 12-24 tends to diminish, so that at 50 or 70 feet the DA 15 is clearly sharper in the corners (as is the DA 16-45).

However, none of this is really all that important, as most people aren't going to notice that the corners are not as sharp as the rest of the image. At large print sizes, people rarely look at the corners. Photographers need to print their best images and show them to non-photographers to gain perspective on what really matters. The sort of manias that afflict too many photographers (such as the mania for corner to corner sharpness and the mania for narrow DOF) don't generally afflict non-photographers, who tend to be more interested in the subject of the photograph, rather than the degree to which the image exhibits the technical prowess of the equipment used in making it.
01-20-2012, 02:57 PM   #22
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QuoteOriginally posted by sheld Quote
This may seem like a silly question, but how does the DA15 work, and why is it so much more compact than the older Film era 15mm F/3.5 lens?
From the kmp.bdimitrov.de website, this is the old film era K15 F/3.5 lens, which is 81.5mm, and 80mm in diameter and weights 550 grams.

And here is the much smaller DA15, which is less than half the size. Both lenses are Pentax mount, with the same distance to the film/sensor, and both have to use a retrofocus design. How does the DA15 manage to get the same amount of reverse telephoto inverse magnification with so little glass? Its almost the same size as a 28mm film lens, 39.5mm long and weights 212 grams or less than half of the KA15. I'm just curious; I really love the DA15 by the way....
- Sheldon
1. The DA is 1/2 f-stop slower than the old 15/3.5
2. it is APS-C only, as has been written previously
3. it has therefor a much smaller angle of view
4. the K/A 15/3.5 sports an integrated filter wheel, which adds to the bulk.
5. the DA has ED glass, which makes it possible to simplify the lens design
6. Pentax once more has decided, that lenses need to be small with the DA series - quite similar as with the M lenses, which sacrificed speed and sometimes quality compared to the K series, just to be smaller.

Ben
01-20-2012, 03:15 PM - 4 Likes   #23
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01-20-2012, 04:36 PM   #24
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QuoteOriginally posted by Ben_Edict Quote
5. the DA has ED glass, which makes it possible to simplify the lens design
Isn't the violet element in the K15 drawing ED?
01-20-2012, 04:50 PM   #25
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QuoteOriginally posted by lytrytyr Quote
Isn't the violet element in the K15 drawing ED?
It's glass AL, but was said to be absented on later versions.
01-20-2012, 05:01 PM   #26
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Hey Sherman, now that is what I call 'Snap'.
01-20-2012, 05:53 PM   #27
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QuoteOriginally posted by wlachan Quote
It's glass AL, but was said to be absented on later versions.
Thanks for the clarification.
Your "later versions" are the "standard" version I referred to.
So that makes two technical differences from the DA15.
01-21-2012, 04:47 AM   #28
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QuoteOriginally posted by lytrytyr Quote
Thanks for the clarification.
Your "later versions" are the "standard" version I referred to.
So that makes two technical differences from the DA15.
No, it is not about 2 technical differences. These are two completely different lenses.

- The K15 is a super wide angle with a 111 deg angle of view (diagonally)
- the DA 15 is a wide angle with a more common 86 deg angle of view

You can't compare those two lenses usefully, unless you also find the comparison between a 30mm fisheye lens for medium format and the old M 30mm meaningful.

Ben
01-21-2012, 07:14 AM   #29
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01-21-2012, 12:01 PM   #30
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I've never had a problem with the DA 15s field curvature, but then again, I own a scanner, so I don't need it to photograph pieces of paper. I mostly take photos of three (arguably, 4) dimensional things. But where this lens is actually better than a zoom is in colour, contrast, and compactness. Those things matter more to me than the definition of the gravel in the corner of my photo. Besides, how would you overcome field curvature / flatness in a photo like this?
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