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05-03-2009, 07:22 PM   #31
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QuoteOriginally posted by creampuff Quote
Subjective enough for you...
In any case, all I meant to say was that you should expect the Pentax to be sharper in some cases (at f/4 from extreme wide to ~50mm, or extreme borders at any aperture), while the Sigma in others (note that the Sigma is wide open at f/4.5 by 70mm).

Also, I think the video is still interesting to watch, whether it's relevant or not.

EDIT: I'll sneak in my 100% crop done at 35mm, f/4 with DA 17-70 f/4, here. I suspect the stuff done by frank, below, is done wrong or an unlucky coincidence.

EDIT2: (3 star JPEG quality)




Last edited by asdf; 05-10-2009 at 07:07 AM.
05-03-2009, 07:58 PM   #32
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QuoteOriginally posted by asdf Quote
Yes, because lenses--and not people--shoot photographs: the photographer never contributes to the result.

photozone's copy of Mr. Pentak's lens was imperfect: it had a de-centering defect. It still wins against Mr. Shiguma at ~40mm.
never mind, deleted ...

Last edited by frank; 05-04-2009 at 11:29 PM.
05-03-2009, 08:09 PM   #33
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QuoteOriginally posted by frank Quote
Okay, here are the comparison results from the two copies I tested,
All testing photos were taken by a K20D camera in JPG at default setting (bright mode, AWB, **** quality), No post processing except cropping.
Thanks. The colored fringes in the first shot indicate you're not focused.

Last edited by asdf; 05-03-2009 at 08:15 PM.
05-03-2009, 08:16 PM   #34
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QuoteOriginally posted by asdf Quote
Thanks. The colored fringes in the first shot indicate you're not focused.
I thought so too. But I took at least three testing shots at the same setting, every time refocus, all came out like that.

That's why we can't judge a lens by just one review


Personally I've used both (not test, but actual use), and I like the Sigma 1770 better Just my experience, that's all.


Last edited by frank; 05-03-2009 at 08:22 PM.
05-03-2009, 08:18 PM   #35
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QuoteOriginally posted by frank Quote
I thought so too. But I took at least three testing shots at the same setting, every time refocus, all came out like that.

That's why we can't judge a lens by just one review
It's possible you mis-focused each time. Pobody's nerfect.
05-03-2009, 08:51 PM   #36
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QuoteOriginally posted by frank Quote
Maybe, my and Klaus's copy of the DA 17-70 f/4 are special (100% crop of a JPEG out of K20D + default settings (EDIT: 3 star JPEG quality), second try--at first try, the white balance was messed up):



I used a tripod, 2s mirror lockup and a cable release (and blacked out the donor number ).

It was shot at 35mm, f/4.

My suspicion is that measurebating should be left to us folks with OCDs.

EDIT: Also, I would recommend doing a less comprehensive comparison, but much more carefully. The more comprehensive the tests, the more dubious the results you'll get.

Last edited by asdf; 05-10-2009 at 07:09 AM.
05-03-2009, 09:46 PM   #37
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Okay, yours definitely looks better than the one I used. Congrats
05-03-2009, 11:51 PM   #38
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QuoteOriginally posted by frank Quote
Okay, yours definitely looks better than the one I used. Congrats
If you still think your photos are in focus, then I think the variable to consider lies on the other side of the pentaprism.

05-04-2009, 12:32 AM   #39
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QuoteOriginally posted by asdf Quote
DA17-70 is sharper than the Sigma at f/4, at least, at some focal lengths, as long as you focus right and do the test right.
I would say that the DA17-70mm and the Sigma 17-70mm are equally sharp. There is sample variation, of course. I once had a faulty DA16-45mm and I compared it to the Sigma 17-70mm. The DA16-45mm was soft on the left side. I had it exchanged for a new one which was all right. It is quite easy to "prove" that a lens is better than another by misfocussing slightly. The DA17-70mm is slightly sharper at the borders than the DA16-45mm when I make comparison shots. But much depends on focussing and subject.

In my experience the DA16-45mm is one of the few lenses than focuses correctly. With my other lenses I focus at the tele end, lock focus, zoom out the the desired focal length and take the picture. I also did this with the Sigma 17-70mm and the DA17-70 and especially the DA18-250mm benefit enourmously by focussing this way. In other words the autofocus system does not work perfectly.
05-04-2009, 12:37 AM   #40
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QuoteOriginally posted by Hythloday Quote
In other words the autofocus system does not work perfectly.
No doubt. There's variability in the cameras as well. Manual focusing does not have to be spot on either. Sometimes you need to change the shim for the split prism focusing screen to be more accurate.
05-04-2009, 12:45 AM   #41
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QuoteOriginally posted by frank Quote
Okay, here are the comparison results from the two copies I tested,
I am sorry to say that you did not test lenses, but which lens behaved best in artificial light. Clearly the Sigma focuses better in artificial light. When doing a test you should exclude all possible influences. My DA12-24mm always misfocuses in artificial light but outside it hardly misfocuses.
05-04-2009, 06:11 AM   #42
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QuoteOriginally posted by asdf Quote
If you still think your photos are in focus, then I think the variable to consider lies on the other side of the pentaprism.
Was that dumbass remark even necessary?
05-04-2009, 06:42 AM   #43
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QuoteOriginally posted by asdf Quote
If you still think your photos are in focus, then I think the variable to consider lies on the other side of the pentaprism.
QuoteOriginally posted by creampuff Quote
Was that dumbass remark even necessary?
For asdf, I guess it was. Aside from blind fanboy-ism, I have no idea why he insults anyone who doesn't agree that the DA 17-70 is "the hand of God made of glass and plastic."

Of course, the stunning images and youtube videos he shows prove he isn't just a measurebater.
05-04-2009, 08:13 AM   #44
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QuoteOriginally posted by Hythloday Quote
At 70mm the pictures are slightly sharper at aperture f11 than at aperture f8.0. A lot depends on focussing. The focussing range is quite short so you can misfocus quite easily.
You are correct, but what does that have to do with the apparent motion blur at f4 and f8?
05-04-2009, 01:04 PM   #45
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Summary

I have the Sigma 17-70 and the 18-50 2.8, the latter providing faster and more likely focus in low/yellow lighting on the K10D and even K2000.

Now I want a 18-70mm constant 2.8, weather-resistant. I really do. I would part with USD $1,000 and my auxiliary dog for it.

Alas
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