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02-27-2013, 09:59 PM   #16
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QuoteOriginally posted by vodanh1982 Quote
Sigma AF 10-20mm f/4-5.6 EX DC (Pentax K) - Review / Test Report - Analysis

It is normal that your lens is soft at corners at f/4. If you need better corner sharpness, go for Sigma 8-16mm.
I don't need it, I just want to know if mine is defective, bec I'm new to the game, and don't know how to judge it myself.

02-28-2013, 07:13 PM   #17
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QuoteOriginally posted by PBandJ Quote
I don't need it, I just want to know if mine is defective, bec I'm new to the game, and don't know how to judge it myself.
It would be unusual for the lens to be uniformly defective across the frame. So if the left/right and top/bottom and all 4 corners have close to the same performance (they may not have exactly the same performance, just due to manufacturing tolerances), the lens is probably "good" in the sense that it's delivering the performance it was designed to.

Paul
03-01-2013, 06:55 AM - 1 Like   #18
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QuoteOriginally posted by PBandJ Quote
I don't need it, I just want to know if mine is defective, bec I'm new to the game, and don't know how to judge it myself.
I would suggest that you look at your shots fromthe amphitheater or of the headstones and analyze them. I think you might be happy with the results and feel more confidence in your lens.
03-01-2013, 08:47 PM - 1 Like   #19
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QuoteOriginally posted by PBandJ Quote
I don't need it, I just want to know if mine is defective, bec I'm new to the game, and don't know how to judge it myself.
I think you may not realize that it's not necessarily a binary judgement of being defective or not. There's a spectrum of performance consistency, from theoretically perfect to obviously horrible. Most lenses fall somewhere in between.

Paul

03-01-2013, 09:25 PM   #20
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QuoteOriginally posted by tibbitts Quote
I think you may not realize that it's not necessarily a binary judgement of being defective or not. There's a spectrum of performance consistency, from theoretically perfect to obviously horrible. Most lenses fall somewhere in between.
Paul
Absolutely. There are almost NO perfect lenses, and many suffer from QC issues such as de-centering. Of course Pentax lenses (from the reviews I've read, anyway) are some of the worst offenders in this area. I think it's instructive to be less worried about getting a good copy of a (to be honest) mediocre lens, when you could be out shooting pictures with it and not worrying about it. When I got my 10-20mm 4-5.6, I shot literally 2 shots of a door handle, one at f4 and one at f8, at 10mm (because I know that's the focal length I bought it for). It was plenty sharp in the middle, so I was satisfied and went out to shoot, never thinking about it again.
It's important to test your lenses when you receive them, simply because of sample variation and QC issues, but it's more important to realize that nothing's perfect (especially lenses), and that while you're wasting time shooting brick walls and newspapers, great shots are passing you by.

My two cents (probably not worth much...)
03-02-2013, 01:42 AM   #21
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Ok, i should have said i want to know if i need to exchange it while i'm in my first 30 days.

Anyway, i'm on vacation with it,having a great time, and quite happy with the pictures. Only seeing them on an iPad, so not pixel peeping.
03-02-2013, 06:00 AM - 1 Like   #22
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QuoteOriginally posted by PBandJ Quote
Anyway, i'm on vacation with it,having a great time, and quite happy with the pictures.
Great, This is what counts. Enjoy your vacation and your pictures / lens.
03-02-2013, 06:38 AM - 1 Like   #23
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QuoteOriginally posted by PBandJ Quote
Ok, i should have said i want to know if i need to exchange it while i'm in my first 30 days.
To me it doesn't look like it. Looks like it's performing within standards. There's a chance it's a little soft, but this lens is never great at the extreme corners anyway. I think your copy sharpens up nicely. And I agree with a prior poster that f16 really isn't (or shouldn't be) the sharpest aperture for the lens. You're looking around f7.1-f8 for that.

Enjoy your vacation and your new lens!

03-02-2013, 06:45 AM   #24
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QuoteOriginally posted by zdwagner Quote
To me it doesn't look like it. Looks like it's performing within standards. There's a chance it's a little soft, but this lens is never great at the extreme corners anyway. I think your copy sharpens up nicely. And I agree with a prior poster that f16 really isn't (or shouldn't be) the sharpest aperture for the lens. You're looking around f7.1-f8 for that.

Enjoy your vacation and your new lens!
Thanks for highlighting what the other poster said about using f16. It didn't sink in that f8 was the target.
03-02-2013, 07:22 AM   #25
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QuoteOriginally posted by PBandJ Quote
Thanks for highlighting what the other poster said about using f16. It didn't sink in that f8 was the target.
Sorry don't know if this is snarky or not. If so, I'm sorry for belaboring a point that didn't need to be.

If not, then let me say that there's nothing wrong with f16 at all, and it's probably not too soft from diffraction at that point. I'm no super techy, so someone else can speak to the limitations of the aps-c sensor/lenses. But I would guess that you start seeing diffraction softness around f10-11, and it gradually increases from there. Doesn't mean you can't get a sharp shot at f16 (as you've proven), but with aps-c sensor cams you don't need to stop down quite as much to get great depth of field as you might on a FF cam. Sorry if this is all common knowledge here; I frequently offer up things when they haven't been asked for.

Cheers!
03-02-2013, 07:35 AM   #26
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QuoteOriginally posted by zdwagner Quote
Sorry don't know if this is snarky or not. If so, I'm sorry for belaboring a point that didn't need to be.

If not, then let me say that there's nothing wrong with f16 at all, and it's probably not too soft from diffraction at that point. I'm no super techy, so someone else can speak to the limitations of the aps-c sensor/lenses. But I would guess that you start seeing diffraction softness around f10-11, and it gradually increases from there. Doesn't mean you can't get a sharp shot at f16 (as you've proven), but with aps-c sensor cams you don't need to stop down quite as much to get great depth of field as you might on a FF cam. Sorry if this is all common knowledge here; I frequently offer up things when they haven't been asked for.

Cheers!
No i was not snarky!
Thanks for bringing it to my attention because I didn't make that connection in my brain before
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