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06-19-2011, 09:53 AM   #16
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QuoteOriginally posted by DanielT74 Quote
Even with sharpness, the MTF graphs don't tell the whole story. Nice contrast can make an image look sharper, for instance. Most tests don't show my old K 135/2.5 to be a particularly sharp lens but the images from it certainly don't look soft (check the Guess the lens thread at the end).
The PZ test of the K135 f2.5 showed optimum aperture results not far behind the FA100 f2.8 macro, a very sharp lens.

06-19-2011, 10:05 AM   #17
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Your title bothers me because it tricked me into reading your thread. I re-wrote it for you.


"Sigma 17-50mm f2.8 as good as some primes in resolution and possibly in contrast?"
06-19-2011, 10:43 AM   #18
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QuoteOriginally posted by 1r0nh31d3 Quote
Your title bothers me because it tricked me into reading your thread. I re-wrote it for you.


"Sigma 17-50mm f2.8 as good as some primes in resolution and possibly in contrast?"

Ha ha, you have a point, but then headlines are traditionally exaggerated to attract the reader.
06-19-2011, 12:36 PM   #19
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QuoteOriginally posted by deejjjaaaa Quote
except Pentax

However, the data is in the lenses themselves (starting with the Kaf2 mount), I believe.

Here are some charts for older lenses:
Pentax K fit 50mm's Photo Gallery by Steve Flynn at pbase.com

06-19-2011, 01:39 PM   #20
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I think that sample variation is likely to be larger with zooms. More stuff to get misaligned and broken.
06-19-2011, 05:29 PM   #21
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QuoteOriginally posted by civiletti Quote
This is true, but not as true as in the past. Post processing can minimize chromatic abberration and linear distortion. Contrast can be increased at the macro and micro level. Color balance can be tweeked and saturation adjusted. Post processing cannot increase resolution, though. Sharpness can give the impression of more resolution, but that's not the same. It's somewhat analogous to the basketball quip, "you can't teach seven foot."
I guess you can fix things up to an extent but you won't quite reach the level that a superior lens reaches especially in demanding conditions.
06-19-2011, 05:35 PM   #22
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QuoteOriginally posted by civiletti Quote
Ha ha, you have a point, but then headlines are traditionally exaggerated to attract the reader.
I know. you totally got me with your tricky journalism speak.
06-19-2011, 09:10 PM   #23
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QuoteOriginally posted by Edgar_in_Indy Quote
There seems to be very few owners of the new Sigma 17-50mm in Pentax-mount so far. There are only four customer reviews on B&H's site, and none whatsoever on Adorama or Abe's. I imagine that the higher price over the Tamron 17-50mm is keeping most people away. And the lack of response on this thread seems to support that notion. But from what I've heard, it's a superior lens and the price is justified.
I've had the Sigma 17-50mm F2.8 since about September last year, and it's a great lens for what I use it for, as a versatile short/normal range for event photography. It is a sharp lens and I've never had any problems with it optically, but then again, I don't pixel peep. Because of this thread, out of curiosity and spare time, and because I also have the Pentax FA 35mm F2.0 and Sigma 50mm F1.4, I decided to do a quick and dirty test, i.e. a non-controlled, non-scientific test, of the Sigma 17-50mm against the primes.

First at 35mm, 100% crop. One lens on the left, one lens on the right. From top, F2.8, F4.0, F5.6 and F8.0, click for full size:



Then at 50mm, 100%. Same deal, one lens on the left, one lens on the right. From top, F2.8, F4.0, F5.6 and F8.0, click for full size:



The results are fairly interesting, though I want to let a few of you have a look at the comparisons and see your thoughts before I make my comments.

06-19-2011, 10:18 PM   #24
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Left columns on both pics looks better to me.
06-20-2011, 04:33 AM - 1 Like   #25
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My guess is the left side is the prime lens in both images.

The 50mm images on the left looks much better than the right side. So, I hope the focus is not off on the right side?

It is a bit more tricky for 35mm. At f2.8 the left image is better, but beyond that they are very close and from this just one edge I would give the nod slightly to the right side as it looks a bit more contrasty.
06-20-2011, 05:11 AM   #26
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I'd say the zoom took the images on the right hand side.

From this comparison, the differences (with a few exceptions) don't seem huge at all. Would be very interesting to see full images (not detail crops) in comparison as well to judge the bokeh.
06-20-2011, 06:32 AM   #27
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I have a hard time believing that either of the lenses are that bad at 50mm f/2.8. I think there must have been some kind of focus issue. Both the lenses are supposed to be fairly sharp there according to all the reviews I've read. I've tried my hand at similar lens tests before, and I know that it's very easy to have the results skewed by a very small focus difference.
06-20-2011, 06:35 AM   #28
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pretty interesting results. I agree with regards to giving some full image crop size samples to see any specific differences between lenses.
06-20-2011, 07:11 AM   #29
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QuoteOriginally posted by Edgar_in_Indy Quote
........... I've tried my hand at similar lens tests before, and I know that it's very easy to have the results skewed by a very small focus difference.
I second that, even a fraction of a twist to the focus ring (less than a mm) makes a big difference....so much so I don't do much of it any more as it is highly vexing.
06-20-2011, 07:15 AM   #30
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Yes, as everyone above has managed picked out, the left hand images were all from the primes, while the right hand images were all from the Sigma 17-50mm F2.8.

QuoteOriginally posted by pcarfan Quote
The 50mm images on the left looks much better than the right side. So, I hope the focus is not off on the right side?
That was one result that I was quite surprised at. I didn't expect the quality difference to be that big, especially at F2.8, but then again, zoom lenses tend to not be their best at the very ends of their zoom ranges, and also, there may be focusing errors as you mentioned, or other issues at play.

QuoteOriginally posted by Class A Quote
From this comparison, the differences (with a few exceptions) don't seem huge at all. Would be very interesting to see full images (not detail crops) in comparison as well to judge the bokeh.
At the 100% crops, three out of the three posters above managed to pick that the primes were on the left and the zooms were on the right, but I personally tend not to bother looking at 100% crops, so here are some comparison shots of the whole image. The photos are the full 18 or however much megapickels the K-5 is (MP isn't something I bother much about either) resized to 800px longest edge and then stitched. The results are a lot closer, pretty much with the exception of 50mm at F2.8 and maybe at F4.0:

Once again 35mm, and from top, F2.8, F4.0, F5.6 and F8.0, click for full size:



Then 50mm (with a red line to separate the columns of photos), from top, F2.8, F4.0, F5.6 and F8.0, click for full size:



My personal thoughts are that at the end of the day, the Sigma 17-50mm F2.8 is a good lens, and in general, there's not too much to differentiate today's top zoom lenses to prime lenses in most situations (i.e. non-pixel peeping); the versatility of a having a zoom range, as opposed to a fixed focal length is also much appreciated from my experience, especially for event photography. Having said that, prime lenses definitely do have their uses, and I'm yet to see a zoom lens that's faster than F2.8 for 35mm or APS-C (I know there's some F2.0 zooms for m4/3 though).
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