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08-07-2010, 01:49 PM - 1 Like   #31
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Deceide for yourself buy looking at the results, I bought the Tammy but after looking at this site I should have got the Sigma..
PENTAX forum Slovenija • Poglej temo - TEST Pentax smc DA*16-50mm F2.8 ED AL (IF) SDM in konkurenca

08-07-2010, 02:32 PM   #32
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QuoteOriginally posted by Nightwings Quote
Positive ..... and if it's supposed to be inferior to the Pentax, it certainly wasn't under the catagory of IQ. The Canon kit lens CRUSHS the Pentax Kit.
I was looking at what must be the older non-IS version of the Canon lens - the IS one has impressive MTF numbers. I also wish photozone would have numbers for the new Pentax kit lens - it's supposed to be better than the first version.

Do you happen to have any shots from that comparison? Comparisons on LCD screens with different camera processing settings can be misleading.
08-07-2010, 02:39 PM   #33
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QuoteOriginally posted by Fl_Gulfer Quote
I bought the Tammy but after looking at this site I should have got the Sigma.
Reviews can be misleading. Easiest way to figure this out is to buy a lens, use it happily, then start reading reviews about it.
08-07-2010, 03:08 PM   #34
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That review/the samples tend to indicate to me that the Tamron's better than the Sigma at most things, anyway.

08-17-2010, 02:44 AM   #35
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QuoteOriginally posted by shang Quote
sorry, I don't know about the canon version. For pentax version, tammy 17--50 suffers from front or back focus problems. Especially considering that k-x doesn't have the in camera focus adjustment function... BUT, if you can try it out in a store that has many copies in stock, then i believe that you will certainly find a good copy, and a good copy will make you WOW.

Maybe it's because of my bad experience... i bought 3 of them all of which had severe front focus problems, and i gave up and bought the 16--50 da*. As Jim said, for k-10d the tammy is usually perfect. Bad copies happen on k-x or k-7 bodies, since these bodies are new.

@future: AbesofMaine's price of the da* is $689-$15 coupon =$674, which is very good.
Please indulge a newbie. I don't understand "front or back focus problems." What exactly does this mean? Front focus would mean what? Close range? Back focus, distant range? A link to a technical explanation might suffice, or a few choice words. Thanks.
08-17-2010, 03:58 AM   #36
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QuoteOriginally posted by Muse Quote
I don't understand "front or back focus problems." What exactly does this mean?
Front focus (FF) means that if you use AF to focus on a subject detail (say the eyes) that the plane of sharpest focus in the image will be in front of it (e.g., the nose).
Back focus (BF) is the dual notion, you focus on the tip of the nose, but the eyes will be sharp in the image.
Technically speaking you can also refer to FF/BF when focusing manually, but most often people are referring to AF FF/BF proplems.

Cameras like the K20D or the K-7 have official means to adjust their AF to deal with such FF/BF issues. Other Pentax models have hidden service/debug menus which can be accessed via a keystroke sequence or software or placing a file on the memory card. The disadvantage with the latter is that there is only one setting for all lenses whereas the K20D and K-7 allow several lenses to be calibrated individually.

FF/BF issues occur with all lenses (dpreview couldn't obtain a copy of the DA* 55/1.4 which didn't have an issue, trying at least three times). Some models are said to be more affected than others. Probably a matter of quality control. Manufacturers are known to swap lenses with issues, though. Hence if you have the patience, you should get a good one eventually. Bear in mind that a zoom can exhibit different FF/BF behaviour depending on the focal length so there might not be a perfect copy at all. Usually, FF/BF issues are so small that you don't notice them under normal conditions (unless the lens is seriously affected).

Looking at the images of the test posted above by Fl_Gulfer (nice comparison, thanks!) (I don't understand the text), I was surprised to see that the Pentax 16-50/2.8 came out worst regarding IQ, at least to my eyes. I didn't expect that. I wouldn't pay more for that even though it's weathersealed. I agree that the Sigma probably has the overall edge (except at the long end where the Tammy looks better).

Last edited by Class A; 08-17-2010 at 04:06 AM.
08-17-2010, 06:35 AM   #37
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QuoteOriginally posted by Laurentiu Cristofor Quote

Do you happen to have any shots from that comparison? Comparisons on LCD screens with different camera processing settings can be misleading.
Yes, that was my thought as well. I recently edited some photographs which included my shots on various Pentax bodies--often with excellent prime lenses--and the shots of another photographer that used mostly the Canon 18-135mm, judged by Photozone to be pretty mediocre. On first glance, the Canon shots might lead one to exclaim something about "crushing" the K-x because the Canon jpegs from the camera are very contrasty, vibrant and have had generous amounts of NR and sharpening applied. The Pentax raw files look blue, faded and less snappy when viewed in Adobe Bridge or Faststone. Run the Canon CR2 files and the Pentax DNG through Adobe ACR with the same settings, and view with some magnification and in fact the Pentax primes have, as expected, ouperformed the Canon superzoom.

Photozone writes that MTF numbers cannot be compared across platforms.

Last edited by GeneV; 08-17-2010 at 06:40 AM.
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