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Old Jan 31, 2006, 2:32 PM   #11
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18mm Lens Test

Here's the Sigma 18-200mm & Tamron 18-200mm compared against the Pentax 18-55mm - unfortunately, I ommitted to save the Pentax RAW format.

Sigma wins over the Tamron, close to Pentax in JPG - better in RAW.

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Old Jan 31, 2006, 2:47 PM   #12
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55mm Lens Test

Here's the Sigma 18-200mm & Tamron 18-200mm compared against the Pentax 18-55mm - unfortunately, I ommitted to save the Pentax RAW format.

Sigma still wins over the Tamron, close to Pentax in JPG - better in RAW.
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Old Jan 31, 2006, 3:01 PM   #13
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135mm Lens Test

Here's the Sigma 18-200mm compared againstthe Tamron 18-200mm.

Sigma still wins over the Tamron - better in RAW.

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Old Jan 31, 2006, 3:13 PM   #14
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200mm Lens Test

Here's the Sigma 18-200mm compared againstthe Tamron 18-200mm.

Overall, the Tamron wins over the Sigma - better in RAW.
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Old Feb 1, 2006, 9:06 AM   #15
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Thanks for posting this - I just got a DS and have been contemplating an 18-200 lens, and was wondering if there was much difference between these two. It's interesting to see what your experience was. Thanks again!
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Old Feb 1, 2006, 2:50 PM   #16
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200mm Lens Test

Here'sanother Sigma 18-200mm compared againstthe Tamron 18-200mm.

This one clearly shows how much better focused the Tamron is over the Sigma; thisdecided me against the Sigma as it wos poor above 135mm & the Tamron which is poor below 135mm.

Conclusion
Overall, the results are in keeping with the review here:

Sigma - http://www.epinions.com/content_185158569604
Optically good, despite vast range. But at 200mm, I have to either manually focus, or use a parfocal technique (i.e. focus at 135mm, shoot at 200mm).

Tamron - http://www.epinions.com/content_192627838596
More optical shortcomings than its Sigma counterpart, but my copy focuses better. Despite optical shortcomings, I can still make decent 8.5"x11" prints.

The Sigma is useful in the range 18-55mm & out to 135mm but given the restrictions on 200mm focusing, it's not for me.

The Tamron quality falls short of the Sigma except at 200mm, again it's not for me.

For the time being I'm sticking with the Pentax 18-55mm kit lens & will purchase the Pentax50-200mm to extend the range - OK it will not be as convenient as using a 18-200mm single zoom BUT I'm not prepared to accept the limitation in optical resolution of either the Sigma or Tamron.
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Old Feb 1, 2006, 6:32 PM   #17
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It does sound like I shouldskip them both right now. I should concentrate on getting used to the camera and all if it's little quirks with the lenses I have. I have a fairly good collection of old, manual lenses (prime 24, 50, 135, zoom 24-50, 70-210, 80-200) plus the kit lens. I'd gain the convenience of one lens and auto focus but I don't think that's worth giving up quality.

style="BACKGROUND-COLOR: #000000"Another newbie question. I'm sure this one has been answered lots of times, but I've missed it somehow along the way. I understand about the old lenses and how you have to multiply by 1.5 to get the 35mm equivalent range for the smaller digital sensor. My question is about these new lenses that are designed specifically for the digital cameras. I assume that the designations for these lenses are specified in the same terms as the old 35mm lenses (even though they are only to be used on dsLRs), and that I should still multiply by 1.5 to get the equivalent value, right?
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Old Feb 1, 2006, 6:37 PM   #18
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correct
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Old Feb 2, 2006, 5:02 AM   #19
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Okay. now I am confused about the lens sizes.

If I have a 18-125 DC Sigma lens it is a 18-125.
If I have an old 100-300mm Sigma lens (non digital) it is in fact a 150-450mm lens.
If I have a new 100-300mm DG Sigma Lens it is fact only a 100-300mm lens.

Am I correct?
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Old Feb 2, 2006, 10:55 AM   #20
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No. All lenses (so far) are sized as if they would be mounted on a 35mm camera, whether they were designed for 35mm OR for the digital APS-C sensor. So all of the lenses you mentioned would have the 1.5 multiplication factor applied when mounted on your digital camera.
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