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Old Apr 26, 2007, 10:05 PM   #11
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Sigma offers two different 18-50 lenses - an 18-50 3.5-5.6 and an 18-50 2.8 EX (or EX DG). I have the first one, hence my comparison to the Pentax 18-55. From the price comparison you mention you must be referring to the EX series lens, which you didn't specify*, and whichis a whole different thing. It is should certainly be the better of the two Sigmas, and costs around $300 more. I can't comment on the EX as I have no experience with it. The only one of that series I have is a 50mm EX DG macro, which is an excellent, professional grade lens. As for the weight of the DA lenses, remember that lenses computed for most digital cameraswould belighter than their predecessorsif they cover a smaller circle the size of the chip rather than a full 35mm frame. The EX Sigma you are thinking about, however, takes a 72mm filter, versus the 67 of the Pentax 16-45, so all other things being equal you might expect it to be heavier because of its larger size. Whetherit uses less light weight materials, I do not know.

As for the flimsiness you mention, it feels like there is a bit of play in the focussing ring of the 18-55 (the 16-45 is better in this regard), which might bother some people manually focussing rapidly, but it does not translate into inaccuracies in autofocussing. A lens that is too well damped manually could be slower automatically - a number of Tamron and Sigma lenses are similarly light and loose, which doesn't seem to hurt their sales. The EX macro 50mm is better damped, but still not like the older all metal lenses. The lighter polycarbonates used in today's lenses may not be able to have the same fine tolerances as metals, but that is a question for the engineers. The way the longerzooms extend themselves when held facing downwardsannoys me no end. I still have a couple of the old Kiron and Vivitar Series 1 (made by Kiron) lenses which were marvels of precision machining - I never have the same feeling of confidence in using a polycarbonate lens, although optically I can't quibble with the results.

*You did mention it in the title, which I overlooked -- sorry.
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Old May 18, 2007, 10:08 PM   #12
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I picked up the 16-45 6 mts ago. I an usually at the lower end of the kit lens, which is very good but did have some vignetting at the low end - 18. The 16 has solved this, and it focuses instantly - with no hunting as the kit was doing. I find the 16 - 45 to be very sharp, no CAing at all. I have read a review that indicated some viginetting at 16 and some CA, however have never experienced it. Maybe I was in the sweet spot of the lens - don't know - bottom line - I like it very much!!

the 16 - 45 is my primary lens - I have no experience with any of the other brands.

Hope that helps
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