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06-30-2007, 09:39 AM   #1
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sigma 28-200mm zoom

I have a sigma 28 - 200mm zoom its about 7 years old. When i use it on my k10d it does not look sharp at 28mm. it looks ok at 200mm It work fine on my film camera. Anyway i can fix this problem?

thanks

07-03-2007, 02:13 PM   #2
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When you say it does not look sharp, is that in the viewfinder or on paper? If the image is ok on paper, but not in the viewfinder, that could be due to the viewfinder diopter adjust or simply because the viewfinder is smaller and the image you see at the wide end is not as 'large' as you are used to. Which camera are you using?

Wayne
07-03-2007, 02:29 PM   #3
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QuoteOriginally posted by tootal2 Quote
I have a sigma 28 - 200mm zoom its about 7 years old. When i use it on my k10d it does not look sharp at 28mm. it looks ok at 200mm It work fine on my film camera. Anyway i can fix this problem?

thanks
From what I have seen, because the sensors of DSLRs are highly reflective, it is more critical that the optics be multicoated to minimize reflections. Many old lenses had good coatings anyway so still work well on DSLRs (pretty much anything Pentax made since they introduced the K-mount it seems, especially the SMC Pentax-M and A primes), but cheaper lenses from the old days did not have quite such good coatings.

The end result is that a lens that looks fine on a film camera may potentially perform horribly on a DSLR. I know this is the case with the first generation Sigma 28-200 that my family used for years with decent results with a PZ-70. (3.8-5.6, 72mm filter) When I mounted the Sigma on my new K10D and took a few shots, the end result was horribly low contrast at any zoom range. The difference between it and the DA 50-200 that I bought within a week of getting that lens is like night and day.

In general - superzooms compromise optical quality (which becomes more apparent on DSLRs than on film), and first-gen superzooms are even worse.
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