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06-10-2010, 08:13 AM   #1
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Is there such thing as a 17-70mm constant f2.8?

Is there such thing as a 17-70 with constant f2.8?
Or any other (16-17) - (55-70) faster than f4 preferably constant aperture
From what I see the closest is the Sigma 17-70 f2.8-4 or the Tamron 17-50 f2.8

I may have to post this as a separate question but in the 18-250 f3.5-6.3: What is the max aperture around the 70mm range?
The only good thing about LBA is that I can dream....


06-10-2010, 08:26 AM   #2
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The Pentax 16-50 , Tamron 17-50, Sigma 18-50 are all constant F2.8
Pentax 17-70 is a constant F4
Sigma 17-70 f2.8-4.5 is variable
Sigma 17-70 f2.8-4 os HSM is also variable
The 18-250 is F5.6 at 70mm
I just bought a Pentax DA*16-50mm and sold my Sigma 17-70 f2.8-4.5. Not fully convinced I made the right move but the Pentax lens is very high quality and weather resistant. The Sigma took some really nice indoor shots with my KX and was much lighter with greater range. Everything is a trade off when it comes to standard Zoom lenses. I think most people would be more than pleased with the Sigma 17-70.

Hope this helps
06-10-2010, 08:34 AM   #3
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There are plenty of 3X standard f/2.8 zooms (eg, DA*16-50, similar Tamron and Sigma lenses), but basically no 4X ones. Take the price, and the size/weight, of a 3X f/2.8 zoom, double it, and now you're in the ballpark of what a 4X f/2.8 would be like - except image quality would undoubtedly suffer as well.
06-10-2010, 08:52 AM   #4
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There was a 28-105mm f2.8 from Tamron (the film equivalent of the 17-70mm) but it was a dog.

It was fairly shortly discontinued as it simply stretched too far. I think 3x is about the limit you will get, to create a 4x lens the cost would be so high I don't think we will see them anytime soon.

06-10-2010, 09:13 AM   #5
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Also, even though it was FF, we're still dealing the same registration distance as an APS-C camera. Making a 17-70/2.8 is bound to a lot harder than a 28-105/2.8 because whether FF or APS-C, those short focal lengths still involve the same kinds of design issues when the registration distance is so much longer than the focal length. And that 28-105 (which I just learned about like a week ago) is already *huge* - almost two pounds, and 82mm filter size.

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