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Old Nov 29, 2010, 6:43 PM   #1
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Default Tamron 17-50 f/2.8 constant mean constant?

I have read that this lens has a constant f/2.8, does this mean it never change, I see people say step it down to f/4.0, or something like that. Does this change like other lens? I am confused, what does constant f/2.8? I am thinking of replacing my 18-55(IS) with this, heard the image quality is outstanding.
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Old Nov 29, 2010, 7:59 PM   #2
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Nope, it means that the widest (smallest f number) is constant. Unlike your 18-55 which has a widest aperture that changes from f3.5 at the wide end and f5.6 at max zoom, the Tamron has f2.8 throughout the range. Like 99.5% of lenses you can still stop down. There are a few fully fixed aperture lenses but usually these are mirror lenses.
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Old Nov 29, 2010, 8:04 PM   #3
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Mark got there first!
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Old Nov 29, 2010, 9:02 PM   #4
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Thanks, so this would be like my 85mm 1.8? I can keep it at 2.8 if I want? Would you think this would be a decent upgrade to the 18-55(IS)??
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Old Nov 29, 2010, 9:11 PM   #5
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Certainly should be, I'm considering replacing my Sigma 17-70 with one for either my wife to use or as a backup if my full frame gear is down (or if I don't want to take something that expensive out with me).
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Old Nov 29, 2010, 10:03 PM   #6
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~Thread Hijack~

Mark, how do you like the 17-70...? I ask because I'm seriously considering the
new version of that lens to pair up with a D7000...

~End Hijack~
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