Need DSLR lens advice

Started Jul 31, 2012 | Discussions thread
Regular MemberPosts: 328
Re: Need DSLR lens advice
In reply to gisle, Jul 31, 2012

gisle wrote:

Jaysun wrote:

Stupid question.... is it locked into 2.8, even at 50mm?

Its largest aperture is constant f/2.8 over the entire zoom range from 17mm to 50mm - if that is what you're asking about.

But it isn't locked into 2.8. You can of course stop it down if you want to, just like any regular lens.
– gisle [ See profile/plan for equipment list ]

Sorry, yes, that's what I meant. I should have been more specific. I don't want to get too deep into another subject, or ask too many questions, but I'll ask this anyway... so, you have the 17-50mm. At 17mm, the max aperture is 2.8. Then you zoom to 50 and it still has a max aperture of 2.8. However, you have a 16-85mm. At 16, max f-stop is 3.5, but when you zoom out to 85mm, the best you can do is 5.6 (I'm just using the lenses you previously posted as examples).

Is that simply a matter of quality/price, or is there a specific threshold, where you hit a particular zoom and the f-stop HAS to decrease?

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