02-08-2011, 12:54 PM
[quote name='genotypewriter' timestamp='1297130472' post='5943']
It's not just faster, it's also constant. As soon as a zoom becomes a constant aperture lens it's usually much larger than a variable aperture lens of the same range, even if the max aperture of the variable aperture lens is the same as the max of the constant lens.
GTW
[/quote]
Not sure I get what you mean here, specific example(s) might help.
Way I see it, for a longer focal length lens, the size will be dominated by the long end of the zoom with the wide end being relatively unimportant. So hypothetically a constant f/4 lens, I can't see that being smaller than a f/2.8-f/4 lens for example. Unless you're comparing the aperture at the wide end, which doesn't make sense to me.
A rough rule of thumb I find that works quite well for comparable (build, quality) longer focal length lenses is to look at the entrance pupil size. It correlates quite well to price, although there is still a relationship between focal length and lens length. Personally I feel that constant aperture lenses are under-designed on the wide end as they should be able to go faster.
It's not just faster, it's also constant. As soon as a zoom becomes a constant aperture lens it's usually much larger than a variable aperture lens of the same range, even if the max aperture of the variable aperture lens is the same as the max of the constant lens.
GTW
[/quote]
Not sure I get what you mean here, specific example(s) might help.
Way I see it, for a longer focal length lens, the size will be dominated by the long end of the zoom with the wide end being relatively unimportant. So hypothetically a constant f/4 lens, I can't see that being smaller than a f/2.8-f/4 lens for example. Unless you're comparing the aperture at the wide end, which doesn't make sense to me.
A rough rule of thumb I find that works quite well for comparable (build, quality) longer focal length lenses is to look at the entrance pupil size. It correlates quite well to price, although there is still a relationship between focal length and lens length. Personally I feel that constant aperture lenses are under-designed on the wide end as they should be able to go faster.
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