What is the technical name for a lens which has the same maximum aperture throughout the entire zoom range?
asked Dec 31, 2011 at 4:27
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"Fixed maximum aperture zoom lens" :-)– VikasDec 31, 2011 at 4:33
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2Do you mean a constant maximum aperture? eg 70-200 f2.8– James GrayDec 31, 2011 at 5:11
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@JamesGray I meant in which the aperture doesn't grow when you zoom the lens.– Aquarius_GirlDec 31, 2011 at 5:59
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More about this type of lens can be found at Why do zoom lenses and compact cameras have varied maximum aperture across the zoom range? and How do constant aperture lenses work? and What are the advantages of a lens having a fixed maximum aperture?– mattdmDec 31, 2011 at 14:09
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1@dav1dsm1th Your edit kind of puts the answer into the question title, making the answer seem even more obvious. I'm not sure if that will be more or less helpful to future visitors. *shrug*– mattdmDec 8, 2013 at 15:48
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3 Answers
This is a constant maximum aperture zoom lens. The "maximum" is often omitted — "constant-aperture zoom" — but is useful to include the word maximum to resolve a possible ambiguity with a fixed aperture lens, which is a much more rare design where there is no ability to stop down the lens from its one and only aperture setting.
Fixed aperture is only common in catadioptric lenses, which use mirrors, and I'm not aware of any that zoom, so in some sense the distinction is pedantic; everyone will know what you mean if you say just "constant-aperture". You will find people calling constant-maximum aperture zooms "fixed aperture", and if they're not talking about mirror lenses you can usually assume that they don't actually mean it.
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2FYI, Pentax Reflex Zoom 400-600mm f/8-12 is a fixed (but not constant) aperture zoom lens– ImreDec 8, 2013 at 17:18
Constant-Aperture Zoom Lens.
constant maximum aperture zoom lens - Lets say the lens is a 2.8f constant aperture and focal length is variable from 35mm - 100mm. It simply means that at 30mm through 100mm the 2.8f is available to use. Many variable lens say 3.5 - 5.6f meaning 3.5f at the 35mm focal and decreases towards 5.6 as the lens is zoomed out towards 100mm. So at 100mm fully zoomed out the largest aperture available to use is 5.6 . All this means is you need more light at the longer end of the lens. So a 3.5 constant can shoot in lower light than a 3.5-5.6 lens can.
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