What is the technical name for a lens which has the same maximum aperture throughout the entire zoom range?
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"Fixed maximum aperture zoom lens" :-) – Vikas Dec 31 '11 at 04:33
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2Do you mean a constant maximum aperture? eg 70-200 f2.8 – James Gray Dec 31 '11 at 05:11
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@JamesGray I meant in which the aperture doesn't grow when you zoom the lens. – Aquarius_Girl Dec 31 '11 at 05:59
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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? – mattdm Dec 31 '11 at 14:09
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This question is ambiguous. The title refers to a "fixed aperture" - but the body of the question then asks about the "maximum aperture" - implying that the aperture of the lens in question has a range. It may be worth correcting the title so the reason for swapping the accepted answer becomes clear. – db9dreamer Dec 08 '13 at 11:48
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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* – mattdm Dec 08 '13 at 15:48
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@mattdm The only value in this question are the links in your comment above. I just removed the ambiguity that caused Itai's answer to be selected and then unselected - which looked odd, when it did answer the question in its original form. – db9dreamer Dec 08 '13 at 20:05
3 Answers
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Constant-Aperture Zoom Lens.
Itai
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4Maybe this answer could be expanded to mention the effects of constant-aperture on the cost, weight, etc. of a zoom lens? – Sean Dec 31 '11 at 08:41
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2Actually had to make it bold to satisfy the minimum number of characters :) – Itai Dec 31 '11 at 15:31
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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.
mattdm
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2FYI, Pentax Reflex Zoom 400-600mm f/8-12 is a fixed (but not constant) aperture zoom lens – Imre Dec 08 '13 at 17:18
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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.
Frank
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