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Lenses Let's talk glass - from ultra-wide to super-tele.

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Old 03-04-12, 07:58 PM
Orbster Orbster is offline
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Join Date: Aug 2010
Posts: 82
Constant apertures

This one has been puzzling me for a while.

There are zoom lenses out there that have a constant aperture throughout the focal range so given that the f number is actually a ratio of the focal length how can this be?

Does the aperture close down as the focal length decreases? This would seem daft as why not have a superfast aperture at the widest focal length instead of a relatively slower one?

Confused
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