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<blockquote data-quote="WayneF" data-source="post: 294264" data-attributes="member: 12496">Many zooms do have the same maximum aperture at any zoom focal length.More likely the FX lenses.14-24mm f/2.824-70mm f/2.870-200mm f/2.824-120mm f/4etc.And the inexpensive ones may not, more typically the DX lenses.fstop = focal length / aperture diameter.So on the first class of zooms, the aperture diameter does become larger at longer zooms to maintain the same fstop calculation.But on some inexpensive zooms, it is harder design work than the price warrants (larger diameter lenses), so then a longer zoom may be stopped down instead - at longer zooms (instead of constant maximum aperture).But at a fstop any focal length can do, the exposure is the same.And of course, some DX lens do maintain constant maximum aperture&nbsp; ... 12-24mm f/4 DX for example.</blockquote>

[QUOTE="WayneF, post: 294264, member: 12496"] Many zooms do have the same maximum aperture at any zoom focal length. More likely the FX lenses. 14-24mm f/2.8 24-70mm f/2.8 70-200mm f/2.8 24-120mm f/4 etc. And the inexpensive ones may not, more typically the DX lenses. fstop = focal length / aperture diameter. So on the first class of zooms, the aperture diameter does become larger at longer zooms to maintain the same fstop calculation. But on some inexpensive zooms, it is harder design work than the price warrants (larger diameter lenses), so then a longer zoom may be stopped down instead - at longer zooms (instead of constant maximum aperture). But at a fstop any focal length can do, the exposure is the same. And of course, some DX lens do maintain constant maximum aperture ... 12-24mm f/4 DX for example. [/QUOTE]

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