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2x zoom lens with same absolute aperture instead of extender ?

Started Aug 16, 2015 | Questions thread
Michael Fryd
Michael Fryd Forum Pro • Posts: 16,059
Re: 2x zoom lens with same absolute aperture instead of extender ?

Steve Balcombe wrote:

...

Yes, but as per my earlier post the front element of a long lens is the size of the entrance pupil. The shorter the lens, the less true this is.

...

The aperture is the weakest link in the chain.  Typically, that will be the size of the front element, but that's an engineering decision, not a requirement of physics.

Thus with a zoom lens, there are times when the effective maximum aperture is smaller than the front element.

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