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

Started Aug 16, 2015 | Questions thread
MitchAlsup Veteran Member • Posts: 5,518
Re: 2x zoom lens with same absolute aperture instead of extender ?

mermaidkiller wrote:

Why not make a 200-400 f/2.8-f/5.6 which replaces a T/C and a prime lens ?

Because the entrance pupil of the zoom lens is inside the optical train, Zoom lenses have to have a larger front lens than the linear aperture, typically by 20%-25% so you would be holding 5" of glass at the front of the 200-400. Thus, the cost will not be what you are anticipating.

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Mitch

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