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

Started Aug 16, 2015 | Questions thread
Mark B.
Mark B. Forum Pro • Posts: 29,756
Re: 2x zoom lens with same absolute aperture instead of extender ?

mermaidkiller wrote:

Using an extender (tele converter) has the advantage that the absolute aperture (in mm, not as f/ number) remains the same with the same lens which allows a relative bright f/nubmer without T/C and yet acceptable with T/C. E.g the bright 200mm f/2.8L with T/C results in a yet acceptable 400 f/5.6.

A zoom alternative (100-400 f/4.5-5.6L) results in a dim f/5 at 200mm.

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

I'm not sure this will be much different in price & weight compared to the 200-400 f/4.

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