Is this possible in lens design?

Started Jul 9, 2012 | Discussions thread
Svein Eriksen Senior Member • Posts: 1,777
Re: Is this possible in lens design?

danroso wrote:

Now we have 20x optical zoom (25 – 500 mm) and F3.2 - F5.8 in compacts (Sony HX20V).
Can we have F1.4/1.8-F5.8 in the same 20x or 10x zoom range, compact size?

Aperture value (f-number) is defined as focal length divided by diameter of the aperture.

  • 25mm with f/1.4 give a diameter of around 18mm

  • 500mm with f/5.8 give a diameter of around 86mm

So, a 500mm at f/5.8 needs a much larger aperture diameter than a 25mm at f1.4 or even f/1.0 and the reason why the limit is f/2.8 (or slower) in the wide end is probably some design limitation or that IQ isn't good enough if the aperture is opened more.

Btw, superzooms of have much shorter real focal lengths, but the relative sizes remain the same.

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