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The EOS-1D X & f/8

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MazV-L:

--- Quote from: PeterJ on October 27, 2011, 02:29:55 AM ---
--- Quote from: MazV-L on October 27, 2011, 02:18:26 AM ---A crazy thought, but would it be possible that Canon are developing and planning to release a new 2x converter that reduces an f4 lens to f5.6 rather than f4- f8 especially for the 1DX, is this technically possible? :-\

--- End quote ---
It's not technically possible, it's a basic optical rule that a 2x converter results in 2 stops of light loss.

Edit - just to explain further the 2x extender means that now your lens is effectively only using half the the front area both horizonally and vertically, so it's gathering a quarter of the light or two stops. That's why you also halve the resolution of the lens which has a varying effect depending on the resolution of the sensor.

--- End quote ---
Thanks, for the explanation! Of course this makes sense.

weixing:
Hi,

--- Quote from: PeterJ on October 27, 2011, 02:29:55 AM ---Edit - just to explain further the 2x extender means that now your lens is effectively only using half the the front area both horizonally and vertically, so it's gathering a quarter of the light or two stops. That's why you also halve the resolution of the lens which has a varying effect depending on the resolution of the sensor.

--- End quote ---
    No... you still use the full aperture of the lenses... the light gathering capacity is still the same. The lost in 2 stops is due to the increase in magnification... basically longer focal length = higher magnification. When the magnification is increase and the aperture remain the same, the image brightness will be reduce.

   Anyway, there is a simple formula for calculating focal ratio: focal ratio = focal length / aperture
   Base on this formula 600mm F4 had an aperture of 150mm (600mm / 4 = 150mm), so when focal length is double, the focal ratio is reduce to F8 (1200mm /150mm = 8 ).

   Have a nice day.

   

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