Have you ever wondered how to calculate the effective aperture of your ultra large format lens compared to 35mm?
I will walk you through how to do the math in this article for a 450mm lens on an 8×20 camera.
To calculate the 35mm equivalent aperture of a lens on a different format, we need to use the crop factor or focal length multiplier. For an 8×20 ultra large format camera, the crop factor compared to 35mm film is approximately 0.07x.
Therefore, the 35mm equivalent focal length of a 450mm lens on an 8×20 ultra large format camera would be:
450mm x 0.07 = 31.5mm
To calculate the 35mm equivalent aperture at f/90, we can use the following formula:
Equivalent Aperture = Aperture x Crop Factor
Equivalent Aperture = f/90 x 0.07
Equivalent Aperture = f/6.3
Therefore, the 35mm equivalent aperture of a 450mm lens at f/90 on an 8×20 ultra large format camera would be approximately f/6.3.
As you see from this example, small apertures like F/90, F/128, and beyond are not unreasonable as you may think because your mind may be used to thinking of apertures in 35mm terms which does not apply to ULF lenses.
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