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6

Well, it's more of 200-ish mm being pretty much 200-ish mm at the best of times, unless you're testing two copies of the same lens design. The stated focal length is usually a nominal value, and only a few companies will tell you what the actual focal length of a lens is for general photography. (Hasselblad is notable in that regard; there's a "...


1

The actual formula involves tangents and arc tangents, but for long lenses the angles are small and the tangents/arctangent can be approximated as a linear function so the results you get with a linear interpolation are going to be accurate enough (the actual focal length is not exactly what is advertised, once you take in account the focusing). This said, ...


1

On a full frame/35mm camera; from about 50mm every time you double the focal length the FOV is approximately halved, and the size something is recorded at doubles (L&W). So for your example beginning from 100mm/50px; 100-200-400-800mm lenses result in 1x-2x-4x-8x or 50-100-200-400px. The 50mm approximation for the full frame starting point correlates to ...


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