High Falls, Pigeon River

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The focal length of a lens is a measurement taken from the rear nodal of the lens to the focal plane when the lens is imaging an object at infinity ( ∞ ). That would be a star or an artificial star, a point of light 3000 diameters distant. In other words, the focal length measurement is only valid when the light rays arrive as parallel rays. If the object ...


I think that you have, in fact, successfully answered this inverse question: How to test actual focal length?. It's not just infinity focus, but that lens focal lengths are generally rounded to familiar even numbers. Two different nominally-50mm lenses won't always give the same field of view even when focused at infinity. (And as a side note, be aware that ...


Either value that close to the actual measurement will be fine. Much more important is making sure the app also knows the correct display size and viewing distance you intend to use. Those factors, which are often assumed to be a specific value and any deviation from those assumptions is ignored, are much more frequently the cause of invalid results when ...


Record with 3:2 still pictures, or 16:9 movies? It matters, a little. Assuming the later, see a field of view calculator at http://www.scantips.com/lights/fieldofview.html Canon 70D is a 3:2 1.6x 22.5x15mm DSLR, but offers 16:9 movies, which is a complication (HD format is only 12.65 tall usable). Instructions: Enter 1.8 m distance at top, Enter 1.6x ...

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