What is the easiest way to measure the magnification of a viewfinder?
Must be able to do it for both electronic (EVF) and optical viewfinders. Also, I only have access to one focal-length.
Use a second camera, preferably a P/S with a small aperture. Take a picture through the viewfinder of your main camera, then a second picture of whatever your main camera is aimed at, and from the same distance. Be careful to use the exact same focal length for both pictures.
Now you just have to compare the sizes of the two images. Take a random element visible on both pictures, measure its size in pixels in both pictures and calculate the ratio.
Viewfinder size = Focal length multiplier * Viewfinder coverage * Viewfinder magnification Check this table: http://photolectic.com/reviews/dslr/dslr-viewfinder-size/coverage-comparison.html