I tried to project an image myself with a concave mirror and it seemed fairly dim; how much light is required?
A precise answer to this question depends on knowing the magnification of the image as well as the diameter of the mirror, since in both cases the brightness scales as the square of the quantity. However, unless you are using a mirror smaller than an inch in diameter, or are trying to project an unusually large image (e.g., one larger than life size), direct sunlight on the subject should result in a quite bright image if you have things arranged correctly. For setups configured as our estimates show they were assembled by Campin, Caravaggio, Lotto, etc., it turns out that the projected image of a subject who is standing in direct sunlight is roughly as bright as if, instead, you look directly at the same subject standing in the light coming from a north window. That is, the projected image has ample brightness. The photographs on page 76 of Hockney’s book, as well as the next (and the previous) movie clip in this FAQ, show that the brightness of projected images isn’t a problem. For e
