Hold the lens toward a light source (window, ceiling light, whatever) and put a piece of white paper behind it. Move the paper until you see an image. If the lens resolves an image, you can take pictures with it. Try the same with a magnifying glass if you're having difficulties and try to get the hang of it. My guess is that the focal length of this lens might be too short for something like a speed, but you never know until you try. Working out the speed of the lens is simply a matter on measuring the diameter of the rear opening of the lens housing and dividing that number by the focal length at infinity. This is a rough estimate at best given the way you will work out the focal length, but it can be a starting place for figuring exposure times. I have found most lenses from slide projectors and movie projectors to be quite fast, in the f1.9 to f4 range, but I have also found that they average 15-35 mm focal length, with some bigger, older ones coming in at 100mm. Again, you won't know until you play with it. Have fun!