Tool of the day. Well not that kind of “tool”, I mean a real tool.
A digital camera that can accept different types of lens mounts is a handy tool check a lens. All cameras are designed with a specific mount type with matching lenses.
Some cameras can use an adapter to permit mounting of a different type. Today, these typically these are mirrorless cameras, because of the short flange focal distance. Most of these will have a FFD of less than 20mm which means they can accept lens types that have a longer distance with an adapter. Most SLR mounts use 40mm or longer, and even the Leica thread mount is about 29mm.
So here is my cool red Sony NEX-3, Fotga M39-NEX adapter, and Canon 35mm f/2.8 rangefinder lens.
I can easily check minimum and infinity focusing.
See how much affect haze and fungus have on the lens elements.
I can also take digital images with this … hmm, I wonder if they thought of that when they made this thing ?