I have a Crown Graphic. Is there a way to know which lenses are capable of remaining within the camera when it is closed? Is the focal length the measurement I should be considering or is there some other lens measurement that is more telling? thanks.

It is the physical size of the lens/shutter assembly that governs. Just try closing the camera gently, if you run into resistance it is probably because something on the lens is contacting something on the bed/front cover, in that case you could not store that lens in the camera. If you can close the camera normally with the lens on the front standard that lens can be stored inside the camera.
Good Luck

C. Henry

To my surprise, I found that I could close the bed of my Century with series VI slip ring attached to lens. You never know what's possible 'til you try.