Years ago I saw an eyepiece adapter for a Tamron lens that allowed direct eye-ball viewing through the lens . . .as with a spotting scope. That was in maybe 1982. It just bayoneted onto the lens like a camera would. Anyone know of such an adapter for any mount lens today? I have just gotten an older Yashica 500mm mirror lens in Nikon mount. I'd like to use it as a spotting scope without the camera body at times. Another project may be to us it for eyepiece projection in large format photography.