Dan, forgive me my newbieness... When shooting flowers with my Korona (no drop bed) the front extension showed up in my negatives. Since I was shooting using the back extension to focus maybe I did something wrong. A drop bed would have helped, though. That's what I meant by macro. My lens was a 190mm, which is slightly short for a 5x7.
Hmm. Forgive my ignorance of Koronas. I know that at least one of the camera's standards has to move to allow focusing, but I don't know whether front, rear, or both can move.
My little Graphics have fixed rear standard -- the box doesn't move at all -- and moveable front standard. This limits somewhat the lenses I can use for closeup work. If the lens is too short, when I have the magnification I want -- set by the extension -- the front of the bed can hit the subject. But I've never had the bed in the image when working closeup. With a short lens when I've forgotten to drop the bed, yes, absolutely, then the bed is in the image and the image is ruined. But it takes a fairly short lens, in 5x7 context roughly a 135, to make that mistake.
If both of your camera's standards move, then when shooting closeup put the front standard at the very front of the rail, set magnification by moving the rear standard to get the necessary extension, and then focus by moving the camera. Use either standard for slight adjustments after the camera is in about the right place.
Cheers,
Dan