The J-8 is easy to shim yourself. I did a J-3 that was front focusing on my Bessa R. Shoot a test roll when you get the lens. If it front focuses you grasp the front of the lens & it will simply unscrew. Most time the original shim is too thick. In my J8 & my J3 both shims were replaced with much thinner shims, like paper thin. The idea I was told by Brian Sweeny is to get the rear glass closer [back] to the film plane. On the J-3 you can screw out the rear part to bring it closer. Not too sure on the J-8. J-8 I have was already shimmed when I got it. Google info about modifying a J-8 lens if I'm confusing you. Good luck with the lens. BTW you can make a shim out of a plastic milk jug. Doesn't have to be metal.