So i purchased a industar 69 about 2 weeks ago and it should be here in the next few days. I understand that you need modification to get infinity focus with the lens. So i know that there is the option of modifying the lens, or the adapter. What i understand is that the same method will not work on all lenses. So i am wondering what is the best, and easiest way to modify this lens for infinity focus. I was planning on buying another adapter for the lens only. The one i was getting has the adjustable inner thread ring. I know you can sand this down to get infinity focus, but how exactly does this work?