I recently picked up a 19" Red Dot Artar mounted in a #4 Alphax shutter. So good , so far. I got it at a low price so I had my friend Bill Peters have a look at it to check it in regard to shutter speeds etc. When he removed the back element, it almost fell out and was not very well threaded. He is going to rectify that. He maestro of the machine lathe. The question for the day , does anyone know the correct spacing of the elements to ensure they are mounted in the correct way.

Thank you