[bojan]

I am trying to improve coma affecting one of my catadioptric telephoto lenses (Opteka 500mm DG), by adjusting the distance between two glass elements (FF group.. I have a crazy feeling the problem could be there because I know of good specimens out there and maybe Opteka decided to cut cost by omitting spacers..).
The idea is to glue the right lens to threaded retaining ring, so the distance can de varied.

I was thinking of using shellac or similar, because it is easily removed by isopropil alcohol.. but not sure where to get it from
Is there a better stuff for the purpose?
Perhaps PVP-based glue stick is OK?


Thanks in advance for any suggestion!