[Leica] 12mm Heliar UW

[Michael Waldron <michael@cadogan.net>]

Regarding the gel filters on the inside vs outside, I would note that the 
biggest advantage is that inside there is less flare and dust, etc. doesn't 
get on the gel, which is a bit harder to keep clean and scratch-free than 
the glass.  For what it is worth, I have used a lee #87 gel, which comes 
with a template for cutting the 4x4" (100x100mm) square gel into various 
circles.  In the US, the gel was about $18.  FWIW, I made a contraption to 
attach the Lee gel holder to the M2 with 15mm heliar and it worked fine.

Michael Waldron