How to get super clean interferograms from your Bath Interferometer

Описание: all about Bath Interferometers: http://gr5.org/bath/
store: https://thegr5store.com/wp/

Index
0:00 Introduction
1:07 Locating Dust
7:56 Cleaning Dust
16:27 Other Tricks

04:21 in video
rotate splitter CW as seen from above, projecting test beam onto paper close to the bath.
spots on front of splitter (side closest to mirror) move not at all or move the least
spots on diverger move to the right
spots on laser move to the left
spots on left side of splitter (side of splitter closest to laser) move to the left faster than laser spots

7:19 in video
with diverger now on the right beam
rotate splitter CW as seen from above
spots on laser move to the right
spots on left side of splitter move left
spots on right side of splitter move right - slightly faster than the laser spots
spots on flat don't move
spots on diverger don't move (so distinguish by moving the diverger and those spots won't move - remember - this is counterintuitive)

I did some more experiments and learned more about those permanently bad diverging lenses that I said had a "bad coating". I was able to remove the coating. I kept mixing stronger and stronger alkalai (aka base) solutions of Potasium Hydroxide (KOH) and eventually at 10 Molar and soaking for 24 hours (20 minutes did nothing), the coating dissolved. The difference was clear (bright white reflections of lights instead of darker bluer reflections on the coated lenses). But the defects were still there. Not in the coating.

Note that 10 Molar concentration is DANGEROUS.

So all those lenses that are bad seem to be unusable (about 95% of the lenses). Anyone know a good source for 10mm FL BCX lenses? At under $15 each in quantities of 10.