Cleaning optical filters
If you are not sure how to treat a particular filter, then don't
try to clean it, but let 'qualified' staff know about it.
Especially, handle filters with soft coatings with extra special care.
Maarten uses alcohol or propanol to clean filters and
sometimes reverts to water and soap in special circumstances.
Normally he treats all filters as if they have soft coatings:
- lay a folded-out optical tissue on the filter
- put some alcohol on the tissue
- slide off the tissue by pulling it from one side
- dont apply pressure on the filter at all if not necesary
If the stain is sticky then he applies a bit of pressure either with an
optical tissue or with a cotton-ball stick. Dip in alcohol and carefully
rub the filter.
Hi Thomas and John,
At the NOT it has (as long as I've been here) been the duty of the
astronomers to clean the filters before installing them.
That is, first by a ligth blow to take away dust, and if there are
stains or something sticky, then with the optical cleaning liquid in
the cupboard (blue liquid in the plastic bottle). It should be done very
carefully with optical paper dipped in this liquid. Never use an optical
paper twice! And never rub. Just slide the wet paper over the surface
and then slide dry (new!) paper over it afterwards. Also, before putting
filters back in their envelopes (in fresh optical paper free of any
dust), I usually blow away any dust that has accumulated during the
time it has been mounted. As far as I know, we've never used alcohol.
A lot of optical paper is spent this way, but it is better not to try
to save paper. Also, filters should not be cleaned more than strictly
necessary since it involves a risk.