RASA8 housekeeping

[tomato]

A while ago I was worried about dust build up on my RASA corrector plate and wondered if I should clean it.

Well this is what I found when I was checking for dew on the plate after an unattended session last night. The shim must have fell off my other camera when unscrewing after a previous session some months ago and it has been there ever since. I can’t see any obvious artefacts on the subs with it sitting there but the next session with it now removed will confirm this.

[ollypenrice]

Compared with the central obstruction - which doesn't inconvenience any of us - it's trivial, and it's also the right shape for dispersing its own diffraction artifacts.

If we are surprised by this, maybe we should blame those misleading O level ray diagrams!

Olly