After some recent tests with a pin hole on my CCD camera, I realised that the edges of my secondary mirror were causing a lot of stray light scatter in the big Newtonian imaging scope.

More on the tests another day, but I didn't realise that the simple frosted glass sides of the telescope secondary mirror were reflecting a lot of light into the wrong place. This coincided with some observations made by Richard Crisp about problems with flat fields in a friends telescope to convince me that an unpainted and unshielded secondary was a very bad idea for the standard of imaging I'm hoping to reach this coming season.

Painting the secondary mirror of a Newtonian tlescope is a pretty scary idea. Certain parts of telescopes do not respond well to paint. Silvering of mirrors is quite high on this list. After selecting some slow drying black enamel spray paint I set about solving this this problem.

My solution was to made a long sausage of blu-tak which I stuck around the rim of the silvered part of the mirror. I then laid this face down on a piece of thick card (one half of a birthday card) and pressed firmly. Hopefully this will work!

I'm not too fussed about blu-tak on the silvering. That secondary mirror is 10 years old and the silvering is starting to come off and I'm generally well overdue for a new set of mirrors.

Anyhow this approach seems to work - see the piccie! In a few days I will reinstall in the telescope tube and see what it looks like.

painting mirror