The main 200mm diameter F5 telescope mirror in my Newtonian telescope is getting rather old. Almost 10 years old.

The telescope wasn't the greatest quality telescope in the world when it was new. It was branded Helios, which was the forerunner to the more familiar Skywatcher telescopes. Although a lot of time has passed, the fundamental design has not really changed.

Because the old mirror has spent many years out of doors in the observatory, it was started to seriously deteriorate. Looking though the back of the mirror, I'm surprised it reflects anything. With the new telescope mount, it seemed proper to get a better mirror.

One of the foremost telescope mirror shops in the UK is Orion Optics. They sell a 8 inch F4.5 mirror for about £300. I asked them if they would make me a one off 8 inch F5 mirror, and was told this would be an extra £160 re-tooling charge on top of the cost of the F4.5 mirror.

That didn't seem to be a sensible use of funds.

The next obvious route was to buy an 8 inch F4.5 Orion Optics telescope mirror and simply slice 10cm off the bottom of the telescope tube. I pondered this one for a while, but was still put off by the cost. At the back of my mind I know I'm going to build my own larger telescope at some point in the future and it seems a bit silly to invest in an expensive mirror now.

I asked a couple of other UK telescope mirror makers, and they all quoted impossible sums of money.

A new telescope OTA from Skywatcher seemed the simplest fix. However, buying a new 200mm OTA sounds like an inefficient use of cash Ė Iíd end up with a lot of hardware I donít need. The £300 cost of a new OTA is close to the cost of an 200mm F4.5 telescope mirror set from Orion. All I have to do is chop 10cm off the end of the OTA!

Spending £300 on an OTA from which Iím going to pinch the mirrors also has to be weighed against the option of getting one of their £400 10 inch OTAs. However, I donít want to rush out and change instrument without consideration to my next camera.

The final option is recoating my mirrors Ė this doesnít give much change from £100 after vat and postage. That seemed like a daft option as I don't know what else is wrong with the old mirrors.

After dithering about this for a few weeks, I contacted Bern at Modern Astronomy, a great UK supplier who often comes up with creative solutions to my problems. He actually managed to get a price out of Skywatcher for a replacement telescope mirror. Whilst it has a lead time of 2 to 3 months, the cost is acceptable.

This is just the primary mirror. There are various UK suppliers for secondary flat newtonian telescope mirrors, such as Orion, who do a 50mm flat for about £50.

So in a new months the new telescope mirror will turn up and we shall have some brighter images!