How easy is it to clean a primary mirror?

[dave364634]

The scope would be a

SKYWATCHER HERITAGE 130P FLEXTUBE DOBSONIAN TELESCOPE

Would I be likely to missalign the mirror?

I'm assuming proper cleaning kits would be avalible.

Ta.

[steppenwolf]

It is quite easy to clean a primary mirror but this should only be done if absolutely necessary - remember, a little bit of dust will do no harm but a scratch will!!

There are no cleaning kits as such but

showing how to do the job but whenever you remove your mirror, it will end up misaligned and you will certainly have to collimate the telescope.

[umadog]

Newtonian telescopes need regular collimation as a part of normal usage. You will certainly need to re-collimate if you remove the primary mirror.

There are no mirror-cleaning kits. You will find a lot of information if you look on Google. Personally, I prefer to just hoze it down with a bottle of distilled water and leave to dry naturally. This avoids water marks. I don't touch it at all with a cotton bud or wick away water with tissue. I've seen both of these recommended at times, but I've found wicking to leave water marks. I don't see the reason for using cotton buds if other (non-contact) approaches will do the job. If the mirror is pretty dirty I will wash it down with pure ethanol or even acetone. Great care should be taken with acetone, however. Neither of those substances will damage the coating, which is aluminium protected by silicon dioxide. Acetone and alcohol won't dissolve this but they will dissolve and carry away any gunk that's on there.

So long as you're careful you won't damage the mirror. In extensive discussions on Cloudy Nights it has been suggested that semi-regular cleaning will extend the life of the coating if done correctly. This is particularly likely to be true if your mirror gets dew-sodden on occasion. Dirt deposited on the coating gets dissolved and stuck to the glass by dew and can then begin to eat away at the coating over time. Cleaning every 6 months (perhaps every 3 months depending on use) will stop this from happening. If done this regularly I would definitely suggest no cotton buds.

[dave364634]

stupid question;

is collimating a bit like tuning a guitar, ie i'd need to buy a collimater.

couldn't i just use compressed air?

also how often do they need recollimateing during normal use? i'd have thought before each time you use it?

ta.

[umadog]

Yes, buy what is known as Cheshire/sight-tube combination tool. It's cheap and sufficiently accurate for your needs. details: Rob Campbell's Home Page I collimate before each session then check it once a night. With a solid-tube Newtonian that doesn't get moved too often you can get away with less. Still, it makes sense to check it regularly.

Experience shows that compressed air isn't enough, unfortunately. Also, if you use very powerful compressed air you risk scratching the coating. I usually blow off the large stuff with a rocket blower than hose down with DI water. Alternatively, you can submerge the mirror in the sink with a few drops of washing up liquid. You can use tap water for this. Leave to soak for 10 minutes. Rinse off ALL soap with tap water. Then hose down with DI water to remove salts. You'll be amazed how much difference washing can make compared to a little air blowing.