Cleaning the primary mirror ?

[Stu Ward]

I noticed what look like a couple of flies or specs of "stuff" on the mirror at the base of my dob

how do you clean them off ?

My guess is very carefully, but seriously how is it done best ?

Thanks

Stu

[mental4astro (Alexander)]

There is an article in 'Projects and Articles' exactly on cleaning a mirror. Have a look.

Like you said, it's done carefully.

[astro_nutt]

If the "stuff' on your mirror isn't affecting your image through your eyepiece and hasn't damaged the coating on the mirror itself, leave it for a year before attempting to clean it off.

[iceman (Mike)]

Like Alex said, the article is here: Cleaning the mirrors of a newtonian telescope.

However like astro_nutt said, if it's just a few specs and your telescope is new, it's extremely unlikely to be affecting the view at this early stage. So you don't need to rush and go and do it.

Just remember you will need to know how to collimate for when you put the mirror back in.

[Stu Ward]

Thanks guys, i'll leave well alone for now

I assumed that it must be having some affect, but i can't see it, due to the fact that these mirrors are so highly polished, any blemish will affect

But as you say, i cant see it, so im not going to mess

Stu

[astronut (John)]

Stu,
Leave it alone...........here is my 12"LB mirror after 4 years of use.
Views are still brilliant.

[bkm2304 (Richard Brown)]

Hi Stu,

I was told by a colleague that the folks up at the Anglo Australian Scope see an accumulation of dirt, bird crap, dust etc etc on the 150" and, counterintuitively, this makes extremely little difference to the scope's performance. As cleaning and resurfacing the "big guy" is an understandably complex task with downtime etc, it's a good thing that the accumulated stuff has so little effect.

My 22" looks pretty fouled up if I shine the torch down the barrel and it was only resurfaced last year. The cure here is don't shine the torch down the barrel!!!!

Richard

[Quark (Trevor)]

Hi Stu,

I have a 16" Newt in my observatory, it is about 16 years old and I washed it as per Mikes article, for the first time last year.

When you observe with your scope the image that you see comes to focus at the optical elements within the eyepiece that you are using. The distance this is from the surface of your primary, when at focus, is the FL of your particular mirror.

It is amazing how dirty a mirror can look and still produce knock out images at the eyepiece. I would go as far to say that the collimation of your optical system is of far greater importance than how dirty the surface of the primary is, regarding the quality of the image you see through the scope.

Regards
Trevor

[Vanda (Ian)]

Its logical a dusty mirror is not as efficient as a clean one. However, its also unlikely the human eye can quantify a small differance at the eye piece - especially when this change is over a long period of time. The 150" no doubt has heaps of mirror in reserve and persistance may mean less downtime!

[Stu Ward]

Thanks guys

I will be leaving the mirror well alone as it is nowhere near as bad as astronuts !!!

I have a few small specs of dust on it, but i thought that as they were polished to such a high standard then some dust must have an impact, obviously not to the eye.

So all good, now we just need the clouds to clear from the Illawarra and i might get back out again.