Cleaning reflector primary

[Glider]

I've taken the whole primary mirror assembly off the end of my Explorer 200P OTA.

I intend to wash the mirror in situe.

Now I've got it on the bench I see the mirror is held in place by 3 clamps. Each clamp has 2 screws. The screws are not particularly tight and the mirror can move side ways a millimeter or so radially if I push on its edge. It is tight enough that it doesn't move vertically though. Is this right. Should the screws be 'tight'. I'm talking another half turn to a whole turn on each to clamp it fully.

Can any body give me a quick reply, the Sunday dinner needs to go on the table in an hour!!!!

[Peter Drew]

Hello Glider. Sorry I missed your Sunday lunch deadline. Leave the retaining screws loose enough so that the mirror can just move. These scopes are mass produced and often the assembler tightens these down too much. This is usually the main cause of initial disappointment with these otherwise excellent telescopes as it causes distortion in the form of triangular or astigmatic star images. It might be usefull to pack the mirror edge to reduce the sideplay but don't make it tight for the above reasons.

[Doc]

You need to be able to get the thickness of a piece of paper under the clips. If you don't you will get pinched optics.

[Glider]

In time honored fashion, it wasn't broken so I didn't change anything.

The mirror is now clean, back in the tube and collimated.

Things to note for next time;

...Don't use a magnifying glass to look at the dirty mirror, it's depressing.

...The mirror assy is heavy, make sure the rest of the OTA is secure otherwise it rolls across the table when the bottom comes off. Luckily the handy focuser stops it going all the way to the floor.

...Put marks on the mirror assy and tube before parting so you get it back in the right orientation.

...IPA doesn't dissolve plastic shower pans.

...Neither did the IPA remove the collimation ring in the middle of the mirror.

...It can take several goes with the warm water, washing liquid and cotton wool to get bug splats off.

...Hold the mirror at 45 degree, pour the IPA from about 11 to 2 o'clock, it's magic to watch it evaporate away down the mirror.

...Have a hair dryer ready for any last water droplets that stubbernly hang on the lip of the mirror.

...Use a magnifying glass to look at your clean mirror, you will be glad you cleaned it.

I'm off for a lie down.

[Doc]

All that panic for nothing....

Well done, did the surgical cotton wool work?

[Glider]

Yes, it was fine over the majority of the mirror. There were half a dozen tough marks, I can only say they looked like bug splats under the magnifier. I used a Q Tip on one near the edge of the mirror to check what happened and it cleaned OK so I spot cleaned the rest as well.

[Astro_Baby]

I found my 200 when new had terribly loose mirror clips so much so that if you rotate the scope you could hear the mirro go 'bonk' from inside the tube.

I took it to bits - used the bit of thin paper test to check tension but moves the clips in towards the mirror. They had a gap of about 2mm from the mirror wall to the clip.

[Glider]

Astro_Baby, mine weren't that bad, what you describe is exactly what I saw though so I guess it wasn't wrong, but it looked suspicious if you weren't expecting it.

[Beulah]

I have just cleaned my primary and rendered the clip tension the same as the factory default - I am going back to loosen them slightly.

Thanks for the heads up, this is incredibly timely!

[Glider]

Just thought some pictures might be useful to people.

The end plate comes off with 3 screws.

The whole mirror assy comes off with 6 screws.

It's a flange with a lip that acts like an end cap.

The dirty mirror.

The 3 mounting clips are each held with 2 screws, these are NOT meant to be tight, otherwise it pinches the mirror.

[Glider]

This is heavy, the mirror is probably 20mm thick.

One of the 3 clamps. You can get a sheet of paper between it and the mirror, it's not tight.

Cleaning kit ready to go.

Spot of washing up liquid, then shower with warm water.

Cotton wool working from centre outwards, just wafted under its own weight.

[Glider]

The hairy bit, there seems something wrong about raining on your own mirror.

[yeti monster]

"bug splats"? how fast is your scope?

[Glider]

Yep, well fast, little yellow splats.

[TopHouse]

That'll be dried drool from doing saturn.

What was the cotton you used? source?

[alfingido]

You need to be able to get the thickness of a piece of paper under the clips. If you don't you will get pinched optics.

Would tightening the clips seriously pinch the optics, bearing in mind the mirror is at least 20mm thick?

I cleaned my 300P mirror and did the clips up good and tight, enough to grip the mirror and then a bit more, no effect on optics, but then again, I think the primary was a little over 20mm thick.

Anyway, glad you got it clean and reassembled easily. Maybe you need an insect-o-cutor near the secondary to keep the bugs away!

Allan

[Doc]

Would tightening the clips seriously pinch the optics, bearing in mind the mirror is at least 20mm thick?

I cleaned my 300P mirror and did the clips up good and tight, enough to grip the mirror and then a bit more, no effect on optics, but then again, I think the primary was a little over 20mm thick.

Anyway, glad you got it clean and reassembled easily. Maybe you need an insect-o-cutor near the secondary to keep the bugs away!

Allan

I've always been told to not tighten the lips fully, I suppose the mirror needs room to contract and expand.

[Glider]

It was surgical cotton wool, Doc ^^^^ gave it to me.

[TopHouse]

Is it just the stuff that comes in the sealed sterile packets?

[Doc]

I think so, it's finer then normal cotton wool.

[Beulah]

I use the pads of my fingers to wash the mirrors - not my right hand fingers though, for they are callused from playing guitar ....

[Angeleyes]

Here is another tip

After washing the mirror/ lens with warm water for the final time,pour loads of de oronized distilled water over it,let it drain,mop the very edges if you like but the water and any spots of water on the mirror/lens will air dry and leave no marks unlike tap water.

Job done.

Regards

Tim

[mdstuart]

Your mirror was not dirty, just a little bit marked! I had a TAL that was misty all over...

How long did the mirror take to get to the needing a clean stage?

I have had my 10 inch for a year and there are one or two very minor marks and hairs so far..

Mark