Removing 200p primary.

[jason.p]

My 200p has got a nasty smear on the primary mirror (long story). I really can't live with it so it's got to come out and be cleaned. I've done this before on the TAL and think I've got the idea about the cleaning process, but thought I'd try and get some advice about how to go about it on the 200. Now got to try and find some distilled water!

Thanks

Jason

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[Baselessum]

Have a look at the astronomy shed videos, goes through the whole process and even suggests were to buy the distilled water, anyway good luck with the cleaning

[jason.p]

Thanks for reply. What I would like is some advice on removing the mirror. I'm sure it's quite straightforward but any tips would be useful, and I'm sure there's many on here who have done it before.

Thanks again

Jason

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[steppenwolf]

Removing the mirror on the 200p is straightforward.

1. Mark the position of the rear unit and optical tube with a piece of masking tape and a pen line so that you can re-assemble in the same mirror cell orientation.

2. If you have an older version, undo the three screws that hold the back blanking plate on. Undo the black cross-head screws around the periphery of the base of the tube

3. Pull the rear unit out gently bringing the mirror cell with it

4. Mark the position of the mirror in the cell with a black marker on the side of the mirror and a piece of masking tape stuck to the mirror cell to ensure that the mirror goes back in the same orientation

5. Undo the three pairs of cross-head screws that retain the mirror clips in place and carefully lift them off

6. Carefully lift the mirror out

7. Clean the mirror using

8. When completely dry place the mirror back in the mirror cell aligning the masking and black marker lines

9. Refit the three mirror clips but don't over-tighten them or you will get distorted stars

10. Align the mirror cell and tube markings and slide the rear unit back into the optical tube and re-fit the black screws

11. Collimate the telescope

Job done!!

[Rustysplit]

Hi Jason,

Is that my old one? If so I can tell you that the mirror cell is very tight in the end of the tube. Mark the position as Steve has said, and use a block of wood held against the tube to knock against the lip of the cell. Work around slowly and it frees up gradually. Getting it back in is tight too. Try to keep the cell square to the tube.

Good luck and take your time.

[NGC 1502]

Good advice already given.

I'd just add that I find it best to put the tube on a sofa with the mirror end protruding off the end.

That way, if the mirror and cell comes away unexpectedly as you pull, the tube will not do a nosedive onto the floor..........

Go easy, you will be fine.

Regards, Ed.

[jason.p]

Yes, that's the one. It's obviously very tight. I'll gently work round it with a hardwood drift now that I know how it comes out.

Thanks

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[jason.p]

Eventually got the mirror cell out. It took a copper drift to get it started! In my haste I forgot to mark the relative positions of the cell and casing. I think I may be able to work it out. Hope it's not too serious if I get it wrong!

I've attached a picture which I hope will show why I had to clean it.

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[Lorne]

I'm sure there's an obvious cut out on the cell where the joint/ weld on the OTA slots in (there was on my old SW250) so it may not be too much of an issue to forget to mark it.

[NGC 1502]

Eventually got the mirror cell out. It took a copper drift to get it started! In my haste I forgot to mark the relative positions of the cell and casing. I think I may be able to work it out. Hope it's not too serious if I get it wrong!

I've attached a picture which I hope will show why I had to clean it.

Sent from my GT-P5110 using Tapatalk 2

I can see why you wanted to clean the mirror. Even with a smear like that, I doubt if it would seriously affect the view, if at all, but I couldn't leave it like that either.

When refitting, as long as the tube to cell screws fit, you will be fine. You will have to recollimate of course, but as long as the secondary was ok before you started, you should be able to just sort the primary.

Errrm, are you going to own up how the smear got there ? The whole of SGL is wondering you know

Regards, Ed.

[Moonshane]

looks like you were eating jelly snakes from the pic n mix and dropped one?

[jason.p]

I brought the scope in and noticed that the primary was covered in condensation. I noticed a black spot which had been highlighted by the dew, and foolishly decided to try and remove it, so I waited till the dew had gone and tried to brush it with a lens brush on a stick. Trouble was, the surface must have still been damp, and whatever it was just turned to a slurry, which resulted in the smear. I've no idea what it was, but it does seem to wash off ok. I've read so many times on here that the mirror can be really grubby with no discernable effect, but I just couldn't help myself:o

Lesson learned (I hope!).

Thanks to everyone for help.

Jason

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[Ouroboros]

Why is it considered necessary to replace the mirror/cell with the same orientation? I must say I usually don't. I always re-collimate my telescope after cleaning the mirror anyway.

Steppenwolf - your video instructions are very useful. Thanks for doing that.

[steppenwolf]

Why is it considered necessary to replace the mirror/cell with the same orientation?

This is a mass-produced mount so assuming all was well before assembly, it makes sense to re-assemble in the same position prior to collimating it so that any deficiencies in the original manufacturing tolerances are automatically allowed for before the re-collimation takes place.

But then again, I am a bit of a nerd when it comes to my gear :grin:

[Ouroboros]

Yes, I see what you're saying. It's probably best to put the mirror clips back on the same points as before too.