Essential to remove primary mirror from cell when washing?

[BrendanC]

Hi all, 

My primary mirror definitely needs cleaning. I've only done this once before with my old 130p. 

I've got the distilled water, the medical grade cotton balls, watched loads of videos etc. 

One thing I'd really love NOT to have to do is remove it from its cell. I just don't want to have to remove the screws and brackets and then get the primary back in there with the screws too loose, too tight, or whatever else could go wrong. 

I've seen videos where people leave it in the cell, and read about people doing it too. 

So, is there any really really really good reason why I shouldn't leave it in its cell? Or is it OK? 

[Geoff Barnes]

Hi @BrendanC,

I have always left my primary mirror intact in its cell. Just undone the six screws around the outer rim attaching it to the main body and carefully pulling the whole unit away. That way, when you put it back together it should still be collimated or near enough as it was before removal. Works fine for me.  

[BrendanC]

Exactly, should have said - it's the collimation I want to avoid, as much as possible. I hate collimating. 

Thanks!

[Geoff Barnes]

I should have added, I stick a small piece of tape by the adjacent screw holes so they go back together in the same way. 

[NGC 1502]

21 hours ago, BrendanC said:

So, is there any really really really good reason why I shouldn't leave it in its cell? Or is it OK? 

You should be ok with all the normal precautions.  Some cells have a disc of black card as a backing to the mirror, that will get soggy if you wash the mirror and cell as a unit.  A few 3” reflectors I’ve seen use double sided foam tape to fix the mirror to the cell, the foam tape would take much longer to dry out having been immersed.  Orion Optics UK have tiny pieces of felt between the mirror clips and the optical surface, that would get soggy too and take longer to dry out.

Can’t think of anything else to consider, maybe others can, but apart from that I’m thinking you should be ok.

Ed.

[BrendanC]

Thank you. The plan is to immerse the mirror upside down in very shallow water so that just the face gets wet, nothing else. 

[DaveL59]

You can do this and it works fine so long as there's nothing to retain water that may cause other effects, as mentioned above. Do consider however that the cell is likely alloy of some sort and the bolts and springs steel. Moisture in the mating surfaces can lead to corrosion issues down the road but hopefully if you've rinsed with distilled water and let thoroughly dry you won't get too many issues.

[wimvb]

Personally, I would never leave a mirror in it's cell while washing it. There's no way you can properly dry the cell afterwards, and water left in a metal assembly is a sure way to get corrosion. You will also trap water between the mirror and clamps. If you leave water there, it can, over time, affect the aluminium, even if that's covered by a hard protective layer.

[NGC 1502]

6 hours ago, wimvb said:

Personally, I would never leave a mirror in it's cell while washing it. There's no way you can properly dry the cell afterwards, and water left in a metal assembly is a sure way to get corrosion. You will also trap water between the mirror and clamps. If you leave water there, it can, over time, affect the aluminium, even if that's covered by a hard protective layer.

Some good points made.  I suppose you could separate the mirror plate from the tube plate that attaches the complete cell to the tube.  That would ensure that the tube plate with bolts and collimation springs do not get wet.  That would leave the mirror still attached to the mirror plate for washing - this avoids undoing and replacing the mirror clips, some folk are wary of over tightening the clips causing problems.

Personally I don’t do the above, just completely dismantle and wash the mirror on its own, carefully reassemble and re-collimate.  It’s not the least difficult when you’ve done it a few times.

Ed.

[Macavity]

I guess it depends on how DEEPLY you want to clean the Mirror...
If it's only a matter of removing odd "insect Poos", clean it in situ? 😉
Avoid dissolving/dragging mounting bracket material onto mirror...

Edited February 1, 2021 by Macavity

[wimvb]

7 hours ago, NGC 1502 said:

Personally I don’t do the above, just completely dismantle and wash the mirror on its own, carefully reassemble and re-collimate.

That's my procedure as well. Better safe than sorry, and collimating a Newt isn't rocket science.

[Louis D]

What about for silicone glued primaries?  Is it worth cutting the factory glue, cleaning it all off both the mirror and cell, and then trying to reglue it with hopefully the same type of silicone glue?

[AlexK]

5 hours ago, Louis D said:

What about for silicone glued primaries?  Is it worth cutting the factory glue, cleaning it all off both the mirror and cell, and then trying to reglue it with hopefully the same type of silicone glue?

If you are talking about standard multi-point cells - don't re-glue it. Replace glue-points with 3M HD Velcro dots! They are great at unloading the weight, hold the collimation very well, but easy to disconnect one by one with a pry plank (I'm using a wood ruler) when needed.

To BrendanC:
I'm +1 AGAINST washing in the cell. It's much dirtier than the mirror. The risk of some abrasive flake or greasy goo getting lose and ending up on the surface is like quad-fold...

Don't be shy, perhaps, you will know your telescope better after the procedure. Mark and image marked everything and you will be fine. You can post your images and step by step concerns right here. We will be with you all the time! And that might became a great work-log to share with other amateurs hesitating to step into the ATM aspect of this hobby a bit 

Finally, learn about proper storage. My z12 have to be stored vertically but I have it stored upside down with two Mylar bags tight on each end. The primary stays perfectly clean but I'm kinda sacrificing the secondary, however so far having no issues with it either (~11 years), just gently blowing it with air sometimes (cheap photo-camera hand blower).

Edited February 2, 2021 by AlexK

[NGC 1502]

5 hours ago, Louis D said:

What about for silicone glued primaries?  Is it worth cutting the factory glue, cleaning it all off both the mirror and cell, and then trying to reglue it with hopefully the same type of silicone glue?

Perhaps for silicon glued primary mirrors you could dismantle the complete cell, separate the mirror and the plate that its glued to from the tube plate then wash in the regular way.  Extend the drying time to allow trapped water to dry out thoroughly.

The tube plate complete with bolts & collimation springs don’t go anywhere near the water.

Ed.

 

 

[barkis]

I would ask you, do you really need to clean it?  It is surprising how well a Newtonial Mirror will
still perform when presumed to be dirty.   
A dirty objective will always  out perform a badly cleaned one. 
I'm sure you will take the utmost care , but I will always draw attention to this possibility
whenever this topic shows up.
Often over zealous caution  itself can create  danger.
I always removed the mirror from it's cell, if done carefully, it can be replaced exactly as before.
Ron. 

 

[Louis D]

23 years, and I've yet to deem my Dob's mirror dirty enough to need cleaned.  It's always been stored with tight caps at both ends and just the center hole in the Rigel Aline cap in the focuser to allow a bit of air in and out.  It's always been stored at the back of a coat closet that is rarely opened (don't need heavy coats in Texas very often).  The enhanced mirror coatings look fine as well.

[BrendanC]

Actually... I've changed my mind! Doh....!

Main reason is, I had a nasty artefact in my shots which I was absolutely convinced was because of the mirror.

I've since done some tests and nope, it's a dust bunny on the sensor.

I can work around that with flats, but I'm also getting an air blower to see if I can shift it. If not I might invest in some swabs, cos I'd just be happier keeping the sensor clean.

So, much as I'd love to have a beautiful clean mirror too, even just looking at my flats, stretched, tells me I don't need to.

At least it was an interesting debate. Thanks to all who contributed.

[wimvb]

I don't think that dirt on the mirror will show in your flats. Any dust bunnies you can see in flats are from much closer to the sensor. I doubt you would see dust bunnies on a coma corrector even, and that's only 55 mm or so from the sensor.

The problem with a dirty mirror is that its reflectivity changes and that it will spread light and not just reflect it. But this will get only gradually worse, so you never really know when enough is enough.

[Louis D]

And an improperly cleaned mirror with added microscratches on the surface is worse for scattering than some random dust and sap that doesn't redirect light nearly as well as scratches.

Ever looked at the clear coat on a car washed regularly versus one infrequently cleaned?  Up close (get out a loupe), there's lots of fine scratches in the clear coat finish of the regularly washed car.  The infrequently washed finish will have much fewer microscratches in comparison.  It may have etching from acidic bird doo left on it too long, but it will have much less fine scratching.  That's why claying fine car finishes is popular because it lifts the crud off straight up reducing the opportunity for scratching.

Edited February 2, 2021 by Louis D

[BrendanC]

Interestingly I do actually clay bar my car, and can verify this! Of course, whenever I do, I always get the song Gay Bar by Electric Six going around in my head. 

Edited February 3, 2021 by BrendanC