Cleaning a mirror

Thanks to everyone for the answers. To answer your questions.

I used the procedure at www.skyandtelescope.com/howto/diy/3437191.html?page=3&c=y . and followed it as closely as possible.

I have no idea if there is any special coating on the mirror but I think not.

I do think I may have missed some of the greasy film as there are some streaks on the mirror. I am not sure if it was ever cleaned before, if so maybe it was not done properly and this may be a consequence. Anyway I'm hoping for clear skies in the next couple of days so I can test it out. Hopefully it won't have an impact on performance.

Just an update. I got outside for a little while just now and it seems very good. The moon was perfect, Orion nebula looked good and Jupiter and all four moons clear. I thought I was seeing one moon double but when I checked afterward I see that Europa and Ganymede are very close together. The only problem was there seemed to be some elongation of Jupiters shape - possibly collimation? I didn't venture above a low power eyepiece, 25mm, so not sure if there are differences at higher mags. Thanks for all the help.

mossief1965 wrote: Thanks to everyone for the answers. To answer your questions.

I used the procedure at www.skyandtelescope.com/howto/diy/3437191.html?page=3&c=y . and followed it as closely as possible.

I have no idea if there is any special coating on the mirror but I think not.

I do think I may have missed some of the greasy film as there are some streaks on the mirror. I am not sure if it was ever cleaned before, if so maybe it was not done properly and this may be a consequence. Anyway I'm hoping for clear skies in the next couple of days so I can test it out. Hopefully it won't have an impact on performance.

You may be able to determine of there is a coating based on the manufacturer. Any manufacturer's markings on the scope?

Distilled water is only really good for removing light soiling and it's certainly not going to break down any greasy materials. The standard mirror wash mix is a 50/50 mix of distilled water and 99% pure isopropyl alcohol (you can buy this on Amazon.com).

The general procedure is:
1. Blow off any loose dust with a bulb blower (blowing on it yourself can leave saliva).
2. Put a towel in the bottom of a clean sink and place the mirror face-up on it.
3. Run lukewarm tap water over the coated surface at low pressure, add a few drops of dishwashing liquid, leave the mirror to soak for a few minutes.
4. Using sterile cotton or Kleenex plain tissues soaked in the soapy water draw the wad across the surface from the centre of the mirror outwards to the edge. Use a single piece for one sweep.
5. Rinse the mirror with tapwater then the mixture of 50/50 isopropyl and distilled water.
6. Do a final rinse with distilled water.
7. Leave the mirror on it's edge on a soft towel to dry completely. You can use the corner of a clean tissue to absorb any persistent drops on the mirror surface.


There are variations on a theme and strong opinions on what constitutes the best method but of all of the methods I've read this one works and reflects what most people consider best practice.

mossief1965 wrote: The only problem was there seemed to be some elongation of Jupiters shape - possibly collimation?

Possibly. Collimate as best you can ( legault.perso.sfr.fr/collim.html ). The test is getting sharp points on stars rather than good views of the moon. It's also worth checking that you have the mirror in properly and the clips holding it in place are not too tight causing it to bend out of shape. It might seem to be ok in a warm house but 20C cooler outside it clips can shrink etc.

good luck with it!

Thanks.

For now I'm going to leave it as it seems ok. I will save your guide and use this next time.