I cleaned my primary mirror on Saturday with water/demineralized water etc and it really made a big difference. I used my telescope all of Saturday night and Sunday morning and had a great time but by the time I was finished the primary mirror was soaked in water (from he dew). Even the inside of the OTA was soaked.
I live in a semi-rural area with lots of pollen and stuff in the air so now my primary mirror is all cloudy again. I'm starting to think that washing the mirror is a weakly task - does this sound right?
I have a 12" GSO dob, I don't mind the effort, just want to know if washing the mirror weekly or every few weeks is "bad" in some way?
I MAY wash my mirror once a year, if that. Its amazing just how much junk can be on your mirror and not really affect the images produced, especially for visual use. Remember that each time you wash a mirror, no matter how careful you are, you do a small amount of damage to the surface so only wash it when it really needs it. Definitely not a weekly task.
Not a weekly task, but I do do it every 3-6 months.
There's other people who say they don't wash it even after 20 years of dirt and crud has built up on it, just for risk of doing damage. As long as you're careful I see no harm in doing it semi-regularly (as needed) but not excessively or obsessively.
Remember that each time you wash a mirror, no matter how careful you are, you do a small amount of damage to the surface so only wash it when it really needs it. Definitely not a weekly task.
Theres no reason to scratch the overcoating of your mirror if you rinse loose dust off first and use detergent and conton wool in cleaning. If you do make a few sleeks , it is in the SiO/SiO2 overcoat and of course not damaging the actual surface of the mirror.
Leaving an oily coat film of dust and dirt on your mirror actually hastens its breakdown as it is the first thing to attract moisture in damp conditions, and the chemicals via air pollution in the moisture break down the coating.
I do mine about every 6 months. I live 50 metres from a salt water lake and the air is very corrosive. I basically "rinse" the mirror with luke warm water, then use a spray bottle with a very dilute solution of PH neutral dish detergent and then do a final rinse on the mirror with distilled water. I avoid touching the surface of the mirror if possible. I usually use pure cotton wool about every 3rd or 4th rinse. If you rinse it regularly the crud comes off a lot easier and you don't need to use cotton or touch the face of the mirror very often.
Once a year, but I'm aware that it depend somewhat on your local conditions, such as living near the ocean or a salt lake. I've also seen the damage that not washing a mirror can do, so I wouldn't leave it too long. 2 years max in my experience.
You have to wash your mirror? Just kidding.............. I've had my 12"LB for two years, without any cleaning. The mirror is dirty, but still gives great views!! But..........I think it might be time to wash the old girl.
You should ensure that your optical tube assembly is capped off at the top and bottom, plus the focuser has a plug in it, thereby you are closing off the system from ingress of dirt and dust.
I have numerous reflecting telescopes going back into the 1960 period, and do not need to clean them at ball, as by taking exquisite care of them they never get dirty.
I recommend you clean a mirror when it gets so dirty that it affects the performance of the telescope, which is when the mirror is filthy. I am surprised that so many of the team are cleaning their mirrors so often, this is both unnecessary and causing damage to the optical coatings.
I have been professionally hand crafting reference grade telescopes for many years and rarely need to clean mirrors, are you guys taking care of your optics, it sounds like a problem for a few of you.
I wash my mirror as often as it needs it...for me that seems to be every 9 months or so...
The task of cleaning a mirror (or eyepieces for that matter) should be done no more or less often than it needs to be. It does not need to be a scary thing to do...a little common sense and good judgement should get you through no problem.
I have been professionally hand crafting reference grade telescopes for many years and rarely need to clean mirrors, are you guys taking care of your optics, it sounds like a problem for a few of you.
Rgds,
Astromelb.
Barry,
That is all fine in theory. It also works in many situations. However, you shouldn't assume that people don't look after their equipment because they have a need to clean the mirror on a more regular basis than you do.
If you have an observatory and don't need to transport the telescope, that in itself goes a long way to keeping the optics clean. If you travel with a scope to remote dark sites, some of which can be exceptionally dusty, as can the roads you travel on to get there, it isn't always a simple task to keep dust and crud off the mirror. The only time the lid on the mirror box on my 18" Obsession is removed is when I am observing, yet the mirror gets covered in crud very quickly. This gets further compounded when I observe from home right by the salt water. We get regular dews which are very corrosive because of the high salt content and this ultimately ends up as "acid rain" on the mirror after it condenses and is held on the mirror by all the crud that collected whilst out in the bush. If I waited years to clean my mirror, I would be using a reflective surface of pure aluminium chloride with a reflectivity co-efficent of about 8%. That doesn't work for me.
I also have a tube scope which I cap when not in use. I actually use rip stop nylon fabric caps which allow the scope to "breathe" and help to prevent the buildup of mould and mildew. Capping a scope using a solid non breathing cap when it has a dewed mirror, can do more damage than good.
I have been professionally hand crafting reference grade telescopes for many years and rarely need to clean mirrors,
Astromelb , Can you enlighten me as to what a `reference grade' telescope is ? Is that one that you tell your mates is really good ( giving it a good `reference'?)
Here is an image showing how the 6.5 metre primary mirror at the MMT Observatory is cleaned.
I can only assume this to a be a "reference grade" instrument that wasn't taken proper care of ? Looks like they are pretty rough in their cleaning habits, yet one must assume they have some clue what they are doing
I agree with the comments above about the increased need for semi-regular cleaning of optics if you are transporting the scope a lot. I find it essential to clean my mirror after a long weekend at Wiruna because of all of the dust.
Like Ausastronomer, I am fastidious about keep the lid on the scope when not observing, and I have even been known to put an elasticised sheet under the mirror box to keep any dust out. I also store my scope in a dry shed away from the elements. But even with all of these efforts, a clean every 4-6 months is necessary because I am out at remote locations observing each month.
Obsession Telescopes provide a free promotional DVD about their scopes which includes a helpful demonstration by Dave Kreige on cleaning a large aperture Dobsonian. I follow the method set out in his DVD, and it works very well. Rinsing any dust off the face of the mirror cell with a spray bottle of distilled water is a must before touching the mirror with a dampened cloth.
I've had my 12"LB for two years, without any cleaning.
