Mirror resurfacing

Moto Moto

Hi,
I'm new to astronomy and thinking of getting a telescope. I've been reading up on the various types and have a couple of questions about reflectors - how often do Newtonians and SCTs need to have their mirrors resurfaced, what's involved and is it expensive?
At the moment I'm using a pair of tripod-mounted Celestron 15x70 bins and Opticron 10x50's (I already had these as I also do some birdwatching).

dbran

Hi

It depends on how they are looked after. A newtonion if it is well looked after would not need to be resurfaced for years and years. Maybe 30 plus. It is relatively cheap to do for a newtonian. I believe there is a company in UK that does it.

I have not ever heard of anyone having to resurface an SCT. I would imagine it would be very expensive though as the mirors are internal and sealed. Probobly not worth it actually. Again it should not be necessary to resurface for a very long time if it is looked after.

hope this helps

dbran

Moto Moto

Thanks for clearing that up, I've read about all the benefits of reflectors but I wasn't sure if they were outweighed by the resurfacing issue.

Seanie M

I have a 200mm F8 reflector. Currently, the optics are in storage, having been put there about 4 years ago when I recoated them last. They are part of a reflector I built in 1995, and from when I bought the optics new from Orion Optics, 4 years ago was the only time I had to get them recoated.

Your key things to remember about having a reflector are:

*Never wipe the mirror except when needed, and do so with a camel hair brush.
*Always allow a fogged mirror to dry off naturally, and preferrably not pointing straight up - have the tube tilted.
*If you ever need to wash a mirror because of e.g. bird crap or bad dew/water marks, soak it in a basin of lukewarm distilled water with a small amount of washing up liquid to make up the suds for about 10 minutes, gently brush with the camel hair brush (do not swirl or use circular motion), then wash off with room-temperature distilled water, tilt the back of the mirror against an object e.g. a book, on a towel, and use a hair dryer on a warm, not hot, setting to dry it.

Dew will always get on your optics at some stage, but if cared for and stored properly, you could get up to 20 or 30 years on a scope getting monthly use before having to get it recoated.

Hope this helps,

Seanie.

Calibos

Just a minor point about washing a mirror. I don't think there is much point wasting a basin full of distilled water(available from Chemists BTW) to do the clean and then putting washing liquid in it. Just use normal tap water with a drop or two of washing up liquid. I use surgical grade cotton wool instead of a camelhair brush but the same methods otherwise to Seanies. Give it a good rinse under the tap to get all the sudsy water off and then rinse off with distilled water. Lean it vertical so most of the water drops run off. The remaining drops I soak up by using the tip of tiny pieces of tissue. No need to touch the mirror, just touch the drop. Surface tension will pull the drop off the mirror into the tissue.

Moto Moto

Thanks for the feedback lads. Seanie, how did you get it resurfaced? Did you have to send it to a specialist company?

Seanie M

Moto Moto wrote: »

Thanks for the feedback lads. Seanie, how did you get it resurfaced? Did you have to send it to a specialist company?

I did. Through the club, we sent a number over via crate to A company,shared the cost and freight. It wasn't Orion Optics themselves I think, even though they do it, I can find out the details if you like for price comparison?

Seanie.

Moto Moto

That's ok thanks, I just wanted to find out what was involved.

Seanie M

Moto Moto wrote: »

That's ok thanks, I just wanted to find out what was involved.

Money to send it over, patience to wait, then anticipation when it comes back to use it on the next clear night... that's about it!