Buying a new primary mirror

Jemmo (Adrian) · #1 29-07-2015, 09:41 AM

So I'm thinking of replacing the old mirror that came in my second hand scope it's over ten years old and when you have the mirror out and hold it up to light there are lots of spots you can almost see straight through.
My question is what improvement can I expect with a brand new mirror will the quality of the image I see be twice as good?

glend (Glen) · #2 29-07-2015, 09:45 AM

Do you know that you can simply get the old mirror recoated with a modern, hard, protected and high reflectivity coat. If it has served you well and is a good 'figure' just get it recoated. I believe there is a guy in Taree, NSW (Wayne S) who has a recoating business, just ship the mirror to him and he will send it back recoated.

Have a look at this thread for details on recoating here in Australia and the contact details for them

http://www.iceinspace.com.au/forum/s...t=92288&page=2

Jemmo (Adrian) · #3 29-07-2015, 09:54 AM

I'll have a look glen. I did have a look at recoating and the price was nearly the same for a new 10" f/5 mirror

Jemmo (Adrian) · #4 29-07-2015, 10:30 AM

For pretty much the same price I can get a new version of my mirror mate with 92% reflectivity and I don't have to worry about posting my one around. Will the viewing be far better with a new mirror than my old holey one?

SkyWatch (Dean) · #5 29-07-2015, 10:45 AM

Quote:

Originally Posted by Jemmo

For pretty much the same price I can get a new version of my mirror mate with 92% reflectivity and I don't have to worry about posting my one around. Will the viewing be far better with a new mirror than my old holey one?

It is really hard to quantify any improvement you will see. The resolution will remain the same, but you will get a brighter image with a bit more contrast with a cleaner and more reflective coating. My guess from your description of the current mirror is that you will probably get around 20% brighter images (a bit like the difference in brightness between a good 9" and a good 10" mirror), so you will notice a difference, but it wont blow your socks off.

Of course if your current mirror has a bad figure, then a new one with a better figure will also give sharper images- but that is a different thing than improving the coating.

All the best,

Dean

Jemmo (Adrian) · #6 29-07-2015, 11:04 AM

Thanks for all the info guys. I may just hold off then on a new mirror. I did read somewhere hold the mirror up to a 60w lift and if u can see the element through it then it's about time to recoat etc.
the mirror is over ten years old I get what I think is a decent image with it but when you look dos. The scope you see thin spots on the mirror. It's been cleaned about 8 months ago. Just worried about it

torana68 (Roger) · #7 29-07-2015, 12:05 PM

who made the one you have now? buying a cheap new one could be a backward step, its all about the quality of the mirror. You can have yours tested in Adelaide to see what its like, then either recoat happily or look for a better new one. Yes its costly but "cheap" and "awesome" don't go together.

Jemmo (Adrian) · #8 29-07-2015, 12:50 PM

The brand is bintel and the new mirror I was talking about for $350 is from bintel so I'm tipping they'd be the same

torana68 (Roger) · #9 29-07-2015, 04:55 PM

Quote:

Originally Posted by Jemmo

The brand is bintel and the new mirror I was talking about for $350 is from bintel so I'm tipping they'd be the same

quality varies from mirror to mirror, I'm sure Bintel would look after you.

Mokusatsu (Australia) · #10 05-08-2015, 12:11 AM

Bintel and Andrewscom both sell mirrors or inexpensive dobs, and both claim their products are diffraction limited high quality mirrors. For the price I am skeptical of just how great the figures would be as you can spend far more on high end mirrors than they charge and I assume people buying those pricier mirrors aren't just doing it for bragging rights...

At the end of this year I intend to buy a much larger telescope, to upgrade from my current 8" which will probably be rebuilt as a travel scope.

The cost of the Bintel and Andrewscom dobs are not much more than the cost of mirrors they sell separately (if you price in the cost of the focuser, spider etc etc).

I suspect the Bintel product is probably made by GSO, just like Andrewscom, so would it be reasonable to expect that their quality is the same?

If I wanted to spend a little more on a mirror than what they're selling them for to get something really great, what are some other suppliers, including overseas ones, that have a good reputation?

glend (Glen) · #11 05-08-2015, 02:56 AM

The mirrors that Bintel sell are made by GSO and are the same (supposedly) as those provided in their F4 & f5 newts. I bought. 10" f5 from them for my carbon truss imaging net and it is a fine mirror - no complaints.

SkyWatch (Dean) · #12 07-08-2015, 11:29 AM

I have a 12" GSO mirror in my dob: when I got it the manufacturer's specs for the mirror were better than for the mirror in their dobs... It turned out to be a very good mirror, with Ronchi testing and star tests showing an excellent figure.
The main difference between the mass-produced mirrors like this one and the more expensive hand-figured ones is the QC (and the love!). You can be lucky (like I was) and get a really good mass-produced one, but you are guaranteed of a really good one if you go for the top-end ones.