16 inch telescope

dolphy2910 · Post by **dolphy2910** » Tue Mar 15, 2011 2:09 pm

Hi,

Is there any place that selling 16inch primary mirror for making reflector telescope?

Gary · Post by **Gary** » Tue Mar 15, 2011 2:15 pm

Hi there. Welcome to Singastro.

This is one such place that does:
http://www.rfroyce.com/stand_mirrors.htm

kimo · Post by **kimo** » Tue Mar 15, 2011 2:34 pm

Hi,

Brother, making a 16 inch Nw/Dob is not a simple task, Lots of hell works to consider. You may require very good experience on making a 16” telescope. How many Telescopes have you build in past? Consider the length of the OTA. If 16“ f/4.5 then the focal length will be about 72”.
Regards

orly_andico · Post by **orly_andico** » Tue Mar 15, 2011 2:35 pm

Royce mirrors are quite expensive. If your tastes aren't so rich, go on ebay and search for seller "hubble optics." i understand that these mirrors are made in China. they are much cheaper.

dolphy2910 · Post by **dolphy2910** » Tue Mar 15, 2011 2:53 pm

I know it is hard to make bro, I thot Singapore can have some stores that selling these mirrors.

rlow · Post by **rlow** » Tue Mar 15, 2011 4:24 pm

So far, no one sells paraboloidal mirrors for newtonian scopes here in Singapore, except maybe a few second-hand sales. No second-hand 16"mirror for sale here...yet.

I got all my mirrors from USA, there are about a dozen sources there. I would not want to assume you lack DIY skills or deep pockets, but it would help if you set your budget and objective. Since we both got this same interest here, you can send me a PM and we can discuss more details.

kochu · Post by **kochu** » Tue Mar 15, 2011 5:44 pm

Hi ,

I was once keen on this project in 2006-2007.

I Got the quotations from Mr Huang . Details and excerpts from his e-mail as below.
---------------------------------
We can custom-make the 16 inches f/5 parabolic mirrors, which have the accuracy of 1/8 wavelength. The unit price is US$750. Thank you.
Yes. We have the 16” mirrors, which can be shipped as request. It’s made with optical glass. The thickness is 40mm and the accuracy is 1/8 wavelength. It’s very cheap by sea freight. But if using EMS, the cost is less than USD100

Zhiqiang Huang
Zhitong Industrial Co., Ltd
Gongye Sixth Road, Industrial Park
Shangrao City, Jiangxi 334000, China
Tel: +86-793-6192008
Fax: +86-793-6192006
Email: srztgs@hotmail.com
Website: http://www.zhitong.net
--------------------

Kochu/15-3-11

orly_andico · Post by **orly_andico** » Tue Mar 15, 2011 10:06 pm

wow that Mister Huang does them quite cheaply! of course I would take the 1/8 wavelength with a grain of salt.

What my own experience has shown me is that a big dob is quite bulky. I only had a 10" and hardly took it out. And to think I was having ambitions of a bigger one, too..

Also in light-polluted skies the extra aperture is wasted.

rlow · Post by **rlow** » Wed Mar 16, 2011 11:44 am

orly_andico wrote:wow that Mister Huang does them quite cheaply! of course I would take the 1/8 wavelength with a grain of salt.

What my own experience has shown me is that a big dob is quite bulky. I only had a 10" and hardly took it out. And to think I was having ambitions of a bigger one, too..

Also in light-polluted skies the extra aperture is wasted.

Mirror prices has been going up, especially in the last few years due to Pyrex glass availability issue. So a mirror quotation from a few years may no longer be valid today.

A true 1/8th PTV wave mirror is technically a very good mirror. However there has been many cases, even in USA, that figures had been manipulated and do not stand up to independant tests or actual observations.

A 1/8th PTV mirror itself does not tell the whole picture. There are other factors that are also important but usually unstated, eg. surface smoothness, edge condition, free of astigmatism, substrate condition etc. So a 1/5th mirror from a reputable source could out-perform a claimed 1/8th wave from a dubious source.

So generally I wouldn't recommend to buy a mirror solely based on it's ptv rating or price, but based on the mirror-maker's reputation and reliability/consistency in quality. Quality mirrors definitely come with a higher price, as generally you get what you pay for. Some may get lucky in getting a decent or good mirror at a rock-bottom price, however their consistency in quality is usually suspect, so one may more likely to get a bad to passable optics. Here's a quick comparison of Huang's 16" mirror price compared with some other mirror-makers:

16" f/4.5 to f/5 (estimated prices in USD)

Zambuto Optical $3270
RF Royce Optical $3600
Lockwood Custom Optical $3000
Stevens Optical ?
Kennedy Optics n.a.

Lightholder Optics $2400
Pegasus Optics $2300
Optic Wave Labs $2230
Ostahowski Optics $2195
Discovery Optics $1699
Edmund Scientific $6125?
Orion Optics $2434-$3326
Optical Mechanics ?
Swayze Optical ?
Galaxy Optics n.a.
Nova Optical ?
Parks Optical n.a.
Coulter Optical n.a.

Hubble Optics $1650
Huang Zhiqiang $750

Frankly, I find a 1/8th PTV 16" f/5 mirror at $750 USD is too good to be true.

If you observe carefully, you will realise that larger aperture is not necessarily wasted in our light-polluted skies. It's quite a myth that large dobs do not perform as well as smaller dobs in urban skies, or that one should limit to say 10" and smaller aperture for observing planets in the city. For planetary observation in S'pore, bigger-aperture (eg. 11", 12.5", 15", 18" etc) properly-optimised scopes has shown more planetary details and more vivid colors than smaller scopes.

rlow · Post by **rlow** » Wed Mar 16, 2011 11:56 am

A big dob may be bulky, but still easier to transport/ setup than other scopes.

For eg, my 11" truss dob is easier to move around and faster to setup than my 6" f/8 apo on EQ6 mount/tripod.

Try to compare moving/setup a 15" Obsession truss dob with a C14 on CGE Pro mount.

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