Make a Reflection Telescope

Post by **weixing** » Sun Jan 21, 2007 10:28 pm

Hi,
If you intend to use it for visual only and don't have transportation issue, a slow one is better. You can have a very small secondary mirror with a decent illumination field and don't need those expensive eyepiece to get decent wide field view.

Have a nice day.

Canopus Lim · Post by **Canopus Lim** » Sun Jan 21, 2007 11:50 pm

Actually you can buy the primary mirror from good mirror makers like Royce, if I am not wrong he sells 6 inch f/5 mirrors that are of very high standards (strehl and interferometry certified 0.95 and above). The rest of the parts like the tube, the spider, the mirror cell you can buy and assemble them together. Together with good optics and good components, you can actually make a fine compact size scope that offers wide field, sharp, planetary performance and colour free. It would cost more than a standard SCT but far less than a 5 inch APO.

If I have the money, I would actually make such a scope.

Robin Lee · Post by **Robin Lee** » Mon Jan 22, 2007 12:12 am

Does a faster telescope bulkier?

Canopus, are you saying to use the 6" mirror to make a achromatic refractor? Making oneself a telescope seems fun!

Post by **weixing** » Mon Jan 22, 2007 1:29 am

Hi,

Does a faster telescope bulkier?

No, a faster telescope is usually more portable, but you'll need to use a bigger secondary mirror and of course better eyepiece to get decent result.

Canopus, are you saying to use the 6" mirror to make a achromatic refractor?

How can one make a refractor out of mirror?? He mean that you can make a newtonian that give APO like performance.

Have a nice day.

jermng · Post by **jermng** » Mon Jan 22, 2007 2:13 am

If I have the money, I would actually make such a scope.

This coming from a 12.5 Obby's owner?? Hmmm ..

Canopus Lim · Post by **Canopus Lim** » Mon Jan 22, 2007 8:55 am

Because of Obby that's why no money.

Actually, I have been thinking of making a telescope. Perhaps next time when I have enough funds to do that, I can replace my C5 with such a compact Newtonian that will anytime give better views than the C5.

rlow · Post by **rlow** » Mon Jan 22, 2007 1:09 pm

Does a faster telescope bulkier?

A faster focal length scope is usually shorter and less bulky. If you are looking for a premium mirror, another excellent choice would be a Zambuto 8" mirror.

Robin Lee · Post by **Robin Lee** » Mon Jan 22, 2007 10:42 pm

Wow.. there are really of good mirrors around. Sorry, weixing, I thought mirror as lens. My sleepy eyes... Why is a f/8 Newtonian so rare?

Post by **weixing** » Mon Jan 22, 2007 11:40 pm

Hi,

Why is a f/8 Newtonian so rare?

F8 newtonian are not rare, just that most of them are in smaller aperture... it'll be cheaper to manufacture, can give better view compare to a fast small aperture newtonian and still not that bulky to carry around.

Big aperture newtonian are usually F6 and below. The reason that big newtonian usually have fast F ratio is due to it's size. Can you image how long and bulky a 10" F8 is?? The focal length will be 2m and you'll need a chair to observe. But a 10" F4.5 will be a lot shorter and will be able to handle more easily.

Also, another reason why small newtonian use slower F ratio is the size of secondary mirror. To give view of good contrast, secondary mirror had to be as small as possible. For a small newtonian, the solution is to use a slower F ratio and you can use a smaller secondary mirror. A big aperture newtonian usually don't have this problem because even they use a large secondary mirror, the obstruction is still very small compare to their big primary mirror.

Have a nice day.

Canopus Lim · Post by **Canopus Lim** » Tue Jan 23, 2007 8:43 am

That is why the new Singastro ironman will not handle a 8 inch f/8!