Mirror lens any good?

[Okeydokey]

Thats about the measure of it, any good if not why not, if so, why so?  I am currently looking at the 200 & 300mm lens range.

Its for DSO,  I am looking for a new frontier in my imaging... that is... to boldy go where my 55mm has not been before

EQ3-2 mount, RA tracking only, Pentax K-m DSLR

[lensman57]

Thats about the measure of it, any good if not why not, if so, why so?  I am currently looking at the 200 & 300mm lens range.

Its for DSO,  I am looking for a new frontier in my imaging... that is... to boldy go where my 55mm has not been before

EQ3-2 mount, RA tracking only, Pentax K-m DSLR

Mirror lenses of the type you describe are usually of the catadioptric type and are too slow for DSO imaging at around F8~F12. You can purchase special design newtonian  astrographs at around F4~F5 but you'd need a very steardy mount to carry them effectively, your Eq3-2 regretably does not fit the bill. You can use the CATS for planetary imaging with your present mount and with a sensitve camera you maybe able to image some very bright DSOs.

A.G

[baggywrinkle]

I concurr with the above. I have the Samyang 800mm F8. Good for lunar work and maybe for very bright DSO, but would be a struggle for the dimmer ones.

It also takes some practice getting the fous right on these and exposure. You have no control on apeture and a good stiff mount is needed to prevent wobble when focusing.

That said it is a lot of lens for a smaller sum of money than many other telephoto lenses.

[laser_jock99]

Optically slow and a devil to focus is my experience of these things. Look out for a 300mm F4 or 200mm F2.8 ED lens instead. 

[Naemeth]

If you go just 100mm more you can get this:

http://www.teleskop-express.de/shop/product_info.php/info/p1840_TS-Travelscope-66---66-400mm-ED-APO-farbrein-auch-als-APO-Tele-Objektiv.html

Yes it's a scope, but they work well as lenses .

[PorkyB]

I use a Sigma 70-300 APO Zoom lens, which works well although it's fiddly to focus.  See here http://stargazerslounge.com/topic/189203-imaging-with-a-70-300mm-zoom-lens/?hl=%2Bsigma+%2Bzoom