Secondary mirror size for 30 telescope.(Photography).

[Robbos30]

Hi, Can anyone help me?
I was talking to a few chaps at Astrofest on the weekend and was pointed to ice in space.
I wanted to know what size secondary mirror I would theroricialy need to turn my f (4.818) Dob into a photographically scope? For visual it has a 4.5 inch secondary currently.
I've been looking at an equatorial platform from Tom O (USA) as well and wondering if the f ratio 4.818 is going to be a major disadvantage? The EQ has a provision for a plug in guider eg ST4.
Just playing with the figures at present.
Thanks.

[clive milne]

Depends how big the chip is and how much vignetting you are prepared to accept... A 5" secondary would be fine for a small chip, but you would need a 6" if you intend to cover something like a 16003

[billdan]

A more complicated alternative if you wanted to keep your secondary, use a low profile focuser that gets the CCD chip closer to the mirror.
Downside is you will have to extend your truss rods by the same distance that you gained to achieve focus.

Cheers
Bill

[Mighty_oz]

Have a chat with Peter Read at SDM he will have some ideas :) The EQ from equatorial platforms ? They look nice.

[AstroJunk]

Oddly enough I did discuss this with Peter and he pointed me here: http://www.televue.com/engine/TV3b_page.asp?id=61&Tab=_phot

In essence, the type 2 Paracorr can be used for both Visual and imaging without the need to change your pole length! I have the type 1 sadly but am looking to change it at some point.

It's better explained with the 3" version: http://www.televue.com/engine/TV3b_page.asp?id=61&Tab=_phot3

[Robbos30]

Thanks everyone , I really appreciate your feedback. Exciting prospect.very deep learning curve.
Peter.

[troypiggo]

Not sure if you're already aware, but check out some of Alex Cherney's deep sky images using his 22" SDM. Most shots are stacks of just 15 second subs!

http://www.iceinspace.com.au/forum/showthread.php?t=74060
http://www.iceinspace.com.au/forum/showthread.php?t=71913
http://www.iceinspace.com.au/forum/search.php?searchid=3820206

[Robbos30]

I'm shocked with the results! That's amazing! I'm hooked!
Thanks so much guys!