Best budget focal reducers for CCD?

[Space Cowboy]

I'm looking for a cheap focal reducer to give me more FOV for my f4.8 1200mm 10" Auto Dob and DFK cam. This is just a sideline imaging M42 and M31 when I normally image Planets. I understand the 0.5 reducers increase FOV by 40% is there anything that increases FOV more thats around the £30 mark?

[riklaunim]

For a Newtonian - nothing. Those telescopes have very little backfocus and they can't be usually reduced even more... but you could use a lens with the DFK - either CS-lens for ultra-widefield, or old M42 for bigger focal lengths for normal widefields

[Space Cowboy]

Thanks Rik. By adding a lens to the DFK you mean using it piggy back on the scope?

[riklaunim]

Either piggyback: http://nauka.rk.edu.pl/site_media/resources/nauka.rk.edu.pl/images/dmk_cs_piggyback.jpg or on a dovetail - http://oi43.tinypic.com/ztg7ig.jpg (designed for 1/4" photo tripod screws screwed from the bottom side of the dovetail)

[Space Cowboy]

Very interesting! So I would need a m42 lens like this one? : CARL ZEISS JENA TESSAR M42 SCREW 50MM F2.8 LENS 87 | eBay

and a T to C mount adapter plus a C mount m42 lens adapter as demonstrated here? :

[riklaunim]

I usa a Baader adapter from T2 for those lenses, but they tend to screw into T2 threads too - for short lenses like that one it should be stable

I would also suggest putting a light pollution filter in the path (either by Baader C->T2 with a filter thread, or similar element) as short focal length + bright f-ratio likes to gather a lot of it.

If you put it on a EQ mount (even some mini-EQ) it should allow "long" exposures - for a DFK that could be around 30-60 sec a low gain.

[Space Cowboy]

Thanks again Rik! Given me food for thought. Certainly would introduce a different dimension to my DFK's use! Sadly I don't have a EQ mount but may be able to get away with 30 sec exposures on the Auto Dob with a shorter focal length.