focal reducer

Hey all
When i take a picture of M31 with my canon it effectively fills the CCD, i would like to fit the whole galaxy into the frame? Are focal reducers the answer?

10" F5.8 Reflector
Canon350D


Thanks

I'd be careful with getting a focal reducer. I'm not sure it would work for the following reasons:

1/ It will move the focal plain inwards and you may not be able to rack your focuser inwards enough (too little back-focus). A very common problem on newts which has driven me crazy in the past.

2/ Since you're already at f5.8 I think it would just introduce alot of coma to your images.

Trev

Thanks Trevor
So heres the big question how can i get objects that are normally outsizing my Camera to fit in the ccd? How about eyepiece projection?

Thanks

I'd like to hop in on this question, as I have thought about getting one for my etx-125.
What are the advantages and disadvantages of using a focal reducer and where do they really come in useful?

Thanks
Darragh

Hey Darragh
Just getting my head around it two. They appear to be mostly used with Cassegrain telescopes to reduce the focal length thus reducing the magnification for a given eyepiece and camera and providing a wider field of view. You can get different focal reduction factors. Thats what i've got so far!!

Hey guy's you more or less know what you are asking already , but just to kind of sum it up a bit . The main goal of a compressor lens is to shorten your exposure time the relationship is the square of the f ratio so for example my celestron 6.3 focal reducer squared gives me a 40% reduction in exposure time. As for image size it does project the same image only a smaller version of it on to the ccd but not as small as you might think as this is not its main purpose, one way around your problem is to get yourself a bigger ccd chip but that can be costly so as you sugested eyepiece projection might be the way to go.