What will a focal reducer do to this?

[bloodhound31]

I have a C11 SCT, which I understand is an F10. This is an example of a photo at prime focus with a Canon 400d.

I also understand a focal reducer will change this to an F6.3? What will this do to my images?

Is that right?

Can anyone post me a comparison photo? Im trying to wrap my head around this, "F" stuff.

Also, I'm thinking of mounting an ED80 to the top. How will the image compare to the C11 at F10 of F6.3?

Baz.

[[1ponders] (Paul)]

Using a 6.3 FR will reduce your imaging time for the same exposure by about 3 (roughly). So if that was a 9 minute shot you would get the same exposure in 3 min. You will also get a much wider field of view.

To get a better handle on this stuff Barry I'd suggest you download the CCD Calculator from www.newastro.com. You can download it from this page It has images that will show you how much you will capture using different setups. You may need to input your 400D details for the camera section but that is pretty straight forward.

You will get vignetting using the 6.3 reducer, but you chip is big enough that a bit of cropping won't be a problem. Once you learn to do flats though, that will help.

[jase (Jason)]

Steve Mogg has some nice information on what a focal reducer will do
http://webcaddy.com.au/astro/Image-Scale.htm

I would recommend getting an off axis guider (OAG) combined with a focal reducer as this provides greater flexibility.
http://www.mapug-astronomy.net/ragreiner/OAG.html