Focal reducers - What type?

[Daz1969]

Hi all, Need some advice - I need to get a focal reducer for use with a Meade DSI and an 8" SCT.

I see two diff types and would like to know the diff between them.

I have seen the ones that thread straight onto the back of the sct and cost typically a £100 (Meade and Celestron) and then there are ones that just thread onto the eyepiece/camera and cost around £30 ish.

Whats the diff ?

Cheers as always

Daz:headbang:

[Ben Ritchie]

then there are ones that just thread onto the eyepiece/camera and cost around £30 ish.

Like the Atik 0.5x one? It's 1.25" format and really only works well with small-chip CCDs - as you're using a DSI then that's fine, but they'd be no good with a DSLR. The Meade/Celestron/Clone f/6.3 reducers are larger, which means they work well with APS-C sized sensors on a DSLR and flatten some field curvature too.

[Merlin66]

As Ben said, the small filter thread units are really only for webcam type cameras, even then they are a compromise. Usually only a small glued doublet, whereas the SCT reducers are usually air spacer triplets to give maximum corrections to the field of view.

A bit like comparing a push bike to a Golf... they'll both get you to where you want to go, but very different in comfort and performance!

[Milamber]

Yeah, the seats in those Golfs were terrible

I am constantly surprised by people that ask about such things to tell the truth... a cursory glance at the optics found in most finderscopes would surprise you I suspect.

Arthur

[Daz1969]

Many thanks guys:) Although didnt quite understand what you were saying Arthur. What do you mean?

Daz

[Milamber]

Well, try taking an objective out of a finder and using it as a reducer... a lot cheaper if you can figure the mounting...

Arthur

[Daz1969]

Ahh. Outstanding idea!

Many thanks Arthur:)

Daz