Focal reducer

[Amit]

Is it advisable to use focal reducer on larger focal lengths to get wide field view and for DSO?

[gboulton]

Depends on what you're after.

The reducer is like "zooming out" a telephoto lens. It makes things "smaller" or "farther away", but, as you say, widens the field of view.

With, say, a 1500mm FL scope, you're unlikely to get all of M45 in a single image or eyepiece. With the reducer, you would be able to capture/see more of it.

You'll also find that long exposure astro images take less time, as the reducer widens the aperture.

So...if that's what you want, then yeah...it's advisable.