Application for Focal reducers

[Nebulosity]

Hello,

Say if I bought a 90mm f/12 refractor, like the Celestron Firstscope 90 EQ and decided that rather than initially buying a Startravel 80 at F/5, I use a focal reducer on this telescope.

Would this be practicle in terms of the views achived from the longer focal length refractor with a focal reducer (if one is available) ?

Thank you in advance.

[Ant]

It's certainly possible.

In the same way that the effect of a barlow is dependant on the distance between the lense and the EP / Cameras. So is the Focal Reducer (FR). The more distance the more effect.

With a FR, the point at which an EP/Camera reaches focus moves in towards the scope. So the FR will certainly work and should work without any serious issues with a refractor.

The only thing that I can think of is that you may not be able to use a diagonal with the FR.

Ant

[Macavity]

I bought an ATIK 0.5x reducer to try VISUALLY with my F14 MAK. Arttached to the end of a 10mm (say) Plossl, it is indeed equivalent to a 15mm e.p. You can also also substitute the negative lens of a standard barlow with the ATIK and it will give 0.5x - Effectively a 20mm e.p. (The ATIK stands a bit proud in some diagonals, since the housing is a bit THICK tho'!). However, you MAY not get "something for nothing" - at least VISUALLY. If e.g. you try to get 0.5x with a 32mm plossl. (Max length for a 50 deg e.p. in 1.25" format) you WILL halve the magnification, but the view may well be vignetted "somewhere" (it is in a MAK) - A bit like peering through a drinking straw at a distant scene. There are no free lunches?

I won't swear to this re. YOUR proposed setup, (MAKs are anyway prone to vignetting, due to their basic construction). If I understand correctly, vignetting does not matter photographically (the true purpose of a focal reducer) since you're anyway only trying to cover a small CCD? But VISUALLY, it might be worth checking your proposed setup in practice, before lasting committment.

[GazOC]

Mak,

AS you say, thats the 'problem' with the Atik, they are supposed to be purely imaging FR (thats why they are cheaper) and they just screw directly into the eyepiece or camera.

With a visual FR (£80+ ) you could just leave it screwed into the Mak/SCT before the diagonal and just swapped eyepieces, its how they are designed to be used and it's a lot less messing about. Most (all?) refractors won't come to focus with the Meade/Celestron etc visual FR.

The Atik imaging FR and a visual FR are different beasts. Either one will give imaging results in a refractor, but neither will work (as intended) visually in a refractor.

Gaz

[Macavity]

Thanks for that. I often end up fielding that one, in the absence of other contributions. Certainly a question most MAK (sic) owners seem to ask (themselves) - Then end up owning an F5 refractor as WELL. Enter the "virtual telescope", consisting of one or more physical ones...