Can you recommend a good focal reducer?

[StuartT]

I have a Meade 8" LX-90 (2000mm f/10) but despite that, I'd like to do some astrophotography. So I'm looking to get a focal reducer, 0.5x or even 0.33x

Can anyone recommend a really good one? I'm happy to spend over £100

Thanks

PS is this the same as a field flattener, or is that different?

Edited April 28, 2021 by StuartT

[fifeskies]

A reducer is NOT the same as a field flattener.

That said many reducers also combine a field flattener function.

( the basic flattener is essentially a x1).

High reduction rates are generally either very expensive or have poor performance , most reducers are in the 0.6 to 0.85 range.

The field flattener modifies the curved focal plane of the telescope to a flat one to suit a camera sensor , the human eye can tolerate a bit of focal plane curvature by adapting the eye lens as you scan the image , a camera cannot do this.

 

What do you intend to image , a small short fast ( f5 ish ) refractor might be a better solution if you are considering wider targets like emmision nebulae. This would work well on your mount (an EQ6R from your signature)

Edited April 28, 2021 by fifeskies

[Davey-T]

You may be better off with the "standard" .63 flattener / reducer, they come up second hand quite regularly, the .33 is pretty obsolete and was introduced when sensors were very small.

Dave

[Louis D]

The Starizona SCT Corrector IV got high praise in this CN post relative to 6 Celestron, Meade, and Antares R/Cs, both Chinese and Japanese made versions.

[StuartT]

Thanks for the advice everyone,

3 hours ago, fifeskies said:

What do you intend to image , a small short fast ( f5 ish ) refractor might be a better solution if you are considering wider targets like emmision nebulae. This would work well on your mount (an EQ6R from your signature)

Yes, I must admit that the more I read, the more I think a refractor might be a good way to go. I do have an old achro but it's f/11 so even less suitable!

I was looking at the WO Zenithstars - they look nice.

[StuartT]

Can someone explain to me what the relationship is between the f ratio of a focal reducer and its effect on the focal length of the telescope? I am seeing some focal reducers described as 0.5x (which I am thinking halves the focal length of your telescope), but others are described by a focal ratio (e.g. a f/6.3 focal reducer). How do I convert one to the other?

[Louis D]

If they have an x at the end, just multiply it by the focal length or focal ratio to get the final FL or FR.

If they say f/6.3, it's really an 0.63x R/C because it was assumed it would be used with an f/10 SCT.

[StuartT]

2 hours ago, Louis D said:

If they have an x at the end, just multiply it by the focal length or focal ratio to get the final FL or FR.

If they say f/6.3, it's really an 0.63x R/C because it was assumed it would be used with an f/10 SCT.

perfect! thanks

[iapa]

On 28/04/2021 at 09:37, StuartT said:

I have a Meade 8" LX-90 (2000mm f/10) but despite that, I'd like to do some astrophotography. So I'm looking to get a focal reducer, 0.5x or even 0.33x

Can anyone recommend a really good one? I'm happy to spend over £100

Thanks

PS is this the same as a field flattener, or is that different?

Not quite sure why you say “despite that”  nowt wrong with a native SCT guided on a good mount.

An 8” SCT will gather a lot of light with it’s nice aperture.

I use the Celestron 0.63 focal reducer, these come in it around £125 new, on my F10, 8” SCT, .

Have a look at http://astronomy.tools/calculators/field_of_view/ and you can get a feel for what targets fit the combination.

Speaking for my self, I’ve not seen a 0.5x specifically for the SCT. There’s a couple  0.33x reducers, but they seem to be quite scarce.

You may need additional adapters for the 0.5x and 0.3x reducers.

 

[StuartT]

3 hours ago, iapa said:

Not quite sure why you say “despite that”  nowt wrong with a native SCT guided on a good mount.

I use the Celestron 0.63 focal reducer, these come in it around £125 new, on my F10, 8” SCT, .

Hi. I think what I was meaning is that many people have told me that an f/10 scope is not really ideal for astrophotography without guiding. Not that it is impossible, of course. So, I have ordered a 0.63 reducer with which I hope to be able to get reasonable 1 minute subs.