Focal Reducer for a Refractor?

[[1ponders] (Paul)]

While in NZ last weekend I was fortunate enough to view some stunning images taken through a Megrez 80 ED( In my dreams). The owner had used a Televue 0.8X focal reducer and field flattener attached while imaging (from what I understand, mainly for the flattening effect). I was impressed to say the least. So much so I want to try to use one, but with a larger conversion rate, so to "speed up" my f/10 Celestron.

My question is....is any one here able to tell me if I can use an SCT Focal Reducer (Meade 6.3) on a refractor to achieve the result I'm after. Or do I need to get one specifically for a refractor. I'm in the process of getting an adapter so I can use the Meade OAG on the Refractor so putting an SCT reducer in the optical train will not be physically difficult. But will it be optically worth while.

Thanks

[mch62 (Mark)]

Paul from my readings on the web it doesn't work very well as the SCt reducers are optimised for the SCT and there field curvature and abberations.
There are cheaper reducers available from Steve Moggs in OZ and Sac imaging in the US have some as well .
Both screw into a camera 11/4" eyepiece holder adapter tube and work at f5 6 ect.

I think but don't hold me to it that they also work in an eyepiece but I am not sure about that or just how good they work either visually or imaging.

The Sac units work with there CCD imagers OK from pics seen .

I think you will need reasonabley good scope optics though as i would imagin using them with an acromatic refractor especially a short focal ratio will only magnify the acromatic abberations further.

I also think TV have different reducers for different focal length scopes

Mark

[[1ponders] (Paul)]

Thanks for that Mark. I'll check into the Chromatic abberation problem. I hadn't thought about that.

[mch62 (Mark)]

I think the field curvature thing is a problem as well.
SCT have a curved field whereas an f10 refractor is less.
So using the SCT reducer will actually make things worse but again just going on memory from some trial and error reports from CN a while ago on the same idea.
Give CN a search and I am sure you will find somthing on it there.

Mark

[h0ughy (David)]

I have seen, but don't quote me on it that, someone in the US had the same problem. they bought a variable adaptor that when you turn it the two prisms as they rotate over each other adjust and flatten the field to your specific need. Sort of like a variable polarisation filter. it adds about 40-50mm to the extension of the scope.

[Stephan]

Here some information about reducer/flattener. A reducer has to be made for certain telescope and has to be in a defined position to imaging plane to work perfectly. However, often they work well enough at other telescopes. TeleVue has one for telescopes with a focal length from 800mm to 1000mm (#REF-3007). On a F10 refractor the field is already very flat, therefore the flattening is not an issue. But F10 means very long exposure times. Here is where the flattener really makes a difference, it makes your telescope F8. But on the other hand it increases the chromatic aberration enormously, as you have an achromatic refractor. The increase of chromatic aberration is a square function over the F number.

The bottom line is, you have to check if the Televue reducer/flattener works for your specific telescope. It might be better for you to use your telescope as it is for fotography. My suggestion is try the TeleVue reducer/flattener only if you can give it back to the dealer if it does not work.