Reducers - Can you get ones that will reduce the FOV and increase speed further?

[swag72]

At the moment I have a SW120ED and use a 0.85x reducer / field flattener, that speeds up the scope to about f/6.3 and increases the field of view.

I have seen a 0.8x reducer that would take my speed up to f/6 and make my FOV slightly larger, but wonder why these reducers seem to stop at around the 0.8x mark for refractors? I see that you can get reducers for some scopes that take the speed from f/10 to f/3.3.

Can I get for example a range of reducers that would enable me to alter my fov with speed as an added bonus for different targets? Would also stop me thinking about changing my scope!!

Probably sounds like a really stupid question!!

[RobH]

Hello Sara.

I've succesfully used a celestron 0.63x reducer on my 80mm WO scope with my Atik 16HR camera (same chip as yours).

That took it down to F4.5.

I tried it with a larger chip though and you no longer have a flat field as these reducers are also flatteners, and specifically designed for meade and celestron SCT's.

The 0.33 reducers thatr are available for SCT's only work with very small chip sizes....I have one and it's fine with a DSI, but shows rotten coma with anything larger.

Cheers

Rob

[swag72]

Cheers Rob - So a 0.63x reducer on my 120ED would give me a FL of 567mm and a speed of f/4.7.

Anyone else tried this?

[Kolenka]

Keep on mind that reducers work by compressing the scope's field of view into a smaller area. The more you compress the field of view, the worse vignetting you get and the worse the full field gets as aberrations are pulled closer to the center of the frame.

So depending on what camera you image with, you can only compress the image so much. The 0.8x compressors/reduces also flatten the field for the refractor to address aberrations but even they have limits of what can be corrected. Especially if you image with a DSLR, you don't want to go much further than the 0.8x from personal experience.

Imaging in the f/6 range is actually pretty decent for a simple setup. You can go faster, although you are looking at either a small imaging chip or big cash outlay to do it.

[RobH]

Cheers Rob - So a 0.63x reducer on my 120ED would give me a FL of 567mm and a speed of f/4.7.

Anyone else tried this?

You would really need to find out if you start to get coma etc due to the flattening aspect of the 0.63x reducers.....as I say, I got good results from mine on a WO F6.9 scope, but don't take that as gospel that it'll work on your 120ED.

Rob.

[swag72]

Thanks for that info Kolenka and Rob - May be something I try further down the line once I get my CCD - If that's the route I go down!!