Reducer to enlarge FOV

[PatrickO]

I want to use my Celestron Nexstar 4SE with a ZWO ASI224MC for close up lunar imaging.

I'd like to use a reducer to enlarge the FOV. A reducer around .5 to .8 will give me the FOV I want and allow for some margin of error.

What type of reducer should I get? They seem to range in price from a few pounds to hundreds of pounds.

Many thanks.

 

 

[vlaiv]

Larger FOV on lunar is usually achieved by making a mosaic rather than using focal reducer.

Focal reducers, while giving you large FOV, introduce optical aberrations. These might not be as bad for deep sky imaging where atmosphere effects are dominant, but if you plan on doing lucky type planetary imaging (and of course you should, and you have right gear for it) - then you don't want to loose any sharpness.

You simply image 4 separate panels (or more) that you stitch together to create large image. I think it took 9 panels, last time I did lunar imaging with 4" mak and ASI178 to cover whole lunar surface (ASI178 is a bit larger sensor than ASI224, but mak has a bit more focal length than SCT, so they should be in the ballpark).

[michael8554]

"close up lunar imaging."

Your image suggests you only want to image part of the moon, not all of the moon.

If you prefer not to Mosaic then the usual Celestron/Meade/Antares etc 0.63 Reducer would be in your range of desired FOV.

Giving 851mm Focal length with 105mm Backspacing from the Reducer.

Michael

 

 

 

[Cosmic Geoff]

As stated above, using a mosaic is a no-cost option for the Moon.

A Celestron f6.3 focal reducer can be used to advantage with various Celestron SCTs, e.g. my C8, to increase the field of view and the imaging speed. 

However, the  4SE is not a SCT - it is a Maksutov and I don't know what focal reducer is specified for it or which of the readily available ones will work well.  Given the unusual construction of the 4SE with its built-in flip mirror you should consider just how a focal reducer might be fitted.

Edited February 18 by Cosmic Geoff

[vlaiv]

If you really want to give focal reducer a try - then simply go for cheap x0.5 1.25" reducer.

I've used it with small sensor on several occasions with different scopes and it works.

Varying the spacing will vary magnification / compression, so you can experiment.

See here for some ideas of what to expect:

 

[PeterC65]

I've used the basic x0.5 1.25" reducer from FLO (this one) with my 72mm refractor and found it caused significant star distortion across much of the field of view. I've since replaced it with the StellaMira x0.6 2" reducer (this one) which is much better but still far from perfect. I've only used reducers with my refractor. I think if you want a flat field then you need to buy a good reducer, preferably one designed for your scope which might not be possible with the 4SE.