1.25" Focal Reducer - Beginner Questions

[Leedsgreen]

Dear All,

I have recently bought a SkyMax 127 scope and am thinking of buying a 1.25" 0.5x focal reducer to do some rudimentary DSO imaging. I have a few questions if OK:

1. Generally, are the 1.25" reducers recognised as any good? Are some btter than others (i.e. I notice Antares, Opticstar. Telescope-Service, Orion)?

2. I have two methods to image, one is afocally with 32mm EP and compact camera but I wonder if 0.5x reducer will cause vignetting of image? Second way is using DSLR at prime focus (well, with reducer in the light path). Would vignetting be less of an issue this way?

3. With regard to point 2, I read that using 1.25" reducer with EP above 25mm will cause vignetting. Does above 25mm mean, say, 32mm or, say, 10mm?

Thanks very much for any advice and help. Whilst I don't wish to waste money, I wonder if there is a reasonably priced reducer that will give a decent image?

Nick

[roundycat]

I can give you a partial answer, I use a 0.5 reducer with my Atik when guiding with my TMB as a 1200 mm focal length for guiding is well to the north of stupid. This is a 1.25" animal and works well with the Atik 16 as it is a small chip. Once you start to increase the chip size you will suffer from an increasing degree of vignetting. My guess is if you use a DSLR with an APS chip, let alone a 35mm one, you will get the effect of looking down a length of pipe.

As regards are they any good, have a look at the price of some of the AP reducers, well over two grand.

I suspect your best bet will always be to use the scope at prime focus rather than afocally.

Dennis

[Leedsgreen]

Dennis,

Thanks very much for your useful reply, which is pretty much what I imagined. I think I will buy a cheap version just to see the limitations myself. I wonder, would a 2" 0.5x reucer work better or perhaps an f6.3 SCT reducer attached with ring (or maybe neither and stick to prome focal stuff)?!

Thanks again,

Nick

[brianb]

The 1.25" focal reducers are only intended to work with small chip cameras - web cam size. The 2" type may cover a slightly wider field but they're simple designs & likely to cause some loss of quality. Probably great with a 1/2" CCD but not for a APS-C sized chip let alone full frame. As for the SCT reducers, these are computed to provide the field flattening required by f/10 SCTs and do not work well with any other design - not even Meade ACF optics which appear to be very similar but deliver an almost flat focal plane, as well as having greatly reduced coma.

[RobH]

As for the SCT reducers, these are computed to provide the field flattening required by f/10 SCTs and do not work well with any other design - not even Meade ACF optics which appear to be very similar but deliver an almost flat focal plane, as well as having greatly reduced coma.

I regularly use a celestron F6.3 reducer with my 80mm WO, and TMB 152 scopes and it works absolutely fine.

Dave 'Centroid' has a 12" ACF and uses the meade F6.3 reducer with this and also has no trouble with it....whatever field flattening characteristics it's supposed to have, in practice, it has no negative effect at all with another type of scope other than an SCT.

I assumed that this would not be the case, but experience proves otherwise.

Cheers

Rob

[Psychobilly]

Sometimes you just have to try things and see what happens... every now and then you may end up being pleasantly suprised .... Of course this process is far less painless if you dont have to spend any money to try it... instead already having the neccesary bits n bobs in the "toy" box...

Peter...