Astrophotography With A Reducer - 1

It's been several years since I bought a 0.5x focal reducer to use on my Meade LX-90. I made a couple of half-hearted attempts at working out how to use it but each time it seemed to get left behind as I pursued other aspects of astronomy and photography.

With the guidance of discussions with Michael Chaytor, from The Binocular & Telescope Shop in Sydney,  I gave it another go. The result was that I found I could use it with an eyepiece but not with the DSLR camera, which simply could not achieve focus.

I thought I might need a focal extender but after considerable experimentation, that did not work either. The telescope would only focus up to distances of about thirty to forty metres.

Thankfully, Michael continued to take an interest in my plight. He spent time carrying out a photographic experiment of his own, using the store's LX-90. Then he got back to me with the news that I needed an  'M42 male to M48 female step ring' to reach the shortened focal point which the camera could otherwise not quite get to.

After the step ring arrived, I carried out the following photographic experiment of my own, to prove that it now works before taking it out at night:

(a) Camera with 300 mm lens attached (no telescope):

The field of view for this lens at 300mm is 6.9˚ x  4.6˚.

Two high tension transmission towers can just be seen on the horizon, about six kilometres distant.

Ignore the foreground tv mast on the right.

 (b) Camera fitted to telescope. Diagonal - no; Reducer - no:

The view at 2000 mm and f/10 through the LX-90.

I estimate the field of view to be roughly 64' x 43'.

The image is not inverted. 

 (c) Camera fitted to telescope. Diagonal - no; Reducer - yes.

The view at 1000 mm and f/5 through the LX-90.

Due to the addition of the focal reducer, the field of view has increased and I estimate it to be about 128' x 86'.

The image is not inverted. 

 (d) Camera fitted to telescope. Diagonal - yes; Reducer - no.

The view at 2000 mm and f/10 through the LX-90, with a diagonal mirror attached.

The field of view is estimated at about 56' x 29' - slightly less than the same image without a diagonal.

The image is inverted vertically.

 (e) Camera fitted to telescope. Diagonal - yes; Reducer - yes.

The view at 1000 mm and f/5 through my LX-90 with a diagonal and a reducer.

The field of view is estimated at about 112' x 58'.

The vignetting has increased and the image is inverted vertically.

The shadow at top right is  a nearby roof top.

EQUIPMENT:

(i) The problem:

Camera fitted with Canon EOS T-Ring, T2 Adapter and 0.5x focal reducer.

The assembly fits into the SCT adapter (right), which screws onto the telescope.

Focus will only be achieved with the focal reducer removed.

(ii) The solution:

Fit the focal reducer and M42 male to M48 female step ring into the EOS T-Ring and insert it into the SCT adapter (right).

Put the T2-Adaptor (centre) back in the kit bag:

(iii) The essentials for using a DSLR with a focal reducer on an LX-90:

Camera, EOS T-Ring, 42-48 step ring and focal reducer:

CONCLUSION:

Using the step ring, the 0.5x focal reducer is usable on an LX-90.

On the basis of the images taken, slightly better results should be achieved without using a diagonal. Also the image is not inverted.

Bintel also advise that, as a result of the experiment they carried out, they are now confident that the 0.67x focal reducer which they sell could also be used. Might be useful later!

Many thanks to Michael and to Bintel in general for going the extra mile in resolving this issue. As they do.