Advice required with 1/2 Bino

[astromerlin]

Hi, Wanting to get imaging DSO'S I realised that my SPC webcam and the SW250 combination just doesn't give me enough

field of view. I purchased what is half of a binocular, 80mm x 300mm focal length.

Together with my modded webcam would give me a satisfactory field of view. Visually it looks a good piece of glass and

coated too. Not a blemish on the objective.

I had to make an extension to fit the end of it to make the webcam get to focus and it now looks the biz. Trying it out on

the first night I seemed to have weird looking stars that have a tail on one side.

Also when focusing to get the smallest star point possible, the stars have a red halo and I found defocusing slightly improved

this but the star size increased.

After a few nights faffing around with it and trying to get better looking stars I gave up and it nearly went in the bin

(very frustrated I was too) but I decided to chuck it back in the box and have a look at it later.

Today I set it up on a tripod and set up an artificial star to see if the collimation of my adapter was off.

Using Metaguide I set about playing with the focus and moving the webcam about but all I seem to get is similar to the

image below. This images is with the webcam slightly defocused, when it is infocus the point of light has a tail to it.

Rotating the webcam moves the tail around the image but no amount of wiggling or jiggling with the adapter or webcam

will centralise the spot within the defocused portion.

Anyone have any ideas or suggestions would be well appreciated.

[Mr Spock]

Looks like a collimation issue. You may find it difficult to correct, binoculars have quite a complex light path.

[astromerlin]

I forgot to post a pic of the setup. Is it known if the objective is ground or placed offset to the central axis?

[Peter Drew]

The setup looks spot on as far as construction is concerned. An asymetric image is likely to be caused by the webcam, mechanically they are not a particularly precise item. A flare line to the image could be caused by the objective as they are usually a cemented design which can cause slight distortion. Binocular objectives are corrected to compliment the prism train and are not always as well corrected for CA and SA without.

[astromerlin]

Thanks guys for the replies. Sounds like I should bin it and save for an ST80 or something else then.

Cheers.