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Afocal adapter

This adapter was designed for a TouCam pro, but can be adapted to any webcam with an external lens.
(click images for a larger version)

Parts:

1- 1 inch plastic conduit adapter. Model number TA20. It is a plastic adapter that has 1 inch pipe threads on one end, and a 1-3/8 inch socket on the other end. It is about 1-3/4 inches long.

1 piece of flat plastic about 1/4 inch thick to fashion your bushing out of. Or some other similar material.

 

The adapter fit a little too snugly over my eyepeice, so I needed to sand it out a bit until it fit easily over the eyepiece. I also ground down the threaded end until only about 1/4 inch of threads protruded.

 

A circle (about 1 inch diameter) was cut from the piece of plastic, and was trimmed to fit exactly inside of the threaded end of the adapter. A hole the diameter of the TouCam lens (minus the yellow rubber ring) was drilled in the exact center of this circle of plastic. I didnt get mine in quite the exact center, so the vignetting is a little off center. The Toucam lens is a little over a half inch in diameter. The largest drill bit I had has half inch, so I had to ream it out a bit...

 

Then the bushing can be inserted in the adapter, and cemented in place.

Thats it! My adapter fits snugly over the barel of my eyepiece, but I still plan on adding a set screw, for holding the adapter at the correct height on the eyepiece.

To use, focus your camera at infinity, then insert the webcam into the adapter. Place the adapter over your eyepiece, and adjust it up and down until vignetting is minimized, or eliminated. I was able to eliminate it using my 25mm eyepiece of my ETX90, but any other eyepieces still had some vignetting. This was fine, because I just wanted this adapter for wide field stuff. When I want higher magnigications, I will use the camera in prime focus.

Here is a picture of the adapter parts, laid out.

 

And here is the finished product:

     

 

 

Results

 

Here are some pictures I took to show relative field of view. These are just temporary pics shot of a nearby hillside about 1.5 miles away. They are very blurry, because they were shot through a plexiglass window!

As soon as the wx permits I will get the scope outside and shoot some replacements. Until then, please bear with me.

             Prime Focus                                   Prime focus with focal reducer

                   

 

           25mm eyepiece                             25mm eyepiece with focal reducer