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Old 30-05-2019, 08:04 PM
Averton (P and C)
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Averton is offline
Join Date: Mar 2019
Location: Melbourne
Posts: 59
Prostar LP-Guide-C2 thread adaptor

We currently use a Prostar LP-Guide-C2 camera for imaging. The camera comes with a 'C' thread on the front of it which apparently is for CCTV lenses. This, however, is not useful for connecting 1.25" filters. The camera is provided with an adaptor from the 'C' thread to a 1.25" thread. However, the adaptor is some 24mm long so when it is used with a filter on it, it does not fit into the recess of all the items we use: namely the focuser body itself and the bodies of the two Barlows we use. This means that the camera sits further out of the item than it should. In practice this has been found to prevent focusing being achieved due to running out of back focus travel. In addition, we tried a 0.5 reducer on this adaptor (ridiculously long) and there was absolutely no way this was going to focus regardless of the focuser travel.

The obvious solution appeared to be to just turn down the excessive length off the inside threaded end of the supplied adaptor. However, on closer examination we found that the 1.25" inside thread only extends 5mm into the front of the adaptor and then changes to a smaller diameter and different pitch thread for the remaining 13mm of internal thread. See picture of inside thread. What on earth this thread is for escapes us as we have found absolutely no information about it on-line but it stopped us from shortening the adaptor. It looked like we would need to turn up an entirely new adaptor with the correct inside and outside threads. It seemed quite possible to make an adaptor with a total length of 9mm.
So at this point we commenced making a drawing to use for machining but decided to 3D print a sample adaptor to test clearances for thread cutting tools. To our surprise the test adaptor, printed in black PLA at 0.1mm layer height, worked satisfactorily straight from the printer. We painted the inside matt black as the PLA was definitely shiny. We can now use this adaptor with the camera, with both Barlows, the IR cut filter and a reducer as required. Everything focuses now.

We have attached the stl file in case someone else has this camera and would like to use a shorter adaptor.
Peter & Clare
Attached Thumbnails
Click for full-size image (3D printed adaptor 001.jpg)
73.6 KB5 views
Click for full-size image (3D printed adaptor 002.jpg)
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Click for full-size image (camera-adaptor-filter 001.jpg)
89.1 KB5 views
Click for full-size image (camera-adaptor-filter 002.jpg)
89.0 KB7 views
Click for full-size image (camera-adaptor-filter and prostar adaptor.jpg)
77.4 KB4 views
Click for full-size image (camera-adaptor-reducer-filter 001.jpg)
72.1 KB4 views
Click for full-size image (Prostar adaptor.jpg)
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Attached Files
File Type: zip Filter adapter std 0.01.stl.zip (426.4 KB, 3 views)
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