Finderscope Webcam

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Steve Holmes

A very good point Jeremy, which I put to Roger to ask for his comments. He said that when he discovered the problem with the 6×30 finder (which was simply the one supplied with his telescope rather than a deliberate purchase) he did indeed consider getting a 9×50 but, as he already had the old webcam and other “bits & pieces” from earlier projects, he decided to give the “electronic” option a go first. It was really only when he discovered that the prototype device worked so well, and that it might be able to be manufactured for a price comparable to that of a 9×50, that he began to think about whether it could be commercially produced.

While the webcam finderscope and a 9×50 will have about the same sort of performance (in terms of FoV and sensitivity), the electronic option does have a number of significant advantages over its optical cousin, which I noted in my very first post:-

1) The view seen through an electronic finder can be easily manipulated, both mechanically and by use of the driver program, to align it with that given by whatever star map or program one is using to define the hopping sequence. This includes the ability to “flip” the image in two axes as well as rotate it, something which is impossible to achieve optically without the use of additional lenses or prisms. It should be noted that, as Roger pointed out, the image in an optical finder is inherently “upside down” but the orientation changes if, for example, a diagonal prism is in use, all of which can be confusing for a beginner. The ability to easily alter the image orientation avoids these sorts of issues.

2) An electronic finder provides the observer with a much more convenient “operating environment”. Even a diagonal prism cannot always avoid the need for a most un-natural stance to be adopted in order to look through the eyepiece of a finder. Viewing the scene on a screen removes this problem.

3) Use of a camera enables the observer to take images during the hopping sequence, which can be useful for analysis after the event (particularly if the sequence went astray somewhere) and to document the sequence, perhaps to teach someone else how to carry out the same operation.

4) Driver software could enable the viewed image to be processed “on the fly” in order to improve the image quality and hence the effective sensitivity, which might permit objects at the limit of detectability to be seen.

Roger also noted that he had tried a 9×50 and found that although the performance was indeed a little better than a 6×30 it was not significantly so. While less bright stars could be seen, the difference was small and the FoV was 1 or 2 deg. less than achieved by his device. In addition, the 9×50 was much heavier which required extra weight to be added to the OTA counter-weight in order to maintain its balance.

All the above persuaded Roger that the device he has created would be of considerable benefit to a less-experienced observer, hence his request that I begin this post.