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Orion Low Profile 2-Speed Focuser Modification
By Don Bray
The modifications described here enabled the Orion Low Profile 2-speed Focuser to be used for viewing and photography without drooping because of the added weight and extension required for a Barlow eyepiece.
The low end operation was fine, and that was all I used for some time. However, when I went to the extended operation, and tacked on two Barlows (2X and 2.5) and either the eyepiece or the camera, it hopelessly drooped, like a rose that had not been watered. Obviously, this made alignment and focusing useless.
Don Bray
The Fix
Since it was not a manufacturing problem, I chose to devise a fix which is shown in the engineering drawings shown below in Figure A and the accompanying photographs. Figure B shows the fully extended focuser, with the two Barlows and an eyepiece.
- The focuser bridge plate is inserted above the eyepiece holder and the eyepiece fits through the plate into the holder.
- The two bolts provide parallel guidance for the plate. It moves freely from full down to full up position using the knobs on the focuser. Free movement is enhanced by careful straightening of the bolts and a small amount of paste lubricant along the travel path.
The focuser bridge in the collapsed position is shown in Figure C. Figure D shows a layout of the individual parts and the drawings of the plate is also finished.
The focuser bridge performs extremely well, there is only a 0.125 inch droop of the eyepiece center, compared to the 0.5 inch droop without the bridge. With the bridge in place, telescope alignment can be set with an eyepiece in place and, when the video camera is inserted, the image appears very close to the same position. Eyepieces can be easily removed and changed with little movement of the image.
Safety Precaution
While this setup works well, it can be misused and made dangerous to the eye. If the two Barlows are removed and the extension tube is down, the user can come down on two posts (bolts) which could cause serious eye damage. This is a problem that is easily fixable with rubber stops on the posts and a link to the extension tube.
Figure A - Engineering Drawings
Figure B - Focuser Bridge Extended
Figure C - Focuser Bridge Collapsed
Figure D - Focuser Bridge Parts