Aiming a Genstar telescope to 5 degrees altitude: A $2.88 solution.
By Luca Vanzella
The ultra-portable 10″ Genstar telescope is a very fine, truss dobsonian that is excellently crafted, requires no tools for assembly/disassembly and has very smooth movements. While its low-profile form factor makes it ultra-portable, the telescope’s unique raceway design that eliminates the conventional altitude bearing does introduce a minor limitation – the lowest the telescope can be aimed is 20 degrees above horizontal. This is usually not a problem since most of my observing is done above 20 degrees but there are times when I really want to observe lower than that.
For a few years I used two small wooden wedges to raise the back foot of the base either 5 or 10 degrees to aim the telescope lower than 20 degrees. Although the wedges are inexpensive and ultra-portable, when the back foot is raised, the telescope can tip forward easily, so I have to carefully hold the telescope when observing low.
I recently made a wooden platform that is inclined at 15 degrees and holds the telescope securely when observing low.
I started with a piece of 3/4″ plywood from a old cabinet that we had removed when my wife and I renovated our 1953 house a few years ago. My wife, who owns a router, routered three blind holes about 1/4″ into the plywood to accept the feet of the telescope base. I cut two pieces of pressure-treated 2×4 wood (left-over from the camera platform I made to image the solar analemma on one piece of film a few years ago) into wedges inclined at 15 degrees. I screwed the wedges onto the platform using ACQ construction screws (so the pressure treated lumber would not corrode the screws).
I bought a 8″ metal mending plate at Home Depot to use as a retaining bar. Some measuring determined that 1.5″ bolt with some rubber washers and a wing nut could secure the mending plate to the platform and allow it to swing over the arm that holds that back foot of the telescope base. Further measuring and test swinging determined where to drill a hole for the bolt.
With this wedge base I can observe down to 5 degrees altitude without concern for the telescope tipping forward. The height of the wedge base ensures that the telescope can still swing a full 360 degrees in azimuth so there is no compromise in movement.
$2.88 for the mending plate (everything else I had on hand).
- one piece of 3/4″ plywood cut to 14″x14″
- two pieces of pressure treated 2×4 wood
- four ACQ construction screws
- one 8″ metal mending plate
- three rubber washers
- one wing nut
- one 1.5″ bolt
- table saw or circular saw (or hand saw if going old school)
- drill + bit same diameter as bolt
- protractor or sheet of paper folded to make a pocket protractor
Footnote: In a pinch when on Maui, my observing buddy Warren Finlay made a Genstar wedge base from some scrap wood and baling wire from Safeway in Kihei. It was the baling wire that inspired me.
© 2020 Luca Vanzella