THE EQUATORIAL TABLEDOB!

This is a short report of an experiment I attempted on 2020 July 14, wherein I tilt a tabletop dob so it becomes equatorial mounted.

Log Entry about the Tabledob. (Note that the "60°" angle in the diagram should be about 30°.)

"Rover" on tripod as intended.

While I was borrowing my friend's Orion SkyScanner 100 (nicknamed "Rover"), I had on a few occasions made use of the compatibility with photo tripods. It can either be mounted such that the optical tube itself is mounted to the photo tripod (with the eyepiece position far to the side), or the tabletop-Dobsonian base can be mounted to the photo tripod, as pictured.

I found the eyepiece position of "Rover" to be problematic. It is difficult to use when pointing at a low altitude because if it's put on a table you have to lean way over the telescope to look straight down into the eyepiece. When put on the photo tripod, you can at least adjust the height of the tripod to find the most comfortable viewing angle. When the optical tube is used on the photo tripod, it is completely to the side, and thus the tripod must be extended so that the eyepiece is at eye level.

An angled focuser position (or a telescope tube that can rotate within tube rings) is necessary for comfortable viewing.

 

One night, as a lark, I set up the SkyScanner mount on the photo tripod, and I tilted the tripod so it was as close as I could get to pointing at Polaris. Then I set the SkyScanner so it was pointed straight up on its mount, which meant that it should be pointing straight north. I then spent several minutes fiddling with the tension adjustment knobs on the tripod, getting Polaris centered in Rover's eyepiece without moving Rover itself. It was tough but I managed to get a rough alignment where Polaris remained in the field of view (though not nearly centered) throughout most of a rotation.

Equatorial Table Dob!

And did it work? Kind of! Was it worth it? Absolutely not. Am I glad I tried it? Definitely.

 For a few reasons. There's no slow motion controls on a Dobsonian mount, which means you're going to have to move the Dob manually anyway. If there was a tracking stepper motor on the dob base, that'd be another thing. Performing two-axis tracking, especially at a low power, is really not a big deal. Making it manual doesn't make much of a difference. Also, newtonians tend to get their eyepieces in some pretty weird positions when on an equatorial mount, and the lack of tube rings makes this worse.

The Table Dob pointed South.

Now, the tube actually can see all the way past the dob base in theory, the base doesn't actually obscure any of the sky. In theory.

But that eyepiece position has come to bite us. The eyepiece prevents the telescope from looking farther than about 10° South (worse than that when you remember you have to fit your head behind the eyepiece). So I could not observe Jupiter or Saturn in this configuration.

Finally, here's an excerpt from that night's log (inverted colors) showing the two observations I recorded with the Equatorial Table Dob. (This was the reference for my small scope sketch of M27 from the Top Ten Deep Sky Objects article.)