Category: Astronomy

Last night, Molly the 16-inch f/4.5 Dobsonian telescope had her public debut at the River Ridge Observatory. It was mostly a successful debut. The images were bright and clear. We looked at the Orion Nebula (M42), Bode’s Nebula (M81), the Cigar Galaxy (M82), M79 in Lepus (one of the few globular clusters in the winter sky). I even chased the International Space Station for a bit until I lost it. I could see that it was oblong instead of a point or circle but I was so busy trying to keep it in view I couldn’t really observe it.
The elastic variable counterweight system worked at first at all angles but later had trouble. I’m not sure what to make of that, maybe temperature. I need to see what weight I can reduce from the top or transfer to the bottom. Also, I brought a light shield for the upper assembly but forgot a way to attach it. That said, I think we just need tweaks now.

I put the 16 inch scope together for the first time tonight. The six truss rods attach with bicycle clamps, collimation knobs and a power button for the fan at the top of the mirror box.  I’m going to shorten the ground board legs and the truss rods a bit before I’m done. The six truss rods are connected to each other and as identical as I can make them. I need to add a bungee or something to keep them together while attaching.  Plenty of fine tuning to do.

I’ve been doing mostly small stuff on the scope since the last post but today I made a couple of major steps forward.

1. I cut the Ebony Star Formica for the altitude bearings and glued them to same. I’m waiting for the contact cement to cure.
2. Took the relevant parts back to the River Ridge Observatory for second measuring session. This time I also took my truss rods so that I could mark them. Then I cut them. I cut them long (hopefully) and will remove a little at a time until they are just right.

I’m very close to first complete assembly but I didn’t want to mess up the contact cement by rushing it. After that will come the trimming of excess truss rod mentioned above, plus excess board for focuser and telrad, probably balancing. Truth be told the design doesn’t allow for proper balancing in advance. Hopefully it will be bottom heavy as that will be easier to address.