Ad Astra Observatory

It should have come as no great surprise to me that I got the focal length right on the first try this time. After all, I already had a scope that could come to focus, and I’d already used it for some photography (my camera eats a ton of backfocus; a little over 2″) and I’d set things up for visual use as well (with an extension tube, naturally).

So as soon as I had the UTA (that’s upper tube assembly) together, all I had to do was measure the old struts, subtract the actual length of the new UTA, and that should be the remaining required focal length.

I went through the motions, though. I found some wood, cut 3 pieces to the calculated length, and clamped the whole mess into place, then took the scope outside, pointed it at zenith, and popped in an eyepiece.

I’d already checked the collimation while inside; it was way off of course. The wood-and-clamp thing is very wobbly.

But of course the 13″ was able to pull in a few stars up at zenith. A couple of “bright” (probably 5th or 6th mag) stars in a field of dimmer ones. I tried out a few eyepieces (32mm, 25mm, 10mm) and then brought out the 350D + MPCC. I could even see a star in the dim little viewfinder of the camera. You gotta love the 13″. It pulls in some serious photons.

a funny aside; as I was putting the camera in, I got a bright light shining on my arm. The scope was reflecting the moon “off axis”. 😀

With the mission a success, I put away all the gear, dismantled the temporary struts, and now I’m ready to start cutting the brackets for the LTA (lower tube assembly). I will try out that “spare” 2×3 I cut this morning to make sure I have the measurements right.

One thing I have to say is that my calculated values for things are not working out as well as I hoped. Everything is within an inch or so, or a degree or two, but it’s really irritating to think you’re calculating everything out and it turns out that you still have to prototype -> debug -> prototype -> loop. hmph. I am clearly not considering all variables, or perhaps I’m not setting my gear up for the angles I think I am. I’ll have to take a protractor to my struts once this thing is done.

Anyway, back to the show. I have my focal length. Next step, prototype the LTA clamps.