Ad Astra Observatory

After a couple of days of being “closed for renovation”, the ad Astra Observatory at Newark, CA is back in business with the new Losmandy G-11 mount.

I had to modify the pier in order to get the mount to achieve polar alignment; It’s not the prettiest installation, but it works. Only 3 trips to the hardware store! By the way, did you know that hardware stores are open before 8am?! crazy, man. crazy.

The new mount is a real “grunt”er compared to the old mount (that is, when you lift it, you say “grunt“). The head is all aluminum, anodized black, and looks and feels just so much more solid than the CG-5. To my eye, it’s noticeably larger as well, which is nice, because I’m betting on it to carry pretty much any telescope I throw at it. I’ve seen G-11s with 14” scopes (in the 60-75# range) mounted. The G11 is a nice beefy object with a very precision feel to it. Fit and finish is top-flight. I had to call the manufacturer for some tech support, and actually got Scott Losmandy himself on the line! Good old made in the USA stuff (in L.A., in fact; the guy also builds rigs to hold lights and mikes and things for the movie industry, for what it’s worth).

There’s no GOTO on the new mount; it was a $1000 option that I couldn’t afford up front. It’ll cost extra to retrofit with GOTO later, but I may forgo GOTO in favor of Digital Setting Circles, which tell you where the mount is pointed, but doesn’t actually move the mount to the position of an object (call it a “push to” mount instead). The mount has encoders for DSCs, which are the gears that determine how much the mount has rotated, but I’d have to buy or build the decoder that can take this information and turn it into celestial coordinates. For now, I’m back to basics; just me, the stars, and “I think it’s around here somewhere…”. Which is strangely gratifying, as these things go.

The mount has a “polar alignment scope”, which is the first time I’ve had one of those. Basically, it’s a reticle that sits in the polar axis of the mount (which is normally the “hole” through which you sight Polaris in order to get a rough alignment), that shows the relative positions of the Big Dipper and Cassiopeia and Polaris; you rotate the reticle until the Big Dipper is in the correct orientation, then move the scope so that Polaris is in the correct spot, and bingo! a more or less “accurate” polar alignment. So I did this, and then decided to test the polar alignment of the telescope. I use a method that makes good use of my Nikon camera to get an accurate alignment (details are on my website), and so I decided to run a check. The longer you run the test, the more accurate the results, but I’ve found that even a 2 minute test is enough to show pretty granular amounts of error. So off I went, checking both axes for precision. I had to check my results several times, because under the 2 minute exposures I ran, I could detect *no* misalignment! What?! I mean, how accurate can a polar scope *be*?!

As a final test, I decided to run some unguided exposures; 30 seconds, 2 minutes, and then 5 minutes. This is all with Veronica and the whole imaging rig onboard ( I haven’t weighed the rig, but I’m betting it’s up near 30# ). So, no guide stars, just pointed at M13 (something that I knew I could find without GOTO), got it centered up and focused, and fired off a few shots. In short, I was floored. The 5 minute image showed some minor trailing. It would have been a “keeper” if I’d been shooting a set of them; the trailing was noticeable, but there was still enough data there to help the whole stack. In the 2 minute image, I could detect no trailing whatsoever. None. Perfectly round stars. This is after simply mounting, levelling, and using the polar alignment scope to align on Polaris. In contrast, with the same telescope/imaging rig, with a guide star, I’d lose about 70% of the images of 2 minutes or longer that I’d shot off of the CG-5. This is, simply, an entirely different class of mount.

I’ll have to check this to confirm, but I’ll bet that if I had done a 5 minute polar alignment test, I’d find that my polar alignment needed some small amount of tweaking. And that once I did that tweaking, I could probably get some 5 minute unguided images as well. What I’m saying is that I think that the trailing I saw in the 5 minute image was the fault of the polar alignment (ie “my fault”) rather than periodic error (ie “the mount’s fault”). In my test, I’d only asked it how accurate the polar alignment was over a 2-minute span…

I am amazed, astonished, stunned, proud… I can not say enough nice things about my experiences with the Losmandy G-11 so far.

sic itur ad astra, indeed.