Ad Astra Observatory

In order to get the new coma corrector working with the OAG inline, I had to try a lot of things before I found the right set that shoved the focal plane far enough up the focuser to work.

I recollimated the scope, that bought a little room.

I replaced the focuser drawtube with one that sits flush, that bought a little more.

I shortened everything as much as I could, and got the whole contraption shoved down into the focuser as far as it would go, but that… didn’t… quite work. I could tell that I was close to focus (I could see Jupiter’s moons), but everything was still a little fuzzy.

So today, I decided to pick up some longer collimation bolts, hoping that would get me close enough. I tore the mirror cell apart and discovered to my immense pleasure that the push and pull bolts have the same thread pitch and length (bonus) and that the thread pitch is Imperial, not Metric (double bonus!). in case you’re curious, Orion’s mirror cells ship with 10-32 x 1” machine screws. The “pull” bolts are countersunk, the “push” ones have a knurled section for easy thumb adjustment.

I bought both 1.5” and 2” replacements to try out. Unless the cap nuts are replaced, the 1.5” ones are as long as you can go, because the bolt bottoms out in the cap. A quick eyeball test informed me that the “all the way back” position of the mirror is going to be just about where the “all the way forward” position was with the old bolts (I guess that means I have close to 1/2” of collimation “travel”). This would be useless for visual use in the stock scope, but given that this scope is pretty much an astrograph full time, it won’t be a problem.

A quick round with the Cheshire, and I was ready to test on the just-past quarter moon in daylight.

In short, it worked. I was able to bring the RCC, OAG, and 300D image train to focus. I could even go a little past focus on the inward direction so I could tell I’d made it.

Now I need to put the scope back into “normal imaging order”, which means swapping back in the 3/8” taller focuser drawtube. I’ll need to recollimate the mirror a little further forward — the focal plane hits the CCD when the focuser is racked to within 1/4” of the bottom or so. No big deal, but not something that I wanted to tackle this evening.

I should be able to get a first light with the RCC sometime in the next few days.

I need to exchange the OAG — it’s wobbly. sigh. But I think I’m on the right track with this latest set of hardware — I should be able to eliminate flexure as a problem in the images if I can use an OAG successfully.

Another step forward.