How To Make The Clouds Arrive

I mentioned a couple of days ago about looking at M51 (the Whirlpool Galaxy) though Big Bertha, and how it wasn't looking quite as good as I had hoped--perhaps because the collimation was a bit off.

Indeed, one of the frustrations of Big Bertha is that it doesn't have a mirror cell in the conventional sense. Instead, at the back of the tube is a big flat piece of wood mounted on a hinge. The collimation screws go through that piece of wood. The hinge allows you to drop the back in order to remove the mirror--absolutely necessary if you are going to move this behemoth.

Well, one problem of the hinge is that at the far side of this square of wood is a gate hasp, to keep it from flopping down in use. Necessarily, that gate hasp means that there as much as one-sixteenth of an inch of play--and that means that, depending on the angle of the telescope relative to the ground, you could have quite a bit of variation in where the mirror is sitting relative to the rest of the optical train. Since collimation involves moving different sides of the mirror thousandths of an inch, this means that collimation has never been spectacular. You can collimate in one position--and as soon as you move the tube across the sky, that collimation is now worthless.

So I got fed up this slop, and sank two 1/4"-20 threaded studs into the back of the tube assembly, on the side of the big flopping square where the gate hasp is. Now there are two nuts that, once tightened down, reduce the slop to something I can't immediately see. Collimation seemed easier and more precise--and since I now have probably increased the optical precision of Big Bertha by a couple orders of magnitude--the clouds came in!