Focus stuff

I really really really like the MoonLite’s, so I thought I’d put up a blog entry on using the CS Model with my AT8RC scope. First, I zero’d my drawtube. I have the 1.5″ one, which at 6135 steps/inch comes to 9202 steps, minus 500 for safety, gets me 8702 total steps of travel. I set the driver to max increment 3000, min step 0 and max step 8702, leaving the steps/second at 125 in Full mode. I jogged the drawtube out manually to 27mm (which is where I measured it by hand with a ruler last time) which ended up being 6443 steps out. My scope comes with two 25mm and one 50mm spacers, and I’m using the 50mm already. If I stick a 25mm in, I’d only have 2mm left of drawtube play, not enough. But I do have a 1″ brass compression extension that I might use and that would use up ~6135 steps of travel, leaving me with ~300. I might or might not use that. So far I haven’t seen a need.

After manually jogging out 27mm/6443 steps out, here’s my initial focus run on SAO 25502, which is Mag 3.7 (4 is recommended, 3.7 is close enough). Puts me at 6423 steps out. Amazingly close to where I manually jogged out.

Since the night was a waste anyways, but I couldn’t do a multi-star collimation with CCDInspector, I just figured I’d take a quick look at rough collimation with the single-star de-focus method CCDInspector also provides. I forgot which star I slewed to, but it was something fairly straight up and fairly bright, but it wasn’t Sirius if I recall. Pushed the drawtube out to 8131 and took an image. Not bad, fairly close.

Pushed the drawtube out to 8331 to de-focus a bit more, and it shows rough collimation to be pretty close. Close enough for imaging work for sure.

Now back to focusing. I wanted to see if my filters were parfocal. Slewed back to SAO25502…

…and did a couple focus runs per filter. Here’s a screenshot of my last luminance focus run.

  • 20:48:   6423 steps out – Luminance
  • 20:52:   6433 steps out – Blue
  • 20:53:   6433 steps out – Red
  • 20:55:   6433 steps out – Green
  • 20:56:   6431 steps out – Luminance
  • 21:24:   6411 steps out – Luminance

That’s pretty close to being parfocal if you asked me…


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