Moonlite Nightcrawler Settings

I just received the Moonlight Nightcrawler and used it on my Orion 80mm triplet last night. I got to focus using a Bahtinov Mask which had me at step 32556 and HFR of 0.77. Following the SGP instructions to figure step size, I went out to step 34700 which gave me a HFR of 2.32. Doing the math, I got like 547 as my ‘step size.’ I’m POSITIVE I’m did something wrong there. I’m curious what others settings are in SGP for those that have the Nightcrawler.

Side note, I thought that when I do a Plate Solve on a previous image from a previous night (to center the scope), the rotator was supposed to kick in and get me lined up. I went through the settings and I believe I have the correct options selected. When it was doing the sequence to center scope, it would give me the pixel errors but rotator error had N/A.

Any assistance would be greatly appreciated! Scopes I’m using are f/6 80mm (with 0.8x reducer) and f/7 115mm (no reducer) refractors with ZWO ASI1600MM-C.

At f6, the critical focus zone is 83 micron in blue.
You can use the calculator here.
http://www.wilmslowastro.com/software/formulae.htm

I’m not sure which NC you have but mine is WR35 and the step size is 0.2667 micron.
So the critical focus zone in steps are 83 / 0.2667 = 311 steps.
Use your step size instead of 0.2667.

You can start with 311 steps.
What I found is that I have to use slightly bigger steps than the critical focus to get a good V curve (due to seeing?).
For me, the critical focus zone in steps is 217 steps but I use 300 as the step size.

Donghun

Donghun,
Excellent info! Exactly the help I was looking for! I have the WR2.5. I think all three formats are 0.2667 microns each step.

I entered data in the formula in the link you attached. With my reducer I believe it puts my scope at f/4.8-ish and the ZWO ASI1600MM-C is 3.8 pixel size. Seems, for Red, I got 274 as critical focus so I should try around 300 or 350 step size.

Not sure the critical focus zone is really the issue with auto focus. The import thing is to give SGP enough HFR data to establish an accurate minimum HFR. You want a statistically valid change in the HFR calculation between data points. As a guide line, you want your max HFR calculation (first one done after focuser is initially moved outward) to be around 4x your minimum HFR. Manually get a decent focus and then play with the auto focus settings, that is, number of focuser steps between data points, to get that 4x range. For example, let’s say best focus produces an HFR reading of 1.0; you would adjust the number of focuser steps between data points so that the worst HFR calculation is around 4.0. Use 9 data points until you can determine that an accurate focus can be achieved with fewer.

One issue to keep in mind, however, is that the more out of focus you go, the dimmer the star images are. If you go too far out of focus on your initial focus frame, SGP may not detect enough stars to do a meaningful HFR calculation. Trial and error are your best friends.

Charlie