Moonlight NightCrawler Focuser at Remote Site

Jerry Gerber · Oct 21, 2025, 07:25 AM

AstroStew · Oct 21, 2025, 07:17 AM

Jerry Gerber · Oct 21, 2025 at 06:44 AM

I’m noticing the Moonlight Nightcrawler (WR3.5) focuser is taking between 3.5 and 4 minutes to focus. This is done remotely, my telescope is at a remote site. It’s been homed this afternoon.

Is there a way to speed up this process? If it focuses 20 times throughout the night, that’s nearly 80 minutes of time not imaging. I take 5 second focus exposures when using LRGB filters and 8 second exposures when using SHO filters. My autofocus step size is 500.

I have the focuser set to AF After HFR Increase (sample size 10, amount 5%).

Thanks,

Jerry

The only way to speed up a focus routine, is to shorten the focus exposures, shorten the amount of steps and shorten the step size, and increase the HFR increase to 10% will limit the amount of times it focuses. 👍🏻

I’ve read that small step size can increase focus time?? I am noticing my autofocus is running about every 15 minutes.

Hi Jerry,

The steps should be ‘just right’ - too small steps it will need to run much more samples to get the min in the curves (the sharpest or most focused point), too large steps it might not get the resolution to really focus well. 4 minutes seems excessive - maybe try to lower the exposure (I lowered it from 5 to 3 seconds for both - broadband and narrowband) and get number of points (in combination with ‘just right’ step) as low as possible. Check and try to lower also settling time after focuser change.

15 minutes (through all night?) is for sure much too often. First ~1.5 - 2 hours I autofocus at period of around 45 minutes because FSQ106 is notorious for slow cool-down, but after temperature stabilizes I don’t need to run it for long time (1.5-2hours or even longer), except if I change filters of course.

You should check what is triggering auto-focus every 15 minutes. You should also check HFR at start and at the end of auto-focus: If it’s approximately the same, for sure you don’t need autofocus so often.

If you are triggering on HFR change it might be that you have some guiding issues which is triggering autofocus. I had problems with my mount and got a lot of bad frames which were triggering autofocus, so I disable it during that period and trigger only on temperature change (trigger when temperature delta of 1°C).

CS,

Jure

Jerry,

Being at a dark site, I think you could get away with shorter focusing exposures. Also, I’m surprised it runs so often using the HFR method. That does almost sound like guiding or something else is incorrectly setting it off once the telescope is thermally stabilized.

Also, that step size seems big. But, I use a ZWO EAF, not the Nightcrawler so I am not sure of its resolution, but I assume it’s greater.

I developed my settings by running through the NINA autofocus guide , “Determining Ideal Parameters” section. By using this guide I was able to develop the autofocus settings (specifically step size and exposure time) that work for me, with the shortest routine runtime. Approx. 2-3 minutes every 45min-2hr depending on thermals.

Good luck!

-Chris

Kevin Morefield · Oct 21, 2025, 02:23 PM

Jerry,

You should base your refocus trigger on temperature change rather than HFR. The HFR can change rapidly with seeing fluctuations and that has nothing to do with focus.

Maybe start with 1 degree C temp change as a trigger and see how that goes.

My focus runs in NINA with the Moonlite take about two minutes. So looking at your setting and optimizing them can surely shorten the time. Dedicate a night to doing successive focus runs with different filters and settings till you get a shorter run that works repeatedly.

That trial and error approach is how most of us learned our software and hardware.

Kevin

Agreed. I gave up on the HFR trigger because seeing HFR deviations are often larger than focus shift HFR variations. I also found temp change triggers were a little fiddly as well. I settled on time and filter change based AF. Generally focus every 30-45 minutes early in the session since the TOA130 takes a long time to settle and then about every hour through the night. Focusing with my Moonlite Nitecrawler takes about 2 minutes. Use 1 second for L, 2 for RGB and 6 for HSO.

Dark Matters Astrophotography · Oct 21, 2025, 10:11 AM

Jerry Gerber · Oct 21, 2025, 06:44 AM

I’m noticing the Moonlight Nightcrawler (WR3.5) focuser is taking between 3.5 and 4 minutes to focus. This is done remotely, my telescope is at a remote site. It’s been homed this afternoon.

Is there a way to speed up this process? If it focuses 20 times throughout the night, that’s nearly 80 minutes of time not imaging. I take 5 second focus exposures when using LRGB filters and 8 second exposures when using SHO filters. My autofocus step size is 500.

I have the focuser set to AF After HFR Increase (sample size 10, amount 5%).

Thanks,

Jerry

Jerry,

You have posted dozens of times here — are you sure you are equipped to run remotely? It seems the more you run your system, the more you need feedback from others — far more than any other remote imager I have ever seen, and on manners so basic it is hard to not say anything about it.

Answer: Use Voyager, it focuses 10 times faster than NINA.

-Bill

Bill—Did you wake up with back pain or a stomach ache? I’ll ignore your unhelpful condescending tone.

Jure Menart · Oct 21, 2025, 07:41 AM

Jerry Gerber · Oct 21, 2025, 07:25 AM

AstroStew · Oct 21, 2025, 07:17 AM

Jerry Gerber · Oct 21, 2025 at 06:44 AM

I’m noticing the Moonlight Nightcrawler (WR3.5) focuser is taking between 3.5 and 4 minutes to focus. This is done remotely, my telescope is at a remote site. It’s been homed this afternoon.

Is there a way to speed up this process? If it focuses 20 times throughout the night, that’s nearly 80 minutes of time not imaging. I take 5 second focus exposures when using LRGB filters and 8 second exposures when using SHO filters. My autofocus step size is 500.

I have the focuser set to AF After HFR Increase (sample size 10, amount 5%).

Thanks,

Jerry

The only way to speed up a focus routine, is to shorten the focus exposures, shorten the amount of steps and shorten the step size, and increase the HFR increase to 10% will limit the amount of times it focuses. 👍🏻

I’ve read that small step size can increase focus time?? I am noticing my autofocus is running about every 15 minutes.

Hi Jerry,

The steps should be ‘just right’ - too small steps it will need to run much more samples to get the min in the curves (the sharpest or most focused point), too large steps it might not get the resolution to really focus well. 4 minutes seems excessive - maybe try to lower the exposure (I lowered it from 5 to 3 seconds for both - broadband and narrowband) and get number of points (in combination with ‘just right’ step) as low as possible. Check and try to lower also settling time after focuser change.

15 minutes (through all night?) is for sure much too often. First ~1.5 - 2 hours I autofocus at period of around 45 minutes because FSQ106 is notorious for slow cool-down, but after temperature stabilizes I don’t need to run it for long time (1.5-2hours or even longer), except if I change filters of course.

You should check what is triggering auto-focus every 15 minutes. You should also check HFR at start and at the end of auto-focus: If it’s approximately the same, for sure you don’t need autofocus so often.

If you are triggering on HFR change it might be that you have some guiding issues which is triggering autofocus. I had problems with my mount and got a lot of bad frames which were triggering autofocus, so I disable it during that period and trigger only on temperature change (trigger when temperature delta of 1°C).

CS,

Jure

Thanks Jure!

Why does it take so long to focus? Is it just slow when it’s moving?

I have not used a Moonlight NightCrawler, but a tip a NINA developer told me for my ZWO EAF: Decrease your device polling interval down to 0.5 (or even 0.35) seconds. The default is 2 seconds, which is a safe default, but autofocus runs can be made much faster if you decrease it.

Also: Just to confirm, do you have filter offsets set up? Focusing 20x in one night is surprising to me… I usually only need to focus maybe 3-4 times with offsets properly configured.

Jerry Gerber · Oct 21, 2025, 06:54 PM

I made an adjustment to NINA’s polling interval time because NINA’s logs were warning that my GM1000 mount was taking too long to respond. This stopped the warning but it seems that this polling interval time applies to every device NINA is connected to, so I am now wondering if the focuser has slowed down because I changed the interval time from 2 to 10. I can change it back to 2 and live with the Log’s warning as that’s far better than having my focuser take so long. I am not even sure that the polling interval time is affecting the focuser, but I think it might be…

Any thoughts?

Jerry

Just asked the NINA dev. He says that all device polling is indeed affected by that same setting.

If your mount behaves normally with a 2-second polling interval (and only logs warnings in NINA), I would definitely try lowering it again. At least for one night to see if that fixes things. It should actually speed up a lot of actions in NINA, so you might find that your whole sequence is much snappier.

I use 1s exposures for LRGB filters and 3s for my narrowband filters on my TOA-130 at f/7.6. Focus runs about 2.5 minutes each.

I am also perplexed at the suggestion to switch from NINA to Voyager. 10 times faster? I would be shocked if any software out there can run a FF sensor AF routine in 15 seconds.

Arun H · Oct 21, 2025, 04:21 PM

the real question here is why you need to focus so often - 20 times a night an absurdly high number. If there is a mechanical drift in your system, you need to address that rather than use focus to compensate. You appear to be using an f/7.6 system, which should be quite forgiving to small drift.

That’s not the real question. I check and adjust focus my system every 6 seconds or so and I see focus drift all the time and sometimes it happens on a pretty short time scale. The real question is: How do you keep focus within the depth of focus for your particular system under varying environmental conditions. The chart below shows how to compute the thermal sensitivity for a Cassegrain type system using (for example) an aluminum OTA structure.

📷 Cassegrain Thermal Stability with Temperature 2-19-19.jpgThe chart below show a computation of the temperature sensitivity for various telescopes using both the known CTE for the OTA and the dn/dT values for refractor objectives. The calculation uses a conservative measurement of the maximum rate of environmental temperature drift that I measured at my site in Oregon. Obviously the more stable the environment, the less focus will drift but these are reasonable starting points to see what works best at your own site.

📷 List of Telescope Sensitivity to Temp 2-19-19.jpgNone of these numbers take into account any mechanical flexure that may affect focus changes due to the changing load on the OTA structure as the telescope tracks. That is often not an insignificant effect; although in most cases, it will be slowly varying.

The fastest variation in focus is most often due to seeing itself. The strongest aberration that seeing induces is normally tilt but I’ve seen nights where that’s not the case. Rapid focus variations can be the most significant factor that drives the seeing limit. There are also times when seeing induced focus variation changes “slowly” (<~1 minute) under fairly stable atmospheric conditions as “waves” of index variations slowly roll through the light column.

Here’s a night with superb seeing with a fairly stable focus signal.

📷 image.pngHere is what it looks like when the focus signal transitions from being unstable to being much more stable—all due to how the stability of the atmosphere affects the focus term in the wavefront.

📷 image.pngClearly, if the atmospheric conditions are very stable, you don’t have to check focus very often but you rarely know what it’s going to do a priori. The trick is to check focus as frequently a possible in a way that it doesn’t take any time away from your total imaging time. That’s is the key advantage of ONAG. Focusing is done in real time, while the shutter is open with zero time penalty. ONAG isn’t possible on all systems and in that case, I agree that the best strategy is to use temperature sensing to trigger focusing events. If it requires focusing 20 times in a night, that’s what it takes.

- John

John Hayes · Oct 22, 2025, 05:33 AM

Arun H · Oct 21, 2025, 04:21 PM

the real question here is why you need to focus so often - 20 times a night an absurdly high number. If there is a mechanical drift in your system, you need to address that rather than use focus to compensate. You appear to be using an f/7.6 system, which should be quite forgiving to small drift.

That’s not the real question. I check and adjust focus my system every 6 seconds or so and I see focus drift all the time and sometimes it happens on a pretty short time scale. The real question is: How do you keep focus within the depth of focus for your particular system under varying environmental conditions. The chart below shows how to compute the thermal sensitivity for a Cassegrain type system using (for example) an aluminum OTA structure.

📷 Cassegrain Thermal Stability with Temperature 2-19-19.jpgThe chart below show a computation of the temperature sensitivity for various telescopes using both the known CTE for the OTA and the dn/dT values for refractor objectives. The calculation uses a conservative measurement of the maximum rate of environmental temperature drift that I measured at my site in Oregon. Obviously the more stable the environment, the less focus will drift but these are reasonable starting points to see what works best at your own site.

📷 List of Telescope Sensitivity to Temp 2-19-19.jpgNone of these numbers take into account any mechanical flexure that may affect focus changes due to the changing load on the OTA structure as the telescope tracks. That is often not an insignificant effect; although in most cases, it will be slowly varying.

The fastest variation in focus is most often due to seeing itself. The strongest aberration that seeing induces is normally tilt but I’ve seen nights where that’s not the case. Rapid focus variations can be the most significant factor that drives the seeing limit. There are also times when seeing induced focus variation changes “slowly” (<~1 minute) under fairly stable atmospheric conditions as “waves” of index variations slowly roll through the light column.

Here’s a night with superb seeing with a fairly stable focus signal.

📷 image.pngHere is what it looks like when the focus signal transitions from being unstable to being much more stable—all due to how the stability of the atmosphere affects the focus term in the wavefront.

📷 image.pngClearly, if the atmospheric conditions are very stable, you don’t have to check focus very often but you rarely know what it’s going to do a priori. The trick is to check focus as frequently a possible in a way that it doesn’t take any time away from your total imaging time. That’s is the key advantage of ONAG. Focusing is done in real time, while the shutter is open with zero time penalty. ONAG isn’t possible on all systems and in that case, I agree that the best strategy is to use temperature sensing to trigger focusing events. If it requires focusing 20 times in a night, that’s what it takes.

- John

This makes sense to me John. I am currently experimenting with autofocus using a 1.67c temperature change threshold, using a 1000mm refractor. This corresponds to your chart above, as I notice the autofocus occurring about every 40-45 minutes. The seeing is good tonight, about 1.09”. If on a night where the seeing isn’t so good, I think it would be a good idea to perhaps reduce the temperature threshold to 1.5c or even 1c, but if it’s the seeing that is producing the focusing challenges rather than just the temperature why not autofocus to HFR rather than temperature? I also notice that when I look at tilt data it changes from sub to sub, they’re not large changes, which seems to confirm what you’ve said about seeing affecting tilt.

Thank you for the clarification, Jerry.

Recently, I revisited my focusing routine and noticed that changing NINA’s autofocus noise reduction setting resulted in a different HFR reading. While it makes sense when you think about it, I was surprised at first. This is something to keep in mind.

Clear skies