Longer focal length SHO imaging - seeking help with NINA/Esatto auto-focus challenges - Forums

Topic starter

Jul 29, 2022

Hi all, after a few years now of imaging small-mid refractors I've taken the plunge to try longer focal length imaging and have purchased a Meade LX850 F8 ACF with 2m focal length. I've fitted this with an Esatto 2 and my ASI294mm (as it has smaller sensor and 2x2 has larger pixels thought it would be an easier start and better match than my ASI2600).

The usual new gear niggles but in the main not so bad and tracking on the CEM120 mostly sub arc second. Have the usual collimation/tilt issues I will work to improve.

The big issue is auto-focussing in NINA (i refocus every filter change - no filters ever seem parfocal enough and as temp shifts so usuallly a dozen or more times a night typically). After hours of trying different settings, night before last, I finally landed on settings that got me decent curves (steps of 4000 and 8000/8000 overshoot backlash in/out). Now that worked great imaging LRGB the NGC253 galaxy, but then last night tried the Helix nebula for some HOO and rubbish...could not get a curve wild up and down even when by eye on the screen I could see focus getting worse better NINA didnt get it. Eventually by bumping up my exposure length to a whopping 20s I got some warped curves that would deliver acceptable focus, but during the night (I can review all the focus results in the morning) it was hit and miss... presumably as the much longer focus runs are far more subject to seeing affects passing cloud etc.

The Helix area doesnt have much by way of stars and they're faint and more-so in SHO... I suspect a lot is to do with simply not enough data to work with. Apart from stupid long exposures what can I do and what do others here do? Are Offsets the answer (focus on say red filter and use offset to set for narrowband?)...if so is there any secret to calculating these or setting up.

I know I should probably post this in a NINA forum, but none exists...there's some thing called "Discord" that's main purpose seems to be to taunt me by giving me anInvite to join that never ever works ... I have higher hopes for fixing my AF issues by accident than ever cracking into NINA Discord ;-)

The previous night when when things worked well enough got me enough data for the image below, which while no masterpiece encouraged me that I can get more detail with this if I get it working well than I can with my refractor.

cheers, rob

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Sean van Drogen

Jul 30, 2022

Yeah NB AF routines need long exposures I had to use 30s with my C9.25. Would highly encourage that you invest time in getting the offsets and work with those as an AF routine with 30s exposures and probably 9 points at minimum will take 4 1/2 minutes which is a lot of lost imaging time if you are doing AF on temp, HFR and filter change.

I always go with L for the AF routine and invested a good hour and half one night to get offset for all filters

Not sure about step size for that focuser but do know you have to pick either in or out for overshoot and not both

Just to try one more time here is the discord link https://discord.gg/nighttime-imaging

CS Sean

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Ruediger

Jul 30, 2022 · Edited: Jul 30, 2022

Hi Rob,

I use 8s, gain=100 with 3.5nm Ha resp. 8s with 4nm O3 at a FL=2563mm and a ASI6200MM. No problems in NINA.
I use 4 points and try to stay below a HFR of 5 when max. unfocused to avoid donuts.
I never tried to use filter offset. I simply run an AF on every filter change.

What also comes to my mind: around Helix area there are not too many stars to use for AF - if I remember correctly. Maybe you try HocusFocus, I use it too, and check statistics and tunes the parameters.

Cheers
Rüdiger

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robonrome

Topic starter

Jul 31, 2022

Sean van Drogen:
Yeah NB AF routines need long exposures I had to use 30s with my C9.25. Would highly encourage that you invest time in getting the offsets and work with those as an AF routine with 30s exposures and probably 9 points at minimum will take 4 1/2 minutes which is a lot of lost imaging time if you are doing AF on temp, HFR and filter change.

I always go with L for the AF routine and invested a good hour and half one night to get offset for all filters

Not sure about step size for that focuser but do know you have to pick either in or out for overshoot and not both

Just to try one more time here is the discord link https://discord.gg/nighttime-imaging

CS Sean

Thanks Sean, much appreciated. That confirms for me likely cause for the focus issue which is halfway to solution and if I eventually have to do offsets will invest the time. If I end up using a reducer may help with the direct approach. I tried Discord again and thought for a moment it had worked, but alas then it said I already had an account and trying to login I got yet another Invite that of course as soon as I clicked said Oops fail or words to that effect... I'm clearly too old and stupid to join ;-)

robonrome

Topic starter

Jul 31, 2022

Ruediger:
Hi Rob,

I use 8s, gain=100 with 3.5nm Ha resp. 8s with 4nm O3 at a FL=2563mm and a ASI6200MM. No problems in NINA.
I use 4 points and try to stay below a HFR of 5 when max. unfocused to avoid donuts.
I never tried to use filter offset. I simply run an AF on every filter change.

What also comes to my mind: around Helix area there are not too many stars to use for AF - if I remember correctly. Maybe you try HocusFocus, I use it too, and check statistics and tunes the parameters.

Cheers
Rüdiger

thanks Ruediger, that's the same narrowband (3.5nm) I'm using here and you're even longer and at a smaller pixel size so I should be able to get it to work.

I suspect it's a particularly bad target the Helix as it has very few and very faint stars in the field. Of course will need some precious clear skies rto sought it out and they are a few days off.

Thanks very much for chiming in with your experience. Means I know it can work!. I've downloaded the Hocus Focus plug in as well and will experiment with it - it might help me resolve tilt issue as well.

cheers Rob

Ruediger

Jul 31, 2022 · Edited: Jul 31, 2022

Ruediger:
Hi Rob,

I use 8s, gain=100 with 3.5nm Ha resp. 8s with 4nm O3 at a FL=2563mm and a ASI6200MM. No problems in NINA.
I use 4 points and try to stay below a HFR of 5 when max. unfocused to avoid donuts.
I never tried to use filter offset. I simply run an AF on every filter change.

What also comes to my mind: around Helix area there are not too many stars to use for AF - if I remember correctly. Maybe you try HocusFocus, I use it too, and check statistics and tunes the parameters.

Cheers
Rüdiger

thanks Ruediger, that's the same narrowband (3.5nm) I'm using here and you're even longer and at a smaller pixel size so I should be able to get it to work.

I suspect it's a particularly bad target the Helix as it has very few and very faint stars in the field. Of course will need some precious clear skies rto sought it out and they are a few days off.

Thanks very much for chiming in with your experience. Means I know it can work!. I've downloaded the Hocus Focus plug in as well and will experiment with it - it might help me resolve tilt issue as well.

cheers Rob

Hi Rob,

You are welcome! I had not mentioned that I use binning 2.

Here also a link to a very useful video about Hocus Focus: https://www.youtube.com/watch?v=M1-izvBlO44

Especially the part about getting the detected stars displayed might be in your case very helpful.
Tonight I ran into exactly the same issue like you for the very first time, but I could quickly fix it by analysing the detected stars in Hocus Focus. It was the firs time I had to increase the exposure time significantly.

CS
Rüdiger

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Linwood Ferguson

Aug 1, 2022

I use NINA and a C11, and want to echo the suggestion to get focus offsets working. Point to a star right area high in the sky one night and invest a couple hours in 3-4 runs through the offset calculator. Best done after the temperature stabilizes to minimize temperature effects, and set exposure as long as needed to get good focus curves on the NB filters (test it before you start the full run).

Once you get filter offsets, you are generally done – you focus with one filter (I use red as I think, maybe, possibly it helps with seeing, most use luminance) and it just adjusts. And no focus on filter changes. With a litecrawler (which has near zero lateral motion as it focuses) I do not even stop guiding for filter changes, so now I run through the filters 2 exposures each, and dither only at the end of the cycle - saves all sorts of guiding start/stop time.

The filter offset calculator works quite well, provided you give it time to run several iterations (no less than 3 IMO, 4 if you can), and provided you do not run it on a night when the temperature has huge change over the time you run it. It averages out some change, of course.

If slightly paranoid (which if you are not you are in the wrong hobby) you can do it again another night, compare numbers, see if they are reasonably consistent.

In Hocus Focus there are some defaults to change for long focal length (on the options, should be obvious, not looking at the screen now) for bloated stars and long focal length.

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robonrome

Topic starter

Aug 1, 2022

Thanks Linwood, that's great guidance and very helpful. Gives me confidence to give this Filter Offset approach a try when conditions permit. Haven't tried Hocus Focus yet, but have it installed and about to watch the Patriot Astro video on it. Have learned a lot from that guy on NINA. Thanks again rob

Linwood Ferguson

Aug 1, 2022

There are a ton of features with Hocus Focus but most of them relate to the aberration detector and to a lesser degree the differences in star detection. To a large degree HF just operates as the standard NINA AF routine, only better. The one exception are the settings in the plugin, options, star detector. Set the Pixel Scale to Long Focal Length and Focus Range to Wide Range (I'm in front of the screen now).

As you watch the videos, when they go off onto tilt, backfocus, etc. unless you are ready to tackle that can of worms, just ignore it.

For questions, there is a dedicated channel on Discord under NINA for Hocus Focus as well as Auto Focus (for general help), and the authors of all parts of this frequent it and help.

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