Sequences for LRGB Stefan Berg Nighttime Imaging 'N' Astronomy (N.I.N.A. / NINA) · Tony Gondola · ... · 20 · 592 · 1

I'm making the switch to mono imaging and realized that the sequences needed just got a lot more complicated. I'm looking for an example that uses filter offsets and does a center after drift command loop during each filter exposure. This would be for LRGB.

This video is a few years old, but it is still applicable and is what I base all of my sequences from.  

https://youtu.be/Gcekn0lw2IY?si=5h5O3Bb-w3X4WDSx

PatriotAstro has some sequencer templates that you can download and customise. They will do what you require as regards filter offsets and centre after drift https://patriotastro.com/nina-advanced-sequence-downloads/

Do you guide?   If not, ignore this posting.

One thing to consider if you want to improve efficiency is whether your rig can handle focus offsets while continuing to guide.  In other words, if you are guiding and imaging red, then switch filters to blue, can you continue guiding while that occurs? 

In most cases the answer is "no", so you need to stop and restart guiding.  Why "no"?  Because a filter offset (especially if backlash is involved) moves the focuser, and most focusers are not perfect in staying precisely aligned during movement – they will shift the field of view an arc second or a few from that motion.  Which will either cause guiding to loose the star, or more likely to know it moved and start chasing it.  You can partially offset this with some kind of delay, but in reality what you need is a "settle" before you start the next exposure or the impact of chasing the guide star causes a star trail. 

So for most cases you want to build a sequence like this: 

- Shoot 20 red exposures, dithering every 2
- stop guiding
- Change filter
- Start guiding
- Shoot 20 Blue exposures, dithering every 2
- etc
- loop

Note that NINA can handle the stop/start guiding automatically. 

If you have something like a nitecrawler (which are super accurate) and find that changing filers does NOT cause a guide star shift, then it's more efficient to do this:

- Shoot 2 red
- Shoot 2 green
- Shoot 2 blue
- Shoot 2 Luminance 
- Dither
- loop

And NOT have NINA stop/start guiding for filter changes. 

This never stops guiding, and moves the dither to every 8 instead of every 2 (because you don't need to dither between colors).  It's very efficient but only if your rig can do it.  Most cannot.

The recenter after drift is just a trigger somewhere after the  DSO target, nothing special.  I'd also add restart guiding as a trigger. 

I didn't follow any of the first postings temperature change stuff.  I recommend using multiple auto-focus triggers, including large temperature change (if you have a probe), after time, and after HFR change, and maybe just in case every  90 minutes or some such. 

Linwood

Excellent, just the info I'm looking for. Taking everything together, here's what I've come up with:

Beginning Sequence:

wait for time
unpark scope
cool camera

Main Instructions:

set target
slew and center
start guiding

Imaging Loop:  (note, repeat for each filter)

Triggers - meridian flip, center after drift, restore guiding, AF after HFR increase
Loop Conditions - loop for iterations
Instructions - smart exposure

End Sequence:
park scope
warm camera


The repeated imaging loop takes a single smart exposure checks the triggers and the iterations and makes the next exposure an so on. Once that imaging loop is done it goes to the next with the only change being the filter.

Linwood Ferguson:
Do you guide?   If not, ignore this posting.

One thing to consider if you want to improve efficiency is whether your rig can handle focus offsets while continuing to guide.  In other words, if you are guiding and imaging red, then switch filters to blue, can you continue guiding while that occurs? 

In most cases the answer is "no", so you need to stop and restart guiding.  Why "no"?  Because a filter offset (especially if backlash is involved) moves the focuser, and most focusers are not perfect in staying precisely aligned during movement -- they will shift the field of view an arc second or a few from that motion.  Which will either cause guiding to loose the star, or more likely to know it moved and start chasing it.  You can partially offset this with some kind of delay, but in reality what you need is a "settle" before you start the next exposure or the impact of chasing the guide star causes a star trail. 

So for most cases you want to build a sequence like this: 

- Shoot 20 red exposures, dithering every 2
- stop guiding
- Change filter
- Start guiding
- Shoot 20 Blue exposures, dithering every 2
- etc
- loop

Note that NINA can handle the stop/start guiding automatically. 

If you have something like a nitecrawler (which are super accurate) and find that changing filers does NOT cause a guide star shift, then it's more efficient to do this:

- Shoot 2 red
- Shoot 2 green
- Shoot 2 blue
- Shoot 2 Luminance 
- Dither
- loop

And NOT have NINA stop/start guiding for filter changes. 

This never stops guiding, and moves the dither to every 8 instead of every 2 (because you don't need to dither between colors).  It's very efficient but only if your rig can do it.  Most cannot.

The recenter after drift is just a trigger somewhere after the  DSO target, nothing special.  I'd also add restart guiding as a trigger. 

I didn't follow any of the first postings temperature change stuff.  I recommend using multiple auto-focus triggers, including large temperature change (if you have a probe), after time, and after HFR change, and maybe just in case every  90 minutes or some such. 

Linwood

I do guide but with a separate guide scope so I don't think the above would apply.

Tony Gondola:
I do guide but with a separate guide scope so I don't think the above would apply.

You are absolutely correct.  I've been using an OAG so long I tend to forget that there is an alternative (I even own a nice one, sitting on my shelf). 

Yes, you can just keep guiding, of course.

Linwood Ferguson:

Tony Gondola:
The repeated imaging loop takes a single smart exposure checks the triggers and the iterations and makes the next exposure an so on. Once that imaging loop is done it goes to the next with the only change being the filter.

While there's nothing wrong with this, it's more complicated than you may need.  THe smart exposure is itself a built in loop.   Unless you are doing something special in those, you can just do this inside one loop:

Smart exposure X for red (dither every Y)
smart exposure X for green (dither every Y)
etc. 

At least I didn't notice anything special you were doing to have a loop for each filter.

Check me on this but it's my understanding that I can't check for triggers while a smart exposure is in progress. In other words, if I start a smart exposure that's set for 120 exposures the triggers won't be checked until after the 120 exposures are complete. That's why I'm setting each smart exposure to one, so that triggers are checked after each each single exposure.

Linwood Ferguson:

Tony Gondola:
Check me on this but it's my understanding that I can't check for triggers while a smart exposure is in progress. In other words, if I start a smart exposure that's set for 120 exposures the triggers won't be checked until after the 120 exposures are complete. That's why I'm setting each smart exposure to one, so that triggers are checked after each each single exposure.

No, the smart exposure acts like a nested loop, so the triggers will be checked after each individual exposure (and the loop conditions are checked in real time, e.g. if a timer expires or an unsafe condition (if you use that trigger) occurs in the middle of an exposure the exposure is aborted.

Triggers do not only affect the loop they are in, but any loop included inside the trigger's loop.

Ahhhhh, that helps me a bunch!

Tony Gondola:

Linwood Ferguson:

Tony Gondola:
Check me on this but it's my understanding that I can't check for triggers while a smart exposure is in progress. In other words, if I start a smart exposure that's set for 120 exposures the triggers won't be checked until after the 120 exposures are complete. That's why I'm setting each smart exposure to one, so that triggers are checked after each each single exposure.

No, the smart exposure acts like a nested loop, so the triggers will be checked after each individual exposure (and the loop conditions are checked in real time, e.g. if a timer expires or an unsafe condition (if you use that trigger) occurs in the middle of an exposure the exposure is aborted.

Triggers do not only affect the loop they are in, but any loop included inside the trigger's loop.

Ahhhhh, that helps me a bunch!

So in that case I can simplify the imaging loop it to this:

Imaging Loop:

Triggers - meridian flip, center after drift, restore guiding

Loop Conditions - none

smart exposure - xxx red
smart exposure - xxx green
smart exposure - xxx blue
smart exposure - xxx lum


Each smart exposure will run for a specified number of exposures and will check the triggers between each exposure?

Yes, I left those things out for the sake of simplicity, will be added as needed now that I understand the general concept.