What is your preferred image acquisition workflow to acquire the best possible data?

Acquisition Auto-Focusing Narrowband Deep Sky
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Steeve Body avatar
Steeve Body avatar
The goal is quality over quantity… so I’m reassessing if what I’m doing here could be improved. Keen to your all your insight on the subject.
I’ve been using filter offsets for a while and have an advance sequence setup in Nina that does the following loop:
Slew, plate solve and rotate to target
autofocus on L filter
using filter offsets capture 1 x 600s Ha, Oiii and Sii then 3 x 15s R, B and G
dither 5 px
loopback to beginning.
Triggers are: If HFR moves by more than 10% refocus. If focus fail wait 2 min and retry, Up to 20 attempts (mostly to stop capturing and wait when clouds are passing by)

The advantage of this method is that I average the seeing on all filters and capture everything I need to make an in each session but the disadvantage is that the focusing may not be ultimate since I’m using offsets and that is not temperature compensated and does not account for any atmospheric turbulence or the altitude of the target… so I’m thinking my method may not yield the best possible data.
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Daniel.P avatar
Daniel.P avatar
Hello Steve,
For R G B, I guess you meant 3 x 150 sec (not 15 sec)  ?

I have no experience in refocusing based HFR.
I would see however 2 problems in doing it this way :
- if the seeing deteriorate, you will keep triggering  autofocus with no improvement
- if the seeing keep improving, you may delay autofocus (due to temp change) and loose some improvement in image quality

I agree with you that rotating filter make quality more equal across them.
I dont think that filter offsets is a problem if they are carefully calibrated. With SGP, I am using temperature compensation and filter offsets, but I refocus if temp change more than 2.5 deg and every 2 hours max.

Daniel
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Steeve Body avatar
Steeve Body avatar
Hello Steve,
For R G B, I guess you meant 3 x 150 sec (not 15 sec)  ?

I have no experience in refocusing based HFR.
I would see however 2 problems in doing it this way :
- if the seeing deteriorate, you will keep triggering  autofocus with no improvement
- if the seeing keep improving, you may delay autofocus (due to temp change) and loose some improvement in image quality

I agree with you that rotating filter make quality more equal across them.
I dont think that filter offsets is a problem if they are carefully calibrated. With SGP, I am using temperature compensation and filter offsets, but I refocus if temp change more than 2.5 deg and every 2 hours max.

Daniel

Hey Daniel, no I indeed use 15sec RGB because this is for a star image only to add RGB stars to my NB data… I get 100s of exposures per filters and then select the best one to make a star image with tight rgb stars that are similar in size to my NB stars. 

true about the HFR trigger… I didn’t think of that
Daniel.P avatar
Daniel.P avatar
Hello Steve,

I see your point for getting the best tightest stars in RGB. This is a good idea.

Alternatively, what you may try to keep the good size of the NB stars, is to apply the (color channels of the RGB data and the Lum channel of the NB image) onto the NB image under a star mask (in PI). This just turn the NB image stars to the right color.
Steven avatar
Steven avatar
Personally I don't switch filters that often and stay on a filter for a long time.
Going for 10-20 x 600 seconds on Ha before switching to Sii.. and staying on that filter for a while before switching to Oiii.

There are even nights where I'd only use 1 filter the entire night; like Oiii during a new moon.. Or Ha/Sii during a bright moon.

I don't know if changing filters often would be better. The idea of "averaging seeing conditions" is ok I guess (?). But since I'm usually working on a target for many nights, over a long period of time (weeks?), I'm averaging out the seeing conditions already. + I change the order of the Ha/Sii/Oiii, so that I don't always shoot one at the same time/height above the horizon, so averaging it out that I will always have some data of a target at its highest point of the sky.


Another reason: 
I also would lose out on a minute after each filter change for the auto focussing routine (And of course; every one of those routines could fail, and ruin the focus for the rest of the night if it loses focus a lot)..  - So.. I'd rather keep the auto focussing limited, and therefor the filter switching limited too.
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Steeve Body avatar
Steeve Body avatar
Hello Steve,

I see your point for getting the best tightest stars in RGB. This is a good idea.

Alternatively, what you may try to keep the good size of the NB stars, is to apply the (color channels of the RGB data and the Lum channel of the NB image) onto the NB image under a star mask (in PI). This just turn the NB image stars to the right color.

I could indeed also try that.. just to clarify, you mean using channel extraction tool in PI on the star RGB image and get the a and b channel information and then apply that using the channel combination tool to the NB + HA Stars processed image with a star mask applied…? Is that the method to do this? the one issue I have with adding RGB starts onto starless narrow band is that some stars that are on the top of bright parts of the nebula get blown out and have to be individually addressed…
Steeve Body avatar
Steeve Body avatar
Personally I don't switch filters that often and stay on a filter for a long time.
Going for 10-20 x 600 seconds on Ha before switching to Sii.. and staying on that filter for a while before switching to Oiii.

There are even nights where I'd only use 1 filter the entire night; like Oiii during a new moon.. Or Ha/Sii during a bright moon.

I don't know if changing filters often would be better. The idea of "averaging seeing conditions" is ok I guess (?). But since I'm usually working on a target for many nights, over a long period of time (weeks?), I'm averaging out the seeing conditions already. + I change the order of the Ha/Sii/Oiii, so that I don't always shoot one at the same time/height above the horizon, so averaging it out that I will always have some data of a target at its highest point of the sky.


Another reason: 
I also would lose out on a minute after each filter change for the auto focussing routine (And of course; every one of those routines could fail, and ruin the focus for the rest of the night if it loses focus a lot)..  - So.. I'd rather keep the auto focussing limited, and therefor the filter switching limited too.


Personally I don't switch filters that often and stay on a filter for a long time.
Going for 10-20 x 600 seconds on Ha before switching to Sii.. and staying on that filter for a while before switching to Oiii.

There are even nights where I'd only use 1 filter the entire night; like Oiii during a new moon.. Or Ha/Sii during a bright moon.

I don't know if changing filters often would be better. The idea of "averaging seeing conditions" is ok I guess (?). But since I'm usually working on a target for many nights, over a long period of time (weeks?), I'm averaging out the seeing conditions already. + I change the order of the Ha/Sii/Oiii, so that I don't always shoot one at the same time/height above the horizon, so averaging it out that I will always have some data of a target at its highest point of the sky.


Another reason: 
I also would lose out on a minute after each filter change for the auto focussing routine (And of course; every one of those routines could fail, and ruin the focus for the rest of the night if it loses focus a lot)..  - So.. I'd rather keep the auto focussing limited, and therefor the filter switching limited too.

Your making some valid points there. However for me being in Melbourne this may not be practical though as I don’t get a lot of good nights, so I need to maximise my acquisition time since having 1 good night per filter could very well take me a month…. This winter has been the worst in living memory for us down here ( thanks to La Niña)… I have had 6 nights of clear sky in about 3 months so far….

One more thing for me is that I love live stacking and staring at the data coming in to get an idea of noise profile and how much more time I need to get a SNR I’m happy with… it is a little guilty pleasure of mine and I would loose that…  

I never had a focus routing fail on me unless a cloud passed by… so If i trigger focusing on each filter change and loose data due to cloud passing by I guess that is probably not a big deal… but I would loose focus time though.. in theory if I did 10 x 600s shots in Ha, Oiii and Sii in one night and refocused at every filter change by rotating the filters at every round I would loose around 1h in refocusing time which is a lot… I guess I could do 2 x 600s per filter before swiping filter and refocusing to 1/2 that, which is a little more acceptable… hopefully I can strike the right balance
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Steven avatar
Steven avatar
Steeve Body:
, so I need to maximise my acquisition time since having 1 good night per filter could very well take me a month….


Well.. that's astrophotography  A hobby of patience. 

We all try and maximise the time we have. if you really want to do that, I'm going to be the "evil person" that suggests multiple rigs! 
While financially not the best solution, it has made the biggest change/improvement to my acquisition and the amount of targets I can hit.

Right now I usually do different targets with the 3 rigs.. - in an ideal world I'd have a rig with 3 identical camera's, 3 identical lenses/scopes on 1 mount.. Each working on their own filter. Maximising a 6 hour imaging window into 18 hours worth of data on a single target... - But the ASIAIR isn't great such a setup.... a man has to dream I guess...  and I'm more than happy turning a 6 hour window into 6 hours per target.
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