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Cycling through filters with offsets to improve imaging efficiency, does it wear on the EFWs and focusers?

Acquisition Sequencing LRGB Deep Sky
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Ashraf AbuSara avatar
Ashraf AbuSara avatar
Hello,

I am looking into improving my imaging efficiency, especially for LRGB imaging. I am in the process of incorporating target scheduler into my imaging sequence in NINA, and I am going to move forward with looking at the most time efficient way of doing acquisition to improve imaging time. 

Was watching Chris Woodhouse excellent series of videos going over TS:  https://www.youtube.com/watch?v=CfpkKCvf6pg&t=2s

In his video he goes briefly over acquiring images where he goes:

L x2 > R x2 > G x2 > B x2 > Dither.

So every two exposures, both his focuser and filter wheel are working, which puts significantly more movement on those devices.

My two concerns are wear on the focuser, and the EFW. My other concern is if moving the EFW so much during the night can introduce movement in dust motes or new defects that could be difficult to deal with flats. 

I will be doing this in remote imaging setups that will get thousands of hours of integration a year. 

Would love to hear everyone's thoughts on this. Thanks.
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AstroRBA avatar
AstroRBA avatar
Hi Ashraf - I've noticed occasional instances where the filter wheel position (ZWO) settles a tiny bit off and then does introduce those artifacts that you mentioned (and moving in always in one direction only of course). I would be cautious about this myself but then again maybe I've just had bad luck? My backyard rig can also see some wild temperature and humidity swings which might also contribute? Wear and tear is probably not an issue, as manufacturing is pretty good these days, but I guess trying it out is the best way to find out?
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Ashraf AbuSara avatar
Ashraf AbuSara avatar
Hi Ashraf - I've noticed occasional instances where the filter wheel position (ZWO) settles a tiny bit off and then does introduce those artifacts that you mentioned (and moving in always in one direction only of course). I would be cautious about this myself but then again maybe I've just had bad luck? My backyard rig can also see some wild temperature and humidity swings which might also contribute? Wear and tear is probably not an issue, as manufacturing is pretty good these days, but I guess trying it out is the best way to find out?

Thanks! I will give it a test tonight and see how it goes.
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Tony Gondola avatar
Tony Gondola avatar
When you think about how many rotations of the FW or anything else, it's trivial compared to common items. If the moving parts are made out of reasonable materials I think it would be a very long time before any evident wear shows up. It always amuses me to see guys replacing perfectly good steel ball bearings in mounts just because. How many full rotations will a mount do in year can compared to something that runs at  say 500 rpm, 2 hours each day.
Rafał Szwejkowski avatar
Rafał Szwejkowski avatar
I've been doing it for years and had no issues with the wear on the parts.

However the filters shift slightly - but it's not a huge problem if you have a "fast" system.  At f/6 or slower calibration is definitely an issue; one of the reasons I shoot L without any filters in my RCs is to avoid being impacted by filter misalignment.
Gary Seven avatar
Gary Seven avatar
I have been doing this for years using the Patriot Astro scripts. No issues.

My sequence is:

G
L  x 3 (dither after each)
B
R
Dither

This is based on the focuser offsets relative to the L filter (for backlash compensation).

I'll have to watch the Woodhouse video you linked to and see why he is doing equal weighting between the color and luminance.
Ashraf AbuSara avatar
Ashraf AbuSara avatar
Tony Gondola (Gondola)When you think about how many rotations of the FW or anything else, it's trivial compared to common items. If the moving parts are made out of reasonable materials I think it would be a very long time before any evident wear shows up. It always amuses me to see guys replacing perfectly good steel ball bearings in mounts just because. How many full rotations will a mount do in year can compared to something that runs at  say 500 rpm, 2 hours each day.

Good point. I suppose the issue is that the tolerance for "wear" maybe different in our applications compared to something else. Just gradual "sag" in the device or increasing inaccuracy could cause significant problems in our flats and aquisition. Will the EFW stop switching filters? probably not, but can it become less precise in its rotations? That's the question I am trying to gauge. But maybe my concern is overblown. 
Rafał Szwejkowski:
I've been doing it for years and had no issues with the wear on the parts.

However the filters shift slightly - but it's not a huge problem if you have a "fast" system.  At f/6 or slower calibration is definitely an issue; one of the reasons I shoot L without any filters in my RCs is to avoid being impacted by filter misalignment.

That's my concern too, because I would be doing this with my TOA that runs at f/7.6. 
Gary Seven:
I have been doing this for years using the Patriot Astro scripts. No issues.

My sequence is:

G
L  x 3 (dither after each)
B
R
Dither

This is based on the focuser offsets relative to the L filter (for backlash compensation).

I'll have to watch the Woodhouse video you linked to and see why he is doing equal weighting between the color and luminance.

You know I completely glossed over that too. You are right, I don't want to get 1:1:1:1 with my LRGB sequence either. I need to look into what would be he most efficient way of getting 3:1:1:1 or 4:1:1:1.
CraigT82 avatar
CraigT82 avatar
For sequencing I don’t bother with a set plan, I’ll see what the seeing is like first after the first few subs then decide whether I want to dedicate the night to luminance (if seeing is good) or RGB (if seeing isn’t great). Don’t want to waste a night of great seeing shooting colour…. If I already have L then I’ll move onto another target and shoot L some more. 

Also for the wear question I wouldn’t worry about it. Us astrophotographers always have our eye on the next upgrade, and you’ll most likely be getting a twitchy wallet and be wanting to switch up your focuser/wheel/whole scope long before any wear starts to become an issue!
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Ashraf AbuSara avatar
Ashraf AbuSara avatar
For sequencing I don’t bother with a set plan, I’ll see what the seeing is like first after the first few subs then decide whether I want to dedicate the night to luminance (if seeing is good) or RGB (if seeing isn’t great). Don’t want to waste a night of great seeing shooting colour…. If I already have L then I’ll move onto another target and shoot L some more. 

Also for the wear question I wouldn’t worry about it. Us astrophotographers always have our eye on the next upgrade, and you’ll most likely be getting a twitchy wallet and be wanting to switch up your focuser/wheel/whole scope long before any wear starts to become an issue!

Hey Craig, 

I agree that would be ideal.  But from my remote locations, I can have bad seeing at the beginning of the evening, and impeccable seeing towards the end of the same evening, and vice versa. I gave up on trying to predict my seeing conditions and just shoot whatever I need at a given time, and sometimes more and just use subframe selector to decide what I need to keep.

Also what I am trying to accomplish is a hands off, automated operation, where not only do I not micro manage the sequence, but in fact let the plugin chose the most suitable target at any given moment in time without my intervention. 

As far as upgrades for the focusers and EFW, they are already the best avaible, including a Moonlight WR35 focuser, and an Optec Leo, both are not things I ever anticipate upgrading. The EFWs are ZWO and Player one, so not the same quality and caliber as the focusers, but are not something I would anticipate upgrading in the future either since they are already housing 50mm round unmounted filters in 7 poisitions.
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Alex Nicholas avatar
Alex Nicholas avatar
I agree with Craig on this..

I shoot what the weather conditions are best suited to. 
Monitoring my guiding, if I'm seeing nice steady stars in guide exposures, and the resultant guide error is > 0.4", I'm shooting Lum or 10min long narrowband subs, if things are a little less stable, then I will split the time between R G and B, usually just setting a schedule to shoot n*R, n*G and n*B, however, I have used NINA's advanced sequencer to runs of 2, 2 and 2 for RGB data, as I have filter offsets calculated and working perfectly… so I lose CONSIDERABLY less time to AF passes, and dither operations. 

If the night is clear, moonless and seeing is very steady, I'm shooting L for as long as those conditions hold out… I've made successful images with 5:1:1:1 ratio's, but typically aim for 3:1:1:1 for LRGB, and 2:1:2 for SHO images.

I honestly do not think that changing filters or changing focus position regularly is going to significantly shorten the lifespan of your equipment. Look at the MTBF for the components in question, it should be rated in the hundreds of thousands of hours… and moving the focuser ~50 steps takes, what, 1 second? or less? think about how many 1s movements fit into a 100,000h time frame, for a $200 part… (which, despite the likes of ZWO not wanting you to know, is just a fancy housing and microcontroller for a $15 stepper motor that is replaceable…. 

Don't worry about focusing or changing filters regularly. Capture your data however you feel is the most efficient to you!
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Arun H avatar
Arun H avatar
I would be concerned that as the mechanism wears, repeatable reposition I h of the filter wheel becomes an issue. Especially with LRGB filter in light polluted zones that can cause issues with flat field correction. If you use filters in sequence and take immediate or same night flats it could be a smaller concern.
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Dunk avatar
Dunk avatar
Ashraf AbuSara:
So every two exposures, both his focuser and filter wheel are working, which puts significantly more movement on those devices.


If you use filter offsets you only need to focus once at the start of the session (assuming no focus-drift) - which means less impact on the focuser.

Astro with RoRo made a good video about this and some other tricks:  https://youtu.be/d4dlh5Yzv80?si=k8tjsgqvRt7-vuME
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Ashraf AbuSara avatar
Ashraf AbuSara avatar
Arun H:
I would be concerned that as the mechanism wears, repeatable reposition I h of the filter wheel becomes an issue. Especially with LRGB filter in light polluted zones that can cause issues with flat field correction. If you use filters in sequence and take immediate or same night flats it could be a smaller concern.

Yes exactly. I can't take immediate flats for sure and it would be prohibitive to do so. Daily flats are doable though. 

Dunk:
Ashraf AbuSara:
So every two exposures, both his focuser and filter wheel are working, which puts significantly more movement on those devices.


If you use filter offsets you only need to focus once at the start of the session (assuming no focus-drift) - which means less impact on the focuser.

Astro with RoRo made a good video about this and some other tricks:  https://youtu.be/d4dlh5Yzv80?si=k8tjsgqvRt7-vuME

What filter offsets do is that every time you switch the filter, the focuser is moving by the offset amount, as opposed to say once every hour or two when running a focus routine. I suppose it is a very small distance, and likely is of no effect on high quality focusers like the NC or the Leo in the long run.
Ashraf AbuSara avatar
Ashraf AbuSara avatar
Alex Nicholas:
I agree with Craig on this..

I shoot what the weather conditions are best suited to. 
Monitoring my guiding, if I'm seeing nice steady stars in guide exposures, and the resultant guide error is > 0.4", I'm shooting Lum or 10min long narrowband subs, if things are a little less stable, then I will split the time between R G and B, usually just setting a schedule to shoot n*R, n*G and n*B, however, I have used NINA's advanced sequencer to runs of 2, 2 and 2 for RGB data, as I have filter offsets calculated and working perfectly... so I lose CONSIDERABLY less time to AF passes, and dither operations. 

If the night is clear, moonless and seeing is very steady, I'm shooting L for as long as those conditions hold out... I've made successful images with 5:1:1:1 ratio's, but typically aim for 3:1:1:1 for LRGB, and 2:1:2 for SHO images.

I honestly do not think that changing filters or changing focus position regularly is going to significantly shorten the lifespan of your equipment. Look at the MTBF for the components in question, it should be rated in the hundreds of thousands of hours... and moving the focuser ~50 steps takes, what, 1 second? or less? think about how many 1s movements fit into a 100,000h time frame, for a $200 part... (which, despite the likes of ZWO not wanting you to know, is just a fancy housing and microcontroller for a $15 stepper motor that is replaceable.... 

Don't worry about focusing or changing filters regularly. Capture your data however you feel is the most efficient to you!

Thanks. I agree I have come to the conclusion I think the effects on equipment like focusers are negligible.
Dunk avatar
Dunk avatar
yes. vs a full focus run, its tiny. not sure the quality of the focuser matters much tbh.