MW stacking question & Sequator

[Bob]

How much star elongation can I allow? Suppose a 20mm lens will allow for a 15-second exposure (300 rule), but adding 10 more seconds would be a better exposure, albeit with more trailing.

Sequator can reduce trails, but only to a certain extent, right?

Or perhaps another way of asking, if using Sequator, what should be the numerator in the "rule"?

 

[nighthiker]

Hi!

Sequator can NOT reduce any startrails. It's just a good stacking tool which can also handle ultra WA lenses where most other stackers have problems with the strong distortion in the corners.

Concerning this rule of 'whatever': I'm rather a pixel-peeper and use a 'rule of 200', but that depends on personal taste. Just make some test shoots with different exposures and see which trail length is acceptable for you.

 

[Sittatunga]

Sequator can only reduce trails in conjunction with a tracker. It can also be used to make star trails if you have enough exposures over a long enough time, but I think that StarStaX does a better job of filling in the gaps between exposures.

 

[Bob]

Sequator can only reduce trails in conjunction with a tracker. It can also be used to make star trails if you have enough exposures over a long enough time, but I think that StarStaX does a better job of filling in the gaps between exposures.

I see. So one would then set up the shot as if that would be the only shot. Then repeat the same settings so that Sequator can improve the S/N ratio. So I should end up with less noise and a darker 'sky' in between the stars. Correct?

 

[Sittatunga]

Sequator can only reduce trails in conjunction with a tracker. It can also be used to make star trails if you have enough exposures over a long enough time, but I think that StarStaX does a better job of filling in the gaps between exposures.

I see. So one would then set up the shot as if that would be the only shot. Then repeat the same settings so that Sequator can improve the S/N ratio. So I should end up with less noise and a darker 'sky' in between the stars. Correct?

On a tracker, yes. It's a much more use friendly program than Deep Sky Stacker.

 

[Bob]

Sequator can only reduce trails in conjunction with a tracker. It can also be used to make star trails if you have enough exposures over a long enough time, but I think that StarStaX does a better job of filling in the gaps between exposures.

I see. So one would then set up the shot as if that would be the only shot. Then repeat the same settings so that Sequator can improve the S/N ratio. So I should end up with less noise and a darker 'sky' in between the stars. Correct?

On a tracker, yes. It's a much more use friendly program than Deep Sky Stacker.

Sorry - I'm not using a tracker. I'm trying to get the MW with some foreground. So just a tripod.

 

[hha]

Bob:

The stars rotate 15 "/sec. With a 20 mm lens and 4 micron pixels (Nikon D7200 typical 24Mp camera), each pixel subtends 41", so in 3 seconds you will create a one pixel trail. The rule of 300 would permit a 15 second exposure, i.e. you will see a 5 pixel trail. With a good lens and for my taste this is no good. If you need 30 seconds exposure, take 10 picture at 3 seconds each and stack them in Sequator. That is what I do when I want to take MW shots without having to carry a tracking mount.

I have used Sequator for as many as 240x1 min exposures with a 200mm lens on a tracking mount.

Sequator solves for one global mean x/y pixel shift between successive images, using a large number of stars in the image. if the input image has elongated stars, the output image stars will be no less elongated.

hha

 

[nighthiker]

Sequator can only reduce trails in conjunction with a tracker. It can also be used to make star trails if you have enough exposures over a long enough time, but I think that StarStaX does a better job of filling in the gaps between exposures.

I see. So one would then set up the shot as if that would be the only shot. Then repeat the same settings so that Sequator can improve the S/N ratio. So I should end up with less noise and a darker 'sky' in between the stars. Correct?

On a tracker, yes. It's a much more use friendly program than Deep Sky Stacker.

Sorry - I'm not using a tracker. I'm trying to get the MW with some foreground. So just a tripod.

That's what Sequator is very well suitable for. Don't forget to select 'best pixel' (which is sigma clipping) and not 'accumulate'. There is also the option for 'freeze ground', but I prefer to do the merge between the sky and the foreground later manually. Just check some videos and play around with the options.

Concerning the dark background: Sequator is only stacking the images, so improving the s/n ratio. There is also an option for a background subtraction (I think), but I wasn't successful with that, but just test it! Removing the light pollution from a MW image (without damaging the MW) is difficult. Maybe somebody else has a simple solution for it, but I gave up after a while and bought PixInsight (slightly expensive and extremely powerful) which has an easy to learn and very good and flexible tool to model und subtract the light pollution.

It's not the best season for the 'Wikings' at the moment to catch the MW as the bright core isn't visible any more. It's only during the shoulder-season around March/April and August/September when we see a little bit of the brighter part of the MW. The core is only visible in the summer time (northern hemisphere), so invisible to us. Check Stellarium for details.

 

[Bob]

Brilliant explanation! Thank you.

 

[Bob]

Can I use Sequator for terrestrial images during the day? For example, for a landscape shot, I might not be able to make the shutter fast enough to avoid camera shake. This often happens with a long lens, cloudy day, and too much wind to keep the tripod still. The lens wants f/8 for max sharpness. The camera wants 1/20”, but 1/250 would be better to freeze any vibrations. Can I stack 12 shots and let Sequator build a good exposure?

 

[Sittatunga]

Can I use Sequator for terrestrial images during the day? For example, for a landscape shot, I might not be able to make the shutter fast enough to avoid camera shake. This often happens with a long lens, cloudy day, and too much wind to keep the tripod still. The lens wants f/8 for max sharpness. The camera wants 1/20”, but 1/250 would be better to freeze any vibrations. Can I stack 12 shots and let Sequator build a good exposure?

I don't see why not, the program is freeware, so it's definite worth a try. If it's that windy though, trees and other vegetation will be being blown about, so may not end up all that sharp. Stacking exposures also reduces noise, so it would be worthwhile to compare a stack of correctly exposed high ISO shots with another of under exposed base ISO shots to see which you prefer.

 

[marter]

How much star elongation can I allow? Suppose a 20mm lens will allow for a 15-second exposure (300 rule), but adding 10 more seconds would be a better exposure, albeit with more trailing.

Sequator can reduce trails, but only to a certain extent, right?

Or perhaps another way of asking, if using Sequator, what should be the numerator in the "rule"?

I realize this thread is a month old but I just ran across it and thought I'd post this image using Sequator.



This is a stacked composite of 20 images (and 4 dark images) using Sequator. These were shot on a Z6 with a Z 14-30mm f/4 lens on a tripod at 18mm, 15 sec exposures at 3200 ISO using matrix metering. The Sequator settings were as follows:







--

https://www.flickr.com/photos/188281258@N05/

 

[Bob]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

 

[marter]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

The length of exposure is based on avoiding star trails. There are numerous "rules" around, but I use the Photo Pills app's "Spot Stars" table where you enter the lens info and it will give you a max exposure time to avoid star trails. I use the NPF rule, and not the 500 rule. Sequator will not clean up trails, only noise.

As far as ISO, I didn't use a light meter, I just did enough research on the web to guess at ISO settings, and shot a full set at 3200, 4000, 5000 and 6400 ISO. I did some post processing in PS on the stack I posted at 3200 ISO. I'm guessing I could have gone a little lower, and probably could have used the higher ISO shots in a composite with adjustments in LR or PS.

And don't try to interpolate the math of # of shots vs. exposure time. Each exposure is "viewable" but has enough noise to make it unusable until Sequator does it thing by taking each shot, aligning them and removing the noise. Hope that makes sense.

 

[swimswithtrout]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

The length of exposure is based on avoiding star trails. There are numerous "rules" around, but I use the Photo Pills app's "Spot Stars" table where you enter the lens info and it will give you a max exposure time to avoid star trails. I use the NPF rule, and not the 500 rule. Sequator will not clean up trails, only noise.

As far as ISO, I didn't use a light meter, I just did enough research on the web to guess at ISO settings, and shot a full set at 3200, 4000, 5000 and 6400 ISO. I did some post processing in PS on the stack I posted at 3200 ISO. I'm guessing I could have gone a little lower, and probably could have used the higher ISO shots in a composite with adjustments in LR or PS.

And don't try to interpolate the math of # of shots vs. exposure time. Each exposure is "viewable" but has enough noise to make it unusable until Sequator does it thing by taking each shot, aligning them and removing the noise. Hope that makes sense.

It should be noted that Sequator , or any stacking program does not "remove" noise like a standard noise reduction filter. It simply averages out the random aspects of noise in the course of stacking all the sub frames.

And without getting into a very lengthy, technical, discussion, yes, 50 x 2" has the same signal to noise strength as a single 1 x 100" shot . It won't look like it at first. It's up to you to be able to bring it out during post processing.

 

[Bob]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

The length of exposure is based on avoiding star trails. There are numerous "rules" around, but I use the Photo Pills app's "Spot Stars" table where you enter the lens info and it will give you a max exposure time to avoid star trails. I use the NPF rule, and not the 500 rule. Sequator will not clean up trails, only noise.

As far as ISO, I didn't use a light meter, I just did enough research on the web to guess at ISO settings, and shot a full set at 3200, 4000, 5000 and 6400 ISO. I did some post processing in PS on the stack I posted at 3200 ISO. I'm guessing I could have gone a little lower, and probably could have used the higher ISO shots in a composite with adjustments in LR or PS.

And don't try to interpolate the math of # of shots vs. exposure time. Each exposure is "viewable" but has enough noise to make it unusable until Sequator does it thing by taking each shot, aligning them and removing the noise. Hope that makes sense.

It should be noted that Sequator , or any stacking program does not "remove" noise like a standard noise reduction filter. It simply averages out the random aspects of noise in the course of stacking all the sub frames.

And without getting into a very lengthy, technical, discussion, yes, 50 x 2" has the same signal to noise strength as a single 1 x 100" shot . It won't look like it at first. It's up to you to be able to bring it out during post processing.

Thank you. Just to clarify, I’m not referring to S/N. I’m asking about exposure time in terms of brightness. In other words, if one could purchase ISO 3200 film which had a fine grain like a roll of ISO 50, would this exposure still be set to 15”?

 

[Sittatunga]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

The length of exposure is based on avoiding star trails. There are numerous "rules" around, but I use the Photo Pills app's "Spot Stars" table where you enter the lens info and it will give you a max exposure time to avoid star trails. I use the NPF rule, and not the 500 rule. Sequator will not clean up trails, only noise.

As far as ISO, I didn't use a light meter, I just did enough research on the web to guess at ISO settings, and shot a full set at 3200, 4000, 5000 and 6400 ISO. I did some post processing in PS on the stack I posted at 3200 ISO. I'm guessing I could have gone a little lower, and probably could have used the higher ISO shots in a composite with adjustments in LR or PS.

And don't try to interpolate the math of # of shots vs. exposure time. Each exposure is "viewable" but has enough noise to make it unusable until Sequator does it thing by taking each shot, aligning them and removing the noise. Hope that makes sense.

It should be noted that Sequator , or any stacking program does not "remove" noise like a standard noise reduction filter. It simply averages out the random aspects of noise in the course of stacking all the sub frames.

And without getting into a very lengthy, technical, discussion, yes, 50 x 2" has the same signal to noise strength as a single 1 x 100" shot . It won't look like it at first. It's up to you to be able to bring it out during post processing.

Thank you. Just to clarify, I’m not referring to S/N. I’m asking about exposure time in terms of brightness. In other words, if one could purchase ISO 3200 film which had a fine grain like a roll of ISO 50, would this exposure still be set to 15”?

Long exposure reciprocity failure with film makes that sort of thing a question of trial and (mostly) error.

 

[Bob]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

The length of exposure is based on avoiding star trails. There are numerous "rules" around, but I use the Photo Pills app's "Spot Stars" table where you enter the lens info and it will give you a max exposure time to avoid star trails. I use the NPF rule, and not the 500 rule. Sequator will not clean up trails, only noise.

As far as ISO, I didn't use a light meter, I just did enough research on the web to guess at ISO settings, and shot a full set at 3200, 4000, 5000 and 6400 ISO. I did some post processing in PS on the stack I posted at 3200 ISO. I'm guessing I could have gone a little lower, and probably could have used the higher ISO shots in a composite with adjustments in LR or PS.

And don't try to interpolate the math of # of shots vs. exposure time. Each exposure is "viewable" but has enough noise to make it unusable until Sequator does it thing by taking each shot, aligning them and removing the noise. Hope that makes sense.

It should be noted that Sequator , or any stacking program does not "remove" noise like a standard noise reduction filter. It simply averages out the random aspects of noise in the course of stacking all the sub frames.

And without getting into a very lengthy, technical, discussion, yes, 50 x 2" has the same signal to noise strength as a single 1 x 100" shot . It won't look like it at first. It's up to you to be able to bring it out during post processing.

Thank you. Just to clarify, I’m not referring to S/N. I’m asking about exposure time in terms of brightness. In other words, if one could purchase ISO 3200 film which had a fine grain like a roll of ISO 50, would this exposure still be set to 15”?

Long exposure reciprocity failure with film makes that sort of thing a question of trial and (mostly) error.

Thank you. 15" was just for illustration purposes. What I'm asking is whether one works out the exposure settings based on image brightness and star trail considerations, then take multiple shots at those same aperture and shutter settings to reduce noise?

For example, I think stacking 120 shots each exposed at 1/8th second will result in a black image. They won't aggregate to the equivalent of a 15-second exposure, correct?

 

[swimswithtrout]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

The length of exposure is based on avoiding star trails. There are numerous "rules" around, but I use the Photo Pills app's "Spot Stars" table where you enter the lens info and it will give you a max exposure time to avoid star trails. I use the NPF rule, and not the 500 rule. Sequator will not clean up trails, only noise.

As far as ISO, I didn't use a light meter, I just did enough research on the web to guess at ISO settings, and shot a full set at 3200, 4000, 5000 and 6400 ISO. I did some post processing in PS on the stack I posted at 3200 ISO. I'm guessing I could have gone a little lower, and probably could have used the higher ISO shots in a composite with adjustments in LR or PS.

And don't try to interpolate the math of # of shots vs. exposure time. Each exposure is "viewable" but has enough noise to make it unusable until Sequator does it thing by taking each shot, aligning them and removing the noise. Hope that makes sense.

It should be noted that Sequator , or any stacking program does not "remove" noise like a standard noise reduction filter. It simply averages out the random aspects of noise in the course of stacking all the sub frames.

And without getting into a very lengthy, technical, discussion, yes, 50 x 2" has the same signal to noise strength as a single 1 x 100" shot . It won't look like it at first. It's up to you to be able to bring it out during post processing.

Thank you. Just to clarify, I’m not referring to S/N. I’m asking about exposure time in terms of brightness. In other words, if one could purchase ISO 3200 film which had a fine grain like a roll of ISO 50, would this exposure still be set to 15”?

Long exposure reciprocity failure with film makes that sort of thing a question of trial and (mostly) error.

Thank you. 15" was just for illustration purposes. What I'm asking is whether one works out the exposure settings based on image brightness and star trail considerations, then take multiple shots at those same aperture and shutter settings to reduce noise?

For example, I think stacking 120 shots each exposed at 1/8th second will result in a black image. They won't aggregate to the equivalent of a 15-second exposure, correct?

At 1/8" second you are not going to collect enough signal to overcome your sensors inherent read noise that is in every shot. You are read noise limited and stacking will not be the same as a single shot

But again. if you stack 10x10" shots, it is the same as a single 100" shot......"after you process it" . It's up to you to adjust the brightness.

 

[swimswithtrout]

Thanks for the post. It’s super helpful!! I’m still a bit confused about Sequator. Your exposure was 15 seconds. I understand Sequator reduces noise, but forgetting about noise for a moment, is 15 seconds what that scene requires according to the light meter? In other words, the software doesn’t add the exposures, right? It just subtracts the noise?

50 two-second exposures doesn’t add up to one 100-second exposure, right?

The length of exposure is based on avoiding star trails. There are numerous "rules" around, but I use the Photo Pills app's "Spot Stars" table where you enter the lens info and it will give you a max exposure time to avoid star trails. I use the NPF rule, and not the 500 rule. Sequator will not clean up trails, only noise.

As far as ISO, I didn't use a light meter, I just did enough research on the web to guess at ISO settings, and shot a full set at 3200, 4000, 5000 and 6400 ISO. I did some post processing in PS on the stack I posted at 3200 ISO. I'm guessing I could have gone a little lower, and probably could have used the higher ISO shots in a composite with adjustments in LR or PS.

And don't try to interpolate the math of # of shots vs. exposure time. Each exposure is "viewable" but has enough noise to make it unusable until Sequator does it thing by taking each shot, aligning them and removing the noise. Hope that makes sense.

It should be noted that Sequator , or any stacking program does not "remove" noise like a standard noise reduction filter. It simply averages out the random aspects of noise in the course of stacking all the sub frames.

And without getting into a very lengthy, technical, discussion, yes, 50 x 2" has the same signal to noise strength as a single 1 x 100" shot . It won't look like it at first. It's up to you to be able to bring it out during post processing.

Thank you. Just to clarify, I’m not referring to S/N. I’m asking about exposure time in terms of brightness. In other words, if one could purchase ISO 3200 film which had a fine grain like a roll of ISO 50, would this exposure still be set to 15”?

Long exposure reciprocity failure with film makes that sort of thing a question of trial and (mostly) error.

Thank you. 15" was just for illustration purposes. What I'm asking is whether one works out the exposure settings based on image brightness and star trail considerations, then take multiple shots at those same aperture and shutter settings to reduce noise?

For example, I think stacking 120 shots each exposed at 1/8th second will result in a black image. They won't aggregate to the equivalent of a 15-second exposure, correct?

Let's try this again. Determine the longest exposure you can take without star trailing. With a 20mm lens, you can shoot 10" using a modified NPF rule if shooting at 0* declination. Set your camera to ISO 1600 and take 10, 10" exposures and stack them in Sequator. Process that stack and it will be the same as a single 100" exposure..... Forget what the single subs look like or what the finished stack looks like, until you process it, it's still just a 10" exposure but with the SNR of a 100" single shot.


This is a stack of 70, 5 minute exposures using my telescope and a tracking mount...a total of nearly 7 hours of data....

This is what it looks like after processing.