Hi,
I'm trying to keep computer costs down for processing dso images.
I'm planning to use Siril, as I've read it is relatively undemanding on computer specs compared to some other software, when stacking. But, is it best to have a small number of long exposures or large number of short exposures, when it comes to demand on computer resources?
Since I'm planning to get an AZEQ6 mount, I am able to go for a shorter number of long exposures, e.g. 5 minutes per exposure.
My other question is, does Siril have an option to auto stack the best exposures or does the user need to manually choose which exposures to stack?
Thanks for your help
Mark
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Obviously less frames to stack = lower demands on the hardware. Note that this has nothing to do on the capability of obtaining a given image given a stack of frames, just how fast you obtain said image. If time is no bar then the requirements are pretty low.
As for the second question, go straight to the manual: Stacking — Siril 1.2.0 documentation |
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andrea tasselli:
Obviously less frames to stack = lower demands on the hardware. Note that this has nothing to do on the capability of obtaining a given image given a stack of frames, just how fast you obtain said image. If time is no bar then the requirements are pretty low.
As for the second question, go straight to the manual: Stacking — Siril 1.2.0 documentation
Thanks Andrea.
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I am using Siril among others - PI and APP. I like Siril because it is very reliable. What is often a bit cumbersome is that you need to provide a lot, really a lot of free space for Siril because the subfolder process accumulates all, absolutely all files and file manipulations during the entire process. It can be several dozen to a few hundred GB, depending on the number of subs and the size of the sensor.
Regarding selecting the best subs - some programs provide aids and algorithms, but I do rely almost always on my personal decision after having them passed the subframe selector in PI. I use the FWHM, Eccentricity and #stars as criteria and then take those which I have decided upon the entered values for those three parameter. But - that is my personal opinion, nothing more...
CS
Georg
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Georg N. Nyman:
I am using Siril among others - PI and APP. I like Siril because it is very reliable. What is often a bit cumbersome is that you need to provide a lot, really a lot of free space for Siril because the subfolder process accumulates all, absolutely all files and file manipulations during the entire process. It can be several dozen to a few hundred GB, depending on the number of subs and the size of the sensor.
Regarding selecting the best subs - some programs provide aids and algorithms, but I do rely almost always on my personal decision after having them passed the subframe selector in PI. I use the FWHM, Eccentricity and #stars as criteria and then take those which I have decided upon the entered values for those three parameter. But - that is my personal opinion, nothing more...
CS
Georg
Thanks Georg, I'm thinking of getting a large external ssd, not sure on how large, but at least 1 Tb, maybe more, to store files. I am very much a beginner, so I'm not sure if Siril will allow processing of files outside of the C drive on the pc. Hopefully yes. Otherwise the laptop I was planning to get (used T430, with 16gB, i5 and 500 GB ssd) will struggle with memory.
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Yes, Siril can work from any drive as long as it contains a directory "Siril" and in that directory the five mandatory subfolders - darks, biases, flats, lights, process. Please note, that Siril recognizes them only if they are written as I did - no capital in front of the word. If you go for an external drive, choose one which is fast in writing, because Siril reads and writes a lot and if you use a rather slow drive, the entire process will take much longer of course.
I suggest you to read the online manual carefully, I did not in the beginning and was stumbling over several steps, which after reading became clear to me.
The scripts, which can be downloaded, are very useful, I recommend using them.
I use a very fast USB stick of 1TB and/or an internal drive, which has got 3TB capacity for working with Siril - but I also use APS and full frame sensor cameras.
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Georg N. Nyman:
Yes, Siril can work from any drive as long as it contains a directory "Siril" and in that directory the five mandatory subfolders - darks, biases, flats, lights, process. Please note, that Siril recognizes them only if they are written as I did - no capital in front of the word. If you go for an external drive, choose one which is fast in writing, because Siril reads and writes a lot and if you use a rather slow drive, the entire process will take much longer of course.
I suggest you to read the online manual carefully, I did not in the beginning and was stumbling over several steps, which after reading became clear to me.
The scripts, which can be downloaded, are very useful, I recommend using them.
I use a very fast USB stick of 1TB and/or an internal drive, which has got 3TB capacity for working with Siril - but I also use APS and full frame sensor cameras.
Thanks Georg, initially my plan is to connect an asiair plus (with 256 gb) to a nikon D7000, although I need to still determine whether it's best to let the AA+ do the capture and/or the dslr with a large sd card inserted. Then later, I plan to move up to an osc camera. Thanks for the tip on the fast write speed for an external drive. I'll look out for that. 👍
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I have found the best way use Siril is with Sirilic. Sirilic Sirilic is basically a GUI for setting up the stacking sessions in Siril. It creates the needed folder structure and starts the stacking process for you. And when you are done with the stacking it will delete all the unneeded files for you. The first few times you try to use Sirilic is will probably fail because an "underscore" gets added to the session names in the script it builds. On some systems you need to open Sirilic as admin so Sirilic can open Siril when the actual stacking starts. Under Edit Properties uncheck the "identical parameters for all layers" and then you can more easily use the image weighting.
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Rich has done some great work putting together videos on Siril. It's worth the time to watch:
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As others have said, fewer lights is faster, but SIRIL is fast enough that whether you take 1 minute lights or 5 minutes, it'll be pretty darn fast.
I'm at the other extreme end of the spectrum: I shoot with an Unguided Alt/Az Goto observational Dobsonian (Orion XT12G) which means I'm using very short exposures due to clunky tracking, no guiding, an Alt/Az means field rotation if I take longer exposures. How short?... how about 4 to 8 second exposures is typical.
Because I can still automate my scope with NINA, I do all night sessions and so I end up with 2000-4000 lights. So I'm all over SIRIL for its speed (as well as its quality). So for maximizing speed and minimizing disk space, here are a few tips:
1) SIRIL can take advantage of any number of CPUs, so get a computer with a fair number of cores.
2) SIRIL doesn't use the GPU, it uses only CPUs so get a fast CPU and don't worry about getting a high end GPU.
3) SIRIL (and APP and PI) write out a ton of intermediate processed files to the disk during the whole calibration and stacking process. To minimize the impact, here are two things:
- Get a fast SSD, preferably an NVME if your systems has NVME slots. And be careful, cheap SSDs often have a fast spec, but that is because it uses some of the drive for a faster cache for short bursts, but it slows way down for continuous writes. Tom's Hardware has extensive testing for very long writes and there you can find which drives are good and which are stinkers with respect to sustained performance. All SSDs will drop to lower performance with sustained writing but some actually drop to BELOW hard disk writing speeds of about 150MB/sec... yes, you heard me correctly. I had 2 year old Intel quad level flash that would fairly quickly drop to under 60 megabytes per second. My "super fast" external SSD would start at 600MB/sec but drop to about 150-200 MB/sec. My current fast 4TB NVME (rated as having good sustained performance) starts at about 4GB/sec but drops to about 1.5GB/sec which is about as good as you can get.
- If you want to minimize storage space and speed requirements, you can turn on the near loss-less RICE compression in the SIRIL preferences. This will save intermediate files compressed and since the algorithm is so fast, it doesn't slow things down much, but your intermediate files will be a fraction of the size and your mass storage is used much less (a fraction of the performance requirements). I've tested the stack quality pretty extensively and it doesn't impact quality. RICE was specifically designed to compress astronomical images without visual loss in quality.
4) SIRIL can also use a fair bit of RAM, but I haven't done enough testing to know if it's just using this opportunistically or if this actually helps performance.
So in a nutshell, to maximize speed and minimize disk space and write performance requirements:
A) Lots of cores
B) Fast SSD with good sustained performance. Peak SSD performance isn't as important as sustained write performance.
C) Turn on RICE compression
Cheers,
Steven
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I have found the best way use Siril is with Sirilic. Sirilic Sirilic is basically a GUI for setting up the stacking sessions in Siril. It creates the needed folder structure and starts the stacking process for you. And when you are done with the stacking it will delete all the unneeded files for you. The first few times you try to use Sirilic is will probably fail because an "underscore" gets added to the session names in the script it builds. On some systems you need to open Sirilic as admin so Sirilic can open Siril when the actual stacking starts. Under Edit Properties uncheck the "identical parameters for all layers" and then you can more easily use the image weighting.
*Thanks Daniel, good tip! 👍
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Steven Miller:
As others have said, fewer lights is faster, but SIRIL is fast enough that whether you take 1 minute lights or 5 minutes, it'll be pretty darn fast.
I'm at the other extreme end of the spectrum: I shoot with an Unguided Alt/Az Goto observational Dobsonian (Orion XT12G) which means I'm using very short exposures due to clunky tracking, no guiding, an Alt/Az means field rotation if I take longer exposures. How short?... how about 4 to 8 second exposures is typical.
Because I can still automate my scope with NINA, I do all night sessions and so I end up with 2000-4000 lights. So I'm over SIRIL for it's speed (as well as it's quality). So for maximizing speed and minimizing disk space, here are a few tips:
1) SIRIL can take advantage of any number of CPUS, so get a computer with a fair number of cores.
2) SIRIL doesn't use the GPU, it uses only CPUS so get a fast CPU and don't worry about getting a high end GPU.
3) SIRIL (and APP and PI) write out a ton of intermediate processed files to the disk during the who calibration and stacking process. To minimize the impact, here are two things:
- Get a fast SSD, preferably an NVME is your systems has NVME slots. And be careful, cheap SSDs often have a fast spec, but that is because it uses some of the drive for a faster cache, but it slows way down for continuous writes. Tom's hardware has extensive testing for very long writes and there you can find which drives are good and which are stinkers with respect to sustained performance. All SSDs will drop to lower performance with sustained writing but some actually drop to BELOW hard disk writing speeds of about 150MB/sec... yes, you heard me correctly. I had 2 year old Intel quad level flash that would fairly quickly drop to under 60 megabytes per second. My "super fast" external SSD would start at 600MB/sec but drop to about 150 MB/sec. My current fast 4TB NVME starts at about 4TB/sec but drops to about 1.5TB/sec which is about as good as you can get.
- If you want to minimize storage space and speed requirements, you can turn on the near loss-less RICE compression in the SIRIL preferences. This will save intermediate files compressed and since the algorithm is so fast, it doesn't slow things down much, but your intermediate files will be a fraction of the size and your mass storage is used much less (a fraction of the performance requirements).
4) SIRIL can also use a fair bit of RAM, but I haven't done enough testing to know if it's just using this opportunistically or if this actually helps performance.
So in a nutshell, to maximize speed and minimize disk space and write performance requirements:
A) Lots of cores
B) Fast SSD with good sustained performance. Peak SSD performance isn't as important as sustained write performance.
C) Turn on RICE compression
Cheers,
Steven
*Thanks Steven, some excellent bits of advice! I'll take these things into account for choosing a used pc too, as well as the ssd drives, which is very useful info. 👍
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I will second the suggestion of an SSD to do your processing on. That more than anything will mean your processing speed will be shorter. If you start messing with starnet++ to do differential stretching between background/nebulosity and stars, raw CPU power is helpful, but the preprocessing and stacking seems to most be I/O dependent. So no old fashioned hard disks please.
(I definitely noticed the difference for starnet++ when upgrading my old intel Macbook to a current M3 model - that went from minutes down to seconds)
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Hi Mark,
Firstly, a quick comment on SiriL and AP processing software ...
I started off in astrophotography using SiriL, and found it reasonably easy to use. I particularly liked being able to automatically select sub-frames based on FWHM.
After a while, I became frustrated with the rather clunky user interface, and switched to Affinity Photo, which has an inbuilt suite of great AP tools. It allows you to automatically select the best x% of sub-frames. Although it is not free like SiriL, it is super-cheap, and allows you to edit your images after stacking them, to adjust colour, contrast etc.
After a while, I upgraded to PixInsight - mainly for the stacking features and Russell Croman's amazing star editing and noise reduction tools - but I still use Affinity Photo for fine-tuning the final image.
Secondly, some thoughts on images files ...
SiriL writes intermediate files to disk - for example, calibrated and aligned images - this can take up a lot of space. PI works the same way. To save disk space, I delete all these files after stacking, but they can be regenerated if needed. In contrast, Affinity does all its processing in RAM, so what you get at the end is just the calibrated and stacked master image - no intermediate files to manage.
Thirdly, in terms of a small number of long exposures vs a large number of short exposures ...
This is a tricky subject, because there are competing requirements.
A small number of long exposures means you have fewer files to manage, so post-processing is faster and you use less desk space. On the minus side, long exposures demand more of your equipment in terms of alignment and tracking. There's also the increased risk of one of your long exposures being ruined by artefacts, such a plane or satellite trails, or by wind, or by accidentally bumping the tripod. So, a few long exposures gives you much less leeway for recovering from these sorts of problems.
On the other hand, a large number of short exposures requires longer post-processing times and more storage space. Having more images also increases the total read noise - so keeping the number of exposures to a minimum is better from this point of view (although the read noise in modern cameras is so low these days that this is becoming less troublesome).
On the plus side, a larger number of exposures means the stacking process gives you *much* better noise reduction. This is a non-linear process - noise is improved according to the square root of the number of exposures, so for example 49 exposures improves S/N by a factor of 7, while 100 exposures improves it by a factor of 10 - so you need to double the number of exposures from 49 to 100 to improve S/N by a factor of 3. The law of diminishing returns also applies - there is a point at which increasing the number of exposures provides no discernible improvement to the noise reduction in the image. Between 50-75 exposures appears to be the sweet-spot.
So, there are good reasons for a large number of short exposures, and competing reasons for a small number of long exposures.
I usually aim for a minimum of 75 exposures - assuming the worst 1/3 of these will be discarded due to poor quality, that leaves about 50 exposures, which means stacking alone improves the S/N by a factor of 7 - which can be improved even further in post-processing.
This rule of thumb puts an upper limit on exposure time, depending on the length of time during which your target is visible. For a 5-hour session, the longest exposure possible is 5*60/75 = 4 minutes - which is about right for my setup with its imperfect tracking.
In terms of the ideal exposure time - that depends on many factors - the best thing is to experiment, but around the 3-4 minute mark is a good place to start - an AZEQ6 is certainly up to the task. It totally depends on your equipment, the target and atmospheric conditions.
Finally, in terms of memory and storage ...
To improve processing speed, you *absolutely* need to store intermediate files on your *internal* SSD - that provides a much higher processing bandwidth with the CPU. Store all your original images (lights, darks etc) on the C drive or an external drive, but set your software to use the internal SSD for processing - this will make a *huge* difference. A computer with 500 GB SSD will easily handle this workload - depending on your setup, this can easily reduce processing times by a factor of 10. Just delete the intermediate files (or copy them to your external drive) when stacking is finished.
Finally - as you mentioned you are a beginner - I strongly advise you to try Affinity Photo. It is super-easy to use, does away with intermediate files altogether, has lots of great built-in AP tools, is super-cheap, and lets you fine-tune the image after stacking.
I hope all that helps 
Cheers,
Gary (Australia)
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Gary JONES:
Hi Mark,
Firstly, a quick comment on SiriL and AP processing software ...
I started off in astrophotography using SiriL, and found it reasonably easy to use. I particularly liked being able to automatically select sub-frames based on FWHM.
After a while, I became frustrated with the rather clunky user interface, and switched to Affinity Photo, which has an inbuilt suite of great AP tools. It allows you to automatically select the best x% of sub-frames. Although it is not free like SiriL, it is super-cheap, and allows you to edit your images after stacking them, to adjust colour, contrast etc.
After a while, I upgraded to PixInsight - mainly for the stacking features and Russell Croman's amazing star editing and noise reduction tools - but I still use Affinity Photo for fine-tuning the final image.
Secondly, some thoughts on images files ...
SiriL writes intermediate files to disk - for example, calibrated and aligned images - this can take up a lot of space. PI works the same way. To save disk space, I delete all these files after stacking, but they can be regenerated if needed. In contrast, Affinity does all its processing in RAM, so what you get at the end is just the calibrated and stacked master image - no intermediate files to manage.
Thirdly, in terms of a small number of long exposures vs a large number of short exposures ...
This is a tricky subject, because there are competing requirements.
A small number of long exposures means you have fewer files to manage, so post-processing is faster and you use less desk space. On the minus side, long exposures demand more of your equipment in terms of alignment and tracking. There's also the increased risk of one of your long exposures being ruined by artefacts, such a plane or satellite trails, or by wind, or by accidentally bumping the tripod. So, a few long exposures gives you much less leeway for recovering from these sorts of problems.
On the other hand, a large number of short exposures requires longer post-processing times and more storage space. Having more images also increases the total read noise - so keeping the number of exposures to a minimum is better from this point of view (although the read noise in modern cameras is so low these days that this is becoming less troublesome).
On the plus side, a larger number of exposures means the stacking process gives you *much* better noise reduction. This is a non-linear process - noise is improved according to the square root of the number of exposures, so for example 49 exposures improves S/N by a factor of 7, while 100 exposures improves it by a factor of 10 - so you need to double the number of exposures from 49 to 100 to improve S/N by a factor of 3. The law of diminishing returns also applies - there is a point at which increasing the number of exposures provides no discernible improvement to the noise reduction in the image. Between 50-75 exposures appears to be the sweet-spot.
So, there are good reasons for a large number of short exposures, and competing reasons for a small number of long exposures.
I usually aim for a minimum of 75 exposures - assuming the worst 1/3 of these will be discarded due to poor quality, that leaves about 50 exposures, which means stacking alone improves the S/N by a factor of 7 - which can be improved even further in post-processing.
This rule of thumb puts an upper limit on exposure time, depending on the length of time during which your target is visible. For a 5-hour session, the longest exposure possible is 5*60/75 = 4 minutes - which is about right for my setup with its imperfect tracking.
In terms of the* ideal* exposure time - that depends on many factors - the best thing is to experiment, but around the 3-4 minute mark is a good place to start - an AZEQ6 is certainly up to the task. It totally depends on your equipment, the target and atmospheric conditions.
Finally, in terms of memory and storage ...
To improve processing speed, you *absolutely* need to store intermediate files on your *internal* SSD - that provides a much higher processing bandwidth with the CPU. Store all your original images (lights, darks etc) on the C drive or an external drive, but set your software to use the internal SSD for processing - this will make a *huge* difference. A computer with 500 GB SSD will easily handle this workload - depending on your setup, this can easily reduce processing times by a factor of 10. Just delete the intermediate files (or copy them to your external drive) when stacking is finished.
Finally - as you mentioned you are a beginner - I strongly advise you to try Affinity Photo. It is super-easy to use, does away with intermediate files altogether, has lots of great built-in AP tools, is super-cheap, and lets you fine-tune the image after stacking.
I hope all that helps
Cheers,
Gary (Australia)
*Tha
Gary JONES:
Hi Mark,
Firstly, a quick comment on SiriL and AP processing software ...
I started off in astrophotography using SiriL, and found it reasonably easy to use. I particularly liked being able to automatically select sub-frames based on FWHM.
After a while, I became frustrated with the rather clunky user interface, and switched to Affinity Photo, which has an inbuilt suite of great AP tools. It allows you to automatically select the best x% of sub-frames. Although it is not free like SiriL, it is super-cheap, and allows you to edit your images after stacking them, to adjust colour, contrast etc.
After a while, I upgraded to PixInsight - mainly for the stacking features and Russell Croman's amazing star editing and noise reduction tools - but I still use Affinity Photo for fine-tuning the final image.
Secondly, some thoughts on images files ...
SiriL writes intermediate files to disk - for example, calibrated and aligned images - this can take up a lot of space. PI works the same way. To save disk space, I delete all these files after stacking, but they can be regenerated if needed. In contrast, Affinity does all its processing in RAM, so what you get at the end is just the calibrated and stacked master image - no intermediate files to manage.
Thirdly, in terms of a small number of long exposures vs a large number of short exposures ...
This is a tricky subject, because there are competing requirements.
A small number of long exposures means you have fewer files to manage, so post-processing is faster and you use less desk space. On the minus side, long exposures demand more of your equipment in terms of alignment and tracking. There's also the increased risk of one of your long exposures being ruined by artefacts, such a plane or satellite trails, or by wind, or by accidentally bumping the tripod. So, a few long exposures gives you much less leeway for recovering from these sorts of problems.
On the other hand, a large number of short exposures requires longer post-processing times and more storage space. Having more images also increases the total read noise - so keeping the number of exposures to a minimum is better from this point of view (although the read noise in modern cameras is so low these days that this is becoming less troublesome).
On the plus side, a larger number of exposures means the stacking process gives you *much* better noise reduction. This is a non-linear process - noise is improved according to the square root of the number of exposures, so for example 49 exposures improves S/N by a factor of 7, while 100 exposures improves it by a factor of 10 - so you need to double the number of exposures from 49 to 100 to improve S/N by a factor of 3. The law of diminishing returns also applies - there is a point at which increasing the number of exposures provides no discernible improvement to the noise reduction in the image. Between 50-75 exposures appears to be the sweet-spot.
So, there are good reasons for a large number of short exposures, and competing reasons for a small number of long exposures.
I usually aim for a minimum of 75 exposures - assuming the worst 1/3 of these will be discarded due to poor quality, that leaves about 50 exposures, which means stacking alone improves the S/N by a factor of 7 - which can be improved even further in post-processing.
This rule of thumb puts an upper limit on exposure time, depending on the length of time during which your target is visible. For a 5-hour session, the longest exposure possible is 5*60/75 = 4 minutes - which is about right for my setup with its imperfect tracking.
In terms of the* ideal* exposure time - that depends on many factors - the best thing is to experiment, but around the 3-4 minute mark is a good place to start - an AZEQ6 is certainly up to the task. It totally depends on your equipment, the target and atmospheric conditions.
Finally, in terms of memory and storage ...
To improve processing speed, you *absolutely* need to store intermediate files on your *internal* SSD - that provides a much higher processing bandwidth with the CPU. Store all your original images (lights, darks etc) on the C drive or an external drive, but set your software to use the internal SSD for processing - this will make a *huge* difference. A computer with 500 GB SSD will easily handle this workload - depending on your setup, this can easily reduce processing times by a factor of 10. Just delete the intermediate files (or copy them to your external drive) when stacking is finished.
Finally - as you mentioned you are a beginner - I strongly advise you to try Affinity Photo. It is super-easy to use, does away with intermediate files altogether, has lots of great built-in AP tools, is super-cheap, and lets you fine-tune the image after stacking.
I hope all that helps
Cheers,
Gary (Australia)
*Thanks Gary, for your really helpful reply! All these details are brilliant. Picking out a couple in particular, for external storage, would you recommend going for any cheap large ssd, so focus more on size than write speed, if all the hard work will be on the internal ssd? Now, whether the ssd in the refurbished T430 is up to the job in terms of writing speed, is another matter... it certainly isn't an M.2 or nvme type. And your comments on exposure times and use of AP, very useful. I guess I could have both to start with.
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Hi,
I'm trying to keep computer costs down for processing dso images.
I'm planning to use Siril, as I've read it is relatively undemanding on computer specs compared to some other software, when stacking. But, is it best to have a small number of long exposures or large number of short exposures, when it comes to demand on computer resources?
Since I'm planning to get an AZEQ6 mount, I am able to go for a shorter number of long exposures, e.g. 5 minutes per exposure.
My other question is, does Siril have an option to auto stack the best exposures or does the user need to manually choose which exposures to stack?
Thanks for your help
Mark
Hello Mark,
I used to stack 800 images with 1.3 sec sub-exposure, once. Siril simply fill out my entire spared space (400 GB) in one minute. I recommend to use long exposure and less No. of images for stacking in general.
Clear skies,
Bortle 9 DimLightChaser
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Hello Mark,
I'm a Siril user since I have started astrophotography about 3 years ago. It has number of adventages for pre-processing compared to Pix for example. Your choice is good to me.
For the exposure time and number of sub, an importante point is the type of setup you have, if you use filter on not and the most important is the type of object. If you use DSLR lens with large opening (below F4) and you shoot bright object, you can't make long exposure. If you use smaller opening (higher then F5.6) with narrowband filters and shoot a faint object, you will need long exposure for sure.
In any cases long or short exposure, the point is the S/N (signal/noise). Less images you have higher noise you have.Eespcially for faint objects, you will need big number of sub and long exposure.
What kind of DSLR and lens do you have and it will be possible to give and average time and number.
An other point for computer CPU, RAM and disk is the type of sensor of you DSLR, it define the size of the subs so the consuming time space and space.
Give us all tis details and we can approximate the reasonnable values.
I hope this will help.
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But, is it best to have a small number of long exposures or large number of short exposures, when it comes to demand on computer resources?
Since I'm planning to get an AZEQ6 mount, I am able to go for a shorter number of long exposures, e.g. 5 minutes per exposure.
Hi Mark,
for efficient disk space usage, a smaller number of files is always an advantage. Thus taking long(er) exposures per frame is recommended.
Tip-1: Mind the seeing!
Often overlooked is the fact, though, that for long exposures like 5 min you really need excellent seeing conditions - because otherwise your stars become bloated due to atmospherical turbulences (scintillation aka "twinkling") while collecting the photons.
I live in the Alps and we might have Bortle 4 skies on average in our valley, which is useful. But concerning seeing I abandoned the idea of taking 5 min subs. I take only 3 min subs now, at most. I repeatedly get better stars with 1 min subs ... which of course flood the hard disk and increase processing time.
Tip-2: Siril's /process and /masters folder
I am still working with a 13+ years old Linux desktop system exclusively. Siril producess tons of files in the /process directory and some stacks in /masters. Hundreds or thousands of files have to be written into and accessed from the /process directory (aka "folder").
Thus I bought a very fast USB3-SSD (a SSD stick!, not an external drive that would need a power cable and/or power supply!) and plugged it in the USB3 port.
Then, before starting a huge processing in Siril, prepare a minimal, temporary working directory for Siril on that new fast SSD (=THERE):
Example:
# go to the ("traditional") hard disk working directory (=HERE)
cd /home/frank/astro/And-M31
# create real folders on the new, very fast SSD (=THERE)
# the new SSD device needs to be already mounted (e.g.) as /astroSSD
# setup the "Andromeda M31" working directory THERE
mkdir -p /astroSSD/And-M31/{biases,darks,lights,flats,masters,process}
# being still HERE, link /process and /master from THERE to HERE
ln -s /astroSSD/And-M31/{process,masters} .
# check the current directory (HERE) for the twolinks
ls -al
...
...
... ......./masters -> /astroSSD/And-M31/masters
... ......./process -> /astroSSD/And-M31/process
...
Okay!
Note: We still have and keep the folders and contents of ./biases, ./darks, ./flats and ./lights HERE: These files are only read once by Siril. The by far most time consuming part is accessing, reading and writing all those interim files in the ./process folder!
Thus, when using Siril manually (without scripts) this would be everything needed - we could star!
When using preprocessing scripts to let it all happen without interaction, then we need to prepare some more things - simply because all Siril scripts make use of "cd ..", which is a relative directory (folder) change to the "parent" directory of the current directory,
Siril cannot find any files in the subdirs ./biases, ./darks, ./flats and ./lights folders' contents from that "parent" directory, because we created them before and they are still empty. So we need to symbolic link all those files from HERE to THERE:
# go THERE (/astroSSD/And-M31) and link (don't copy!) all files within ./biases, ./flats, .darks and ./lights from HERE to THERE
cd /astroSSD/And/M31
for dir in biases flats darks lights; do cd $dir; ln -s /path/to/original/$dir/* .; cd ..; done
Go!
Being at the right place now (the former THERE called directory "/astroSSD/And-M31") already, we can now start Siril and set the current directory THERE (/astroSSD/And-M31) to be Siril's working directory.
Launch an appropriate preprocessing script from the Scripts menu ... and get a coffee. But hurry up ... because you'll have much less time than expected for it! 
Good success and clear skies,
Frank
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Thierry Boufflet:
Hello Mark,
I'm a Siril user since I have started astrophotography about 3 years ago. It has number of adventages for pre-processing compared to Pix for example. Your choice is good to me.
For the exposure time and number of sub, an importante point is the type of setup you have, if you use filter on not and the most important is the type of object. If you use DSLR lens with large opening (below F4) and you shoot bright object, you can't make long exposure. If you use smaller opening (higher then F5.6) with narrowband filters and shoot a faint object, you will need long exposure for sure.
In any cases long or short exposure, the point is the S/N (signal/noise). Less images you have higher noise you have.Eespcially for faint objects, you will need big number of sub and long exposure.
What kind of DSLR and lens do you have and it will be possible to give and average time and number.
An other point for computer CPU, RAM and disk is the type of sensor of you DSLR, it define the size of the subs so the consuming time space and space.
Give us all tis details and we can approximate the reasonnable values.
I hope this will help.
*Thanks Thierry, the dslr (Nikon D7000) has an aps-c sensor. It would be connected to an ed80 with reducer giving focal ratio of F6.375. I plan to control the guiding with dslr connected to asiair and zwo asi120mm. Hope this helps.
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But, is it best to have a small number of long exposures or large number of short exposures, when it comes to demand on computer resources?
Since I'm planning to get an AZEQ6 mount, I am able to go for a shorter number of long exposures, e.g. 5 minutes per exposure.
Hi Mark,
for efficient disk space usage, a smaller number of files is always an advantage. Thus taking long(er) exposures per frame is recommended.
Tip-1: Mind the seeing!
Often overlooked is the fact, though, that for long exposures like 5 min you really need excellent seeing conditions - because otherwise your stars become bloated due to atmospherical turbulences (scintillation aka "twinkling") while collecting the photons.
I live in the Alps and we might have Bortle 4 skies on average in our valley, which is useful. But concerning seeing I abandoned the idea of taking 5 min subs. I take only 3 min subs now, at most. I repeatedly get better stars with 1 min subs ... which of course flood the hard disk and increase processing time.
Tip-2: Siril's /process and /masters folder
I am still working with a 13+ years oldLinux desktop system exclusively. Siril producess tons of files in the /process directory and some stacks in /masters. Hundreds or thousands of files have to be written into and accessed from the /process directory (aka "folder").
Thus I bought a very fast USB3-SSD (a SSD stick!, not an external drive that would need a power cable and/or power supply!) and plugged it in the USB3 port.
Then, before starting a huge processing in Siril, prepare a minimal,temporary working directory for Siril on that new fast SSD (=THERE):
Example:
# go to the ("traditional") hard disk working directory (=HERE)
cd /home/frank/astro/And-M31
# create real folders on the new, very fast SSD (=THERE)
# the new SSD device should be already be mounted (e.g.) as /astroSSD
# setup the "Andromeda M31" working directory THERE
mkdir -p /astroSSD/And-M31/{biases,darks,lights,flats,masters,process}
# being still HERE, link /process and /master from THERE to HERE
ln -s /astroSSD/And-M31/{process,masters} .
# check the current directory (HERE) for the twolinks
ls -al
...
...
... ......./masters -> /astroSSD/And-M31/masters
... ......./process -> /astroSSD/And-M31/process
...
Okay!
Note: We still have and keep the folders and contents of ./biases, ./darks, ./flats and ./lights [i] [/i]HERE: These files are only read once by Siril. The by far most time consuming part is accessing, reading and writing all those interim files in the ./process folder!
Thus, when using Siril manually (without scripts) that would be all. Because all scripts make use of "cd ..", we need to prepare some more things:
# change directory to THERE and link (don't copy!) the directory contents of ./biases, ./flats, .darks and ./lights from HERE to THERE
cd /astroSSD/And/M31
for dir in biases flats darks lights; do cd $dir; ln -s /path/to/original/$dir/* .; cd ..; done
Go!
Being at the right play now (in /astroSSD/And-M31) already, start Siril and set the current directory (/astroSSD/And-M31) as Siril's working directory.
Launch the required script from the menu ... and go for a coffee. But hurry up ... because you'll have much less time than expected!
Good success and clear skies,
Frank
*Thanks Frank! I have basic IT skills, but I followed what you were saying to some extent. So you use some command line code, in addition to the Siril scripts, to make sure the main work is done on the USB-ssd. I didn't realise you could buy a stick. I do have a couple of ssd drives that can be connected via USB cable, but it sounds like the USB-ssd looks more like a classic USB stick. Very interesting, and I'm off to Amazon to look now. 😉
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*Thanks Frank! I have basic IT skills, but I followed what you were saying to some extent. So you use some command line code, in addition to the Siril scripts, to make sure the main work is done on the USB-ssd. I didn't realise you could buy a stick. I do have a couple of ssd drives that can be connected via USB cable, but it sounds like the USB-ssd looks more like a classic USB stick. Very interesting, and I'm off to Amazon to look now. 😉
Samsung SSD/USB3 Stick - links to the nice model I got. I hadn't know I could get such a small SSD with 1 TB as a USB stick.
Concerning my code example for the temporary /astroSSD setup: I made a carefully thought shell script for my needs, which avoids messing things up and of course saves the work.
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Scott Fisher:
Rich has done some great work putting together videos on Siril. It's worth the time to watch:
https://www.youtube.com/@DeepSpaceAstro
Deep Space Astros videos are amazing.
Any newbie like me needs to watch his siril tutorials asap.
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Thierry Boufflet:
Hello Mark,
I'm a Siril user since I have started astrophotography about 3 years ago. It has number of adventages for pre-processing compared to Pix for example. Your choice is good to me.
For the exposure time and number of sub, an importante point is the type of setup you have, if you use filter on not and the most important is the type of object. If you use DSLR lens with large opening (below F4) and you shoot bright object, you can't make long exposure. If you use smaller opening (higher then F5.6) with narrowband filters and shoot a faint object, you will need long exposure for sure.
In any cases long or short exposure, the point is the S/N (signal/noise). Less images you have higher noise you have.Eespcially for faint objects, you will need big number of sub and long exposure.
What kind of DSLR and lens do you have and it will be possible to give and average time and number.
An other point for computer CPU, RAM and disk is the type of sensor of you DSLR, it define the size of the subs so the consuming time space and space.
Give us all tis details and we can approximate the reasonnable values.
I hope this will help.
*Thanks Thierry, the dslr (Nikon D7000) has an aps-c sensor. It would be connected to an ed80 with reducer giving focal ratio of F6.375. I plan to control the guiding with dslr connected to asiair and zwo asi120mm. Hope this helps.
Regarding your setup note very fast, you will need more or less long exposures (about 180 to 300s). The number could be around 100 subs. In Siril you can automaticaly or manually select the best subs by FWHM, stars shape or sub noise.
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Thierry Boufflet:
Thierry Boufflet:
Hello Mark,
I'm a Siril user since I have started astrophotography about 3 years ago. It has number of adventages for pre-processing compared to Pix for example. Your choice is good to me.
For the exposure time and number of sub, an importante point is the type of setup you have, if you use filter on not and the most important is the type of object. If you use DSLR lens with large opening (below F4) and you shoot bright object, you can't make long exposure. If you use smaller opening (higher then F5.6) with narrowband filters and shoot a faint object, you will need long exposure for sure.
In any cases long or short exposure, the point is the S/N (signal/noise). Less images you have higher noise you have.Eespcially for faint objects, you will need big number of sub and long exposure.
What kind of DSLR and lens do you have and it will be possible to give and average time and number.
An other point for computer CPU, RAM and disk is the type of sensor of you DSLR, it define the size of the subs so the consuming time space and space.
Give us all tis details and we can approximate the reasonnable values.
I hope this will help.
*Thanks Thierry, the dslr (Nikon D7000) has an aps-c sensor. It would be connected to an ed80 with reducer giving focal ratio of F6.375. I plan to control the guiding with dslr connected to asiair and zwo asi120mm. Hope this helps.
Regarding your setup note very fast, you will need more or less long exposures (about 180 to 300s). The number could be around 100 subs. In Siril you can automaticaly or manually select the best subs by FWHM, stars shape or sub noise.
*Thank you. I think it seems 4 minute subs would be a good place to start. 👍
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Mark Worthington:
*Thanks Gary, for your really helpful reply! All these details are brilliant. Picking out a couple in particular, for external storage, would you recommend going for any cheap large ssd, so focus more on size than write speed, if all the hard work will be on the internal ssd? Now, whether the ssd in the refurbished T430 is up to the job in terms of writing speed, is another matter... it certainly isn't an M.2 or nvme type. And your comments on exposure times and use of AP, very useful. I guess I could have both to start with.
Hi Mark,
Many thanks for the compliment
In terms of your computer gear, I'd recommend the following :-
1. Assuming you use your AAP in local mode, buy a large SSD with reasonably fast write speed.
The RAM inside the AAP spools images to the disk while the next image is being exposed, so write speed is not the main consideration.
But if you copy your files to another drive for processing, you want something with a very fast read speed.
Of course, if you get one, you usually get the other.
Also have TWO SSDs in case one becomes faulty, particularly if you image in the field.
2. Try performing a read/write speed test on your internal RAM, then match the R/W speed of your SD card to that, plus a 50% margin.
No point paying for extra speed on the SSD if your PC can't make the most of it.
3. The AAP has a 256 GB internal SSD which is pretty fast (RW = 121/95 MB/sec).
That's more than enough to store all your images for a night (256 GB will store about 2,500 APS-C RGB images), so you don't really need an SD card.
But it does make things easier if you want to copy images to your PC without using a network.
Of course, you can copy images direct from the AAP to your PC via WiFi, which can take a very long time - or ethernet, which is much faster.
But it's still a good idea to have an SD card handy just in case you run out of memory ...
It happened to me once on my AAP after I forgot to erase the images from the previous night's imaging.
4. For storing all your image files, it is *really* risky to use an SD card or USB stick.
I highly recommend against this.
USB sticks have a finite failure rate, so if the drive fails, you could lose everything.
Much better to invest in an inexpensive SSD RAID drive for storing all your RAW and processed images.
RAID gives you redundancy, so one SSD can fail completely and you won't lose any data.
Considering the cost of your mount, and the cost of all your other gear, IMHO it's definitely worth investing in a good RAID - just part of the overall package.
Just one other thing to follow on my my earlier comment ...
In terms of the ideal exposure time - that depends on many factors - the best thing is to experiment, but around the 3-4 minute mark is a good place to start - an AZEQ6 is certainly up to the task. It totally depends on your equipment, the target and atmospheric conditions.
By 'atmospheric conditions' of course I'm referring to seeing. Seeing is composed of a number of elements - fast turbulence, slow turbulence and short-term density changes.
One way to reduce the effects of fast turbulence is to use really short exposures - in the order of milliseconds. Anything longer than that makes little difference in terms of fast turbulence.
To reduce the effects of slow turbulence you can use short exposures - in the order of seconds. Anything longer than that makes little difference in terms of slow turbulence.
To reduce the effects of short-term density changes you can use limit exposures to less than a few tens of seconds. Anything longer than that makes little difference in terms of short-term density changes.
See as example of seeing in the short movie I posted on Astrobin here.
You can see the fast and slow effects, both of which will affect any exposure of more than a second or so.
So, although better seeing and shorter exposures will always give you sharper images, any exposure exceeding a few seconds will still suffer from the effects of seeing. But shorter exposures will also suffer from more noise.
As I said before, the best thing to do is experiment. Try imaging a single target on the same night using different exposures - 1/2/3/4/5 minutes, and make sure to record the seeing. Measure the noise and star size in each set of RAW images and in the stacked result - that will be your best guide.
Cheers,
Gary
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