Building up data over several sessions

[M00NMonkey]

Hi all,

Haven't posted for a while, been in denial and have used every fibre of my being to suppress the fact that I want to observe and image the night sky. This cloud/rain/sleet/snow, weather in general has just been, well, a real pain in the proverbial and has driven my to the point of insanity!!

OK, so my question is about building up data over several sessions (even continuously adding over years) on the same target.

What things do I need to do, to be able to add different session data together?

Does everything need to be lined up exactly the same (framing), or does software like DSS cope with slight variations in alignment?

Basically I would like a little advice on how to go about building up my data. I am not even sure that you need to have the optical train setup exactly the same, as I have seen people combining data from different imaging sources.

I am a newbie to imaging and have only had a few sessions to get to grips with the whole AP experience, so any info, even if it seems trivial, maybe of high value to me, so please post any advice, tips/tricks as I assure you they will be appreciated.

Thanks for reading and clear skies for us all!!

ATB

Jez

[Tim]

Keep things as similar as you can each session, and the whole process will be a lot simpler and yield better results.

Camera orientation is particularly important, as you will end up cropping a load of the frame away if it is too different on each session.

Also, positioning of the target. I usually find a significant point of interest within the target, and make sure it is positioned in such a place on the frame that I can get it back there night after night, month after month.

Keep exposure times similar, or at least the ADU values of the image, on darker nights you may be able to expose slightly longer to achieve the same ADU as the reference frame.

I usually name my images with the date as part of the filename, makes it easier to read them, and put each session in its own folder, so that removing any problem sessions is easier than having them all in one folder.

Depending how dark noisy your camera is, it might be an idea to have a matched set of darks for each session. I just use a darks library that I gather on cloudy nights, but some cameras need more carefully managing.

Finally, if you are using DSS to stack them, when they are all registered but not stacked, go through the background values column and root out any which are too wide of the mark, and check the FWHM values to make sure you aren't accidentally polluting good data with poorly focused stuff.

I usually take images of one target over several months, and with a bit of a logical process, it usually works out ok

Hope that helps.

Tim

[Shibby]

All I want to add to Tim's comments is that, if you do end up with slightly different orientations (and temperature) between sessions, then you'll be using different calibration frames (i.e. flats as well as fore-mentioned darks). DSS provides a "grouping" functionality that allows you to group your subs together with the correct calibration frames before stacking.

PS: I feel your pain. I've been waiting over a Month now to try and gather a few extra subs on the target I've been trying to image

[M00NMonkey]

Keep things as similar as you can each session, and the whole process will be a lot simpler and yield better results.

Camera orientation is particularly important, as you will end up cropping a load of the frame away if it is too different on each session.

Also, positioning of the target. I usually find a significant point of interest within the target, and make sure it is positioned in such a place on the frame that I can get it back there night after night, month after month.

Keep exposure times similar, or at least the ADU values of the image, on darker nights you may be able to expose slightly longer to achieve the same ADU as the reference frame.

I usually name my images with the date as part of the filename, makes it easier to read them, and put each session in its own folder, so that removing any problem sessions is easier than having them all in one folder.

Depending how dark noisy your camera is, it might be an idea to have a matched set of darks for each session. I just use a darks library that I gather on cloudy nights, but some cameras need more carefully managing.

Finally, if you are using DSS to stack them, when they are all registered but not stacked, go through the background values column and root out any which are too wide of the mark, and check the FWHM values to make sure you aren't accidentally polluting good data with poorly focused stuff.

I usually take images of one target over several months, and with a bit of a logical process, it usually works out ok

Hope that helps.

Tim

Hi Tim,

Great info there, thank you. I use BYE so all my data is fully labelled with all info and I am keeping everything in order and all sessions in separate labelled folders, like you say, it makes life so much easier

As i stated i am new to AP, and until this thread I haven't been aware of ADU or FWHM values. But a little googling later I am now informed of what they are/mean to a certain extent, though I will need to run through a few things to clarify my understanding. All part of the enjoyable learning curve!

I have got darks library but I havent collected enough data yet to make it a workable option. Basically every session I have, I collect all the different frames (light/dark/flats/bias) in one sitting. I realise that you dont have to take all these at the same time, but I wanted to do it all in one session until I have a better understanding of all the processes. Does make for a long night, but with all the excitement, sleep isnt really an option anyway

All I want to add to Tim's comments is that, if you do end up with slightly different orientations (and temperature) between sessions, then you'll be using different calibration frames (i.e. flats as well as fore-mentioned darks). DSS provides a "grouping" functionality that allows you to group your subs together with the correct calibration frames before stacking.

PS: I feel your pain. I've been waiting over a Month now to try and gather a few extra subs on the target I've been trying to image

Hi Lewis

thanks for your input.

So basically if I have understood you correctly, in DSS i would group each sessions light dark bias and flat frames together, and when DSS processes them it will create a master for each session and then stack them for the final result? thats really helpful, and I wouldnt have done that had you not mentioned it.

Anyway, thank you both for your help. I have just brought a coma corrector so I would imagine all previous data will be irrelevant now as the CC wasnt in the optical train?

My target/s were M42 and M31 but as these are now getting a bit low in the sky, I will move to something new. M51 is a favourite of mine so possibly that, but there is so much up there I am spoilt for choice! It has been suggested to me to work on star clusters to start with, as these will show up any problems in my setup, like collimation etc, as these targets are much less forgiving of anything that isnt quite right. So maybe it would be best to pick one of these as the next target.

TBH, the weather doesnt look like its getting any better for the next month!!! So i guess the first thing to work on is more patience. I thought i was a patient man, but only being able to have 2 sessions in 3 months I am really putting it to the test.

Thanks again

Jez

[Gina]

Yes, the weather has been, still is and looks like being for some time, absolutely dreadful for us Every so often we are promised a cold, clear night but what do we get - snow flurries and complete cloud cover!!! Aarrrgghh

[Sp@ce_d]

I used to think in terms of hours for imaging.. Then it became days... Then Months... Now maybe I'll finish that image in a couple or so years..

RegiStar is pretty good at aligning different camera/scope combinations

[x6gas]

Imaging with a refractor or SCT also makes life easier when imaging over multiple nights as you don't have the problem of diffraction spikes at slightly different orientations.

All the advice above is very sound... I usually find a bright star or something else that I can put at a repeatable place in the frame. I'm lucky on that I use off-axis guiding which means it's easy with PHD to put the guide star in exactly the same place if I am so motivated...

[M00NMonkey]

Yes, the weather has been, still is and looks like being for some time, absolutely dreadful for us Every so often we are promised a cold, clear night but what do we get - snow flurries and complete cloud cover!!! Aarrrgghh

Hopefully, when the weather decides to equalise, we will all be reward with a month or so of amazingly crystal clear skies! Here's to hoping

[M00NMonkey]

I used to think in terms of hours for imaging.. Then it became days... Then Months... Now maybe I'll finish that image in a couple or so years..

RegiStar is pretty good at aligning different camera/scope combinations

Cheers Sp@ce_d, I've not heard of RegiStar, Il check it out. Hoping it doesnt come with a hefty price tag

[Sp@ce_d]

Cheers Sp@ce_d, I've not heard of RegiStar, Il check it out. Hoping it doesnt come with a hefty price tag

I was posting from my phone so couldn't work out how to add the links.. It's here http://www.aurigaimaging.com/

I'm also finding PixInsight's alignment routines quite good too.

[M00NMonkey]

Imaging with a refractor or SCT also makes life easier when imaging over multiple nights as you don't have the problem of diffraction spikes at slightly different orientations.

All the advice above is very sound... I usually find a bright star or something else that I can put at a repeatable place in the frame. I'm lucky on that I use off-axis guiding which means it's easy with PHD to put the guide star in exactly the same place if I am so motivated...

Thats a very good point, I hadn't thought of the diffraction spikes. I do really like them, they seem to add that little bit more magic to an image, though thats personal taste and opinion. But yes, I would imagine aligning them would be a nightmare!!. I suppose it is more than possible to get lucky with alignment, but this is something I will have to play around with.

All my imaging is unguided, and for the record I am not buying any more equipment this year (I keep telling myself ) so I want to learn as much as I can with the equipment I have got. Saying this, I really want the dual focuser as I can waste a lot of valuable time playing around with image focus, though I think bad seeing has been a big part of this. Oh, and a nice 2" 32mm EP and a .............. ARRRGGHH!!!!!

TBH I am not even sure of what off-axis guiding is yet. I have too much other infoformation to process before I even begin to think about this. Il leave that to the experts for now

[M00NMonkey]

I was posting from my phone so couldn't work out how to add the links.. It's here http://www.aurigaimaging.com/

I'm also finding PixInsight's alignment routines quite good too.

Thanks for the link. If its as good as it sounds the £100 would be well worth it. But, at the rate I am going, i wont need to use it before around 2020 so hopefully this will become freeware by then

[x6gas]

I would suggest that you don't need RegiStar unless you are trying to combine subs using different scope and camera combinations (it comes in to its own when combining images with different fields of view).

[Sp@ce_d]

I would suggest that you don't need RegiStar unless you are trying to combine subs using different scope and camera combinations (it comes in to its own when combining images with different fields of view).

Yes I agree, if your kit stays the same you probably don't need it, but the OP did mention acquiring data over possibly years. So one would assume camera/scope changes during that time.

[Gina]

I find RegiStar very useful with data from several nights as I rarely get the image in the same place in the frame or at the same angle. Before I had it I aligned by hand in PS and it was very tricky. I've certainly never regretted buying it.

[Epicycle]

Concerning framing the same object over different nights one could also use some plate-solving via Astrotortilla or directly at the web astrometry.net. That would give you precisely

the coordinates of the center of your image which you can input in your Cartes du Ciel or similar planetarium software and it will take you exactly where you were the previous night/month/year.

The better aligned the images to begin with the less cropping and the easier the stacking as pointed out above,

cheers

E.

[Gina]

I think I've only had one night of clear sky to try AT since I installed it several weeks ago I think I have it working but won't know until we get a clear night... Keep getting forecasts of clear, frosty nights but the clear part never seems to materialise

[M00NMonkey]

I would suggest that you don't need RegiStar unless you are trying to combine subs using different scope and camera combinations (it comes in to its own when combining images with different fields of view).

Yes I agree, if your kit stays the same you probably don't need it, but the OP did mention acquiring data over possibly years. So one would assume camera/scope changes during that time.

I find RegiStar very useful with data from several nights as I rarely get the image in the same place in the frame or at the same angle. Before I had it I aligned by hand in PS and it was very tricky. I've certainly never regretted buying it.

Sounds like it is software worth having if I ever upgrade the kit. Its been noted. Thanks for the advice

Jez

[M00NMonkey]

Concerning framing the same object over different nights one could also use some plate-solving via Astrotortilla or directly at the web astrometry.net. That would give you precisely

the coordinates of the center of your image which you can input in your Cartes du Ciel or similar planetarium software and it will take you exactly where you were the previous night/month/year.

The better aligned the images to begin with the less cropping and the easier the stacking as pointed out above,

cheers

E.

I have seen this data from astrometry.net before somewhere, probably on SGL. But I have an EQ5 with dual motor upgrade only. No guiding, st4 port etc, so this is not a possibility for me for the foreseeable future.

It would be nice to tap a few buttons and let the computer do all the finding and aligning. But wheres the fun in that

[Epicycle]

Hi MoonMonkey,

I don't think you need guiding or ST4 for what I was saying above. Once you have the coordinates (RA and Dec) of your previous image and your mount

is aligned you can implement them manually and it should take exactly where you were; of course a goto and software makes it easier,

cheers

E

[Sp@ce_d]

To be honest, to progress in AP you should focus attention first to the mounts stability & guiding capability for any decent length exposures. Comes before anything else really.

[M00NMonkey]

Hi MoonMonkey,

I don't think you need guiding or ST4 for what I was saying above. Once you have the coordinates (RA and Dec) of your previous image and your mount

is aligned you can implement them manually and it should take exactly where you were; of course a goto and software makes it easier,

cheers

E

Thanks E,

But i dont use the clocks on my mount, they are hopeless IMO half of them dont even lock into position so one knock and you've had it. I cheat when polar aligning but it works with great success so far

[M00NMonkey]

To be honest, to progress in AP you should focus attention first to the mounts stability & guiding capability for any decent length exposures. Comes before anything else really.

I was hoping that the dreaded "you need to upgrade your mount" wouldnt rear its head.

I know My setup is on its limit, I knew it would be before I made the purchase. And TBH i am glad I haven't shelled out 1k+ on a heavier mount. It would just be sitting around gathering dust, maybe holding the odd hat or coat! If only I grew money trees and not chillies I assure you things would be different, but it was just not a feasible option for me.

I have done a lot of research on people using the same setup as me and the results I have seen are stunning. So, as stubborn as it maybe, I am determined to get results that I am proud of, using the set up I have. I am already pleased with the small amount of data I have managed to capture so far, though I am sure a lot of the more advanced AP-ers would bin the lot.

I also want to get some widefield subs just mounting the camera, if the weather ever gives me the time too, so my mount is more than adequate. And besides all this, I still have to get to know all the bells and whistles on Photoshop and other processing software so I have plenty to learn before the exposure time and guiding become a problem for me.

I do understand your point and thanks for advice. But I hope you understand my way of thinking

Jez

[Sp@ce_d]

I was hoping that the dreaded "you need to upgrade your mount" wouldnt rear its head.

I know My setup is on its limit, I knew it would be before I made the purchase. And TBH i am glad I haven't shelled out 1k+ on a heavier mount. It would just be sitting around gathering dust, maybe holding the odd hat or coat! If only I grew money trees and not chillies I assure you things would be different, but it was just not a feasible option for me.

I have done a lot of research on people using the same setup as me and the results I have seen are stunning. So, as stubborn as it maybe, I am determined to get results that I am proud of, using the set up I have. I am already pleased with the small amount of data I have managed to capture so far, though I am sure a lot of the more advanced AP-ers would bin the lot.

I also want to get some widefield subs just mounting the camera, if the weather ever gives me the time too, so my mount is more than adequate. And besides all this, I still have to get to know all the bells and whistles on Photoshop and other processing software so I have plenty to learn before the exposure time and guiding become a problem for me.

I do understand your point and thanks for advice. But I hope you understand my way of thinking

Jez

Jez I do understand.. I struggled piggybacking my dslr on a Meade ETX125 for quite a while until I saved for the EQ6. So, I'm sure you'll be doing much better with the EQ5 & widefield is the way to go with this. I guess I'm trying to say beware of false economy. Forget most of the other expenditure discussed in the thread so far.. If you are wanting to get serious about AP the next step would be to focus on improving the mounts stability & tracking. You're also right about a heavy mount.. the EQ6 did my back in.. I ended up building an obsy for it...

[x6gas]

To be honest, to progress in AP you should focus attention first to the mounts stability & guiding capability for any decent length exposures. Comes before anything else really.

You are correct, of course, but in fairness the OP's question was quite specific about what was required to combine subs from multiple sessions and the advice given is sound...