Images over multiple nights

[AlistairW]

Hi,

So I have only processed images taken on a single night. What if I want to take several sets of images over multiple nights ?

Currently I use SGP and slew to the target based on the RA and DEC setting from archives in Astrobin. Do I simply make a note of this RA and DEC settings and use that on subsequent nights ?

Then how best to stack these multiple nights of data together. I am playing with AstroArt, so do I simply add all the files over the nights to the Images selection, and then stack. I am wondering if the software handles and 'deviations' between the different nights.

Sorry if these seem like obvious questions :-)

Thanks

Alistair

 

[MikeODay]

Re-using the same RA and Dec should get your scope pointing back at the target ( subject to any differences in scope alignment etc. between the nights ).  I would normally then take a photo and compare the position of the target in the image with that in an image from the previous session.  If not completely aligned I tweak the position of the scope and recheck.  Repeat until happy.

I would normally just add all of the images from all sessions ( with the same exposure ) into a single stack for processing ( having discarded any with poor quality ).

I hope that helps.

Mike

[Adreneline]

Hi. Even after 10 months I am still at the bottom of every learning curve, however, I also use SG Pro and have found the add-on to allow plate solving very good for repeatedly going back to a target.

In terms of combining images I have used PixInsight (which I decided was a worthwhile investment compared with what I'd spent on hardware) but not found it particularly easy for combining images and not always been that pleased with the end result, although that is probably down to my novice skills at PI. In all other respects I have been very pleased with PI and obtained far better processing results than I ever did with PS.

I have recently started using Registar and so far I have been very impressed with the way it can register and combine images taken on different nights, using different camera systems (414ex osc, 428ex mono and even a 70D dslr), and produce a very good end result which I have been able to further process in PI and obtain a positive end result. I am hoping to get even better results once we are finally blessed with some nice long, clear and very dark nights. I've nearly forgotten what one of those is!

You know I never noticed the cloudy nights before I took up AP - I must have constantly had my head in the clouds.

[wimvb]

If you can leave your equipment parked and don't have to tear down / set up each imaging session, imaging on several nights is easier. If youcan do platesolving andhave a computer controlled mount, great.

If none of the above:

Make sure you can position the tripod in the same position (markings on the ground).

Level the tripod each session. (Not essential, but makes everything easier.)

Accurate polar alignment and star alignment (I use a barlowed 10 mm eyepiece with reticle, works great on my az eq6 mount).

Align your camera with RA by slewing the mount in RA+ while doing an exposure. The star trail should line up with the image/sensor edge. If not, rotate the camera and repeat.

Take a test exposure and check if it lines up with a frame from the previous night. If not, adjust RA and DEC.

Good luck

[Stub Mandrel]

If you can stoop to using DSS, I posted this in the 130P-DS thread a short while ago in response to an almost identical question:

Quote

 

When you have stacked in DSS, you get the option to save the file list.

If you get more images, load the file list and all your old files will reappear. At the bottom you will see a tab called 'main group' and next to it is 'group 1'. Select Group 1 and add your new files, and any updated flats, darks etc. (not essential if nothing has changed, but you can do things like add, say, 1-minute subs to your 30s subs). If you don't add new ones, it will use the main group ones.

Then stack as normal, and it will choose the best across both sessions.

You can re-save the file list and add more subs if you have another session.

I have combined sessions a year apart to get improved results, but they must use the same optical setup (scope, any lenses, and camera) as it won't stretch images at different scales to match each other.

 

 

[ollypenrice]

The problem variable might be flats. If something has changed in your light path between nights 1 and 2 or 3 etc then your workflow will have to allow for this. If it doesn't, and your flats are good to go, just ask AA, on the second pre-processing page, to give you a good range of rotation. If you have a meridian flip to deal with, set the rotation to 180. You might as well set it there anyway.

If your flats or other calibraton files have changed between nights you should, ideally, calibrate them individually. Make a set of Night One subs with night one flats and save them without combining them. AA will give a _P fit suffix to each. Do the same for Night 2 subs, etc.

When you have enough data take all the _P fit subs and load them into preprocessing with nothing else added and combine them using Sigma average and star alignment- translation and rotation. This way you will get full value from the number of subs in your set and benefit, above all, from the Sigma routine.

Olly

[Stub Mandrel]

1 hour ago, ollypenrice said:

If your flats or other calibraton files have changed between nights you should, ideally, calibrate them individually. Make a set of Night One subs with night one flats and save them without combining them. AA will give a _P fit suffix to each. Do the same for Night 2 subs, etc.

DSS sorts this automatically, I'm still not sure why it is 'looked down upon' - much of the criticism seems to be for features it has that you don't have to use.

[ollypenrice]

16 minutes ago, Stub Mandrel said:

DSS sorts this automatically, I'm still not sure why it is 'looked down upon' - much of the criticism seems to be for features it has that you don't have to use.

My attempts wth DSS left me wondering if I would live long enough to see the final calibrated stack. How does it know which set of flats go with which lights?

Olly

[Stub Mandrel]

Just now, ollypenrice said:

My attempts wth DSS left me wondering if I would live long enough to see the final calibrated stack. How does it know which set of flats go with which lights?

Olly

You put each session in a separate group tab, if you don't include flats etc. it uses the ones from the default group, otherwise it uses the control frames in a group with the subs in that group.

 

[ollypenrice]

4 minutes ago, Stub Mandrel said:

You put each session in a separate group tab, if you don't include flats etc. it uses the ones from the default group, otherwise it uses the control frames in a group with the subs in that group.

 

OK, that's quite nifty. Thanks.

Olly