New to mono - basic workflow questions

[Spaced Out]

Hi All

I’m brand new to Mono imaging and have come from using a simple process of DSLR without calibration frames. I’m trying to get up and running and I have a couple of BASIC questions regarding workflow.

1 – When imaging over multiple nights should you take a range of LRGB frames and calibration frames on each night or can you (should you ?) spread the filters over different nights, for example one night each for each filter and the calibration frames for that filter ?

2 – Which calibration frames should I do each night ? I have a cooled camera so can create master darks and I also dither (so do I need the darks ?). I can do flats but I haven’t tried doing bias frames yet and I don’t know what dark flats are but I’m sure google will help me !

Thanks for any advice you can offer.

[MarkAR]

I think getting flats might be more important each night as dust motes might change. I'm probably wrong as I've yet to make a start but will follow with interest.

Dark Frames, may as well create some masters.

[Adreneline]

21 minutes ago, Spaced Out said:

1 – When imaging over multiple nights should you take a range of LRGB frames and calibration frames on each night or can you (should you ?) spread the filters over different nights, for example one night each for each filter and the calibration frames for that filter ?

I would tend to go for a range over one night because at least you will end up with something you can start to process and add to over future nights. Be aware that focus positions may vary betwen filters even if they are parafocal; my experience is that blue can be a problem in this respect. If you are going to go back to the same target over a number of nights the ability to plate solve is a real bonus.

23 minutes ago, Spaced Out said:

2 – Which calibration frames should I do each night ? I have a cooled camera so can create master darks and I also dither (so do I need the darks ?). I can do flats but I haven’t tried doing bias frames yet and I don’t know what dark flats are but I’m sure google will help me !

I would take darks on a cloudy night and create a master dark that would suffice for all your filters; same for bias if you want to take bias.

I agree flats are best taken each time but having said that if you are using a 'sealed' filter wheel you can probably get away with only taking flats periodically or if you notice something like a dust bunny on one of your integrated stacks.

Dark-flats are exposures taken with the same exposure time as corresponding flats but with the lens cap on (no light on the sensor).

Stand back for a whole range of answers!

HTH

Adrian

[MarkAR]

3 minutes ago, Adreneline said:

Stand back for a whole range of answers!

 

BTU

[Adreneline]

9 minutes ago, MarkAR said:

BTU

? What's the connection with British Thermal Unit ? Lost me on that one!

[Skipper Billy]

1 hour ago, Spaced Out said:

1 – When imaging over multiple nights should you take a range of LRGB frames and calibration frames on each night or can you (should you ?) spread the filters over different nights, for example one night each for each filter and the calibration frames for that filter ?

2 – Which calibration frames should I do each night ? I have a cooled camera so can create master darks and I also dither (so do I need the darks ?). I can do flats but I haven’t tried doing bias frames yet and I don’t know what dark flats are but I’m sure google will help me !

Point1. - it doesn't really make any difference whether you take one filter per night or all filters on each night - the only advantage I can see is you could shoot your Lum when the seeing is at its best and take the RGB when the seeing is not so good.  

Point 2. - Personally I take a full set of all calibration frames at the start of the season and use that library throughout that winter - then delete them when the rig comes inside for the summer. I use Flats, darks and Bias but others have different methods. If you remove the camera or move anything in the imaging train then you will need to retake them all.  Technically you should take a set of flats for each filter but in practise I have never seen any advantage over using Lum flats for all filters.

What I don't know is whether you are using a set point cooled camera - if you aren't then you might need calibration files at differing temperatures.

Most importantly enjoy it!

 

 

[MarkAR]

1 hour ago, Adreneline said:

? What's the connection with British Thermal Unit ? Lost me on that one!

Oops, its Big Thumbs Up.

[Adreneline]

32 minutes ago, MarkAR said:

Oops, its Big Thumbs Up.

Haha. Um? Could this be a generation thing? I'm verging on neolithic - where are you

My son's despair of me - my grand-daughter is too young to despair of me - but the time will come.

Thanks for educating me - just goes to show you're never too old to learn.

 

[Spaced Out]

On 06/03/2020 at 15:21, Adreneline said:

I would tend to go for a range over one night because at least you will end up with something you can start to process and add to over future nights.

Thanks for this answer.

I can certainly see the attraction of using multiple filters in one night and slowly building your image up over time. However I don’t have an obs with a fixed rig (just have an outdoor pier), I have to move my telescope indoors at the end of each night. I thought if I take this multiple filter approach I’d have to take a load of flats every night (because each night I’ll have moved things about and maybe removed the camera to check collimation etc) ? This is why I was wondering if using one filter per night and playing the long game might be a better approach for me ?

On 06/03/2020 at 15:21, Adreneline said:

Be aware that focus positions may vary betwen filters even if they are parafocal; my experience is that blue can be a problem in this respect.

Thanks, I’ve read this and have been re-focussing between filters.

 

On 06/03/2020 at 15:21, Adreneline said:

 If you are going to go back to the same target over a number of nights the ability to plate solve is a real bonus.

 

I use APT and CDC, I have just downloaded astro tortilla for plate solving but haven’t used it yet.

 

On 06/03/2020 at 15:21, Adreneline said:

I agree flats are best taken each time but having said that if you are using a 'sealed' filter wheel you can probably get away with only taking flats periodically or if you notice something like a dust bunny on one of your integrated stacks.

If I am moving my telescope back indoors each night with the camera (and sealed filter wheel) still attached does this still stand ? If I remove the camera to check collimation I assume I have to re do the flats next time ?

Thanks again. 👍

[Spaced Out]

On 06/03/2020 at 16:13, Skipper Billy said:

Point1. - it doesn't really make any difference whether you take one filter per night or all filters on each night - the only advantage I can see is you could shoot your Lum when the seeing is at its best and take the RGB when the seeing is not so good. 

Great advice ! Thank you.

On 06/03/2020 at 16:13, Skipper Billy said:

Point 2. - Personally I take a full set of all calibration frames at the start of the season and use that library throughout that winter - then delete them when the rig comes inside for the summer. I use Flats, darks and Bias but others have different methods. If you remove the camera or move anything in the imaging train then you will need to retake them all.  Technically you should take a set of flats for each filter but in practise I have never seen any advantage over using Lum flats for all filters.

Thanks.

I have a permanent pier outdoors but usually bring the telescope carefully inside at the end of each session. It has the camera still attached and I do a star check with the camera to assess collimation at the beginning of the next session. Assuming I don’t remove the camera could I still use the same flats in this situation or should I re do the flats each night because I’ve moved it? If I remove the camera to re-collimate then I assume I must re do flats etc ? 

On 06/03/2020 at 16:13, Skipper Billy said:

What I don't know is whether you are using a set point cooled camera - if you aren't then you might need calibration files at differing temperatures.

I am using the ZWO ASI 1600 and usually set it to -20, creating a darks library should be easy (I hope !)

On 06/03/2020 at 16:13, Skipper Billy said:

Most importantly enjoy it!

Thanks ! 👍

[dannybgoode]

I am fairly new to imaging but have been honing a workflow over time.  Mine is as follows:

1/ First night I always try to take an equal number of subs for each LRGB.  I also take a flats sequence - using APT's flat sequence generator and then running it takes a matter of minutes to complete so no real reason not to.  At least that way you can have an initial play with some data to see where you are heading with the overall image

2/ If I know I am going to try to take more data over the coming nights I try to bring my scope in fully 'assembled' so I can just take it back out with no need to re-do the flats.  It seems to be quite often that at least one of the channels was interrupted by cloud or whatever so I concentrate on imaging the 'missing' data first before adding to the data overall.

3/ I am building up a calibration library so if I get chance I take some darks of varying exposures but don't take dark and bias frames per session - just building up the library over time.  Can be a good use of cloudy nights if you have a cooled camera - just run a sequence every now and then  

Note you don't need Astro Tortilla, just download Plate Solve 2 and the accompanying UCAC3 library and set up PointCraft in APT.  Once you've acquired an target using Goto++ you'll never look back

[Adreneline]

18 minutes ago, Spaced Out said:

If I am moving my telescope back indoors each night with the camera (and sealed filter wheel) still attached does this still stand ?

It's what I do but I use a refractor and have no experience of using a reflector.

I don't have a permanent obsy or even a permanent pier. I pick up the mount and tripod and position it on little reference marks on the patio and then I attach the scope, filter wheel, camera and focusser complete. I connect two cables between the mount/scope and power supply, plug into the mains and I'm good to start.

Some advocate only using the Luminance flat for all filters. I use Baader 1.25" filters (broad & narrow, in an eight position wheel) and when I examine the flats in PI for each individual filter there are noticable differences.  Because it is sealed I make the assumption nothing will get in, or out, and I stick with the same flats until I make a fundamental change. I always use the same gain, same offset, same temperature and a small range of exposures, generally 120s or 180s.

I used to be always making changes but I found I was spending more time messing around that imaging!

Good luck.

Adrian

[dannybgoode]

6 minutes ago, Adreneline said:

It's what I do but I use a refractor and have no experience of using a reflector.

I don't have a permanent obsy or even a permanent pier. I pick up the mount and tripod and position it on little reference marks on the patio and then I attach the scope, filter wheel, camera and focusser complete. I connect two cables between the mount/scope and power supply, plug into the mains and I'm good to start.

Some advocate only using the Luminance flat for all filters. I use Baader 1.25" filters (broad & narrow, in an eight position wheel) and when I examine the flats in PI for each individual filter there are noticable differences.  Because it is sealed I make the assumption nothing will get in, or out, and I stick with the same flats until I make a fundamental change. I always use the same gain, same offset, same temperature and a small range of exposures, generally 120s or 180s.

I used to be always making changes but I found I was spending more time messing around that imaging!

Good luck.

Adrian

Do you never rotate the camera.  If you do then the dust spots and other blemishes will be offset from the position they were in when the flats were taken.  Assuming you have a flat box then taking flats every imaging session is a trivial task and I see no reason not to do so each time.  Dark and bias frames don't matter as much.

Further, dust has a habit of getting into 'sealed' units and a filter wheel and camera combo is hardly IPX rated!

[Adreneline]

39 minutes ago, dannybgoode said:

Do you never rotate the camera.  If you do then the dust spots and other blemishes will be offset from the position they were in when the flats were taken.  Assuming you have a flat box then taking flats every imaging session is a trivial task and I see no reason not to do so each time.  Dark and bias frames don't matter as much.

Further, dust has a habit of getting into 'sealed' units and a filter wheel and camera combo is hardly IPX rated!

I don't rotate my camera, in fact I never change the alignment of the camera - it is always aligned with the sockets on the back parallel to the vixen bar.

All I can say is taking flats at the outset of an arrangement hasn't been a problem for me. As long as I don't open up the imaging train I've never noticed any new dust bunnies appearing in my images. Maybe I've just been lucky!

[carastro]

Quote

I don’t have an obs with a fixed rig (just have an outdoor pier), I have to move my telescope indoors at the end of each night. I thought if I take this multiple filter approach I’d have to take a load of flats every night (because each night I’ll have moved things about and maybe removed the camera to check collimation etc) ? This is why I was wondering if using one filter per night and playing the long game might be a better approach for me ?

If you are having to set up every night (including replacing the camera), it makes sense to do one filter per night and take appropriate flat frames.  Though this is rather a laborious way of doing it as if you are taking a whole set of filters each night, a couple of nights might be all that you need.  

However if you are leaving the camera attached, then no reason why you can't take a whole set of filters each night and re-use the flats.   

N.B. You said you didn't use calibration frames when using your DSLR.  Flats are probably the most important to use, and you can probably get away without doing darks if you dither.  However Darks and Bias need only be taken once and kept in a dark/bias library for future use provided the camera is always kept at the same temperature for the darks.

N.B. I always do twice as much luminance to RGB. 

Similar applies to narrowband if you are going down that route.

If the camera is not moved, you can either use plate solving to find the target again, or merely move it manually getting the stars in the same place as before. 

 HTH

Carole 

 

[dannybgoode]

12 hours ago, Adreneline said:

I don't rotate my camera, in fact I never change the alignment of the camera - it is always aligned with the sockets on the back parallel to the vixen bar.

All I can say is taking flats at the outset of an arrangement hasn't been a problem for me. As long as I don't open up the imaging train I've never noticed any new dust bunnies appearing in my images. Maybe I've just been lucky!

I envy you. I have to rotate my camera to frame certain targets so flats are part of my workflow. As mentioned previously though, luckily the APT sequence generator makes it a trivial 5 minute task so it’s not too bad.