Imaging over several nights.

[martin_h]

Common files go in main group...so in your case the 30sec lights + 30sec darks + flats + bias.

Group 1 - 60sec lights+60sec darks if you have them(+ new flats if you made them for the second night)

You only get Group 1 when you "fill" the Main Group" - Group 2 when you "fill" Group 1 etc.

[martin_h]

See the DSS help file - Technical Info - File Groups

[yesyes]

Ah, but of course... the help file... why didn't I think of that...

I'm beginning to understand this. Just one thing I didn't get yet:

"Dark, Flat and Offset/Bias Frames from the Main Group *may* be associated to Light Frames of any group."

Does that mean that when a specific group does not have any, say, bias frames in it, the bias from the main group are used. But when I load bias frames into a group, these will be use and not the ones from the main group?

Don't I need to make bias frames for each session?

[martin_h]

Thats right - you got it! ish:confused:

Ok here's the deal - you image over 3 nights and you break down the kit each night------

Night 1 - 1min exposures

Night 2 - 1 min exposures

Night 3 - 3 min exposures

You will need a set of 1min darks, a set of 3min darks, 3 sets of flats, and 1 set of bias.

Main Group - 1 min exposures + 1min darks + flats(for that night) + bias.

Group 1 - 1 min exposures + flats(for that night).

Group 2 - 3 min exposures + 3min darks + flats (for that night)

The 1 min darks are "common" to Main Group AND Group 1

The Bias are "common" to all groups

If you dont break down the kit each night then one set of flats would go in Main Group and be "common" to all groups

[IvanT]

Hi,

I know this is quite an old thread now but I found it an interesting read. One additional question I have. If the cumulative data extends over a long period doesn't the processing time increase significantly as you add more data?

Is there a downside to stacking say night 1 and producing a master flat, bias, dark, light, then store that in the main group. Then rinse and repeat for each subsequent night, storing the masters in group 1, 2 etc as you go. Wouldn't this way let you see how the project is progressing without having to wait longer and longer for the cumulative data to be stacked?

The reason I ask is that I'd like to try a longish (several hours worth) M31 and in the absence of a super computer, the stacking would take ages.

Thanks

[ollypenrice]

You can 'stack the stacks' if you like. I sometimes do this rather than start again from scratch provided I can weight the stacks reasonably correctly. Eg you wouldn't want to use an average combine routine on a 30x5mn stack and a 10x5mn stack because you'd slew the arithmetic badly.

On this thread I never did ask why you'd want to combine different sub lengths. I think you should work in one solid run of same length subs. If you need to get some shorts (eg for the Trapezium in M42) then you should take a new set for them and process them separately before layer masking them in later in Photoshop.

I believe Dennis (Roundycat) did test stacking the stacks in 'average' mode against full restacking and found nothing to choose. I concur from my own imaging.

Olly

[Black Knight]

Yep. But dont forget to add any new calibration frames to the new set......The Main Group will hold the calibration frames that are 'common' to all groups. So if your first group was 10 min exposures and your second group was 15 min exposures you would need to put 10 min darks in the main group and 15 min darks with the second group. All the calibration frames that are common to both sets go in the Main Group

Ahh ... I didn't realise it was done like that. I shall have to re-organise my (2 - I know, don't larf!), multi-night projects .

[IvanT]

Thanks for clearing that up.

Sent from my iPhone using Tapatalk

[martin_h]

On this thread I never did ask why you'd want to combine different sub lengths. I think you should work in one solid run of same length subs. If you need to get some shorts (eg for the Trapezium in M42) then you should take a new set for them and process them separately before layer masking them in later in Photoshop.

I was just using different sub lenghts as an example of what could go into "groups" within PHD, I agree with you that its a bit pointless stacking 1 min 5 min subs together.

[cardinals1225]

Thanks for all the info in this thread, I have a question, do all the frames in the main group and group 1, etc have to be the same ISO? Could the main group have 1600 ISO images and group 1 have 800 ISO's. I realize that different darks, etc would need to be taken for each group. Would this work?

[martin_h]

Yes that would work.

[Komet]

Hi all I’m building a small observatory/shed to try and get better setup for AP. I want to be able to return to objects on different nights to add more data to an image. How do you guys go about realigning an object to image it over several nights and how accurate do you need to be? Thanks,,,,Paul.

If you use Astroart or Nebulosity then there is a lovely front end piece of software that also runs the plate solving program Elbrus.

Now Sequence Generator uses Elbrus in such a way that you can ...

Plate solve and sync any location.

Having done this you can then slew to your target with more accuracy.

Nothing unusual there but it can also bookmark your focus star and your target so you can slew between the two if changing filters say. This is very handy.

Also, SG can load a reference image say from a previous imaging run. This it will plate solve and then slew the scope to that position validating the new position before reporting the difference in pixels between the centre of both images. You can run this a few times and the distance usually comes down to 0 - 2 pixels difference.

This is so useful as you can return to a previous target and centre the image automatically.

For example last night imaging run for me went thus .....

I started everything up, slewed to Capella and plate solved. I put Capella directly onto the centre of the CCD, added the Bahtinov Mask and focused with the Ha filter in line.

Went back to the Lum filter. Loaded my reference image from a previous run at IC410 (about a month ago?) into Plate Solving in SG. Clicked GO to automatically slew and solve to the reference image. A few seconds later the target was on the chip at a distance of about 120 pixels or so. Ran it again and once again and had a distance from the original centre of 2 pixels.

Set up a sequence in SG, calibrated the guider and clicked Start.

The time taken was a few minutes.

I use AstroArt but this also works with Nebulosity although I have never used it with that program.

Seriously useful software though - and free.