Calibraing and platesolving but not stacking?
Stacking program, astrometric (plate) solver, fits file viewer
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Hi!
I'm fairly new to ASTAP (mainly been using for platesolving integrated
in Ekos), but slowly getting to know the program. I'm now wondering if
there is a smooth way to calibrate images and plate solve them, but not
stack. I'm working with variable stars and need to process images of
maybe 30 different stars to then upload to VPhot and measure there. What
is needed is only calibration and platesolving, preferably as a batch
process to save a lot of time. however, I can not this far see how to do
it. I know how to batch plate solve, but calibrate....? I guess there is
a good description somewhere - someone could give me a hint or link? :)
Magnus Larsson
1) In stack menu (ctrl+A), tab stack method you can select "calibrate only" or "calibrate + align" This will calibrate all selected images in tab images with darks, flat, flat darks.
2) In the viewer tool menu you can select batch solve the images,
Probably more efficient:
3) In tab photometry you can measure the absolute magnitude of a star in a series of images and select, copy and paste the result to a spreadsheet. (solving and calibration is included so not required in advance.)
Here are two YouTube links demonstrating the photometry (option 3):
part1
https://www.youtube.com/watch?v=wfFWmtj9Oes
part2
https://www.youtube.com/watch?v=4orWemJYzMw
Option 1 and 2 are only very briefly mentioned in the manual
Or do this:
http://www.hnsky.org/astap.htm#star_annotation
Last edit: han.k 2020-11-25
hi!
Thanks! Since I don't do time series that much, but have a bunch of images of different targets, options 1 + then 2 seems to work best. But the fits files become huge - over 100 MB. The are 17 MB originally. Why is that?
Magnus
Normally they should become a little less then twice the size. This is because you go from 14 bit to 16 bit and no compression. The solved files should be 16 bit fits. Can you check in the header
16 bit:
BITPIX = 16 / Bits per entry
or
32 bit
BITPIX = -32 / Bits per entry
For you it is a factor 6. Did you convert them to colour? Yes then you get 6 times the size.
Han
Hi!
OK, I did it again and noted the "Convert OSC to color" - that was
checked. Mine are monochrome 16 bits images. Now they are 33,9 MB instead
THe fits header does say BITPIX = -32. Why 32 and not 16?
And what with going from 14 to 16? Mine are 16 bits originally.
Best,
Magnus
Den 2020-11-27 kl. 23:15, skrev han.k:
Normally if they are 16 bit, they should stay 16 bit. Can you describe what steps you did and at which step they doubled in size?
Han
Hi!
Images obtained with Atik 383+ L. I use Ekos to image. Transferred to
computer as fits, no conversion.
In ASTAP:
I use the Stack menu (tool). Choose image files in Images tab, 50 darks
in the Darks tab, one flat in the Flats tab, them Stack method tab. Here
I switch stacked image to Calibration only. Uncheck Convert OSC images
to colour. Press Stack (Calibration only).
So: 17 MB input to Stack procedure, 33,9 as output images
That's it :)
Btw: are the image automatically plate solved in this process as well?
They were marked as WCS by VPhot.
Magnus
Den 2020-11-28 kl. 09:41, skrev han.k:
That is normal. For stacking ASTAP has to switch to floating point values so 32 bit FITS (Bitpix=-32) For example if you stack 2 images and one pixel has the value 100 and the next 101, once you combine them you will get (100+101)/2 equals 100.5. You don't want to store that as 100 or 101 loosing gray levels. So the stack will be double in size compared with a single image.
Last edit: han.k 2020-11-28
OK!
Thanks for clarifying! This size is very acceptable too.
How about plate solving, is that part of the process I described?
Best,
Magnus
Den 2020-11-28 kl. 10:37, skrev han.k:
You can also see that in the status bar. For the stacked image the pixels have floating point values, so decimals behind the comma/dot. If you save to jpeg or png pixel values will become integers again but then you stretch the image to be in range.
Here is a checklist for solving:
http://www.hnsky.org/astap.htm#conditions
Hi!
I'm still not getting this right. The calibrated images have a medium ADU of around 25 000 - 40 000, while the original lights hae some 5000. I have uploaded two fits files to:
https://www.dropbox.com/sh/y4v8b5gaw1k8vle/AAAEByaQdMR5UHZ0PjM63K_9a?dl=0
I'm using 50 darks, 5 flats, testing with or without 180 bias frames loaded as flat darks (no difference in results).
Any idea on what is going on here?
Magnus
Hello Magnus,
The dropbox is not accepting me even when I make an account. Maybe something with sharing permissions.
Een ADU of around 25 000 - 40 000 is wrong. It should stay close to the 5000. Can you share some images, darks , flats, flat-darks ? Dropbox or try this one https://ufile.io/qpbcf
Han
You could share the dropbox files to:
idezlunrhhblescsxr@upived.online
Hi!
I tried sharing with the emailadress - not sure if it works (I have
alerted my IT-department about the difficulties of sharing). And here
are a few files, unfortunately in three packages:
https://ufile.io/f/kduxj
https://ufile.io/kre47il6
https://ufile.io/f/p4ihw
Does this work?
Best,
Magnus
Den 2020-12-05 kl. 13:01, skrev han.k:
I duplicated the 300 seconds images and it stacks all normal with the dark and the combined flats. The background stays around 4900.
The dropbox still doesn't allow me to download.
Can you upload several lights and flat darks.? Combine the file in a zip file so I don't have to solve puzzles for each image.
Han
Hi!
OK. Here is a batch of bias (I take them with shortest possible
exposure) and more light frames.
https://ufile.io/giq4qdcw
My guess is that the files are OK (they calibrate fine in AstroImageJ)
but that I do something very wrong in ASTAP that I just cannot see ....
what could I do that causes this?
Magnus
Den 2020-12-06 kl. 22:19, skrev han.k:
I have only look to the 240 sec light. The other lights are of a very different exposure time. Flat and bias are combined correctly. The two 240 sec images combine correctly. The third light is poor and suffering from ice on the sensor. I assume it is time to replace desiccant.
As you can see in the header log it used 5 flats, 10 bias frames, one dark and 2 lights. The background is equal.
Hope this helps, Han
Hi!
Yes, there are very different times since these are for variable stars,
not several images of the same image. I know there is an issue with the
dessicants on this camera, to be handled.
But still, what might I be doing wrong to get the very different
background brightness? I just can't see it. I mean, I get the same too
bright background on the "good" lights here, as on the "bad". It must be
something in my process, rather than the quality of the lights.
What I'm working on, is to get a more efficient process for several
(more than 50) different images on different targets, different exposure
times, each night, to be prepared to upload to VPhot and measure there.
ASTAP seems to offer a very smooth and quick process for this - if I get
it right....
Best,
Magnus
Den 2020-12-06 kl. 23:26, skrev han.k:
Different exposure times is not a problem if you have the corresponding different darks available. With "classify" of exposure time it will select the corresponding dark. But I would standardize on a limited amount of exposure times. Personally I only use 50 and 200 seconds.
Start also with a small amount of images first to get confidence in the process. Once your happy with the setup start with a large amount of images.
Filtering on the image quality and excluding poor images is also important.
Clear skies, Han
Last edit: han.k 2020-12-07