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Hey all,
i'm hoping some of you more experienced imagers can help me out with this image. first time imaging for this duration of time and number of sessions. just started AP a few months ago. this is m101 that i imaged over 5 sessions of data. i'm having a hard time color correcting this in APP to get the stars of proper color. I seem to be getting a slight purplish color to some of the really small background stars. at least i think they are stars, maybe its really noise? also, noticed still have a few hot pixels(red color) that the BPM didn't pick up. any suggestions on how to address these? feel free to take my fits file and play with. here's what i collected:
this is about 11-12 hours worth of data
lights: 2minute exposures, 800 iso canon 6d, william optics gt81, guided
darks: i collected 20-50 darks each session at 800 iso, same temp, focus
flats: collected 40 subs at the same focus for iso 100, and iso 800
bias: 200 bias subs
my fits file, BPM, and example lights, dark, flat, and bias subs are located in the following google drive link: https://drive.google.com/drive/folders/1p2fhKsWJzBRtFNHeFLok2xBLOUBsKxU7?usp=sharing
would appreciate any guidance you could give! been sitting on this since april!
@cheastside Hi Cory, it may be hard to find the cause with only a few files. Still, I have some questions. You write that you have images for 5 sessions and flats for both ISO 100 and ISO 800. Does that mean you have flats for two ISO values for one or more sessions? Or does each session only have flats for one ISO value and some sessions have ISO 100 and others ISO 800?
Did you try to integrate the data of only one session to see if that produces correct colors?
And could you upload, say, 5 to 10 lights, darks, flats and bias of each session to
https://upload.astropixelprocessor.com/
using upload4 for both username and password? Please create a folder called cheastside_purple_stars and put the files in there. It would help if you created sub-directories for each session and put the corresponding files in there. Thanks!
@cheastside Hi Cory, it may be hard to find the cause with only a few files. Still, I have some questions. You write that you have images for 5 sessions and flats for both ISO 100 and ISO 800. Does that mean you have flats for two ISO values for one or more sessions? Or does each session only have flats for one ISO value and some sessions have ISO 100 and others ISO 800?
Did you try to integrate the data of only one session to see if that produces correct colors?
And could you upload, say, 5 to 10 lights, darks, flats and bias of each session to
https://upload.astropixelprocessor.com/
using upload4 for both username and password? Please create a folder called cheastside_purple_stars and put the files in there. It would help if you created sub-directories for each session and put the corresponding files in there. Thanks!
i did flats for each session of 100 iso and 800 iso. the 800 iso flats for each session match the same exposure duration as the lights (120s). for each session there is also flats at 100 iso for 1s duration. i uploaded all of these into APP. i use a white tshirt pointed at the sky in the morning, away from the sun to make the flats.
i think i was having the purplish color with just one integration as well.
i've uploaded 10 files or so for all sessions, lights, flats (100 and 800 isos), darks, and bias frames. i guess i only did 4 sessions here: https://upload.astropixelprocessor.com/sharing/I8hwKz39Y
thanks for any help and suggestions!
@cheastside Thanks very much, I am downloading the data. It looks like the ISO 800 flats are 1 sec as well, just like the ISO 100 flats. At least, that's what the file names say. But I'll have a closer look as soon as the data have been downloaded.
@wvreeven looks like i messed those flat iso 800s up. supposed to be at the same exposure duration as the lights and darks. maybe that is the problem that's causing the purple color and bpm not picking up all the hot pixels. ugh....
@cheastside What I don’t understand is why you aim to have flats with the same exposure time as the lights. That’s not necessary at all. Also, combining flats of different ISO values may cause problems. ISO 100 with exposure times of 1 to 5 seconds is more than sufficient. If you use a different ISO then you’ll need darks with the same ISO for better dark noise compensation. But honestly that’s all.
@wvreeven i guess i don't understand either haha. so eliminate the 800 iso flats and keep everything else is the way to do it?
@cheastside Not necessarily. I’m still downloading the data and will have a look tomorrow probably.
@cheastside I integrated the images of the first session using only the flats of ISO 800 and the result looks very promising:
Now I am integrating the images of all sessions using only the ISO 800 flats. Once that's done I'll report back here.
FYI I have used all default values in APP 1.083 Beta 1 apart from ticking "create 32-bit Masters" in tab 2. Did you change any of the default settings in APP? And what version of APP are you using?
@cheastside With all four sessions again no purple stars:
Again I checked "create 32-bit Masters" in tab 2 and the only other modification I made was to integrate both the sessions separately and all together in tab 6.
thanks Wouter! i left everything at the defaults in all tabs and am using 1.082. i think the purple stars started showing up when i was using the calibrate star colors.
i did rerun all session yesterday and only used the iso 100 flats. looks like i got a better result that way, no hot pixels and after playing with calibrate star color i didn't have the purple color issue.
so for flats which iso should i be using? iso 100 with 1-5sec duration or iso 800? really hard to get long shutter speeds at iso800.
thanks for all your help!
@cheastside For flats the ISO version is not very important. Much more important is to make sure that the histogram is as far to the right as possible without clipping. If you use a different ISO then you’ll need darks of the same ISO, temp and exposure time as the flats.
