hi, I've recently purchased a C925 XLT with F6.3 reducer and ASI294MC Pro.
sharpcap/Phd2/OAG
hoping it was to be a step up from my 10'' reflector for imaging.
I'm starting to think it was a step backward.
After taking 120 subs @ 180s gain 119 and stacking M83 I can see only the faintest hint of the galaxy...what am i doing wrong? or have i made a very expensive mistake?
any help would be appreciated.
thanks in advance.
Rem.
I use the QHY version of that camera, and although my scope is faster than yours (f4.75) i'm still getting plently of signal on that target after 6 hours of integration.
what software are you using to stack the images? what are you using to process the stacked image? were the sub frames calibrated with darks/flats/bias etc?
If you’re imaging a dim galaxy under LP skies B6 to B9 then your stacked linear image is always going to be faint where you just see the bright core and very little detail in the spiral arms.
Did you stretch the image ?
With that amount of data even under LP skies you should see some detail above the noise floor when stretched, particularly with a big scope.
Was your scope focused correctly on a small star ?
I also concur with Richard , a calibrated data set will adjust the background to the correct brightness values.
Cheers
Martin
Perhaps you could post a screen shot here of a single subframe with just a screen stretch?
How did you decide that 180 sec was sufficient?
Did you use flats and were they calibrated correctly?
M83 is a pretty bright subject. This seems to be an odd issue so I suspect as others have mentioned that something is going wrong with your processing. However, if single subs in a linear state look poor then stacking will not magically improve the situation. You need decent signal on each sub.
Peter,
I will need to recapture the image as I deleted it in disgust.
am i wrong in thinking single sub exposure time ie 180s isnt that important and that the total integration time that matters..
ie 180s x 100 vs 360s x50 = the same end result.. ?
This image was taken with a 1986 vintage Celestron C8, using a Celestron focal reducer and an ASI294MC Pro camera, with 300-second exposures captured in Bortle 5-6 skies. I processed these subs about two years ago.
If you’re not directly under a streetlight, you should be able to achieve results on par with or potentially better than this.
Without seeing your stacked image, it’s challenging to pinpoint the exact issue. However, I recall my initial experience with an IMX571-based camera: after processing the subs, I was disappointed with the dark and low-detail result. In my case, I had taken the dark frames with the camera set to a 50 bias offset, but the NINA imaging session defaulted to a 20 bias offset. As a result, when the darks were subtracted from the subs, the image lost its nebulosity and went too dark. It might be worth checking if something similar happened with your setup.
Just a thought….,
When you gather more data why not try stacking in a bonafide DSO stacker.
Autostakkert obviously does stack DSO subs but it’s primarily a planetary stacker and was designed mainly for Planetary imaging. Emil did provide an option for stacking DSO but I believe it doesn’t have pixel rejection algorithms , struggles with any field rotation and a few other short falls.
I use ASTAP , it’s open sourced freeware, and the results are right up there with Pixinsight. Been using it for nearly 2 years now and its fits viewer is top notch for reviewing subs on the fly during a session.
