Last night I completed one of my first imaging sessions and was pretty disappointed with the results. I tried to take subs of 20s, 30s, 45s 60s, 90s. The 90s subs were totally washed out and the 60s mostly were. I image on a parking garage in the downtown of one of the largest cities in the US. I have a LP filter but I wonder if my broadband setup is no match for the LP and full moon or if I am doing something wrong
Scope: Orion ED80
Auto Guider: Orion Starshoot
Mount: Sirius EQ-G
Focal Corrector: Orion .85 Reducer and Corrector
Camera: QHYCCD 168C
I blinked, debayered, aligned, stacked and stretched my images and they are terrible! The 90s image you couldnt even see the center of M31 hardly. Should I stick to 100s of 20s images or am I doing something wrong on my 90s subs? I attached some of the subs and the stacked image (mostly 20 and 45s subs). I haven't incorporated my darks, flats and bias because it seemed pointless after the initial processing.
Stacked image is
20s Subs - 13
90s - 1
All other subs were terrible. I realize this is very little as far as subs go but I thought even a sinlge 90s sub would be better than the stacked image was. Something doesnt seem right.
Thanks for all the help!
You have a difficult situation, but...
Under a full moon imaging anything other than a star cluster is pretty futile. For anyone.
I image in light polluted skies, Bortle 7, mag per arc sec squared low 18s. What you see on the stack is correct. You fix it with gradient reduction in processing. Example below. It's shows simply one pass of ABE in PI, using only a ScreenTransferFunction to visualize the images. You must change the default correction from none to subtraction. Otherwise ABE does nothing (PI can be pretty idiosyncratic).
The fact that my background is blue instead of green has no significance.
You set exposure by computing the average value of a sub in electrons (PI gives data numbers or adus <same thing>). Compare it to the read noise of your camera squared. It should be between 5 and 10X that number.
Then shoot more subs. Total imaging time is crucial in light polluted skies. You did about 9 minutes, way too little. My rule of thumb is 1 hour minimum, two is better, 4 is good.
Bias, flats, and darks are necessary, For one thing is, if you omit them, you'll almost certainly learn bad habits in processing. Processing is hard enough without having to unlearn bad habits. <smile>
The LP filter is useless on galaxies. It can work some on emission nebula, but has drawbacks. I basically don't use one, even on emission nebula like that below. You can see the results on my astrobin, although some emission nebula images used narrowband filters, which are light pollution filters that work (on emission nebulae).
Edited by bobzeq25, 15 November 2019 - 01:23 AM.