Imaging comet C/2022 E3 (ZTF) - capture settings?

[Moonstruck]

Hi, I will be imaging comet C/2022 E3 (ZTF) soon, and was wondering if you can recommend the ideal capture settings for this in Sharpcap (gain, exposure, etc). I have a ZWO asi 294 camera, Skywatcher Esprit 100 scope, and EQ6R mount. It would seem that a short exposure time would be best since the comet is moving in comparison with the stars, but what is ideal? I have read about people using anywhere from 2sec to 60sec exposures. Also I am assuming that a guide scope isn't needed here due to the short exposure time, correct? Any assistance you can give me will be appreciated!

[oopfan]

From astronomy.com:

Currently visible to observers in the Northern Hemisphere, the best time to view C/2022 E3 is in the early morning just a few hours before dawn. The comet's brightness now stands at about magnitude 7, making it easily visible through binoculars or any small telescope. And if the comet brightens to magnitude 6 or better, C/2022 E3 will be visible to the naked eye under good conditions.

As the comet approaches the Sun this week, a waning gibbous Moon dominates the early-morning sky, cutting down on visibility. Nonetheless, it’s worth trying your luck tracking it down with binoculars or a telescope. 

So then the sky should be dark enough to use your typical DSO exposure. How long of an exposure do you typically use? Also remember that the Moon will brighten the sky, so I'd recommend halving your exposure to deal with that.

Do you have a feel for unguided picture quality? You have three issues to contend with:
1. The accuracy of your polar alignment.
2. The periodic error of your mount.
3. The effects of atmospheric thermals and refraction.

They all have an effect.

Obviously the shorter the total integration time and exposure is best but I wouldn't recommend putting all your eggs in one basket. I'd recommend doing what is typically done in the situation of a Total Solar Eclipse. That is to run a series of different length integrations and exposures. Basically, have a plan and stick to it.

Modern digital cameras are very fast and magnitude 6 to 7 is very bright, so I think that you can get away with relatively short integration times.

Brian

[turfpit]

This might give you some ideas.

https://www.astrobin.com/search/?q=Come ... %29&page=2

Dave

[Moonstruck]

Thanks Dave and Brian- I appreciate the info. Hopefully I can give this a shot within the next week... it has been really cloudy here in CT lately, and there will hopefully be a window of opportunity to get an hour or so of imaging in at some point. I was also looking at DSS stacking options- from what I have seen from other posts DSS has a feature for comet stacking, and I want to try it out.

[admin]

Hi,

SharpCap 4.1 beta now has a comet stacking feature in live stacking - all very new and a bit experimental, but maybe worth a try.

Discussion here : viewtopic.php?p=34131#p34131

Latest download here : https://www.sharpcap.co.uk/sharpcap/sha ... p-4-1-beta

cheers,

Robin

[Moonstruck]

Robin, thanks for the info on the new comet feature!

I have another question. I imaged the comet using 30, 45, 60, 120 and 180 sec subs the other night, and processed them using dss and its comet stacking option #3 (comet and stars together). The comet and stars stacked well, but in my final image (processed using startools) I had an excessive amount of noise which I couldn't process out. I was wondering if you can tell me how this happened - did I use the wrong settings in sharpcap? I also noticed that the camera settings file says my camera temp was 9.8 degrees, in spite of me setting it to -10... could that have affected it?

If you have time to look at this, I included my raw stack (using about 80 30-sec subs) and final image so you can see all the noise. I also included my camera settings file. Any advice so I can avoid this in the future?

Raw stack:
https://drive.google.com/file/d/1ANB3SH ... sp=sharing

Final image:
https://drive.google.com/file/d/12bv9nk ... sp=sharing

Camera settings:
[ZWO ASI294MC Pro]
FrameType=Light
Debayer Preview=On
Pan=536
Tilt=0
Output Format=FITS files (*.fits)
Binning=1
Capture Area=3104x2822
Colour Space=RAW16
High Speed Mode=On
Turbo USB=80(Auto)
Flip=None
Frame Rate Limit=Maximum
Gain=117
Exposure=30.837s
Timestamp Frames=Off
White Bal (B)=52
White Bal (R)=52
Brightness=21
Cooler Power=100
Temperature=9.8
Target Temperature=-10
Cooler=On
Auto Exp Max Gain=0
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Trail Width=3
Minimum Trail Length=100
Trail Detection Sensitivity=9
Remove Satellite Trails=Off
Background Subtraction=Off
Planet/Disk Stabilization=Off
Banding Threshold=10
Banding Suppression=0
Apply Flat=None
Hot Pixel Sensitivity=5
Subtract Dark=None
NegativeDisplay=0
Display Black Point=0.0297196293290043
Display MidTone Point=0.0371611732235259
Display White Point=0.907805735930736
Notes=
EQMOD ASCOM HEQ5/6=RA=08:53:40,Dec=+79:11:09 (JNOW)
TimeStamp=2023-01-31T00:04:52.9721367Z
SharpCapVersion=4.0.9478.0
StartCapture=2023-01-31T00:04:48.1604760Z
MidCapture=2023-01-31T00:29:58.4314760Z
EndCapture=2023-01-31T00:55:08.7019310Z
Duration=3020.541s
FrameCount=97
ActualFrameRate=0.0321fps
TimeZone=-5.00

[admin]

Hi,

on the temperature side, it does look as though the cooling on your camera wasn't working - the cooler power is recorded at 100%, but the temperature is 9.8C. My first suggestion would be to check the 12V power supply to the camera - if that wasn't on, or had a bad connection then that would explain things (and be a cheap and easy thing to fix). If the 12V power was good then I would be concerned that the camera has a cooling problem

For the final image, the streaking pattern that is visible looks like it ties in with the direction of drift in the individual frames due to the motion of the comet - looking at the autosave TIF, you can see that the angle is similar to that suggested by the edge effects at the bottom and the right.

Capture.JPG (37.7 KiB) Viewed 1464 times

My guess is that the streaking is something not quite working as it should in the DSS comet stacking procedure, but I haven't used that for a long time, so could not really begin to suggest what needs to be done to correct it. It would certainly be interesting to look at one or two of the raw frames with a strong stretch to see if the diagonal streaks were visible, but I doubt it.

cheers,

Robin

[Moonstruck]

Thanks. I’ll check the cooler power next time. Also I may try a different stacking option in dss for comets. There are 3 options: stacking both comet and stars together (which I chose); stacking on the comet; and stacking on the stars.

Thanks again,
John