Still struggling with some settings...

[GoFraRo]

Hi everyone,
after a couple of weeks, I could run a session overnight and could capture various objects. I'm still struggling with the right settings of the cam and hope to get some hints and tips.
As an example, I have taken one of the images. M74 - Phantom Galaxy.
My setup in this case is a TS Photoline 60/360, a Neptune-C, Skywatcher LPR, iOptron Cube Pro (Alt/AZ mode).
Sharpcap 4.0 / 32bit (latest version) - Livestack
At the beginning, I took 10 Darks with the same parameter as used during the session. Exp 15 sec, Gain 400, Offset 150.
Livestack in Default setting.
FWHM was between 4.5 - 5.5. Focusing was done before with a Bahtinov mask.
I captured 300 frames (unfortunately, but for some reasons, I didn't store the individual frames).
Attached is a screenprint of the resulting fits-file.
After an initial stretching with ASIFitsviewer and processing with Astrosurface and Fitswork I've got eventually an acceptable image.
However, looking on the fits file, it seems to me very noisy, as well as banding is present. On the right hand side, there are still remains of ampglow.
What should I do different the next time.

M74_Phantom_Galaxie_2.jpg (227.54 KiB) Viewed 1161 times

Thx a lot in advance, regards and always CS
Gottfried

[admin]

Hi,

the first thing to try to sort out is the banding issue - that is best done by testing capture of dark frames and using the display stretch functionality in SharpCap to enhance the brightness of the frame and see how much banding is visible. Sometimes changing the gain of the camera can help, other times, banding can be caused by noise in the USB power supply to the camera, so try different USB ports, a powered hub, different PC, etc.

Another option is to use the banding suppression feature of SharpCap - see https://docs.sharpcap.co.uk/4.0/#!2!Pre-processing for details. In either case, get this sorted before capturing darks or light frames and make a note of the settings that work best.

Amp glow *should* subtract out fairly well when using darks, however as always, make sure that the dark is captured at exactly the same settings as the light frames (and, as closely as possible, the same temperature of the camera sensor). The problem is that subtracting out 'fairly well' may still leave a small amount of amp glow in the image, which can then be made visible again when you stretch the final image - I think this is what is happening to you.

Noise reduction should come with increases in the numbers of darks and light frames - remember that the number of dark frames matter here too. If you take 1000 light frames but only 10 darks frames, your final image will be limited by the amount of noise in the master dark frame, rather than the amount of noise in the stacked light frames.

Hope this helps,

Robin

[TimHaymes]

Hi Gottfried,
Thats a good image with a 60mm refractor and LPR filter. The gain of 400 is rather high (My range is 50 to 480). I would try 300. Not sure why USB speed is set to 100. I use a value of 1 or zero, however i dont think it will effect long exposures - but worth checking that. Your camera is not cooled, but the CMOS was at -1.7 C, does this mean your outside temp was way bellow zero ! In this case you need to take darks every time the ambient temp changes. Robin suggest at least 10. (I guess you know this)

Im not a colour imager, i use a QHY174m (cool). The gain setting is important for the best results. I use gain 200, exp 15sec and 5 to 10 darks at -10C. I think i should use more darks.

I dont need banding suppression for long exposures at low gain, and i find the dark subtraction quality is key, even when cooled.

Cheers Tim

[GoFraRo]

Hi Tim,
thanks for sharing your experience.
It was the first time I used a gain of 400 with Darks. Previously, I used 250, without calibration frames. The cam has built-in so called DPS (death pixel supression). Compared to my ZWO ASI 120MC-s a huge advantage.
Well, it was cold outside. Around -8° regarding an external thermometer.
Just checked the logs of the various sessions. At the beginning, the ASI cam logged -7°C which sounds plausible. But, the Neptune-C logged at that time between 0,2°C and -0.5°C while doing the Darks. Later, the logged temperature was going down from -0.8°C to -2°C from session to session. It seems to me, it's not so different.
Either the temp probe of the Neptune-C doesn't work properly, or someone is boiling eggs on the circuit board of the cam.

btw. I used the "Capture Dark Dialogue" to create the darkfile I used later in Livestack. I followed the instructions, set the number of frames to 10 and got a fits-file I selected for Livestacking.

Gottfried