Is this level of noise normal?

[edjrgibbs]

Both these photos were taken at -20 on a QHY163c and QHY183c respectively. Stacked with darks. Is the level of noise normal?

Details - QHY183c @ -20 degrees, 20 lights at 300s each, 44 darks 300s each, stacked

 

Details - QHY163c @ -20 degrees, 10 lights at 300s each, 20 darks 300s each, stacked in Siril

[edjrgibbs]

No one...

[david_taurus83]

The 163 image looks too grainy. Looks like a DSLR image when it's too warm. You sure the cooler was running? What does the FITS header say for the individual subs?

[Synchronicity]

I'll reply from my meagre store of experience.  I have over 3 hours of M31 lights using a QHY10 OSC  (-25c) which have similar noise and from seeing others unprocessed images I'd say yours were quite typical.  A lot of the skill in processing seems to be in reducing noise while retaining faint detail.

I'm surprised that you have spent twice the time taking darks as lights - more data is always going to improve an image.

Hope that helps

Michael

[vlaiv]

There is no real answer to that question.

I'm going to say - yes, that is rather normal under some circumstances.

In any case, there are some other things that can be said - for example QHY183c is vastly over sampled.

Both images are processed / stretched more than the data allows. Both have very high background levels.

 

[michael.h.f.wilkinson]

Much depends also on the sky background. Where I image the sky background is a worse source of noise than dark current even in an uncooled camera

[edjrgibbs]

7 minutes ago, Synchronicity said:

I'll reply from my meagre store of experience.  I have over 3 hours of M31 lights using a QHY10 OSC  (-25c) which have similar noise and from seeing others unprocessed images I'd say yours were quite typical.  A lot of the skill in processing seems to be in reducing noise while retaining faint detail.

I'm surprised that you have spent twice the time taking darks as lights - more data is always going to improve an image.

Hope that helps

Michael

Thats what I thought. Cooler was definitely running. Fits header says

 

Image #1
    SIMPLE  =                    T / file does conform to FITS standard
    BITPIX  =                   16 / number of bits per data pixel
    NAXIS   =                    2 / number of data axes
    NAXIS1  =                 4656 / length of data axis 1
    NAXIS2  =                 3522 / length of data axis 2
    EXTEND  =                    T / FITS dataset may contain extensions
    COMMENT   FITS (Flexible Image Transport System) format is defined in 'Astronomy
    COMMENT   and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H
    BZERO   =                32768 / offset data range to that of unsigned short
    BSCALE  =                    1 / default scaling factor
    OBJECT  = 'M82     '           / The name of Object Imaged
    INSTRUME= 'QHYCCDCameras'      / The model Camera used
    DATE-OBS= '2020-10-09T20:18:27' / The UTC date and time at the start of the expo
    EXPTIME =                 300. / The total exposure time in seconds
    XPIXSZ  =                  3.8 / Pixel width in microns (after binning)
    YPIXSZ  =                  3.8 / Pixel height in microns (after binning)
    XBINNING=                    1 / Binning factor in width
    YBINNING=                    1 / Binning factor in height
    XORGSUBF=                    0 / Sub frame X position
    YORGSUBF=                    0 / Sub frame Y position
    EGAIN   =                   1. / Electronic gain in e-/ADU
    FOCALLEN=                 1000 / Focal Length of the Telescope in mm
    JD      =     2459132.34966435 / Julian Date
    SWCREATE= 'Astro Photography Tool - APT v.3.33' / Imaging software
    SBSTDVER= 'SBFITSEXT Version 1.0' / Standard version
    SNAPSHOT=                    1 / Number of images combined
    SET-TEMP=                 -20. / The setpoint of the cooling in C
    IMAGETYP= 'Light Frame'        / The type of image
    GAIN    =                  120 / The gain set (if supported)

[edjrgibbs]

12 minutes ago, Synchronicity said:

I'm surprised that you have spent twice the time taking darks as lights - more data is always going to improve an image.

Unfortunately due to limited imaging time. I took the darks the following day. 

[david_taurus83]

In that case I'd say more subs. Lots of subs. Do you have much LP? This target is a no go for me at Bortle 6. Tried a few times and its just too faint to bring out the dusty stuff without messing it up. Tried mono with an ASI1600 and also with a 6D.

[edjrgibbs]

3 hours ago, david_taurus83 said:

In that case I'd say more subs. Lots of subs. Do you have much LP? This target is a no go for me at Bortle 6. Tried a few times and its just too faint to bring out the dusty stuff without messing it up. Tried mono with an ASI1600 and also with a 6D.

Probably bortle 5. Sounds like the conditions weren't the best... Just need some clear skies to retry!

[ollypenrice]

These are dusty targets which always need very substantial integration in order to come out looking smooth. In fact they never really do because I suspect the dust is naturally grainy. The Iris shows that the second image has had a harder stretch which goes with its higher noise. I think you just need much longer integration on this kind of target.

Olly