Equipment used:

  • Lumix G85
  • Lumix 100-300 f4-f5.6
  • SA-GTI

Image:

  • 10 sec, f/6.3, 6400 ISO
  • 1200 Lights
  • 50 Biases, Darks, Flats

Stacked using Siril and edited in GIMP

As you can see, there is a lot of noise, even with heavy editing and noise reduction in siril as well as in GIMP, and I’m out of ideas of what could cause it. I tried different exposures (from 10s to 30s), different ISOs (1600-6400). I tried to manually dither by moving the mount through the App every 30 minutes or so. I also used a lens dew heater at different temperatures ranging from 15°C to -5°C with no difference in noise.

I got a successful result a few months ago with the Orion nebula, the only differences were the exposure of 5 seconds and a Omegon Mount MiniTrack LX3 Essentials mount which couldn’t be polar aligned very well. I can’t imagine that the difference from 5 to 10 seconds exposure did all the difference.

Can anyone help me?

  • vastunknown@lemmy.worldEnglish
    2·
    13 days ago

    Late to the party but wanted to help:

    What you are seeing is a fixed pattern noise that is actually being reinforced by your many, short subs. This is called “walking noise”, especially common with cameras of this class when used for AP due to their sensor noise characteristics.

    You must dither more frequently. For non-dedicated astronomers camera, you will also want to dither a fairly large amount. Dithering every 30 minutes is effectively not dithering at all.

    Things you should aim for to help fix your image:

    • Dither often (every 5-10 frames is a good target) and large (~20-30px, anything larger and you’re cropping a lot)
    • Inspect calibration frames for fixed pattern noise (up bias to 200 frames, ensure flats do not capture artifacts from your light source like LEDs by increasing exposure time to ~2s)
    • Use dark-flat calibration frames to improve your flats and reduce the chance that’s what’s contributing
    • If you are using the same calibration frames from your success on Orion a few months ago, there’s a chance they are poorly matched now due to differences in ambient temperature, camera settings, etc which could explain poor calibration performance which could result in walking noise like this
    • Depending on other factors, like the moon/light pollution/etc, you could be stretching this image harder than you did for Orion, which could also result in the walking noise being more pronounced in the final image
    • Ensure long exposure NR setting in your camera is off, in body stabilization is off, mechanical shutter is on…sanity checks for your camera specifically
    • ISO 6400 is high - learn about ISO invariance, your camera (source: https://www.dpreview.com/reviews/panasonic-lumix-dmc-g85-g80/7) will yield the same resulting photo (from a noise perspective) when set much lower, without limiting your dynamic range…ISO 1600 is a good rule of thumb for DSLRs in my experience
    • Use winsorized sigma-clipping for stacking
    • As always, the name of the game is longer exposures! Aiming for 30s or more would benefit you a lot. When working with a DSRL and more/shorter subs, the quality of your calibrations frames becomes very important and dithering often is essential