Hi. I have some weird artifacts that look like hair / fur in certain parts of my result image after stacking. I wonder where they come from.
They are visible with both methods I tried “Sum Stacking” and “Average with rejection / Additive with scaling/ Winsorized Sigma Clipping”.
Camera is a Nikon D5600.
Lights shot at ISO 400 @ 2mins.
Number of frames:
Light 40
Flat 19
Dark 37
Bias 20
Unfortunately I took the darks in the morning after the capture, since I didn’t close the scope correctly. Flats and bias frames were also taken in the morning
I also took the darks, flats and bias with an incorrect ISO of 3200. Is this the problem?
Can I fix this?
Hi, this is a pattern caused by the camera, it happens with many of them if you don’t have enough signal or if you always stack them perfectly aligned, like when using auto-guiding.
Apparently it does not appear in darks or offsets, it’s a noise added to the real images. But it’s so faint it’s hard do see, much darker than a flat in particular.
The best way to get rid of it is to use a technique called dithering, which is forcing the guiding to move by a few pixels in random direction every few frames taken. That way, the pattern cancels out over a large number of stacked frames. Or have more signal/noise ratio in general by taking longer exposures or more of them.
Thanks for the explanaition. Apparently my polar alignment was on spot, since I do not use auto-guiding.
I also didn’t encounter this pattern before as apparently as in this image.
M33 has a low surface magnitude, what we see in the pictures you posted is that the signal of the galaxy is quite faint compared to the background (low signal to noise ratio), the sensor’s bad pattern comes out of the noise as soon as you stretch the histogram. Maybe you don’t see it with brighter objects or more signal in general.
