Sensor issue or am I missing a setting? Noise (Calibration files)

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SteveP86 New Member • Posts: 2
Sensor issue or am I missing a setting? Noise (Calibration files)

Hi there,

I've decided to post in this forum to see if any Sony A7iii experts may be able to help prior to me taking it to a repair shot.

I've owned this camera 5-6months and recently decided to get into astrophotography. Taking photos about 4mins long etc.

As part of the 'astro' process, I need to create calibration files to help improve the signal to noise etc. After doing a few attempts at astro I started to notice terrible noise in my photos, even after doing some calibration shots - darks, lights and flats. I was learning that DSLRs have a stable bias and that could assist in my processing for reduction of noise and scalable for my shots. I followed:

Take camera and shoot:

- some bias subs (you don't need a lot of then - something like 8 of each is fine).

- some dark subs of certain duration - say 30s darks

- some dark subs of double duration - say 60s darks

Stack each to their respective stack using simple average algorithm and then using pixel math create the following image: 2*(30s_dark - bias) - (60s_dark - bias)

The resulting image should have an average ADU value of 0 and no discernible patterns in the image - it should be pure noise.

Upon investigating further I did a test of dark calibration files - 30s and 60s ( My long exposure noise reduction is turned off but don't think it impacts at that time anyway).

So what I'm finding is that I'm having strange histogram (distinct values) and 4 column pattern . Like two columns are fine and two columns are very noisy.

Further to this , I stack them and deducting the bias I should have an ADU of 0... it's not the case

Is this a sensor issue/problem.. I'm far from knowledgable in this area and had help from a friend in completing this (stacking, ADU measurement and then using PixelMath to reduce ).

I would love to know anyone has info/knowledge or advice on this?

Thanks

Steve

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