Weird noise streaks on my subs?

[AstroBrian]

Hey everyone. I have a ZWO294 MC PRO using Sharpcap Pro and I am doing 5 minute subs and I get these odd streaks... 2 minutes doesn't show any but the 5 minute has. Does anyone know how I can stop this from happening? I know theres a word for this but I doni't know a fix. Image of M106 processed shows the streaks. You can see what looks like noise ribbons. This is about 2 hours worth of data. 24 images of 5 minute subs. Thanks for any help offered

[Budgie1]

Is that image the stacked 24x 5min subs or is it one sub?

If it's the stacked image, do you see the noise in the single subs?

Are you guiding and do you use dithering?

It looks like "Walking Noise" caused by not dithering, but I'm not 100% sure so hopefully others will be able to assist.

[Whirlwind]

As noted above this looks like "Walking Noise".  It's caused by fixed pattern noise on the CMOS camera that can't be corrected using dark frames.  Again as noted you have to use aggressive dithering to remove it.  This 'blurs' the noise across the image in an areas rather than rely on slow drift to remove it during processing which was more commonly relied on for CCD images.  I speculate that that the difference between a 2min / 5min exposures is that for some reason 2 mins is more heavily dithered and/or is generally more noisy so hiding the issue (rather than not being there).  For the 5 min exposures other noises sources will be lower (relatively) and/or there will be less images being dithered because of the longer exposure and hence more aggressive dithering is required. 

[AstroBrian]

7 hours ago, Budgie1 said:

Is that image the stacked 24x 5min subs or is it one sub?

If it's the stacked image, do you see the noise in the single subs?

Are you guiding and do you use dithering?

It looks like "Walking Noise" caused by not dithering, but I'm not 100% sure so hopefully others will be able to assist.

Thanks so much. It is stakced 5 minute subs x 24 so two hours total intergration. Do you know how I can dither in SharpCap? Walking noise thats the word I was looking for!

3 hours ago, Whirlwind said:

As noted above this looks like "Walking Noise".  It's caused by fixed pattern noise on the CMOS camera that can't be corrected using dark frames.  Again as noted you have to use aggressive dithering to remove it.  This 'blurs' the noise across the image in an areas rather than rely on slow drift to remove it during processing which was more commonly relied on for CCD images.  I speculate that that the difference between a 2min / 5min exposures is that for some reason 2 mins is more heavily dithered and/or is generally more noisy so hiding the issue (rather than not being there).  For the 5 min exposures other noises sources will be lower (relatively) and/or there will be less images being dithered because of the longer exposure and hence more aggressive dithering is required. 

I dont do darks, probably should but have trouble taking darks. Two minute subs seem to do the trick. Walking noise is the word for it and dithering. I am not sure is there a way to do dithering in sharpcap function? I'll have to test all this Sunday night  Thanks for the reply!

[Whirlwind]

Doesn't Sharpcap use PHD for guiding - isn't the function in there?

As for darks what is the issue as darks are just the same exposure/temperature with the lens cap on (assuming no light leaks)?

[Budgie1]

10 hours ago, AstroBrian said:

Thanks so much. It is stakced 5 minute subs x 24 so two hours total intergration. Do you know how I can dither in SharpCap? Walking noise thats the word I was looking for!

I dont do darks, probably should but have trouble taking darks. Two minute subs seem to do the trick. Walking noise is the word for it and dithering. I am not sure is there a way to do dithering in sharpcap function? I'll have to test all this Sunday night  Thanks for the reply!

I use PHD2 for guiding but looking at the SharpCap user manual there are two items under "Dither" in the Topics menu HERE and HERE.

As for Darks, you do need them with ASI294MC Pro because of the Amp Glow on the top righthand side of your image above. I use a cloudy day to create my Darks Library, which consists of darks for every exposure time I'm likely to use. I only ever use Gain 120 and Offset 8 (ZWO default) and remove the camera from the scope.

With the camera removed from the scope, put the cover over the nose piece on the camera and connect to your laptop. Cool the camera to your normal operating temperature, I use -10°C, and set up a plan for the darks. I normally do 20 - 30 images per exposure time and store them in a separate folder for each exposure.

Once this is done, you can re-use the Darks until you notice something has changed and the darks are not calibration correctly.

This is what your Master Dark for 300s at 120 gain should look similar too (this has been stretched to show the results but they are not stretched when used for calibration ) . You can see the main "Amp Glow" on the right, but there is also some on the left and bottom right. The Darks allow this to be removed from you final stacked image, giving a nice clean background.

Edited January 8, 2022 by Budgie1

[rcwinter]

As has been said it’s amp glow I am afraid, the 294 and 183 have plenty, I had the 294 myself

Even when you reduce the exposures so it hardly notices, when you stack it up it will be there, unless you remove the noise it will be always there 

Darks as said are a must for these cameras. 

Rich