Colored Snow

[AngusMcDuff]

Any ideas on what is causing the "colored snow" on this image? I have been told it looks like chrominance noise but my camera is new and the sensor is cooled. I stacked almost 700 5 second subs using ASTAP. I processed with Star Tools. The camera is an ASI 2600MC pro and the telescope is a Stellarvue SVX102T. These are both new. My Astropheric app rated the seeing and trasparency above average and there was no cloud cover.

I used the smart histogram brain to calculate everything. It has always worked on my other rig. The other rig is a Raptor 61 with ASI 183MC Pro and the brain always gave exposures between 15 and 90 seconds.

[AngusMcDuff]

I just remembered that the Rapt 61 was always used with an Optolong L-eNhance Filter. That probably accounted for the longer exposures

[admin]

Hi,

it does look like chrominance noise, but also looks rather more pronounced than I would expect.

It's difficult however to be sure of the cause by looking only at the finished image - for instance even with relatively good data you could end up with a very noisy image like this if you stretch the image a lot and then also boost the saturation to try to bring out the colours.

It somehow looks like something odd is going on as the image quality seems poor for nearly 1 hour of total imaging. Were you using the camera in 8 bit mode by any chance, as that would cause a lot of extra noise in this sort of imaging.

cheers,

Robin

[AngusMcDuff]

Thanks for the quick reply. I have attached the Camera Settings file so you have more information.

Yes, I think that Star Tools can make very large adjustments.

I will perform a new sensor analysis and make new flats and darks. This morning I read about chrominance noise being introduced by flat frames taken with ASI294MC cameras. I use an LED panel for the flats

A lot of people say I need longer exposures and more integration time but I have always good results with "the brain."

Thanks again.

[oopfan]

Have you got a lot of light pollution? The difference between 15 and 90 seconds is quite large. It indicates to me that you've got some LP hot spots in your sky.

5 seconds for M101 doesn't seem right. If you live in northern latitudes it can get rather high in the sky. If that's the case, LP should be relatively small. Could you see the galaxy in each 5-second frame as you acquired it? Not all of it, just the inner arms?

I agree with you, rerun sensor analysis.

BTW, I agree with those people that say you need more integration time. I've got a 71mm f/5.9 refractor. I've got two cameras, a CCD and a CMOS. Neither camera produces anything close to great with less than 5 hours integration time. Of course there are exceptions for bright nebulae but those are rare. M101 is faint. You need more time to let it cook.

[admin]

Hi,

I do feel that gain 350 is a bit high - it means that the image is being brightened by a factor of about *55* over the zero gain start point - that's a lot, and you are well out into the zone of diminishing returns when it comes to reductions in read noise. If I was using that camera I would be aiming for a gain of 100-250 and longer sub-exposures (so long as your mount tracking was up to it).

cheers,

Robin

[AngusMcDuff]

Thanks for the input

oopfan: On the individual subs, only the core can be seen and only if I increased the exposure in Lightroom. I have rerun a new sensor analysis, darks and flats.

Robin: The subs were taken at 100 gain as suggested by the Brain. The 350 is the maximum setting in the configuration. With the ASI2600, there's not much sense going beyond 100 so I'll change that setting to 150.

Although SkyTools said imaging would be okay that night, the moon was almost full. I think that created a big part of the problem. when the moon and weather are better, I'll repeat this imaging and get 2 hours of subs.

If the Brain still suggests less than 60 seconds exposure, should I overide it?

[admin]

Hi Angus,

oops, sorry, I read the wrong line from the capture settings file. 100 gain is fine

You should feel free to go *longer* than recommended by the brain - you will not gain much in terms of final image quality, but it may make things easier (less files to stack, brighter stars, etc). On the other hand, don't go longer if it requires you to upgrade your setup (add guiding, buy a fancier mount, etc) - only go to longer exposures if your current set up will cope.

cheers,

Robin