Moving from CCD to Cmos

[Sarum]

Owing to limited funds when I needed to replace my QHY 8 Pro, I decided to go with an ASI 1600mc Pro cmos camera.   From the moment that I opened the box it was obvious that the build quality was far superior to the QHY camera,  but now the learning curve begins!   This is an image from last night consisting of 30  five minute subs.  I'm reasonably pleased with final result, although the strong halos around the brighter stars are bit of a distraction.  Most of the tips for removing star halos seem to be for images taken with a refractor, but if anyone knows how to remove star halos on images taken with a Newtonian I'd be grateful .

Roy

[GuLinux]

Hi!

Not sure about the halos (though I'd be interested to know as well), but that's a heck of a good start!

Welcome to the CMOS world

 

[Sarum]

Thanks GuLinux, if I ever get to the bottom of the halo problem I'll let you know.

Roy

[Allinthehead]

Nice job. Some lovely detail there. Regarding the halos i have the same issue with my Asi 071 and only with my Newt. I must try my Asi 1600 with it.

 

[Adam J]

12 hours ago, Sarum said:

Owing to limited funds when I needed to replace my QHY 8 Pro, I decided to go with an ASI 1600mc Pro cmos camera.   From the moment that I opened the box it was obvious that the build quality was far superior to the QHY camera,  but now the learning curve begins!   This is an image from last night consisting of 30  five minute subs.  I'm reasonably pleased with final result, although the strong halos around the brighter stars are bit of a distraction.  Most of the tips for removing star halos seem to be for images taken with a refractor, but if anyone knows how to remove star halos on images taken with a Newtonian I'd be grateful .

Roy

Are you using a Skywatcher Coma corrector?

 

[Sarum]

Thanks Richard.  Adam I'm using a Baader coma corrector coupled with a Baader UHC-S filter (2 inch).  The scope is SW 200PDS.

Roy

[blinky]

From what I read this is a common problem with these cameras - the CCD CMOS does not have anti reflection coating on it.  I think what was suggested was to use lower bit more exposures

[Sarum]

4 minutes ago, blinky said:

From what I read this is a common problem with these cameras - the CCD CMOS does not have anti reflection coating on it.  I think what was suggested was to use lower bit more exposures

That's certainly worth trying, perhaps shorter exposures and more of them will help.

Roy

[GuLinux]

Yeah, I heard about the coating too, actually, that's probably the reason.

I usually go with 1/2 minutes exposures with that camera, that might explain why I rarely saw star halos.

It's also a general pattern with CMOS cameras anyway: since the read noise is usually very low, it is usually preferred to take more shorter exposures, rather than fewer longer ones.

This also help increasing the dynamic range (this camera has a 12bits only ADC, so stacking more exposures helps a lot) and getting more "valuable" frames (you'll have more tolerance against tracking issues, or satellites/planes passing through your field).

[Adam J]

45 minutes ago, Sarum said:

Thanks Richard.  Adam I'm using a Baader coma corrector coupled with a Baader UHC-S filter (2 inch).  The scope is SW 200PDS.

Roy

Which version are you using? The original and mk2 both produce reflections, the new MPCCMKIII has better coatings. 

The UHC-S is a visual filter and has not IR block and so depending on if your camera has a IR cut window or not that might cause it. Not sure if Astronomik are as diligent with AR coatings on the filters made mostly for visual. The coma corrector could well be interacting with the filter.

The other possibility is that its the camera, 1600 sensors are not AR coated, if that is the case the there is nothing that you can do about it. The change in shape of the reflection as it moves across the image slightly discounts this though. 

Those are the only possibilities really 

Its still a lovely image though.

Adam

 

[Adam J]

16 minutes ago, blinky said:

From what I read this is a common problem with these cameras - the CCD CMOS does not have anti reflection coating on it.  I think what was suggested was to use lower bit more exposures

Its a problem with the Panasonic chips not CMOS chips in general, sony are fine as an example. 

[Sarum]

Many thanks for the info Adam. 

I'll see what I can do with the optical side of things, but if all else fails I may have to live with the reflections and try to minimise them during processing.

Roy