ZWO ASI183MM PRO bad amp glow on S2 filter

[TerryMcK]

The ZWO ASI183MM Pro and other cameras that share the same IMX183 sensor all exhibit bad amp glow. This can normally be completely taken out with calibration frames. However on one of my recent projects the amp glow when using an S2 4nm Baader filter stubbornly refuses to be completely removed.

I use PixInsight's WBPP script to do the integration and done many iterations of it. The dark master of course contains the amp glow in all its glory. The flats seem to look ok to me. Using NINAs flat tool set at 50% ADU per filter the Ha frames took 13.13 seconds, O3 18.75 seconds and the S2 just less than a second.

This is consistent with my other cooled ASI294MM on another scope. S2 always takes less that the other 2 filters.

 

So when it comes down to it you can see the amp glow in the red channel only showing up as bright red in RGB.

 

Here is the double stretched view of the starless integrated image so you can see it in all its hideous grandure

 

 

Looking at the 3 masters stretched again after final stretching so you can see it is very apparent

 

S2 double stretched below

 

 

Ha double stretched for comparison

 

 

And then finally O3 double stretched

 

 

I think the O3 is exhibiting bleed through from the amp glow too

 

If you are not familiar with hideous amp glow this is what it looks like in the dark master 

 

So either something in the WBPP script isn't working properly or the camera can go in the bin. Unfortunately cropping is not an option with this image and the camera is too expensive to bin LOL.

 

As way of comparison the ASI294MM does not have any issues with the slight amp glow present in the camera and it calibrates out perfectly.

 

Back to the drawing board on this one.

 

[TerryMcK]

I suspect just using master darks of 180s duration has over compensated within the flats as they are of course dissimilar durations.

Now shot some dark flats of matching length to the flats using NINAs excellent FlatWizard to see how PixInsight copes to calibrate the flats.

 

Something to do while the weather is dire!

[TerryMcK]

Well good news. I shot a whole new batch of flats (cooled) with matching dark flats per filter. I had to use a neutral density photographic film between the front element and the white flat panel so that the sub time was increased for the S2 filter. This gave just over 5 seconds flats/darks for S2.

The Ha and O3 matching flats/darks were the same as before as I didn't use the ND film for those.

 

I read somewhere (probably on CloudyNights) that some CMOS cameras need flat exposures longer than 1 second - I can't remember why now though. Probably the IMX183 based sensors come into this category.

 

So in PixInsight using the WBPP script loaded with flats calibrated with dark flats, lights calibrated with darks and no bias frames seems to be the way to go with the IMX183 sensors.

[Graeme]

1 hour ago, TerryMcK said:

I read somewhere (probably on CloudyNights) that some CMOS cameras need flat exposures longer than 1 second - I can't remember why now though. Probably the IMX183 based sensors come into this category.

 

That's a good experiment Terry. And it's a good way to get optimum calibration for your ASI183MM. My ASI294MC Pro has similar Amp Glow. But the ASI1600MM has very little. 

 

Thanks for the Flat Frame exposure > 1 second tip. My flats are < 1 second and don't calibrate out the vignetting very well so I'll have to put a resistor in the LED circuit, or add another sheet of A3!

 

Graeme

[TerryMcK]

I got some of this Graeme and cut it into smaller sizes to suit my flat light.

https://www.amazon.co.uk/gp/product/B08PFW95RN

 

Lighting Neutral Density Gels Filter Sheet 16x20 inches Kit, ND3,ND6,ND9 for Photo Studio Video Flashlight Led Light Photography, 6 Packs

 

[Graeme]

Good shout.

 

Cheers Terry.

 

Graeme