The Leo Triplet 2019-02-26 -> 2019-03-07

[The Thing]

Hi Folks,

Been a long time, been a long time since the rock and roll... (Led Zepplin IV)

You can see from the long timescale I have been experimenting with subs to try and solve the colour blob problem I have with my camera. There are actually many more evenings subs for this subject but they are going in the bin as the combinations of settings I used didn't work to help with the problem.

What I did in the end is use a very clear night to run a SharpCap sensor analysis and smart histogram routine on a dark patch of sky. It turns out the main problem seems to stem from the Offset value in the camera driver. This defaults to 30. SharpCap proposed 4. Quite a difference! What a value of 30 seems to do is truncate/compress the low signal data in some manner, I don't think that's what its supposed to do. Seems to be the same in the camera driver and ASCOM driver. So you end up stretching the image a lot more than you should have too and up pop the coloured blobs. That's my very non-technical take on whats been happening.

So the exposure setting I used were 119s, gain 121 (1 over unity), offset 4, temperature -15c. There are 99 subs in this image stacked in PixInsight. I have also found that normal Bias calibration frames are to be avoided at all costs with this camera. Flats were 4s, exposures shorter than 3s are to be avoided due to a 'feature' built into the CMOS chip. So I have used 20 Flats and 20 FlatDarks along with 10 Darks.
To make this work in PixInsight I downloaded and installed a script - BatchPreprocessingFD which is a modded version of the standard script by Micheal Covington. I used the default values for everything.

There is colour in the diffraction spikes on the bright star but I don't know why the stars lost their colour. The amp glow on the right 1/3 of the way down hasn't calibrated out properly (more darks?) and there are still gradients but hey ho, no blobs! Loads of itsy bitsy background galaxies as well.

Image date, time and location:        2019-03-07 Manche, France
Telescope aperture and focal ratio:   TS1506UNC f4, TS Komakorr
Camera and filters used:                 ZWO ASI294MC Pro, Baader Neodymnium 1.25" filter
Processing applied:                         Pixinsight, GIMP


Click for full size uncropped PNG image (24Mb).

[Carole]

Well the colour blob problem does not seem to be present but strange what happened to the colour.

The galaxies are a bit blurry, so I rang a HP filter on the image and it looks a lot better.

This camera is causing you a lot of problem and need to diagnosis, but well done for persevering. 

I gave up on my OSC camera (for different reasons) as I was also using a Mono camera and found the latter much easier to use.

Carole

[NoelC]

Good work Duncan.
The camera is super sensitive isn't it.
Shame about all the issues with it.

Noel

[The Thing]

Thanks Noel.
I'm just happy I can get images again. I was thinking I'd have to sell the camera.

[MarkS]

It's looking good but I think the processing has "bleached" the colour.

Mark

[The Thing]

Thanks Mark.