What is this?

[Ryderscope]

The attached two images were taken in the same part of the sky in Leo. They are 100% zoom and cropped. Image 1 was taken tonight (Thursday) and image 2 was taken last Monday, three days ago. Image scope is a Skywatcher 100mm APO, Camera = Canon 60Da. Shots are 450 second ISO 800. Image 1 is showing what appears to be chromatic aberration. I double checked the focus in case it had drifted out and also used a Bahtinov mask to be sure. The sky looked reasonably transparent but it is possible the seeing was out as the stars were twinkling quite a lot. Nothing has changed in the imaging train in the three days between the shots so I am a loss as to why these orange halos have suddenly appeared. I checked the dew heaters and they seem to be working OK and there was no obvious dew on the lens. Sensor temperature tonight was about 7 degrees where on Monday night it was about 12 degrees.

Any ideas?

[Merlin66]

Rodney,
Was there any significant difference in the altitude of the target between the shots?
Could be atmospheric dispersion??

[Ryderscope]

Possible as I did get on to it a bit earlier than the first night.

I just did another check of the lens on the refractor and they may possibly be a tiny bit of fog on it but I am not sure. Next time I will try throwing on another dew heater to see if that makes a difference.

[Ryderscope]

On another note, I just checked the Weatherzone site for my location and it is showing current humidity at 99%.

[raymo]

You will note that the bright stars in both images have halos. In one
image red, and in the other image, orange. The different coloured halos are the result of the base colours of the two images being very different.
Neither background looks like a reasonably dark site background should
look, so I think your problem is software related, rather than in the
optical train. I obviously have no idea what processing, if any, you did.
raymo

[Ryderscope]

Hi Raymo, thanks for the post. Both images were the raw images straight from the cr2 file from the camera. No processing at all. My sky is not too bad and the background will be noticeable due to a reasonably long exposure time for these subs. As it turns out, I processed the final collection of subs in Pixinsiight with no noticeable flaring around the stars in the final image.