Halos around stars in green/blue data but not red...

[dsnay]

Hi all,

Anybody know what could have caused the halos shown in this image?

http://autostarsuite.net/photos/dsnay/picture5717.aspx

It's the green data from an attempt to image with a DSI-Pro using the Meade filters. The camera is attached to a Pentax SMC (good quality multicoated) camera lens. I don't see the halos in the red data. I thought maybe I had some dew forming, but I still didn't see them when I switched back to the red filter as a test.

This was shot under last night's moonlit sky, don't know if that matters.

I didn't see the halos when I plugged the camera into my LX90, but that's not the image I'm after. I want that wide field.

thanks,

Dave

[twilbur]

My first thought was dewing also, but that would affect the red when you switched back.

High thin clouds with the moon out would do it, I assume the moon caused the gradient coming out of the top left corner. Maybe the camera isn't as sensitive in the red as it is in the blue and green and isn't showing it as much? 

I've noticed that I get similar effects (all filters) when going very wide field - e.g. using a camera lens for Milky Way shots - when the moon is out, but no such effects when switching back to shooting through a scope on the same night.

[dsnay]

High thin clouds with the moon out would do it, I assume the moon caused the gradient coming out of the top left corner. Maybe the camera isn't as sensitive in the red as it is in the blue and green and isn't showing it as much? 

Actually, it's more sensitive. That gradient is amp glow because I didn't get my darks right and I decided not to bother until I figured out what the halos were from.

I've noticed that I get similar effects (all filters) when going very wide field - e.g. using a camera lens for Milky Way shots - when the moon is out, but no such effects when switching back to shooting through a scope on the same night.

I'm thinking this might be the cause as I didn't see the halos when I shot through the scope.
Someone on the autostarsuite.net forums said something about stopping down and/or including an IR filter in the path. I can stop down, but there isn't any way for me to include another filter in the light path with this setup....

Thanks for the clues Ted.
I'm pondering the impact of adding two step-up rings and a filter between the camera and the lens. One to accomodate the lens size and another to bring it back to the size needed by the adapter.

clear skies,
Dave

[dsnay]

Hey Ted,

Hutech might have just come to the rescue. Check this out:

http://www.sciencecenter.net/hutech/idas/uibar.htm
UIBAR-52   52mm UV/IR blocking filter   $129.00

It attaches to the front of the camera lens just like the ones I use in my B&W imaging!

Dave