Color Shift Problems

Hi All,

Every time I image Jupiter, I end up with a very pronounced red halo and a blue halo around Jupiter after I stack the frames. This happens even when the seeing is good. I use the RGB shift feateure in Registax to try and align the colors but it never seems to work right. I'm wondering if I may have a problem with my camera? Anyone else have this problem? I attached an image I took a few weeks ago. I shifted the blue and red channels around as best I could but I always end up with a a large area of smeared blue around the planet's limb (look on the right side of the image). My equipment is a C11, a Toucam 740 pro, A Shular IR blocking filter, a Celestron 2x shorty barlow, and Registax and K3CCD tools for software. Thanks.

John

Attached Image:

Couple thoughts:

I find the Registax RGB shift feature a bit tricky sometimes.
It seems to work best when done manually. And you need to hit
the "do all" button after you change the settings, or it won't
always show you what its doing.

Might try a different Barlow; could be chromatic error in
the Barlow.

You can get funny colors around the limb of the planet if
the zero level and contrast aren't optimal for each
color. The Registax "histogram" feature can be used to adjust
this. I'll set the slider for each color so that the
spike on the left side of the plot is moved just off the
left side of the plot (this sets the zero point just above the
background). And then use the number settings to get the
right side of the plots (where the histogram graph goes to zero)
lined-up for the different colors.

I made the attached image by using the Registax histogram
feature and adjusting the parameters for blue. Also a
little tweak on the RGB shift.

Attached Image:

SCTs have sphero-chromatism due to the nature of the corrector plate. Assuming that the scope was fully corrected for green light, then the blue end of the spectrum is undercorrected, and the red end is over corrected. This spherical aberration manifests itself as a slight out-of-focus halo and will be enhanced when using shorty Barlows, which themselves have sphero-chromatism. If you can take 3 seperate R,G and B images, you can minimize this by slight refocusing of the red and blue images, but there will always be a bit of softening, especially in the blue end.

By the way, the new "RC" corrected SCTs from Meade will have even more sphero-chromatism than a standard all-spherical SCT, so the effect will be more pronounced, especially if you intend to Barlow the image with a "shorty".

Roland Christen