Comet Schwassmann-Wachmann

Be sure to not waste anytime when imaging something moving quickly.  It is very difficult to get the comet and stars around it to line up.  Short exposure times, and lots of stacking is the key to a successful image of this object. 

For these particular images the stars do not line up with the comet’s movement so a different approach had to be taken. 

First go through each frame just like in the previous image.  Take each color frame and stack it, being sure to set it to Log and 8-bit form. After flattening the four images, use the Lasso Tool and trace out the comet in the red, green, and blue pictures.  Cut and paste them over one another and adjust them accordingly, the same way as before. 

Then open up and stack the Luminance frames as you normally would, then copy the R, G, B, comet over the luminance frame comet.  The order changes for this stacking because when it is time to screen the images, if luminance was on top the stars used in the background would be screened as well.  Go back and play the action and adjust using the levels, curves, and saturation / hues. 

After this is complete use the smudge tool to make the cut and paste look less defined and more natural to the image.  Be sure to change it to a smaller brush so no stars also get smudged.  Also the intensity of the brush can be changed at the top of the screen so you can decide if it becomes too blended.

Using the sponge tool, the comet can be made more profound so attention is drawn to it, then using the burn tool, make the edges of the comet’s tail lessen to draw less attention to that area due to the cut and paste that was necessary.

This is another time when a second Photoshop is useful.  Due to the comets movement, the stars behind the comet do not line up, and if looked at closely it is evident that there are different color stars in it.  Using the paintbrush tool, you can paint these spots over and make it look more natural.  This may not work completely but it certainly improves how it looks.

Another problem that may happen is getting a dark ring around the comet from cutting and pasting.  This can be helped using the burn tool around the dark area.  Be sure not to use it in the dark area itself so that does not become darker.  For that the dodge tool is useful to lighten it up and make the colors match.

Problems:

Here is an example of what the comet looked like when trying to line up both the comet and the stars, the same sets of stars are in the blue and green, but there is a different star field even in the red.  Be sure to go quickly when imaging moving objects!