The Rosette Nebula

Here is a recent reprocessing effort on some data collected last year. H alpha nebulae have always been a difficult target as I use an unmodified Canon DSLR which doesn't have the best sensitivity at those wavelengths. In order to make the nebula visible, extreme stretches are generally needed. These stretches usually result in bloated and excessive numbers of stars that tend to obscure the nebula as shown in the image below. The picture that shows up when your mouse is not over the image is a 58 minute exposure at ISO 1600. Calibration and stacking was done in Deep Sky Stacker. The seeing was rather poor and some haze produced a light polution gradient across the image. The stacked image was stretched, split into red, green and blue channels and deconvolution run applied to each. Finally the channels were recombined and sharpened a bit in Paint Shop Pro. The red channel was given a slightly (?) excessive midlevel stretch to try to emphasize the nebula over the stars.

Click on the image to see the reprocessed version. In this case the calibrated and stacked image was contrast enhanced using digital development processing in Images Plus, the then bloated stars were reduced in size using a single pass of star shrink processing . The gradient was removed and the background equalized. A duplicate layer was produced and given an extreme contrast enhancement using the clarify function in Paint Shop Pro. The two layers were recombined using a mask made from the luminance channel to blend them together based on brigntness. Star colour was enhanced and masked noise reduction was applied. Finally the result was sharpened using Focus Magic and the unsharp mask function in Paint Shop Pro.

The images are at slightly different scales as the original was cropped to remove amplifier glow while the reprocessed version has had it removed.

Object Rosette Nebula NGC2238 RA 6:30.7 Dec 5:01
Exposure 60 minutes (30 X 2 minutes)
ISO 1600
Camera Canon 350D DSLR
Optics 8" f/4 Schmidt Newtonian Telescope

St. Croix Observatory

Processing See above