…continuedGoing Deep with a DSLR
My experience with my modified Canon EOS 20Da shows that it is necessary to increase the color saturation in Photoshop by +20 for daylight images, so I automatically apply this adjustment to all my astrophotographs. Next I perform a final color balance for the sky background. I examine a few areas of blank sky (if available) and use the Levels palette to neutralize them.
At this point I apply any sharpening I think will be beneficial. While there are many different ways to sharpen an image, mostly I prefer to use the Lasso tool with some feathering to select an area I wish to sharpen, and then apply the Unsharp Mask filter with a radius of 1 to 2 pixels. I rarely, if ever, sharpen the entire image.
My final step is to minimize noise, which shows up in virtually every astrophotograph. Here again we are fortunate to have many choices, though I prefer Noise Ninja. It’s easy to use and does a good job. Although the program works on RGB images, I find I can achieve better results by splitting the red, green, and blue channels in Photoshop, saving them as individual grayscale images, then using Noise Ninja to perform luminance noise reduction on each channel separately. I feel this gives me better control.
Some imagers try to achieve the smoothest possible result. Human eyes are accustomed to seeing detail in everything down to the limit of our visual resolution, but much of the time that “detail” is noise where our brains fill in the blanks. The trick is to have just the right amount of noise. Too little makes the image look plastic, and too much distracts from the subject, so I attempt to process my images to achieve a smooth but not completely noise-free result.
Unfortunately, the 20Da is no longer manufactured, but similar results can be obtained with other modified cameras. Regardless of which digital SLR camera you choose for astrophotography, these processing steps will help you get the most out of your equipment. DSLR astrophotography has come of age!
Chuck Vaughn has been photographing the universe from the Northern California mountains for nearly 20 years.