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…continued

Wide-Field Imaging with CCD Cameras
by Steve Mandel

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Color Imaging

taken from the suburbs!

This 2.3°-wide view of the emission nebula IC 1848 in Cassiopeia was obtained by Robert Gendler from his driveway near Hartford, Connecticut, using a 300-mm Nikon lens at f/4 and an ST-10E and CFW-8 from Santa Barbara Instrument Group. It is a combination of individual exposures through a hydrogen-alpha filter (160 minutes) and red, green, and blue (RGB) filters (10, 10, and 20 minutes, respectively). All CCD images in this article are oriented with north up.

There are two ways to produce a color image with a CCD camera. You can either use a "single-shot" color camera, such as Starlight Xpress's MX5-C and MX7-C, or assemble a tricolor image from separate exposures through three different color filters. For the latter you need a filter wheel so you can shoot individual exposures through sets of red, green, and blue (RGB) or cyan, magenta, and yellow (CMY) filters, and then combine them digitally with image-editing software such as Adobe Photoshop, MaxIm DL, AIP for Windows, MIRA AP, or StellaImage. You can get away with using small filters if you place them between the lens and the chip.

I experimented with a narrowband (4-nanometer) hydrogen-alpha filter made by Custom Scientific, which can help resolve subtle detail in emission nebulae. I quickly discovered that this setup recorded even more detail than I had captured previously with my Schmidt camera and hypersensitized Tech Pan film.

I was anxious to try color imaging, but I immediately encountered a mechanical problem. With my SBIG motorized CFW-8 filter wheel in place, I was unable to reach focus when I attached a 35-mm camera lens to my ST-10E. I needed a way to use both my RGB and hydrogen-alpha filters with my existing camera and filter holder.

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