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The sword of the constellation of Orion is home of the Great Orion Nebula, M42. North is up in this image. This image was done in bright light pollution of the Denver metro area.
Camera: Canon 10D 6-MPixel digital camera, set at ISO 400. Lens was a 5-inch aperture, 500 mm focal length F/4 (Canon's 500 mm f/4 IS L telephoto lens) plus 1.4x teleconverter giving 700 mm at f/5.6. Data were recorded in raw mode, 1 minute exposures, and 44 exposures were added in ImagesPlus. Raw mode image falloff was characterized and removed from the images to give a uniform response across the full frame. Raw mode dark frames were also averaged and subtrracted. Contrast stretch in ImagesPlus using digital development and in photoshop using LAB mode luminance channel only in 16-bits. Lab mode luminance channel operations preserved color in stars and the brightest portion of the nebula. Unsharp mask on luminance channel and Levels adjustments in photoshop. The sky was several times brighter than most of the nebula, resulting in extremely low contrast.
The Exposure Factors, CEF, CEFA are measures of the relative amounts of light received from a subject. It can be used to fairly compare wildly different lens/telescope apertures and exposure times. For this image:
Image guided with an ST4 autoguider on a 3-inch f/8 refractor and a Losmandy G11 mount.
The sky brightness at the zenith in the Canon red, green, and blue pixels was: red = 17.1, green = 17.9 and blue = 18.6 magnitudes per square arc-second. Dark country skies are typically fainter by about a factor of 100 in red and green magnitudes about 22 to 23). The sky was brightest in the red channel because of the sodium street lights.
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Keywords to this image = astrophoto-1 nebula Messier night low-light digital_astro
Image ID: m42-700mm_crw_8588-8631.44min.16b.try3.v12-800.jpg
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Last updated January 21, 2016