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Image ID: m45-700MM-8534-8561_RJ-add27-v8-800.jpg

TITLE=The Pleiades Star Cluster, M45, from Denver

The Pleiades star cluser, also known as the Seven Sisters is immersed in nebulosity due to scattered starlight. The surface brightness of the nebulosity is very low. It usually is not imaged from deep within the light pollution in large cities such as Denver, but this image was done in bright light pollution.

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 27 exposures were added in ImagesPlus. Note: this was an experiment using jpeg 8-bit files extracted from the raw files. No dark subtraction! Processing included light fall-off correction in photoshop using lighting effects to generate a light fall-off profile and reducing the falloff using a color burn layer. Contrast stretch in ImagesPlus using digital development and in photoshop using LAB mode luminance channel only. Unsharp mask on luminance channel and Levels adjustments in photoshop. The light fall-off correction was significant because of the strong stretch needed to separate the galaxy from the bright sky background. The sky was several times brighter than the nebulae, resulting in extremely low contrast.

Compare this image with the other M45 in the astrophoto gallery. That is the same data as for this image, but the other was processed using 16-bit raw data. Note how the 16-bit processing brings out a lot more detail.

Image guided with an ST4 autoguider on a 3-inch f/8 refractor and a Losmandy G11 mount.

The sky brightness 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.

Keywords to this image = astrophoto-1 star_cluster Messier digital_astro

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Last updated October 05, 2008