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Flat-Field Comparison:  M57



Object The Ring Nebula (M57), in Lyra
Telescope (Photo) Celestron 8" SCT on Losmandy G-11 Mount @ f/6.3
Telescope (Guiding) Meade ETX 90mm OTA @f/13.8 on Losmandy G11 Mount
Camera (Photo) Canon 50D DSLR
Camera (Guiding) Meade DSI II w/PHD Guiding
Exposure Detail Uncropped, median combination of 17 images at 60 seconds each, ISO1600; RAW file conversion, full calibration (flat, dark, bias, and flat-dark), and initial image processing using ImagesPlus 3.75; final image processing using Photoshop CS3
Location Caesar Creek State Park, Ohio (N39.513, W84.020)
Date 06/05/098
Comments The top image in this sequence is the identical image and was put through identical image processing as the image on the bottom, with the exception of the flat field.  See the Glossary for a definition of Flat Field.  The bottom image shows graphically how using flat fields with an image can improve the overall appearance by eliminating optical-train defects like dust specks and dark corners.