Cone Nebula. NGC 2264. 118 X 300sec Narrowband (About 10 hours) Separate RGB stars 60 X 30sec. 700mm f5.4 Petzval. Approx. 1.4 degree F.O.V.
Each of the 178 monochrome “Light “ frames is calibrated by various subtraction and division methods using Bias Dark & Flat Frame images. Bias data is a camera “signature” comprised of the average of 30 frames of the shortest exposure the camera can take while exposed to zero light. Many of the 16 million pixels perform differently and a predictive pattern of this can be derived and eliminated from Light Frames. A Dark frame also has the lens cap on and zero light leakage but is matched exactly to the light frames in exposure time, gain and temperature. Dozens of these provide the average noise for, say a five minute exposure. Flat Frames are critical to decent images and the most exasperating to perfect. They are images of a perfectly evenly illuminated color balanced field such as a perfectly clear eastern sky near sunset or an LED panel properly diffused. I stretch a pristine white tee shirt over the telescope objective and snap 30 exposures thru each filter. Flat Frames record the donut shaped halos of dust on any of the dozen surfaces in the optical path. They also record any vignetting that exists in almost every optical system. While the stacking of images is ideal for eliminating random noise as it boosts weak signal it tends to multiply anomalies like vignettes, dust donuts and camera sensor flaws, so calibration before any other processing is paramount.
Cone Nebula. NGC 2264. 118 X 300sec Narrowband (About 10 hours) Separate RGB stars 60 X 30sec. 700mm f5.4 Petzval. Approx. 1.4 degree F.O.V.
Each of the 178 monochrome “Light “ frames is calibrated by various subtraction and division methods using Bias Dark & Flat Frame images. Bias data is a camera “signature” comprised of the average of 30 frames of the shortest exposure the camera can take while exposed to zero light. Many of the 16 million pixels perform differently and a predictive pattern of this can be derived and eliminated from Light Frames. A Dark frame also has the lens cap on and zero light leakage but is matched exactly to the light frames in exposure time, gain and temperature. Dozens of these provide the average noise for, say a five minute exposure. Flat Frames are critical to decent images and the most exasperating to perfect. They are images of a perfectly evenly illuminated color balanced field such as a perfectly clear eastern sky near sunset or an LED panel properly diffused. I stretch a pristine white tee shirt over the telescope objective and snap 30 exposures thru each filter. Flat Frames record the donut shaped halos of dust on any of the dozen surfaces in the optical path. They also record any vignetting that exists in almost every optical system. While the stacking of images is ideal for eliminating random noise as it boosts weak signal it tends to multiply anomalies like vignettes, dust donuts and camera sensor flaws, so calibration before any other processing is paramount.