1. Signal vs Noise: Image Calibration First… some terminology:  Light Frame: The individual pictures you take of your target.  Dark Frame: An image taken with no light hitting the sensor.  Flat Frame: A half saturated white light picture used to correct for optical path problems  Flat Dark: Same as a Dark frame but at the exposure time of the Flat (it is applied to the Flat).  Bias Frame: A minimum time exposure dark frame taken to account for CCD internal baseline charge. (can be safely ignored unless doing advanced imaging & cal).  ADU or PV: Anolog Digital Units or Pixel Values. The “count” of how many photons hit a given pixel. Deep Sky Photography: Image Calibration

2. Image Calibration: Images (Light frames) are “calibrated” to remove noise from the Sensor and Optics chain. Dark Frames  Taken with the scope/camera covered and the sensor at the same temp as the Light frames to be taken.  The Dark frames exposure length should be the same as the Light frames. Several frames (5 to 8) should be taken and stacked/averaged to make a “master dark”.  The Master Dark frame is subtracted from the Light Frames.  This removes the noise added by hot pixels, dark current, and bias noise in the CCD itself. Deep Sky Photography: Image Calibration

3. Deep Sky Photography: Typical Dark Frame

4. Flat frames  Used to correct for imperfections (dust, vignette, etc) in the optical train.  Taken at focus, under a uniform, white, dim source, at an exposure time long enough to about half saturate the CCD pixels. Taking flats doesn’t take much time. Typical exposure lengths are 0.3 to 2 seconds each. Like the darks, many frames should be taken, stacked and averaged.  After the Flat is stacked. It is normalized (each pixel value divided by the average PV of the frame).  The Flat is applied by dividing it into the Light frames.  The process of Applying the flats is typically accomplished by your calibrating/stacking software Flat Darks  Flat Darks are taken at the same exposure time as the Flat frames.  Used just like regular dark frames against the individual Flat frames to corrects the Flat frames for CCD noise. Deep Sky Photography: Image Calibration

5. Deep Sky Photography: Typical Flat Frame

6. Deep Sky Photography: Raw Light

7. Deep Sky Photography: Dark Subtracted

8. Deep Sky Photography: Flat Applied