|
Hi Leon
If we ignore other optical system effects such as vignetting, a 100% clean sensor would not require any Flats to calibrate the image. Let’s say that some dust particles have over time, settled on your sensor, in various locations.
Simplistically, each dust particle location will have a specific x-y coordinate, such as x=259 pixels across and y= 748 pixels down for a particular dust particle. Your Flat will capture the shadow of each dust particle for each x-y location.
If you clean off the dust from your sensor, then all x-y locations on the sensor are now clean, but the “old” x-y locations on the Master Flat still show the dust shadows. If you now use the “old” Master Flat to calibrate the newly cleaned sensor, you will be removing “imaginary” dust shadows and therefore introducing unwanted artefacts into the light frame.
So, whenever you clean the sensor, ideally you should generate a new Master Flat to map to the current “dust spot” status of your sensor.
Cheers
Dennis
|