Darks

Darks

When you take a picture with a digital camera, the sensor’s pixels record electron activity, photons, from the subject (this is Signal), but along with it comes activity from the sky, light pollution, haze, etc., and the camera itself (all this is Noise). It gives your picture a milky, snowy, curdled feel to it.

The design of your camera contributes significantly to the level of noise it produces, and the temperature it’s operating at does too, the lower the temperature, the lower the noise level, which is why cameras dedicated to astrophotography have cooled sensors, whereas your standard digital cameras don’t.

However, there is a simple way to rid your picture of camera noise, and that is to take a Dark Frame, or better, take a series, at least 5, and average them.

The Dark is exactly the same as the light frame but with the shutter closed.

Take your light frames, then put the cover over the telescope so no light can get to the sensor, and immediately take a series of darks, exposed for exactly the same time as the lights. The darks must be taken at the same temperature as the lights, so immediately after is the best way to do it. And don’t change any other settings either. Save them under the same name as your lights, but add “dark” to the name.

Your lights will consist of the data from the subject and the data from your camera too, and the darks will consist of just the data from your camera. Average the darks to a master dark and subtract it from the lights, to produce images without the noise from the camera. Your processing software will do this automatically for you.

BJ.

 

Copyright © 2018 Doncaster Astronomical Society. Registered Charity No: 1091486