Darks

ConceptDarks⚓

The darks are taken with the same exposure time and ISO as the images to be pre-processed, but in the dark.

Note

Again, you can use either the lens cap or the telescope cap.

They must also be made at a temperature very close to the recorded images.

This is why it is recommended to do them at the very end of the session or in the middle.

Advice

In the same way as for BIAS, the more dark images recorded, the less noise added to the pre-processed images.

Warning

Again, stack the darks with a median or Winsorized Sigma Clipping algorithm (always checking the rejection levels at the end of the process) and be careful not to normalize.

Advice

Remember that each dark image is made up of the true dark signal but also the bias signal. If you don't apply dark optimisation, you can leave the bias signal in the master and it will actually be masterDark+masterBias.

Warning

Therefore, subtracting this master from the images will remove both the dark signal and the bias signal. However, if a dark optimisation is applied, a multiplicative factor other than 1 is applied to the masterDark. In this case the masterBias signal must be removed from each dark image.

Here is a dark master obtained from 10 images with a Winsorized Sigma Clipping stack.