Darks and Black Level

[giraud]

Hello

Is it important to have the same Black Level values for the Darks/Offsets/Flats and for the Light frames?

Many thanks.
Eric.

[admin]

Hi,

it's important that they match between

light frames and dark frames

also between

flat frames and dark flat frames

but there is no need for the light frames to match the flat frames.

cheers,

Robin

[giraud]

Thanks.

For someone like me, who is not doing livestacking, isn't it better to always set the black level at zero as I'll address the black level later anyway during post-processing? This way I would ensure that my dark library is robust over time (providing I use a BP value of 0 as well).

Regarding the "dark flat frame", is it what is also called "biases" or "offsets" or something else (I only run lights, darks, offser/bias, flats)?

Cheers.
Eric

[admin]

Hi Eric,

yes, you can often use bias frames in place of dark flat frames in most circumstances (unless you take long exposure flats), so in that case the black level should be the same between flat frames and bias frames.

The choice of zero for black level may be fine, but you will need to check. The way to test is to take full length dark frames at the settings that you propose to use and then check that the histogram of the dark frames is separated from the left hand side of the graph. If you test and the peak extends all the way to the left, increase the black level until it is separated. Once you have found that black level, you can use it for all imaging.

cheers,

Robin