Canon 450d bias frame levels

Smiley (Zdenko) · #1 14-09-2008, 04:50 PM

Hi.

I have a new canon 450d DSLR and I am a bit confused by the very high levels in the bias (offset) frames done at 1/4000.
The median value of the entire frame is 1020.
In the attachment is the histogram from MaximDL.

Is that normal? To me, it seems a lot!!!

If there is any other 450d user, can you please comment on this. Do you have the same readouts?

Thanx,
Smiley

CometGuy · #2 14-09-2008, 09:55 PM

Smiley,

This is normal, Canon add an offset in images. For the 450d black level starts at about 1024 or so.

This is offset prevents clipping of the black level. This is especially important for dark frame subtraction.

Terry

Smiley (Zdenko) · #3 14-09-2008, 11:35 PM

Thanx Terry,

it's good to know that it is normal...

Still it seems a bit high, a few hundred would probably be enough to prevent clipping.

Regards, Smiley