Question on long exposures

[M4gery]

On my 20D Whenever I take a long exposure, 10 min for example, My screen flashes busy for an additional 10 min after the picture is taken. During this time I am not able to take another picture. 5 sec, has a 5 sec delay. I assume it is writing it to the memory card. Is this normal with a DSLR. Memory card is scan disk ulra
thanks in advance

[dietcookie]

i don't own a 20D but I assume it's the noise reduction doing it's job. you can turn that off in your CFN.

[molesrkool]

yeh that sounds like noise reduction

i think if i remember correctly its CFN option 2.. then just turn it off.
its in menu on the last section i think (correct me if im wrong)

[Billginthekeys]

yes that is the noise reduction function, takes as long as the shot is taken to process.

[Mathiau]

:D was curious about this myself.

[NeoDude]

What is actually happening is that the camera is taking another 10 minute exposure with the shutter closed. This will result in a black image with just noise present. The camera then digitally subtracts this image from the original exposure theoretically removing the noise.

[FlashZebra]

What is actually happening is that the camera is taking another 10 minute exposure with the shutter closed. This will result in a black image with just noise present. The camera then digitally subtracts this image from the original exposure theoretically removing the noise.
This is what happens, and it does remove part, but not all, of the noise.

Enjoy! Lon