Bulb mode on K5iis

I'm not sure if this is the right forum for this, so if the mods want to move it I won't mind.

I've been trying out some long exposures attempting to get some good star trail shots. It's not something I've ever tried before, and I obviously need more practise. I had to give up tonight because it clouded over.

Anyway, the reason for the post is some advice on whether my camera is working correctly. If I take a 30sec exposure in manual mode then the camera will save and be ready for the next shot straight away. If I take a shot in bulb mode then it seems to take as long as the original exposure to save the image. Eg. A 60 sec exposure takes about 60 sec to save and displays a countdown timer and "nr" in the viewfinder. A 5 minute exposure takes 5 minutes to save. It's this correct?

nr will stand for Noise Reduction. With very long exposures the sensor generates random noise, so the camera makes a second "dark" exposure, analyses the noise pattern in that and removes that noise pattern from your shot. It's called Dark Frame Subtraction. This is why a 1 minute exposure needs another 1 minute for the dark exposure to be made.

Thanks for the quick reply. Sounds as if I need to factor in this extra time every time I use bulb mode then. It seems odd that a 30 sec manual exposure doesn't have the same issue. I think I'll try experimenting with a 30 sec bulb exposure and see what that does.

Hopefully I'll get a couple of clear nights this week to try again. There's too much light pollution at home, but I'm in Norfolk at the moment. There's still light pollution on the horizon, but I can find a spot in a field with no street lights in sight in any direction and get some good views of stars.

30 sec will not give you much of a trail . this was K5 with 107 30 sec exposures blended together in Star trax , a free piece of software, at least in 2013. ISO200 ,f5.6, 15mm limited on Gorillapod tripod on the ground, camera set to continuous shooting , fired with wired remote and just let it run. Had a full moon behind me shining on gate. no dark frame reduction, you can turn it off. Shouldn't be needed at 100-200 iso levels i don't think.

I'll have a search in the menus and see if I can turn it off, and look at the outcome. I realise 30 sec wouldn't give much of a trail, but I was just surprised that a 30sec manual exposure doesn't have the same issue as bulb exposure does.