400D bulb exposure - how long to record image to CF?

[-halli-]

I've been trying some star trails but have found my Canon 400D is taking almost the same amount of time to record the image to CF as it has to take the image e.g. 5 min exposure results in around 5 mins of "busy" whilst it records to the CF card.

Is this normal? I'm saving in Raw and Jpeg if that means anything.

 

[digitalfailure]

It is indeed normal for an image to take much longer than you'd expect when shooting a long exposure, you can reduce it a little by turning off / down any in camera noise reduction but you risk an unusable image.

 

[-halli-]

It is indeed normal for an image to take much longer than you'd expect when shooting a long exposure, you can reduce it a little by turning off / down any in camera noise reduction but you risk an unusable image.

Cheers, I was beginning to get concerned.

I'm going to do some further experiments to see how I can get the time down. It was ruddy cold in the garden last night waiting for it to record, and I missed a few satellites/aeroplanes that I wanted to capture whilst waiting for it to record the image

 

[silverJON]

I'm not sure there's any way round it - either you turn NR off, or you live with it. It's trying to reduce noise with dark field subtraction, where it takes an identical exposure but with the shutter closed to see the sensor's 'hot spots', and then adjusts the first image to compensate. Try shooting without for a bit?

 

[Guerillaphoto]

its noise reduction taking an equivelent image to the exposure

 

[-halli-]

Thanks, that makes sense.

After a few tests , the first image captured after the camera has been off for a few minutes records to CF almost instantly. After that it takes about the same amount of time as the exposure. Is that something to do with the sensor temperature or something?

Turning off the noise reduction results in instant recording. I just need to go outside and test it now (brrrrrr!)

 

[-halli-]

took some test shots. All have had a dark frame added to remove hot pixels in "UFRaw" (Ubuntu Linux)

All are 100% crops with EV adjusted +1 but no other raw processing. Two images of similar length of exposure. Lens was my PB fit Pentacon Prakticar 28mm lens @ f4 ISO 100

#1 No camera noise reduction (308 seconds exposure) Instant save to CF card.

#2 Camera noise reduction switched on. (343 seconds exposure) Similar amount of time to record to CF card.

#3 (as #1) with noise reduction applied in UFRaw (+100) Seconds to apply!