Slow shutter question

[qwertyluck]

When using a slow shutter (15 seconds) the camera seems to take > 40 seconds to complete the cycle for the next shot to be taken (RAW mode). This is true for continuous shooting, or high speed shooting, etc. It seems this time is related to the shutter speed, i.e. for a 1 second exposure this time is ~10 seconds. I would expect some overhead for image processing,storage, etc. however, the amount of overhead should be constant for any shutter speed. The image processing seems to be related to the shutter speed as well?

When using the lowest image size (640x480), where the image processing and storage time is minimum, the cycle time is around 31 seconds (for a 15 second shutter), It seems that there is an extra 15s of something? in the cycle. Same is true for any other shutter speed, except the extra time is equal to the shutter speed.

Can anyone tell me what this extra time is? And if there is anything that can be done to reduce it.

Any settings for the camera, manual focus, aperature, ISO speed, have no effect. I have turned off any special effects as well.

I am using a Canon S60 but I suspect this issue would be true for all of the Canon camers with a 15s shutter speed.

I am using this camera for long exposures and this extra processing time is significant. Any help would be appreciated.

[adas]

Welcome to the forum, qwertyLuck.
Believe it or not, after the 15s exposure, your camera takes another 15s exposure, this time with closed aperture, a so called "dark frame". Then this will be subtracted from the real exposure to avoid the hot pixel effect in the image. This procedure starts only from shutter times longer than 0.3s - 1s (on my s50), depending on the ISO.

[qwertyluck]

Thanks.

Is there any way to disable this feature?

[adas]

No. There's no way to disable this in P&S cameras, at least to my knowledge. The noise would be high . But it can be turned off in DSLRs. Imagine a 25min exposure with the Rebel XT, and you'll have to wait another 25 min before you can actually see your shot.

Also remember not to touch the camera during the two exposure time period, as static plays a big role in hot pixel development.