Lumix and long exposure lead into more noise compared to cameras with a larger sensor like the Canon 5D MK II. This was the painful experience on my last vacation.
Taking long exposures in the night or in daytime with the help of a strong ND filter the sensor will heat up. This heat will lead into hot pixels in the resulting image.
Take a look on this shot above taken under pretty extreme conditions. First i used and ND 3.0 and a ND 1.2 in combination to get an exposure time of 50sec. and at the same not close down the aparture too much which results in diffraction blur. Secondly the image was taken at arround 34° C.
Almost all of the modern cameras offer a setting “Noise reduction on long exposures”. Selecting this setting the camera after the original image is taken will take a so called dark frame without opening the shutter. Both images are rendered to one image. This porcedure has the disadvantage that the dark frame takes the same exposure time as the original image.
And this is the reason i never used this setting on my Canon 5D MK II because even exposure time with 3 or 4 minutes could be done without any problem.
This is different on images done with the Lumix G81, so i made a little practical test.
I captured images with the ND 1.2, the ND 3.0 and a combination of both filters both with the noise reduction activated and deactivated. I also captured such a sequence with the Canon camera, but i won’t show them here, because you couldn’t recognize a difference.
A significant difference is recognizable for those images taken with exposure time of 120 sec. and longer. One reason for this should be the lower room temperature (24° C).
I liked to do an additonal capture with 4 minutes, but after 2 min. 10 sec. the Lumix closed the shutter. I couldn’t figure if that is a problem of the camera or the used cable release
Sensor warming depends on the temperatures, the exposure time and obviously on the sensors size. On my Lumix i will keep this setting for “Noise reduction on long exposure”, but on my Canon 5D MK II i leave this setting deactivated. But i must admit to uner estimate the results of this setting.