I've been experimenting with some long exposures with my relatively new (6 months) Canon 30D. I've noticed on several of the exposures that there are numerous red, blue, and white dots that are not otherwise in the frame. Any thoughts on this? defect? dirty sensor? or just how it goes?
Also, what do people recommend for long exposures, over 1-2 hours, since the battery life seems only good for ~1 hour. I've read about using a car battery and the power cord...any thoughts on this?
I think a car battery might just void your warranty. The pixels you are seeing are basically "stuck" pixels that will show up over long, long exposures. Not to worry about them, though, as they shouldn't show up in normal exposures.
I wouldn't even try to make a one hour exposure, too much noise, hotpixels etc. It depends on the temperature outside and how long you already have been shooting. If you don't like hotpixels try to keep the temperature of the sensor as low as possible.
In the winter I can make a single exposure up to 20 minutes (with a few hotpixels).
In the summer however it's getting pretty noisy at about 10 minutes.
If you really want to make a 1-2 hour exposure, you can think about stacking mutiple exposures or buy a 1DSmk2
You can also use the 'long exposure noise reduction' custom function (02 on a 20D, not sure which it is on the 30D but will have a similar name). I believe it basically takes a second image for the same amount of time with the shutter closed and then uses that to remove any noise in the original image - it works very, very well too. Of course, it halves the maximum amount of time you can leave the shutter open because of battery life...or get a very, very long power lead
Ronan, the colored pixels you see are very normal. Instead of using the in-camera long-exposure noise reduction (which basically does a dark-frame subtraction by taking an equally long exposure with the shutter closed to expose the noise against a dark frame) - you could do it later in post-processing by taking a dark frame yourself and use it as a reference.
Here's more details on this: http://photo.net/learn/dark_noise/
Discussion
4 repliesAlso, what do people recommend for long exposures, over 1-2 hours, since the battery life seems only good for ~1 hour. I've read about using a car battery and the power cord...any thoughts on this?
Thank you all for your time,
-Ronan
In the winter I can make a single exposure up to 20 minutes (with a few hotpixels).
In the summer however it's getting pretty noisy at about 10 minutes.
If you really want to make a 1-2 hour exposure, you can think about stacking mutiple exposures or buy a 1DSmk2
Good luck!
Here's more details on this: http://photo.net/learn/dark_noise/