I went out the other night and took some long exposure shots in RAW and noticed a couple of things: there were about 5-10 red spots (dead pixels I assume) and another 5-10 white spots.
I recently bought the camera used from a shop. They are easily fixable in PS but I'm wondering if I should send the camera back for servicing. How many is too many? I would say I have between 10 and 20.
I had one red pixel and sent it in for CMOS recalibration. As I used ISO 1600 a lot and it was showing up on every photo, it was worth the time it took to get warranty service on it
Those are called hot pixles.
How long of an exposure?
When you get over 5 seconds, it's often worth it to use
the long exposure noise reduction, which is a second exposure
with the shutter not opening and lasts as long as your last exposure
and is subtracted from it. The default setting is auto.
Lightshow,
Exposures were well over 3minutes long.
Can you explain more in detail how to use the long exposure noise reduction? I have the book on the camera, perhaps it's located in there?
So are you saying I don't have dead pixels??
EB-1, I have done the sensor cleaning but have yet to try it again and check it out. Will do that later today.
Well, I had the same problem, so my 40D is acutally in the mail to Canon Factory Service for this right now. There were 16 dots, red, green, and blue through out photos with a long shutter speed. The manually clean trick, (in which the camera would remap the sensor) I think got deleted in a firmware update.
I think what Lightshow is trying to say is that the noise reduction will get rid of the consistant red dot, which it might. It did not work for me.
Zach_Eberl wrote:
I think what Lightshow is trying to say is that the noise reduction will get rid of the consistant red dot, which it might. It did not work for me.
Long Exposure NR would have done - it is specifically designed to remove noise caused by long exposure, by creating a second, reference "dark frame" image of read noise (including hot pixels) which is then subtracted from the image frame.
Zach_Eberl wrote:
I think what Lightshow is trying to say is that the noise reduction will get rid of the consistant red dot, which it might. It did not work for me.
It should remove the hot pixels, providing the hot pixels are in both exposures, you can do the same thing in Photoshop.
Do the hot pixels only show up in long exposures? if they show up in 1/50 exposures too then you may have stuck pixels. which Canon can have mapped out.
I found that ACR does a good job of removing hot pixels.
40D menu:
C. Fn II : Image
1: Long exp. noise reduction
0: Off
1: Auto
2: On
settings 1 or 2 should help, default is 0.
