Sensor noise?

Following up on Mannesty's comments to my Full Moon picture in the Your Photos section, I began to wonder if there might be a fault in the sensor.

I made a couple of test shots with the lens cap on, on both the K200D and the K20D. Images are 100% crops at 600x600 pixels.

K200D noise:
[IMG]http://i233.photobucket.com/albums/ee91/terje-l/K200D_noise.jpg[/IMG]
K20D noise:
[IMG]http://i233.photobucket.com/albums/ee91/terje-l/K20D_noise.jpg[/IMG]

Using Levels in PSE8 I dragged the right handle towards left to bring out the noise specles, as shown below.

[IMG]http://i233.photobucket.com/albums/ee91/terje-l/levels.jpg[/IMG]

Since the noise level seems to be pretty much the same in both cameras, I assume that this sort of noise is normal, and to be expected. Any comments, anyone?

Hi Terry, Taking a shot with the lens cap on could give very misleading results as you cannot asses when you have attained a correct exposure.
Perhaps if you provided the ISO and exposure settings that you used might shed a little more light on the problem (pun intended)
I think it far better to take a correctly exposed night shot of a subject using a low ISO (100-200 is most likely to give the least amount of noise).
Best Regards - Pete

I see what you mean, Pete, I was merely trying to take pictures of a "dark" area.

Both images at ISO 200, 1/180, one at f/16 the other at f/11.

[quote:3496ace15f="terje-l"]I see what you mean, Pete, I was merely trying to take pictures of a "dark" area.

Well you sure did that, You could`nt get much darker than that! (unless you stood in a cupboard at night with the light off when you took the photo with the lens cap on!)

Regards - Pete.

To be serious though, You really need to take a correctly exposed image of a subject and assess the noise from that. My normal Night shots are taken at 100 ISO and beginning around 30 minutes after sunset using around 20 seconds at F18 and usually continuing until i can no longer see any light in the sky at 30seconds at F11. I use the Noise Reduction in Camera and a very tiny amount in PP as i do with all of my images. I also use the Highlight / Shadow warning. so that the shadows are`nt too dark as it would increase the noise if i tried to bring them back.
There is no way on earth that you could make a correctly exposed image with the cap on as it would be too dark even if you took an hour at f1.2.


Regards - Pete

You should make two photos because you've different types of noise and if you can see if it's random or not tells a big deal.

Pete with f/18 FOD also because a problem, better to use the lens wide open and OOF.

Thanks for the comments, both of you. But I think you are missing the point of the exercise. Mannesty claimed I had noise specles in the background in my Full Moon picture, and I suspected this to be sensor background noise.

Therefore I assumed that a short exposure at a dark level (lens cap on) would reveal this noise, and it did. At 1/180 and ISO 200 none of the noise reduction functions in the camera should be active. Hence what is observed must be background noise.

If I drag the right lever in the Levels to a value of 30, there is no visible noise at all.

looks like fairly normal dark current to me. I get this sort of thing off my scientific grade CCDs if I operate them at room temp so not at all surprised to see it on a normal camera sensor.