High ISO without noise?

Question

Hi there, I realized that in photography, when you are using a DSLR and pump up your ISO, if can get noisy at times.

But however, there are also times when I pump a 350D camera to it's maximum at 1600, it doesn't produce any visible noise in the photo at all.

Can someone explain the rational behind, what actually causes noise to occur and how can we avoid it when using high ISO??

Answer 1

You can see some noise level tests on this page. Look at the samples AND the graphs below the samples:

http://www.dpreview.com/reviews/canoneos400d/page17.asp

Although the CMOS sensors are supposed to be superior at handling noise at high ISO's, I also think your camera has a noise reduction feature that kicks in at ISO 800. If you look at this page, you can see how much they sacrifice sharpness to eliminate noise.

http://www.dpreview.com/reviews/canoneos400d/page18.asp

In other words, noise is more objectionable than a slight degree of unsharpness and Canon has chosen to cut out the noise at the expense of another image quality. It's probably a good choice.

Answer 2

Noise is caused by the fact that to increase the ISO of a digital camera, the 'gain' of the photo diodes forming the CCD is increased. Now why this should happen, some one who knows more about electronics will have to explain. But I can tell you this. There is nothing that can be done to avoid it, other than by using a camera which reviews tell you is not 'noisy', or where noise is at a minimum. I have two digicams that I use regularly. One is a Minolta Dimage 7i., 5 megapixel. At 800 ISO, the maximum it will go to, pictures are virtually unusable because of noise. That camera dates from 2002. My other is a 2004 Pentax ist*DS where the maximum is 3200 ISO. I don't use that speed, but pictures taken at the next lower speed, 1600 ISO, are perfectly acceptable (at least I think so), Now whether that is due to advances in chip design in 2 years, or to in-camera processing, or what I don't know. Just one tip - noise will always be more noticeable on large areas of one colour - the sky, for example, can be very speckled indeed if you pump up the ISO to take a picture just after sunset, say,

Answer 3

Clean high ISO > noise reduced high ISO > noisy high iso.

u can remose the noise w/ program but The less noise you have to remove, the less detail you lose. dig cam cant use high iso (if u want clear pict w/out noise) it will always like this if u used high iso...

Answer 4

I would suspect either a different lens or lighting conditions.

beaux