Understanding your camera's ISO control
Posted 03 April 2012 - 12:26 PM
For action shots, I usually set my camera so that it will try to adjust exposure using the shutter speed first, but if it decides that it would need to go slower than about 1/400th of a second, *then* it will begin raising ISO in order to ensure adequate exposure.
Posted 03 April 2012 - 02:16 PM
Posted 03 April 2012 - 02:44 PM
First, the sensor's sensitivity to light is not increased as ISO is increased. It's gain is increased. It's like turning the volume up to 11.
And that's what causes the noise. The amplification of the signal coming off the sensor is what causes random colored pixels to give the image a rough texture and some funky color. It's easy to make the mistake of thinking the sensitivity of the sensor is being increased, but it's not.
Second of all, the author doesn't even touch on the issue of the size of the sensor. The bigger the sensor, normally but not always, the lower the noise for a given ISO. I say normally but not always because I've been shooting with a Nikon D800 for almost two weeks now, and it defies conventional wisdom of the pixel density vs noise. It's almost as good as the Nikon D4 at ISO 6400, with double the resolution and then some.
Size of the sensor is one of the reasons why pros prefer to shoot with full frame cameras. The smaller the sensor, the more noise (again, normally). So most DSLRs are not going to compete with the full frame bodies when you get into the ISO settings above ISO 800 or even less. Some point and shoots have noise even at ISO 100 and should not be taken over ISO 400 if you want to make pictures bigger than a decent Facebook/Flickr image size.
And it doesn't necessarily mean a thing for the camera to have a setting of ISO 12,800. It might be so noisy that it's useless, but the manufacturer put it on there to be "competitive." Shoot, most cameras aren't any good at ISO 3,200 let alone higher settings. But in the end, it's a matter of taste, and what level of image degradation you're willing to put up with for a given purpose.
For example, shooting surveillance photos would mean that ISO 200,400 on the latest Canon and Nikon pro bodies is acceptable since it gets the job done.
As for software, Lightroom 4 has ACR 7.0 now. Photoshop still runs on ACR 6 - including the CS6 public beta. And it's noise control is something to behold.
Noise Ninja was great, but they dropped support for Macs as Photoshop went 64 bit, because they've decided to develop their own RAW file converter rather than just simply do noise reduction. Aperture does have the the Noise Ninja plug-in, and it works pretty well, but ACR is way easier to understand and use.
I was also a beta tester for Kodak's black and white TMAX P-3200 film when I was in grad school. Let me tell you, its grain structure was sharp - but noisy!
This post has been edited by leicaman: 03 April 2012 - 02:46 PM
Nothing in all the world is more dangerous than sincere ignorance and conscientious stupidity. - Martin Luther King, Jr.
Posted 03 April 2012 - 04:58 PM
Untrue! Depends on the camera and how one exposes. An ISO 800 image can actually have less noise than an ISO 100 image. Absolutely true for Canon DSLR's.
See the image samples at: http://digitaldog.ne...100vs800iso.jpg
On a camera where a significant portion of the total noise is added after the ISO amplification (my Canon), the higher the ISO the larger the ouput Signal to Noise Ratio is for a given a amount of photons reaching the sensor and the result is less noise.
The image on the left was shot as suggested by the meter (1/60 at F5.6 @ ISO 100). The image on the right was shot with the identical settings but at ISO 800. It was normalized to produce a similar visual match. The ISO 800 image has less noise than the ISO 100 image thanks to ETTR!
One may use the same aperture and shutter speed (because you are somehow restricted to those settings), it can be advantageous to increase ISO because it can reduce the noise as seen above!
Under exposing even the lowest ISO capture, or using a 'normal' exposure without ETTR will add more noise to the image than using ETTR when appropriate for the capture (lots of light).
Author “Color Management for Photographers”
Posted 04 April 2012 - 12:32 AM
Posted 04 April 2012 - 08:23 AM
Nik makes a very good denoiser called Dfine. You can download a demo.