Nikon D7100 and Noise at High ISO
Jack Hass wrote:
I remember reading this "trick" in the sony forum a while back, when people were complaining about noise when the 24mp apsc sensor was new. When people claim you can overexpose using longer SS, it shows they weren't using proper technique in the first place. Perhaps you should spend less time programming "software" and more time learning good photography technique, at least before you try giving advice to strangers.
Or perhaps you should get an actual clue about how things really work before mistakenly "correcting" someone else.
What were you saying?
Check the jpg samples at IR. 70D has much less noise at 12800.
I have both sensors.
If you cannot get a correct exposure at the aperture and shutter speed settings you need, then by all means adjust the ISO setting. However, do not be fooled into thinking this increases the exposure, as it has absolutely no effect on the amount of light hitting the sensor, nor does it increase the sensitivity of the sensor, which is fixed.
So, I hear you ask, why does the exposure meter show an increase in exposure when I increase the ISO setting? In reality the ISO setting just instructs the camera to boost the brightness of the resulting picture to the correct nominal brightness after a darker than nominal picture has been captured. The movement of the exposure meter is just illustrating that this will happen, albeit after the picture is taken and during post-capture processing within the camera.
I'm afraid the disappointing reality is that at any ISO setting above base ISO (normally 100) the sensor is going to be under-exposed, increasingly so as the ISO setting goes up, and without the post-capture brightening promised by the ISO setting you would actually get a dark picture.
So what is the problem with upping the ISO setting? There is not a problem as such, at least it avoids getting dark pictures on the screen which would make it hard to review your shots.
However, there is no such thing as a free lunch. Remember that as your ISO setting goes up it is just a reflection of the fact that your cannot compromise further on aperture or shutter and are effectively just accepting a certain degree of under-exposure at the sensor. The chosen ISO setting just instructs the camera how much it needs to amplify the captured signal later to boost the brightness.
Noise which would be very low level compared to the high level of captured signal at base ISO is relatively higher compared to the lower signal captured when the sensor is under-exposed, which is the case when using higher ISO settings. As a result the signal to noise ratio (SNR) is degraded, making the noise more easily visible relative to the wanted signal.
This degradation of SNR not directly caused by the ISO setting, it is just a result of shooting with the sensor under-exposed, which coincidentally is what you do when you take pictures at higher than base ISO. Unfortunately when the camera brightens the under-exposed picture post-capture, according to your selected ISO setting, it boosts the noise and signal equally so cannot do anything the remedy the already degraded SNR.
This also explains why darker areas of the picture appear noisier. The exposure level you set when taking a picture, either chosen by you or automatically by the camera, is a compromise designed to be a best fit average taking into account the size and position of the darker and brighter parts of the scene. If you exposed entirely for the darker parts the lighter parts would be burned out, and if you exposed just the for brightest parts most of the picture would come out too dark.
The result is that the darkest parts of the scene you capture are bound to be under-exposed compared to the averagely bright parts. The parts of the sensor capturing the dark parts of the image are therefore relatively under-exposed and already have an inferior SNR to other parts of the picture, even at base ISO, and more so at higher ISO settings.
I'm afraid photography is often just a series of compromises between conflicting requirements, and the skill lies in getting that compromise as good as possible.
"We are so small between the stars, so large against the sky." Leonard Cohen c1967
You got it right Fred, sadly i explained this conversation had already taken place dozens of times in the last couple years in the sony threads. Ever since they developed their newer generation of sensors the idea that base iso is the same as iso6400 in terms of real exposure is lost on people here today. Some people just don't get it and run around accusing others of being uneducated. That Draek guy is most guilty of this, iv'e seen him in many threads pretending to correct people. This thread is a perfect example that people like that are so busy handing out poor advice that they don't realize the new technology that is here now.
I don't expect a response though, id be embarrassed too if it was me. I just hope that other people read this thread so as to learn the way it really is. Telling people to risk overexposure for a false advantage is unacceptable. Hopefully these guys with their head in the sand will simply stop posting.
|Morning At Picture Lake by Buzz Lightyear|
from Dawns first rays
|AT-6 Harvard by jarud|
from Trainer aircraft
|Matterhorn by ewng|