Exposure Basics, lesson three?

Started Mar 18, 2013 | Discussions thread
Great Bustard
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Re: Correct for...
In reply to richarddd, Mar 21, 2013

richarddd wrote:

Great Bustard wrote:

richarddd wrote:

Somewhat counter-intuitively, for fixed aperture/shutter speed, it is best to use the highest possible ISO (without clipping highlights) ... Read noise at high ISO is much smaller than read noise at low ISO, in terms of the error in photon counting that it represents. Thus, better image quality is obtained for using the highest ISO for which the signal is not clipped.

http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#ETTR (paper written in 2008 and updated 2010).

...when the higher ISO settings result in less read noise, which is not true for all sensors, and, even for sensors where it is true, the read noise almost invariably levels out after some point (e.g. ISO 800 for the EM5), after which point, optimum IQ is achieved by not raising the ISO any higher.

As I said earlier in this thread "On my camera, I can get lower noise (read noise) by increasing ISO, at least up to about ISO 800 or 1600. How does that fit into the slide?"

Ah!

The quoted statement was meant to counter the notion that higher ISO necessarily means higher noise. I like the way Bob put it "It's rooted in a misapprehension that raising ISO of itself increases noise, which is a nonsense. What increases noise is reducing exposure."

Yes.

BTW, while we're quibbling, "Higher ISO settings result in narrower apertures, faster shutter speeds, and/or more flash power" is correct only if the camera is in an auto mode.

You mean something like this?

  • Wider aperture, more light on the sensor (less noise) and less DOF.
  • Narrower aperture, less light on the sensor (more noise) and more DOF.
  • Lower shutter speed, more light on the sensor (less noise) and more motion blur / camera shake.
  • Faster shutter speed, less light on the sensor (more noise) and less motion blur / camera shake.
  • Apertures at the very wide end (low f-ratios) often result in less sharpness (lens aberrations).
  • Apertures at the very narrow end (large f-ratios) often result in less sharpness (diffraction softening).
  • Lower ISO settings result in wider apertures, lower shutter speeds, and/or less flash power, or result in a darker photo for a given aperture, shutter speed and flash power.
  • Higher ISO settings result in narrower apertures, faster shutter speeds, and/or more flash power, or result in a brighter photo for a given aperture, shutter speed, and flash power.
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