If I understood correctly, base ISO is in full stop steps from the lowest possible ISO setting on my camera. For example if the lowest setting on my camera is ISO 100, than the following table would be base ISO:
- 100, 200, 400, 800, 1600, 3200, 6400
While steps in between like
- 125, 160, 250, 320, 500, 640, 1000, 1300, 2000, 2500, 4000, 5000
would be third-stop "pulled" values, which result more noise than perhaps higher base ISO values (for example 2500 is worse than 3200).
- Did I get this right or missed by a mile, what did I miss?
- Do non-base ISO values generate more noise than next higher base-value ISO stop?
- How do I find what are my base-value ISO stops (is it the lowest ISO value multiplied by 2n)?
Answer
I think you might be confusing a few issues here. The terms "Base ISO" or "native ISO" are often used to refer to the unamplified sensitivity of the camera.
In addition to this digital camera sensors have built in amplifiers to amplify a weak signal (such as you get in low light) before it is digitised in order to reduce read noise and increase signal to noise ratio.
Some camera makers also use digital amplification (i.e. increasing the numerical values in a RAW file in software).
Canon for example use hardware gain for the whole stop sequence, and software gain for the in between stops. Software gain is generally inferior as it happens after readout and so you amplify the read noise, plus it doesn't do anything you couldn't do on your computer in post processing if required.
Some manufacturers use hardware amplification for all ISO settings so this isn't a problem.
No comments:
Post a Comment