What does ISO "Low" Mean?

Discussion in 'Olympus Cameras' started by Heavy Doody, Sep 13, 2013.

  1. Heavy Doody

    Heavy Doody Mu-43 Regular

    Sep 17, 2012
    On the new EM-1 the low-end ISO is listed as LOW (approx. 100).

    I think I've also seen "High" on cameras, but I'm not certain.

    Is there a reason, other than it's an approximation, that they can't attach an actual number to it?
  2. monk3y

    monk3y Mu-43 Hall of Famer

    May 14, 2013
    in The Cloud...
    On the E-P5 it's also the same.

    As far as I know, Low and High are not native ISO of the camera.

    Sent from my GT-N7100 using Mu-43 mobile app
  3. Heavy Doody

    Heavy Doody Mu-43 Regular

    Sep 17, 2012
    And what does "not native" mean, in relation to ISO? Software trickery?
  4. drd1135

    drd1135 Zen Snapshooter

    Mar 17, 2011
    Southwest Virginia
    I think it means it's really shooting at iso 200. I have no idea how it's correcting.
  5. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    Base ISO of the sensor is 200.
  6. mister_roboto

    mister_roboto Mu-43 Top Veteran

    Jun 14, 2011
    Seattle, WA, USA
    It's simulated to be lower than what the actual lowest ISO goes to. So it's not really a true say 100iso, but for exposure it's 100iso.
  7. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    I think it means that the shot is exposed at ISO 200 and then pulled back 1 stop in processing (either in camera with JPGs or via the raw processor on a PC).
    • Like Like x 1
  8. meyerweb

    meyerweb Mu-43 Hall of Famer Subscribing Member

    Sep 5, 2011
    Correct. If you shoot raw, you could do the same thing by setting EC to +1 stop, overexposing, and correcting in post processing. If you shoot jpeg, doing this in camera is better than doing it in post, because the camera can "pull" the image before converting to jpeg. If you tried to do it after, you wouldn't be able to recover blown highlights.

    The camera may also apply a different tone curve during the jpeg conversion.

    "High" works essentially the same way. The camera underexposes, and corrects in the jpeg conversion or raw processor.
  9. robbie36

    robbie36 Mu-43 All-Pro

    Sep 25, 2010
    rob collins
    I am not an expert on the subject but I have a fair idea how it works. So I will explain a bit and hopefully people can fill in the blanks.

    First take a quick look at this video (it is less than 2 minutes)....

    [ame="http://vimeo.com/10473734"]Canon EOS 7D ISO Noise test on Vimeo[/ame]

    The guy has taken footage with a Canon 7D with the lens cap on and then looked at all the 'noise' at iso levels from 100 to 6400.

    Note that the lowest noise is actually at iso160 and that the 2 next lowest noise levels are at multiples of 160, namely 320 and 640. Iso 640 is roughly as clean as ISO 125. Also I feel that noise rises linnearly after iso 2500.

    Now what happens with a sensor is that it receives the same light at every setting. With higher isos the signal is either boosted analogue or digitally (namely either before or after analogue digital conversion.) Boosting the signal increase noise particularly digital boosting.

    So what is going on with the Canon sensor.

    The sensor actually has a base ISO of 160 - that it is the ISO at which the signal is not manipulated (apart from a/d conversion).

    320 and 640 are clean because these are 'real' isos. Namely the signal has an analogue boost. The same would go for 1280 and 2560 (probably). The other iso have had their signal boosted digitally (or reduced digitally) and are not so 'real' - that includes 100.

    Anyway, as I read it and apply it to M43 cameras with sensors with a base iso of 200. First you should really not use the imbetween isos of the multiple of the base iso. Namely only use 200, 400, 800, 1600, 3200. Secondly for RAW shooters, at the very least, you should avoid the 'low' setting.
  10. goldenlight

    goldenlight Mu-43 All-Pro

    Jan 30, 2010
    The upshot is that it would be a mistake to routinely use ISO 100 on the E-P1, thinking that it will give better quality than ISO 200. In fact, the reverse is true. ISO 100 is useful for being able to use a larger aperture in bright light, or a slower shutter speed if you want some creative blur. Other than that, leave the ISO at 200.
  11. Heavy Doody

    Heavy Doody Mu-43 Regular

    Sep 17, 2012
    Excellent explanations and usage tips all the way around. Thanks, everyone.
  12. Ian.

    Ian. Mu-43 All-Pro

    Mar 13, 2013
    I thought Low is an extra Auto range. Useful when you want to keep a high quality but still allow some ISO freedom.
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