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I like to shoot in Aperture priority mode on my Canon 600D. When i activate auto-iso, the camera ramps it up quite quickly, and selects, accordingly, very high shutter speeds, far higher than i would have selected manually.

Is it possible to tune the auto iso ramping algorithm, so that it settles on shutter speeds at, say, the usual 1/f (edit: it actually seems to select that, accounting for crop factor, but with stabilization, we could go a few stops lower than that), or is the only recourse to set A and T manually (or avoid auto iso altogether)?

  • In my experience, my 550D won't go faster than 1/(1.6*f) which is the equivalent (pun intended) rule for (Canon) crop sensors. Are you getting shutter speeds faster than that? – Philip Kendall Jan 16 '15 at 21:31
  • hm, just tested it. now that you mention it, you are right. my actual thought at previous trials was that it doesn't compensate for IS, which should be good for ~3 stops. – ths Jan 16 '15 at 21:39
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    Yep, it doesn't reduce the shutter speed if IS is in use. Probably worth reading Does Av mode on my Canon DSLR take IS into account when deciding shutter speed and ISO?. – Philip Kendall Jan 16 '15 at 21:42
  • ah, thank you, i didn't find that. but the answers there basically amount to "no" anyway. – ths Jan 16 '15 at 21:47
  • The Canon 7D II has a much "smarter" auto-ISO function than your 600D, but even its algorithm doesn't have adjustments for all the things you're looking for. Perhaps this is something that Magic Lantern could take on at some point. – D. Lambert Jan 17 '15 at 15:32
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No. There are cameras that do though. However, they are almost all based on setting a parameter which decides how ISO is increased from its base sensitivity. In some cases (Pentax) you specify a relative rate, while in others (Nikon) you specify a minimum shutter-speed.

Except for some Panasonic cameras, the change of ISO has nothing to do with the scene or subject which is why it is better to learn and set the right value yourself. Simply considering stabilization would increase your chances of having blurry subjects while the background may end of cleaner, it will not necessarily make a better photo. Panasonic tries to do better my measuring subject motion and set an ISO to get a shutter-speed which freezes motion better. This works best with a mirrorless camera or at least in Live-View where the camera can read the entire sensor and analyze motion.

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    Itai, on some Canon cameras you can also define range of autoISO plus minimum speed. And I personally see it try to keep ISO mostly as low as possible – Romeo Ninov Jan 17 '15 at 4:27
  • interesting funcionality, but when i shoot in Av, i'm obviously not concerned about subject motion. on the 600d i can only set max auto iso, but restricting that too much effectively disables the "auto". – ths Jan 17 '15 at 15:21
  • @ths, I just clarify the answer of Itai. Such functionality (unfortunately for you) exist on higher models (x0D, xD) of Canon – Romeo Ninov Jan 17 '15 at 15:51

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