ISO

ISO change is needed when you cannot get a fast enough shutter speed for your situation – and no other time (unless you want noise for an arty look – which is a legitimate use). A faster shutter speed is needed when faced with one of two problems –

  • 1) a fast moving subject that you’d like to freeze  OR
  • 2) to offset camera movement (shake) which is not the case when using a tripod.
  • If neither of these two cases describe your situation then do not raise the ISO above your camera’s normal minimum. [See note at bottom re. “normal” minimum.]

Over the past few days two people said that they raised ISO to brighten an image. Hopefully, next month’s lesson on exposure will correct that misunderstanding. (I apologize for not doing exposure first as it should have been.) As an exposure preview please note that

  • When shooting in aperture or shutter priority modes, the only way to change exposure (lightness/darkness of your image) is by changing the exposure compensation setting (EV). This will be covered in detail in upcoming lessons.

Here’s a test to demonstrate that ISO has NOTHING to do with shifting your histogram/exposure. Demonstrate this to yourself by shooting a scene while changing only one thing – ISO in 1-stop increments (200, 400, 800, 1600) – nothing else. Use aperture priority mode. Don’t worry about how dark or light the image is, that’s not the point of this test. After taking those four pictures (hopefully the ambient light did not change during the sequence) look at the EXIF data. Specifically look at the shutter speed. You should see the following – each successive shutter speed is 1/2 the previous one (the previous being the one with an ISO 1-stop less). This illustrates my point – increasing ISO will yield a faster shutter speed.
Also, in this test note that the exposure (light/dark appearance) doesn’t change from image to image – only the shutter speed changes. If you find otherwise, please report back (and include all of your settings).
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NOTE – some camera’s have “extra-high and extra-low” ISO options. For example, my Nikon’s default low ISO is 200. However, the camera offers a 100 which it calls L1.  This L1 setting, albeit lower than the default 200, is not the normal minimum. When someone tells you to use your lowest normal ISO, if you were using my Nikon, you’d use 200 and not the L1 (100). I won’t go into the reasons – just don’t.

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