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06-30-2011, 07:08 AM   #1
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Fast Auto-ISO

Could someone please explain to me the practical use(s) of Fast/Normal/Slow Auto-ISO? I've fiddled with these settings and can't really see what difference they make. Thanks.

06-30-2011, 08:15 AM   #2
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Practical example, if you are using Av mode :
- "Slow" will use half the shutter speed, thus using a one stop lower ISO.
- "Fast" will double the shutter speed, thus using a one-stop higher ISO.

Same goes if you are in Tv mode but with obviously the aperture as a variant...

Trickier still, if you use P-mode with "sport" as P-line, you'll be able to tweak the lowest speed used.
06-30-2011, 09:52 PM   #3
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Thanks for trying, but I'm still not getting this, sorry; and the manual says so little. Try again? Or can anyone point me to an explanation? Thanks.
06-30-2011, 10:00 PM   #4
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"Fast" means the camera is "Fast" to increase ISO so it can maintain a high shutter speed or a large DOF. So in Av mode, as the light drops, the camera will pump up ISO rather than sacrifice shutter speed.

So for a 70mm lens in Av mode:
FAST may result in ISO3200, 1/250
Normal may result in ISO1600, 1/120
Slow may result in ISO800, 1/60

Or there abouts

07-01-2011, 06:49 AM   #5
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Choose fast if you want the camera to increase ISO rather then use a larger aperture or slower shutter. This will give you images with more ISO noise/grain, but keep your fast shutter speed and/or small aperture (large depth of field)

Use slow if you want the camera to keep the ISO low, and rather adjust the other two parameters. This setting will give you less ISO noise/grain, but at the expense of depth of field and/or shutter speed.

Normal is normal Something in between.

Fast, normal or slow indicates the priority in which the camera changes ISO. In P mode the fast setting would be "shutter speed & aperture priority", and the camera changes the ISO before it messes with shutter or aperture. Where as in "low" it's a "ISO priority" and the camera alters your shutter speed and aperture rather then turning up the ISO.

I hope you understood me (English is not my first language). Someone please correct me if I'm wrong.
07-01-2011, 11:15 AM   #6
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Twitch and Skog -- thank you!! Got it!! (whew... makes sense now)

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