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Thread: Questions about the basics: f-stop and shutter speed

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    brucep is offline Contributor photozoholic
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    Aug 2005

    Sebastopol, California


    Default Questions about the basics: f-stop and shutter speed

    I got this PM and will try to answer it in the public forum so others may learn from the discussion or have other answers.

    Quote Originally Posted by jwarren
    Bruce - I tried what you suggested, starting with the smallest number of f-stop and slow the shutter speed down, in hopes to blur the background but as I attempted that the darker my image got....what am I doing wrong?
    You may be in too dark a place to even get a decent image. I'd suggest you start outdoors. With your camera on Manual mode, go to your largest aperture (f-stop) which will have a low number such as f/4, f/2.8, f/2, etc. Then adjust your shutter speed until the needle in your viewfinder is in the center. That's a good place to start. You may want to over or underexpose from there.

    An old rule of thumb for exposure is that at f/16 in full sunlight, your shutter speed should equal your ISO (ASA back then). It's called "sunny sixteen."

    So with your ISO at 125 and your aperture at f/16, your shutter speed should be about 1/125th of a second. Opening your aperture from f/16 to f/11, to f/8, to f/5.6, to f/4 and then down to f/2.8 (five stops), your shutter speed would go up from 1/125th five stops to get the same amount of light reaching the sensor: 1/125, 1/250th, 1/500th, 1/1000th, 1/2000th, to 1/4000th of a second. Some cameras don't have that fast a shutter speed capability, so you'd have to stop your aperture down a bit from wide open. Regardless, center the needle and then open the aperture as large as you can (since you're trying for a shallow dof), and compensate by reducing the light with your shutter speed.
    Last edited by brucep; 04-27-2012 at 04:12 PM.

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