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Old Aug 25, 2003, 1:39 PM   #1
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Default Could somebody explain shutter & aperture priority?

And exactly what they do and how they affect pictures?

Thanks.
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Old Aug 25, 2003, 2:23 PM   #2
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I'm sure there are better explanations out there, but they say the best way to ensure you understand something is to teach it to someone else. So here goes my best shot at it.

First some basics, shutter speed is expressed in fractions of a second (at least until you get up to 1 second and longer exposures). Easily enough, the longer the shutter stays open, the more light it lets into the film or CCD. Slow shutter speeds can show motion blurs while faster speeds essentially freeze the action.

Aperture is how big the hole where the light comes into the camera. Larger apertures (lower f-stop numbers) let in more light, but with less depth of field (how much depth in front and behind the focus point is in focus). Smaller apertures (larger f-stop numbers) give greater depth of field, but let less light in.

For any given situation will have a balance of shutter speed and f-stop to give a 'good' exposure. If you increase shutter speed, you let less light in so the aperture must open further to let the correct amount of light in and expose the picture properly. The reverse is also true.

Thus, in aperture priority mode, at f- 2.8 your camera may want to use a 1/500 second shutter speed. But maybe you would like greater depth of field for your shot so you crank your f-stop down to say, 5.6. Your camera will then adjust the shutter speed down to (for example) 1/200 of a second to compensate for the less light coming in due to the smaller aperture.

In shutter priority then, you adjust the shutter speed you want while the camera then decides the appropriate aperture value.

Hope this helps.

Norm
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Old Aug 25, 2003, 5:59 PM   #3
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Hi there,

Here is a great site I recently found that explains this and many other things that us newbies really want to know about photography: http://www.shortcourses.com
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Old Aug 25, 2003, 7:39 PM   #4
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Default Re: Could somebody explain shutter & aperture priority?

Quote:
Originally Posted by mckeand13
And exactly what they do and how they affect pictures?
See the pages of my Nikon Coolpix 4500 user guide @ www.cs.mtu.edu/~shene/DigiCam

CK
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Old Aug 25, 2003, 7:47 PM   #5
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You were doing well untill you started using numbers.
Quote:
Originally Posted by Norm66
...
at f- 2.8 your camera may want to use a 1/500 second shutter speed. But maybe you would like greater depth of field for your shot so you crank your f-stop down to say, 5.6. Your camera will then adjust the shutter speed down to (for example) 1/200 of a second to compensate for the less light coming in due to the smaller aperture.
A change in the value of the f/stop by a factor of the square root of two (1.41) produces the same change in exposure as a factor of two in shutter speed. So going from f/2.8 to f/5.6 is a change in the f/number of a factor of two so the exposure will change by a factor of four - from 1/500 to 1/125 - to have the same exposure.

You will see some of us geezers refer to changes in exposure in terms of "stops" where a 1 stop change is either a change in f/number by sqrt(2) or in shutter speed by a factor of two.

Do some reading, but don't worry about it untill you start thinking about manual controls or exposure compensation. Keep shooting and have fun.
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Old Aug 26, 2003, 6:57 AM   #6
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[quote="BillDrew"]You were doing well untill you started using numbers.

LOL

I was at work and going from memory and without benefit of your formula. At least I was fairly close! Thanks for the correction.

Cheers,
Norm
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