F stops in relation to shutterspeed and aperture

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Ashish Aleti
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p.1 #1 · F stops in relation to shutterspeed and aperture

I am new to photography and I found this topic when i was reading about how to use GND filter's.

its a topic about how to use a GND filter when shooting a landscape with a snowy mountain top and a foreground with a bed of flowers.

"Take a meter reading of the snow on the mountaintop. Remember to use a narrow-angle meter, such as your spot meter, as you want to meter the snow and only the snow. Your meter gives you the direct values of 1/125 sec. at f/16, but you know that this will render the snow as a medium tone. To make the snow a pure white, you must open up 2 stops to 1/125 sec. at f/8.
Now meter the foreground --the shadowed meadow. It's basically a medium toned area. There are some slightly lighter flowers and a few darker leaves, but it averages out to a medium value. Take a meter reading here using an overall metering pattern. The values read out as 1/60 sec. at f/2.8.

Now count how many stops difference there are between these two readings. Well, you slowed the shutter speed by one stop and you opened the aperture by three stops, for a total of four stops"

How is it that it is 1 stop between the shutter speeds? i really cant understand this

correct me if I am wrong, 2.8 X 3 is close to 8.0 is that how it is 3 stops difference between the apertures

thanks

Ashish

Edited on Dec 13, 2007 at 12:50 AM

Dec 13, 2007 at 12:19 AM

Joel Kern
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p.1 #2 · F stops in relation to shutterspeed and aperture

Let's see if I can explain this quickly...
Shutter speeds in full "stops" go from 1/500 to 1/250 to 1/125 to 1/60 to 1/30, etc., etc.
Each jump is one "stop", therefore a change from 1/125 to 1/60 is one stop.
Aperture f "stops" go from 2 to 2.8 to 4 to 5.6 to 8 to 11
Each change to the aperture stop, say from 2.8 to 4, is the same as changing the shutter speed by one stop, only in the opposite direction, say from 1/125 to 1/250 if you were changing the shutter speed instead.
Hope that helps!

Edited on Dec 13, 2007 at 12:50 AM

Dec 13, 2007 at 12:34 AM

Ashish Aleti
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p.1 #3 · F stops in relation to shutterspeed and aperture

Thanks a lot Joel

, that was simple and easy.

Dec 13, 2007 at 12:50 AM


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