2/3 of a stop.


TPF Noob!
Jun 20, 2010
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Vancouver, Washington
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So i always thought that 1 stop was either just 1 change of the shutter speed or aperature, but was reading and dude says, adjusted my aperature until it indicated a -2/3 exposure. can anyone clear this up for me please?
if your camera is set to adjust in 1/3 stop increments, one click of the wheel is 1/3 of a stop. two clicks is 2/3 and three clicks is a full stop.

can refer to ISO, shutter speed or aperture.
A 'stop' is essentially the unit of measurement for exposure. One 'stop' refers to either doubling or halving the amount of light used for the exposure. For instance: If ideal exposure is ISO 200, 1/125 and f8, you might decide to increase exposure by one stop because of the conditions: You could increase shutter speed to 1/250 or aperture to f11 (Note: whole aperture values don't follow numeric progression). Each one of those would allow twice the amount of light to hit your sensor. 2/3 of a stop would be an increase would mean increasing shutter speed to ~1/200 or aperture to ~f10.

ISO is measured in stops as well, and increasing ISO from 200 to 400 would be a one-stop increase, but rather than allowing more light to enter the camera, it increases the sensitivity of your sensor.
On modern cameras, when adjusting manual settings, they usually go by 1/3 stop increments. You can set it for 1/2 stop too. A full stop down is equivalent to cutting your light in half, a full stop up is like doubling your light. With shutter speed, going from 1/60 to 1/30 is going up a full stop. With aperture (and I could be wrong on this maybe) going from f/5.6 to f/4 is going up a full stop as well.

Hope that helps. On your light meter in the viewfinder or on the screen, it probably shows a range of 6 stops - my Rebel does if I remember right. They're further broken up into 1/3 increments.

If the guy said in the book he was looking at his light meter and it was giving a -2/3 exposure, he was purposely exposing his image on the dark side.

Hope I could help.

EDIT: wow 3 replies in 3 mins :D
for example;
for example;
And is the basic premise behind Bryan Peterson's popular book 'Understanding Exposure'.

While those are all the same exposure, only one of them is the correct 'artistic' exposure, because the shutte speeds will each render motion differently and the different lens apertures will produce differences in the depth-of-field.

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