Basic F Stop Question

M

Mark-P

Well-known member
I am very new to the HVX and production in general.
1.) Is changing F stops done by adjusting the IRIS?
2.) If the IRIS/F-stop on the display shows F4.0 and I am told to drop the F stop by 1 full stop, what value should this be? I do not see F3.0 as an option when adjusting the IRIS.

Thanks!!!
 
The F stop is the ratio between the focal length of the lens and the diameter of the iris.

Hence the quantity of light getting to the sensor is inversely proportional to the square of the F stop. I.e. F 8 lets in four times more light than F 16 because (16/8)^2 = 4.

Because we want each single F stop to conveniently represent one doubling/halving of light quantity, the ratio between adjacent F stops is always the square root of 2, or 1.4.

Hence the series is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32....
 
It is worth noting that the HVX allows adjustment in very fine increments of 1/6 of a stop. Just because the LCD shows f4.0, doesn't mean the camera is actually at 4.0 (it could be 4.0 +/- 2.3 of a stop).


Jason
 
Thanks for the excellent explanation! So I am guessing that this is all controlled by the IRIS? Just want to be sure.

capitanfracassa said:
The F stop is the ratio between the focal length of the lens and the diameter of the iris.

Hence the quantity of light getting to the sensor is inversely proportional to the square of the F stop. I.e. F 8 lets in four times more light than F 16 because (16/8)^2 = 4.

Because we want each single F stop to conveniently represent one doubling/halving of light quantity, the ratio between adjacent F stops is always the square root of 2, or 1.4.

Hence the series is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32....
Click to expand...
 
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