Lens Aperture

By Rahul Nair
In Cinematography
Oct 23rd, 2013

All the lenses available in the market have an adjustable aperture or iris which controls the amount of light that passes and strikes the film. A wide opened aperture allows more light to pass through to film than a small opening, it differs from the available source of light present to film the scenario. The numbers which defines these openings are called an f-stop. It’s a mathematical calculation equal to the focal length of the lens divided by the diameter of the aperture opening. The standard series of f-stop numbers are 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 ans so on.

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All lenses absorbs some amount of light passing through them, therefore there is a precise representation of the amount of light reaching the film through the lens. This calculated number is called a t-stop. A t-stop is the actual amount of light that transmits through the lens at a particular aperture openings. The t-stop is more accurate and should always be used while setting up an exposure meter.

The t-stop numbers are the same as f-stop numbers, but a t-stop is not the same as an f-stop. Many times a lens will be calibrated for both f-stops and t-stops. When setting the exposure precisely on the lens, you should always use t-stops. When measuring the intensity of the light with a light meter or when calculating depth of field, you should always use f-stops. Whenever you film at a frame rate other than 24 fps, you must change the stop compensate for the new frame rate.


Rahul Nair loves everything about Cinema, Photography, Cinematography and likes Journalism.