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SET (exposure reference)

Use this to set the desired exposure. Use the sliders to select the shutter speed, f-stop number and ISO for the scene, without and ND filter fitted - usually, the ones the camera's automatic metering gives you. The "Exposure Value" is shown, labelled "EV".

Pressing the "SET" button enters the selected exposure as the target value for the offset function: use the offset slider to set the number of "stops" the ND filter you will use gives and/or adjust the aperture / ISO settings, and read the required exposure time from the line underneath.

If the time gets too long (more than 30 seconds) the display changes to indicate the shutter open time you need to use with the "BULB" mode.

The RESET button lets you go back to "SET" the exposure reference value again.

The Theory

This web application combines the theoretical solution for "Exposure Value" with a set of commonly used values for shutter speed, aperture and ISO available in modern DSLR cameras (1/3 and 1/2 stops).

"Exposure Value" was introduced to allow photographers to more easily estimate the appropriate exposure setting, on the basis of "stops". One "stop" is a change of 1 (up or down) in the Exposure Value (EV).

The basic formula for EV is: EV = log2(n2/t * 100/S), with n=aperture (the f-number), t=shutter time and S=ISO number. This gives a value of 0 for t=1 second, f = 1 and ISO = 100, which are all part of the definition of EV. It also, for example, reflects the familiar doubling of the shutter time for one stop increase in exposure.

This application calculates the theoretic "ideal" exposure, as given by a light-meter or the automatic light-metering function of a camera, when the aperture or shutter time need to be offset from the value given for creative reasons, such as using an ND filter for long exposure times.

This application gives purely theoretical results for an "ideal" camera. It does not take into account the "Reciprocity failure" of film, nor the behaviour of digital sensors when they are used at the extremes of their normal range (e.g. noise). These are all different, depending on the technological prowess of the manufacturer.

DAFOS makes no claims about the usability of this application, nor for the results obtained. If it works for you, fine! If not, keep experimenting!! :) ...