Apertures, Shutter Speeds and Film speeds in 1/3 stops.

Ian Grant

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Emmanuel Bigler

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Thanks to Ian Grant for the chart
In addition, please find as downloadable jpeg image, a bar-chart showing the correspondence between the old series of speeds (e.g. on certain Compur shutters)
1 1/2 1/5 1/10 1/20 1/50 1/100 1/200 1/400
and the modern standard series
1/2 1/4 1/8 1/5 1/30 1/60 1/125 1/250 1/500
The old series differs only by 1/3 of a stop to the closest value of the modern series.

Emmanuel Bigler

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Another useful tool: a circular slide rule, a pdf document to download, ready to print and glue on cardboard, to compute at a glance the exposure values (EV) by 1/3 of a f-stop, when you are using very small apertures (e.g. f/500 with a pinhole camera) or very long exposure times (e.g. if you use a dark neutral grey filter).

This slide rule, of course, is not an exposure meter (except if you consider that the "sunny-16 rule" is your favourite metering system ;) ) and does not take into account reciprocity failure, which has to be added; you should increase exposure times according to the film manufacturer's specifications for non-reciprocity.