Photography::EV - Calculate exposure value (EV)
version 0.07
use Photography::EV; my $ev = ev(5.6, 1/1000); # EV for f/5.6 at 1/1000s
This module provides functions for calculating photographic exposure values. Some light meters can give readings in "Exposure Value" or EV. On some cameras the exposure can be locked into a specific Exposure Value (EV), such that changing the aperture or shutter speed will adjust the shutter speed or aperture to maintain the same exposure.
my $ev = ev($aperture, $time);
Takes the aperture (f-stop) and shutter speed (in seconds). Returns the integer Exposure Value (EV).
my $aperture = aperture($ev, $time); my $aperture = aperture($ev, $time, \@apertures);
Returns the correct aperture corresponding to the given EV and shutter speed (in seconds). By default returns the closest full stop aperture between 1 and 64.
If the optional third argument is given (a reference to a list of possible aperture values), then the returned aperture will be the closest possible from that list. This is helpful, for example, when you are using a lens that provides fractions of a stop. My Nikkor 50mm f/1.2 for example has stops at f/1.2, f/1.4, f/2, f/4 f/5.6, f/8, f/11 and f/16, so to get the correct aperture for 1/60 at EV 9 for that lens:
my $aperture = aperture(9, 1/60, [1.2,1.4,2,4,5.6,8,11,16]);
my $time = shutter_speed($ev, $aperture); my $time = shutter_speed($ev, $aperture, \@times);
Returns the correct shutter speed (in seconds) corresponding to the given EV and aperture. By default returns the closest full stop between 1920s (32 minutes) and 1/8000s.
If the optional third argument is given (a reference to a list of possible shutter speeds), then the returned shutter speed will be the closest possible from that list. This is helpful for older cameras that have a different set of shutter speed stops, or newer cameras that use half stop shutter speeds. At least some Rolleiflex TLRs have shutter speeds of 1, 2, 5, 10, 25, 50, 100, 250, 500 instead of the modern values. To get the correct shutter speed for f/3.5 and EV 5:
# map displayed shutter speed to 1/t to get time in seconds
my $time = shutter_speed(6, 3.5, [map { 1/$_ } 1, 2, 5, 10, 25, 50, 100, 250, 500]);
This module requires Perl 5.20 or better.
Graham Ollis <plicease@cpan.org>
This software is copyright (c) 2015 by Graham Ollis.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.