Tempo/diaframma equivalenti

Slide rule that allows you to obtain all the time / aperture pairs equivalent to the one in use and the variations as the ISO sensitivity changes. For its use, purely didactic and not practical, it is enough to report the time / aperture couple found by the exposure meter of the camera and you will have all the equivalent couples. To change the ISO sensitivity, in the innermost part, there is a graduated circle (variations of 1 and 1/3 of stops), whose values ​​increase counterclockwise, and decrease clockwise. Suppose we have a shutter speed / aperture of 1/15 at F8 and want to find the value corresponding to ISO 400, knowing that we are now at ISO 100. The difference between ISO 100 and 400 is two stops (100, 200, 400), so we will have to move to the second notch counterclockwise, at the time 1/60, we turn the internal ring so that our F8 aperture goes to correspond with the aforementioned time value, and here the ruler will show all the pairs equivalent to 1/60 at the aperture F8, at an ISO sensitivity of 400.