I agree with this especially for older shutters. One thing that is
not widely known is that most between the lens or leaf shutters are
calibrated for the equivalent speed when the iris is wide open. The
speed is measured between the half light transmission points, i.e. one
stop down. So given the finite opening and closing times this method
tends to indicate increased speeds for the higher speeds. For instance,
a shutter labeled 1/500th second may in fact do that for its maximum
aperture but may drop to maybe 1/300th for smaller stops. Since opening
and closing times are constant (mostly) the effect is less as the
shutter speed becomes slower. Nonetheless, the best mechanical shutters
are no better than about + or - 20%.
Also, focal plane shutters are no better. The effective speed of a
focal plane shutter is a complex of its slit size and the distance from
the film and angle of the light cone from the lens. So, the efficiency
varies with the slit dimension, distance from film in comparison to the
slit width, and distance and stop of the lens. In general, the smaller
the slit, further from the film, wider the angle of light from the lens,
the lower the efficiency will become. At the highest speeds the
efficiency of a FP shutter like the ones in Speed Graphics and Graflex
cameras can be quite low, lower than a leaf shutter at the same speed.
I have an old Calumet shutter tester. With some care about the
light source its possible to demonstrate the efficiency loss of a focal
plane shutter.
On 10/21/2015 2:12 PM, Tim Daneliuk wrote:
On 10/21/2015 03:49 PM, `Richard Knoppow wrote:
See the article at: https://en.wikipedia.org/wiki/Exposure_value
The new series was introduced by Deckel for the EVS system about 1960.
Also see: http://www.kenrockwell.com/tech/ev.htm
I am not sure but think the system may have been introduced on a
Rolleiflex camera.
On 10/21/2015 1:32 PM, Eddy Willems wrote:
can someone tell when the old serie shutterspeeds 1 2 5 10 25 ...
changed in the new serie 1 2 4 8 15 ....
best regards
I have tested many mechanical shutters on a reasonably accurate shutter test
system over the years. I'd suggest the differences between these nominal
speeds is irrelevant, at least for mechanical systems. So I treat them
interchangeably. most usually mapping 1/5 -> 1/4. 1/10 -> 1/8 and so on.
