On Thu, 10 Jan 2019 03:51:41 -0800 (PST), Whisky-dave
wrote
--- snip ---
This illustrates the disadvantage of not using the language with
precision. As I said, all my lenses make use of f/numbers which are a
measure of stops. Your thoughts have jumped the rails and are now
talking about the intervals of Exposure Value of which the camera is
capable. The exposure value may be used to set lens aperture, shutter
speed or ISO. They are not identical to stops.
they absolutely are.
So I double the shutter speed. I have halved the exposure value but I
haven't affected the stop setting.
Exposure value is really a measure of the brightness irrespective of the shutter speed or aperature. Which is why sensor can have EV values which aren;t referenced to shutter speeds or stops.
Exposure value is a measure of the total quantity of light falling on
the sensor. i.e its a function of lens aperture and length of time of
exposure.
If you look at the table here.
https://en.wikipedia.org/wiki/Exposure_value
example EV 10
10 1/1000 1/500 1/250 1/125 1/60 1/30
If you are referring to Table 1 it shows "Exposure times, in seconds
or minutes (m), for various exposure values and f-numbers"
The shutter speed columns are headed with a corresponding F number:
EV 1.0 1.4 2.0 2.8 4.0 5.6
10 1/1000 1/500 1/250 1/125 1/60 1/30
It all makes perfect sense once you take the two separate parameters
into account.
so changing the shutter speed has NO effect on the EV.
It doesn't if you make the corresponding change in the lens aperture
as well.
See up above a 1/1000 doubling that is 1/500, you can even double it again it's still the same EV value of 10
Because the aperture has gone from 1.0 to 1.4 to 2.0 respectively.
What will change is that the shutter will open for twice as long allowing more light onto the sensor or the film or even the human eye.
The shutteer will open for twice as long allowing light to fall on it
for longer. But the lens will be stopped down to halve the
illumination of the sensor. 2 x 1/2 = 1. No change.
--
Regards,
Eric Stevens