OK. I have learned many things over the last three years and am continually learning more. But EV numbers elude me, just beyond my grasp. Here is what I need to know. And long wordy explanations are welcome and encouraged.
According to Ansel Adams' 'The Negative', f11 @ 1/60 exposure is equivalent to EV13. As are f8 @ 1/125, f16 @ 1/30, and so on. I know that, correspondingly, f11 @ 1/30 (one stop increased exposure) would relate to EV12. f16 @ 1/60 would relate to EV14. Now. For the fun part, at least for me.
Does EV13 relate ONLY to f11 @ 1/60 and other related combinations? Or does EV13 shift exposure settings depending on the film being used (ISO rating)? To which ISO rating do these standards relate;50, 100, 200, 400, 800? I thought that EV13 was to denote a specific range of camera settings in line with 11@60, regardless of ISO and you simply adjusted the EV you used +/- however many according to which ISO you used. Which begs answer again to the which ISO does the EV Index relate to.
Any and all answers welcome. Thank you.
Last edited by Christopher Walrath; 09-30-2006 at 05:14 PM.
Reason: clarification
OK. I have learned many things over the last three years and am continually learning more. But EV numbers elude me, just beyond my grasp. Here is what I need to know. And long wordy explanations are welcome and encouraged.
According to Ansel Adams' 'The Negative', f11 @ 1/60 exposure is equivalent to EV13. As are f8 @ 1/125, f16 @ 1/30, and so on. I know that, correspondingly, f11 @ 1/30 (one stop increased exposure) would relate to EV12. f16 @ 1/60 would relate to EV14. Now. For the fun part, at least for me.
Does EV13 relate ONLY to f11 @ 1/60 and other related combinations? Or does EV13 shift exposure settings depending on the film being used (ISO rating)? To which ISO rating do these standards relate;50, 100, 200, 400, 800? I thought that EV13 was to denote a specific range of camera settings in line with 11@60, regardless of ISO and you simply adjusted the EV you used +/- however many according to which ISO you used. Which begs answer again to the which ISO does the EV Index relate to.
Any and all answers welcome. Thank you.
This will hopefully not be wordy (the subject doesn't merit a long explanation).
A given EV is a number that transcends all combinations of exposures of equal amounts of light passed to the film.
The EV is not affected by the ISO of the film used.
__________________
Art is a step from what is obvious and well-known toward what is arcane and concealed.
The Ev represents both the shutter speed/aperture combination and the film speed/scene brightness combination.
Ev = Tv + Av = Sv + Bv
Time value; Aperture value; [Film] Speed value; and Brightness value.
Tv = 0 for a shutter speed of one second.
Av = 0 for an aperture of f/1.
Sv = 0 for a film speed of ISO 3.125 arithmetic (and hence Sv = 5 for ISO 100).
Bv = 0 for a scene brightness of 1 foot-lambert.
Best,
Helen
__________________
Some of my snaps are here and here.
In 1955, the term exposure value (EV) was adopted into the ISO standard. The purpose of the EV system is to combine lens aperture and shutter speed into one variable. This can simplify lightmeter readings and exposure settings on cameras. EV0 is defined as an exposure equal to 1 second at f/1. EV tables cover typical settings, and with it, a lightmeter EV reading can be translated into a variety of aperture and shutter speed combinations, while maintaining the same exposure. Each successive EV number supplies half the exposure of the previous one, following the standard increments for film speed, aperture and exposure time. This makes EV numbers an ideal candidate to communicate exposures in the Zone System, since zones are also 1 stop of exposure apart from each other.
Most lightmeters have an EV scale in one form or another. Usually, a subject reading is taken and an EV number is assigned to that reading. This EV number can be used for exposure records and an appropriate aperture/time combination can be chosen depending on the individual image requirements. Some camera brands allow for this EV number to be transferred directly to the lens. Aperture ring and shutter speed settings can then be interlocked with a cross coupling button, and different combination can be selected, while maintaining a given EV number and constant film exposure. On Hasselblad lenses, this button is appropriately referred to as the ‘reciprocity lock’.
EVs are shorthand for aperture/time combinations and, therefore, independent of film speed. However, a change in film speed may require a different aperture/time combination and, therefore, a change in EV. As an example, let’s assume that a spotmeter returned a reading of EV10 for a neutral gray card, and a moderate aperture of f/8 is chosen to optimize image quality. Looking at an EV table, we see that a shutter speed of 1/15 s would satisfy these conditions. Let’s further assume that we would be much more comfortable with a faster shutter speed of 1/60 s, but we don’t want to change the aperture. The solution is a change in film speed from ISO 100/21 to 400/27, where the faster film allows f/8 at 1/60 second. Again looking at an EV table, we see that this combination is equal to EV12. Changing the film speed setting on the meter from ISO 100/21 to 400/27 will result in a change of measured EV to maintain constant exposure.
Some meters make fixed film speed assumptions while measuring EVs. The Pentax Digital Spotmeter, for example, assumes ISO 100/21 at all times. This meter will not alter the EV reading after a film speed change, and due to its particular design, this does not cause a problem. However, it is important to know that some meters simply return a light value (LV) instead of an exposure value (EV). We can still use their exposure recommendations in form of aperture and shutter speed, but LVs are only numbers on an arbitrary scale, measuring subject brightness and must not be confused with EVs.
[QUOTES=Helen B;371427]
"The Ev represents both the shutter speed/aperture
combination and the film speed/scene brightness combination."
Ev = Tv + Av = Sv + Bv"
Can that be? I must lack a full understanding.
"Time value; Aperture value; [Film] Speed value; and Brightness value.
Tv = 0 for a shutter speed of one second.
Av = 0 for an aperture of f/1.
Sv = 0 for a film speed of ISO 3.125 arithmetic (and hence Sv = 5 for
ISO 100).
Bv = 0 for a scene brightness of 1 foot-lambert. Best, Helen"
And, EV 0 is an exposure value of f1, 1s, at ISO 100.
Sv = 5 for ISO 100? What do I not understand? Dan
A rather simpler explanation:
Deep confusion has resulted from sloppy use of terminology (mainly by camera and meter makers).
Exposure value (EV) strictly speaking has nothing to do with any light level, it is simply a number and a shorthand way of expressing the fact that going one shutter speed faster and one aperture larger (or vice-versa) gives the same exposure. EV 14, for example, is ALWAYS 1/125 @ f11 (or 1/60 @ f16, or 1/250 @ f8, etc.).
EV 1 is 1 second at f1.4. It is possible to say that the light level that requires an exposure of 1 second at f1.4 WITH ISO 100 FILM has a "Light Value" (LV) of 1. Unfortunately, the term EV is used for everything, even when LV is meant. Meters are stated to be able to read down to EV 0 (1 second at f1 with ISO 100 film, etc.).
Exposure Value Numbers (EV) 
Linear Mode
