EV constant or film speed dependent?

ITD

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Many sources that I've read appear to suggest that EV is independent of film speed, so you can judge or measure EV (say for an incident reading) and then apply that to a whatever EI you're using to obtain a shutter speed / aperture combination.

My Sekonic meter however seems to measure EV constantly only for a range of film speeds - a reading under my desk light of EV 6 is good for ISO160 - 250, then reads EV7 from 320 to 500 and so on.

Which is correct then? I was trying to use the meter to check my judgment of EV's by eye, but the film speed dependence has thrown me somewhat.
 

Jim Noel

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First, I think it is a mistake that people can judge light quantity using EV or any other scale. The eye is too dependent on the quantity of available light, and what may appear as EV 10, might actually be EV 5 or any other number because of the normal adaptation of our visual sense.

I have always thought that the EV scale is as you say, and has essentially nothing to do with the film speed. If an incident reading yields an EV of 7, it is an EV of 7 and adjustments must be made to the exposure based on the film sensitivity.
 

Dave Miller

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EV is independent of, and nothing to do with film speed. It is a measure of illumination only. Knowing the EV will allow you to choose any two of the three parameters necessary to give correct exposure, the third will then be dictated. The three are, the E.I. of the film, shutter speed, and aperture. My veiw is that you can learn to estimate the EV with reasonable accuracy, just as you can using the sunny 16 rule. The more you practice the better you get. Cameras fitted with an EV interlock just made life a little simpler for the snapper that didn’t understand the relationship between the three parameters given above, and thereby increased their chances of maintaining the correct exposure when changing aperture, or shutter speed.
 

Chuck_P

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I agree with Dave it is simply a measure of light intensity by incident or reflective means. I have found that I can estimate fairly good a change in EV once I am out in the field. I may detect a change in brightness and say to myself there's a 2/3 drop in EV and I sometimes can do that quite well, but it is only once I'm out and in the light for a while and in tune clearly with what I'm doing at the time.

Chuck
 

BrianShaw

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David(s) & Chuck, are you sure you don't have your EV (exposure value) and LV (light value) confused?

EV6 @ 200 ASA would indeed be EV7 at 400 ASA. Just as it would be EV5 at 100 ASA.

For the same light level, exposure always needs to be more/less if the film speed is more/less than the one your are comparing against.

ITD's meter is not telling lies... it is correctly giving the average/recommended exposure for a given light level at a specific film speed.
 
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BrianShaw

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Jim is right - the eye and brain accomodates too much to be an objective light measurment device. What I do when I don't have the time to meter ever shot is to meter before I start shooting in an "average" lighting situation. If it is generally sunny with only occasional passing clouds, that is what I measure and that is the "base EV" that I'll use for that session, say EV13. If a cloud floats by, I'll open up a stop: EV12. When the cloud passes and it is sunny again, I'll go back to EV13. If I start shooting in a totally different environment, like shade or deep shadow, I'll often re-meter or guess how much light I lost and set the shutter to, say, EV11.
 

BrianShaw

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Please examine the following two sources:

http://en.wikipedia.org/wiki/Exposure_value

Note that in Table 2 it specifies "EV(subscript)100" The "100" is ISO film speed or advertised EI. If you want to use thes EVs with another film speed, you'd have to adjust your exposure accoringly. (But you know that!)

http://www.fredparker.com/ultexp1.htm

Note Chart B ( the left-hand columns). Each row has a "O" (zero) to indicate the EV(subscript)ASA, and every other ASA indicates the exposure value adjustment required - +1 for 1-stop slower film, -1for 1-stop faster film, etc.
 

David H. Bebbington

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Big APUG thread on this a few months ago:
(there was a url link here which no longer exists)
One of my postings was this:

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.).
 
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ITD

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Thanks David, I've been back and read through the thread that you've linked. If I interpret your posts correctly, you aren't happy with Fred Picker's way of doing things, but I want to be able to use a pocket version of his information in order to improve my judgment of exposure requirements when using my M2.

The other thread appears to have two camps, however. One insists that EV is independent of ISO, the other that EV is shorthand for EV at 100. Or maybe that is what the meter is using. Slightly confused...:confused:

In practical terms, my meter seems to most closely match the Picker chart when set at ISO 100 - 160, so I guess that for my purposes I should just set the meter to that range and get on with it.

Cheers
 

David H. Bebbington

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Can only emphasise again - the term EV is used for two related but different values, both of which you may encounter in everyday practice. The EV numbers on a 50s/60s Compur shutter (Rollei TLRs, Hasselblad, etc.) are not related to film speed, while the EV numbers (strictly speaking, light values LV) that many exposure meters indicate are related to film speed. My comments related to Fred PARKER, not so much because he seems to me to be wrong but because he is not simplfying matters as he claims but making them more complicated. I am not familiar with the teachings of Fred Picker - a quick search has revealed the suggestion that exposure is simply a matter of measuring a highlight and placing this in zone VIII, which does actually work if you are working with reversal material or even with b+w negatives if you are not bothering to vary development time away from standard.

In a nutshell, there is no reason not to work with tables instead of a meter if you prefer this, but in 50 years' picture-taking as an amateur and pro, I've never felt any desire to dispense with a meter!

Regards,

David
 

Dave Miller

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I'm having a quiet chuckle reading this thread, simply because the EV system was invented to make life simpler for photographers, and here we are making it as complicated as possible.

ITD David is correct, forget Fred he lead many on a wild goose chase.
 

David Brown

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BrianShaw said:
David(s) & Chuck, are you sure you don't have your EV (exposure value) and LV (light value) confused?
Click to expand...

Alas, apparently you are correct. My sig line used to be: "Of course, I could be wrong." Maybe I'll just put that back in there.
 
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ITD

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Dave Miller said:
forget Fred he lead many on a wild goose chase.
Click to expand...
Actually, his descriptions of lighting levels have been quite useful for me under circumstances where an incident reading has been impossible, and reflective readings unreliable - live bands in small venues as an example. My intention has been to check what his descriptions meant in real life (a bit like figuring out what level of 'sunny' is used for 'sunny 16'), and to check for myself whether his writings were valid.

I don't use EV settings on a camera - only my Autocord has them anyway. And if metering is a possibility, then I will meter - this was only for those times when taking out a meter would lose a shot, or the meter is knackered.
 

Gord Wood

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climbabout

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ev

EV is has nothing absolutely nothing to do with film speed - think of it this way: I use an old pentax analog spotmeter - when you point it anwhere and look through it, the needle indicates ev dependent on the amount of light it's pointed at. Then you use the dial on the side to get your f-stop/time setting based on the iso you set the dial on. That little needle inside has no idea, nor does it care what film you are using - the ev it points to is stricly based on the amount of light it sees. Case closed - could'nt be simpler as a previous poster alluded to. The ev system makes light measurement simple.
Tim
 

BrianShaw

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Tim, it isn't as simple as that. You can say "case closed" but let's not be too presumptuous without re-reading the intent of the original question.

The fact that "EV 14, for example, is ALWAYS 1/125 @ f11 (or 1/60 @ f16, or 1/250 @ f8, etc.)" - Bebbington's quote - isn't being argued; in fact, it doesn't really even appear to be ITDs question. I believe we can all agree that Bebbington is speaking truth. It is a fact that can be verified on any camera shutter with EV interlock, or any meter that displays EV on the caluculator dial.

ITDs question was one of application, not definition. Let's face it... just because your Pentax tells you that a 1-degree spot has an EV of 11, you're not going to use the same "11" as the exposure setting on a Compur EVS shutter (for example) for ISO 25 film and ISO 1600 film and expect the correct exposure - right?

I use a Sekonic L-558, Gossen Luna-Pro, and Weston Master III, all of which will recommend an EV SETTING based on the light level and the ISO of the film - to recommend a good exposure. It is in the application of an EV reading that EV becomes ISO/EI "dependent." And, indeed, for the same light level all will recommend a different EV SETTING for different film speeds. I think this was ITDs question.
 
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Gord Wood

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climbabout said:
That little needle inside has no idea, nor does it care what film you are using - the ev it points to is stricly based on the amount of light it sees. Case closed - could'nt be simpler as a previous poster alluded to.
Click to expand...

Hi Tim,

The needle doesn't know or care what film you are using, but the calculator dial does, and makes the necessary adjustments based on the film speed that you have specified.

I have an analog meter (Sekonic L-398) and digital (Sekonic L-508). Both can display the EV - and this value is shifted with adjustments to film speed.

For further confirmation, look at any lens that has an EV indicator (such as Hasselblad lenses). The shutter speed ring and aperture ring are linked to indicate the corresponding EV. When a light meter provides an exposure reccomendation as an EV, the film speed has been factored into this value. This value may then be dialed in on the lens and then adjusted to the desired shutter speed/aperture pairing you want.

EV standards are defined at ISO 100. Values used to calculate your exposure must be adjusted to the relevant film speed.

Gord
 

BrianShaw

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Dave Miller said:
I'm having a quiet chuckle reading this thread, simply because the EV system was invented to make life simpler for photographers, and here we are making it as complicated as possible.
Click to expand...

I chuckle with you - EV (whatever one wants to think it is) is much easier to use than to explain!
 

BrianShaw

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Gord Wood said:
EV standards are defined at ISO 100.
Click to expand...

I almost hesitate to suggest this because I haven't used a Pentax spotmeter for more than 25 years... but that was always my understanding of the "EV display value" given by that meter.

EDIT: Please see page 6 (step 10) of the Pentax Digital Spot meter manual at http://66.49.230.119/pentax_pdf/pentax_digital_spotmeter.pdf

... and page 27 of the Pentax V spotmeter at
http://66.49.230.119/flashes_meters/pentax_spotmeter_v.pdf
 
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Murray@uptowngallery

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I agree with Gord. My reading of various texts, papers, etc. indicate EV from the APEX context is indeed defined at ISO 100.

It HAS to have a film speed reference, just as saying f/5.6 @ 1/60 isn't the whole picture (ugh, bad pun). Any analog meter that gives you an f-# and shutter speed first had to have a film speed set on a dial, or is implied to be at a given ISO/ASA.

My Pentax analog spot meter (don't know what series) manual is adamant it's scale is not EV, but I must be making whatever correction is needed just fine - I have been treating it as EV (in the APEX context) for years ... & it works. Maybe they were covering their aperture because it isn't formally complaint with EV definition.

If you can find the ANSI paper on line or quotes from it (I'm running from memory), I think EV is extracted from the equation:

2^EV = (A^2)/T,
with A being f-# and T being shutter speed.

I can't recall any reference to film speed in close typographic proximity, but may have dragged the ISO 100 bit along contextually as I began to experiment with the equation (at that point in my thinking, no longer dwelling on the ISO question).

There is also an APEX (Additive Photographic EXposure?paper available on the web, and somewhere between that and the ANSI spec, there is a thorough discussion of combinations f-# & shutter speed, light level and film speed, and maybe one other way of analyzing exposure I can't remember.

Most people probably don't need to know all the details, but by the time someone so inclined grinds through the theory/math, it is well understood.

I even think EV with shutters marked in conventional (and anachronistic) shutter speeds. I look at f/5.6 and see AV (aperture value) = 6, I look at 1/125 and see TV (time value) = 7 (EV = AV+TV in APEX). I look at 1/100 sec and see TV = 6.64, about 1/3 stop slower than 1/125.

Both my Pentax analog spotmeter and GE PR-2 serve me results in EV, so it works for me.

All because someone gave me an Argus C-3 Matchmatic after I found the matching lightmeter and a Polaroid 95B in a store's junkbox and I was curious what the numbers were for.
 

Murray@uptowngallery

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Apologies to Dave - I don't want to leave wrong info with my signature on it, so I'll leave one last boring comment.

Doug Kerr's website has a nice APEX paper.

EV only has a film speed dependency in the less-commonly used relationship between Brightness Value and Speed Value.

Ev = Av+Tv = Bv+Sv

The assumption of ISO 100 comes from the condition where AV+Tv = Bv+Sv.

A = Aperture
T = Time
B = Brightness
S = ISO film speed.

I still find it interesting, but I like the science side of photography as well as the art side.
 
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