Describing brightness with EV

NedL · Nov 29, 2014

It can be confusing that people use EV to refer to both the camera exposure and the brightness of a scene. There is plenty of discussion about this in APUG threads. My question is: if I write about the brightness of a scene in terms of EV, can I assume people will know that I mean EV@ISO100?

For example, the other day, in response to a question about a paper negative, I wrote something like:

"20s at F/32, EV a little less than 11"

Is that clear? Since I give the exposure and f-stop, it seems obvious that EV must refer to the light level I was exposing for. But is it necessary for me to write: "EV a little less than 11 at ISO 100"?

Is there a better way to say this that more people would understand? Should I have said "4-1/3 stops below sunny 16"?

Bill Burk · Nov 29, 2014

You could fill out one of Ansel Adams' exposure records.

NedL · Nov 29, 2014

true but might not fit as a brief reply to a comment on my photo!

BrianShaw · Nov 29, 2014

Oh, no... the EV thread... what hath you wrought?

I wouldn't be making any assumption that folks will assume your report of EV as EV@100 unless you say so. I tend to think of EV specific to the meter reading associated with the film I'm shooting. All I need to know is what EV number to set the shutter (on the shutters with EV indications). On everything else I think in terms of ASA/f-stop/shutter speed.

As far as conveying light level, I tend to keep the description more generic... like the old Kodak film boxes did: bright noon sun, slightly hazy, etc. I'm not sure that too much more exacting language really conveys useful information. But that may be a complete shortcoming of my understanding.

NedL · Nov 29, 2014

Ha! That's why I started by saying there's been "plenty" of discussion and tried to ask a specific question. If you tend to think of EV in that practical way, I'm sure you are not alone. You've answered my question.

Chan Tran · Nov 29, 2014

To avoid confusion I generally say EV11@ISO100 or LV11. But then photographic terms are full of confusion may be it's the nature of photographers.

wiltw · Nov 29, 2014

When camera manufacturers provide specs for sensitivity of AF in low light, they (Canon, in this example of 70D specs...) write things like "AF works in light levels as low as 0 EV" only with specifying 'at ISO 100' except as a footnote, or metering sensitivity as 'Metering Range EV 1-20 (at 73°F/23°C, ISO 100).

BrianShaw · Nov 29, 2014

Gossen did the same thing WRT low light reading ability of LunaPro. In that situation I believe they are using the "dictionary definition" of EV... which is @100ASA (as you said).

NedL · Nov 29, 2014

I went back and changed my reply to the comment to read "20s at F/32, EV11@ISO100". I definitely understand that this does not convey everything, especially the thinking that went into deciding to expose for that light level.

Trying to write in terms of "sunny sixteen" has some of the same problems... it might refer to the exposure needed in bright full sun, or it might refer to the whole sunny-16 system. At the end of the day, it's how you meter and decide what light level to expose for that matters, it seems like we should have an easier objective way to say "after metering, I decided to expose for X light level".

BrianShaw · Nov 29, 2014

Wouldn't it be just as easy to say the ASA/ISO of the paper? Most photographers think in terms of those three exposure variables (film/paper sensitivity, exposure time, and aperture) to describe a specific photographic exposure. I'm still a bit hazy on what you are trying to convey with EV as a measure of scene brightness.

NedL · Nov 29, 2014

Yes I probably should have written that I rated the paper a little less than ASA 6. Avoiding the whole problem.
( off to edit again!! )

Sirius Glass · Nov 29, 2014

To be useful one must specify the ISO with either the EV level or f/stop and shutter speed. For example EV 14 @ ISO 100 or f/11 1/250 with ISO 400.

Chan Tran · Nov 29, 2014

BrianShaw said:
Wouldn't it be just as easy to say the ASA/ISO of the paper? Most photographers think in terms of those three exposure variables (film/paper sensitivity, exposure time, and aperture) to describe a specific photographic exposure. I'm still a bit hazy on what you are trying to convey with EV as a measure of scene brightness.

If you want to convey the scene brightness and not using the term EV@ISO then you have a couple of options. For example if the OP said EV11@ISO100 he could say

1. 5120 Lux if he made an incident measurement with the flat diffuser.

2. 287 Cd/m^2 if he made a reflected light reading.

Neither is easier for a typical photographer to comprehend.

RalphLambrecht · Nov 29, 2014

NedL said:
It can be confusing that people use EV to refer to both the camera exposure and the brightness of a scene. There is plenty of discussion about this in APUG threads. My question is: if I write about the brightness of a scene in terms of EV, can I assume people will know that I mean EV@ISO100?

For example, the other day, in response to a question about a paper negative, I wrote something like:

"20s at F/32, EV a little less than 11"

Is that clear? Since I give the exposure and f-stop, it seems obvious that EV must refer to the light level I was exposing for. But is it necessary for me to write: "EV a little less than 11 at ISO 100"?

Is there a better way to say this that more people would understand? Should I have said "4-1/3 stops below sunny 16"?

|EVxx at ISOxxx seems clear to me

RalphLambrecht · Nov 29, 2014

NedL said:
It can be confusing that people use EV to refer to both the camera exposure and the brightness of a scene. There is plenty of discussion about this in APUG threads. My question is: if I write about the brightness of a scene in terms of EV, can I assume people will know that I mean EV@ISO100?

For example, the other day, in response to a question about a paper negative, I wrote something like:

"20s at F/32, EV a little less than 11"

Is that clear? Since I give the exposure and f-stop, it seems obvious that EV must refer to the light level I was exposing for. But is it necessary for me to write: "EV a little less than 11 at ISO 100"?

Is there a better way to say this that more people would understand? Should I have said "4-1/3 stops below sunny 16"?

keep in mind that brightnesshas no unit as it is a human response.on the other hand luminance and llumination have units.

NedL · Nov 30, 2014

Thanks Ralph!

Chan, compared with lumens or footcandles, I guess EVxx @ ISOxxx has the advantage of the log2 scale that is handy and intuitive for photographers used to working with f-stops.

It's too bad we couldn't have used a different name for it.

And yes, not only was I being vague about the measurement, I was being vague about what was being measured too!

RalphLambrecht · Nov 30, 2014

NedL said:
Thanks Ralph!

Chan, compared with lumens or footcandles, I guess EVxx @ ISOxxx has the advantage of the log2 scale that is handy and intuitive for photographers used to working with f-stops.

It's too bad we couldn't have used a different name for it.

And yes, not only was I being vague about the measurement, I was being vague about what was being measured too!

and knowing the calibration factor of your meter ,EVs can be converted into lux and cd/m^2

Steve Smith · Nov 30, 2014

NedL said:
Is there a better way to say this that more people would understand?

Yes. Use LV (Light Value). Same numbers as EV at ISO 100.

It seems silly to use a scale intended to indicate shutter and aperture combinations as a measure of light where it has to be qualified with another variable when a scale for measuring light already exists.

http://camerapedia.wikia.com/wiki/Light_and_Exposure_Values_(LV_&_EV)

Steve.

NedL · Nov 30, 2014

Steve Smith said:
It seems silly to use a scale intended to indicate shutter and aperture combinations as a measure of light where it has to be qualified with another variable when a scale for measuring light already exists.

Exactly!

I did not know the definition of LV. Reading your link, I see that LV = EV@ASA100. Perfect!
Off to edit my comment again. I hope the fellow I'm answering hasn't gone back and read my answer several times, he'll think I'm crazy

Chan Tran · Dec 1, 2014

I like the term Light Value (LV) but whenever I used it many would ask what it means.

NedL · Dec 1, 2014

Chan Tran said:
I like the term Light Value (LV) but whenever I used it many would ask what it means.

We need a "facepalm" smiley emoticon thingy! The plain truth is that I did not know until now. But thank you, I did notice that you also mentioned LV.

dtmateojr · Mar 11, 2015

Isn't EV constant/fixed/standard values? For example EV15 corresponds to f/16 at 1/ISO in terms of camera settings.

NedL · Mar 11, 2015

dtmateojr said:
Isn't EV constant/fixed/standard values? For example EV15 corresponds to f/16 at 1/ISO in terms of camera settings.

Yes, it is often used that way which is why I started this thread... it is also used sometimes to describe how a scene metered. I thought it was confusing to use the same term for both. In this thread I learned about "LV", which seems to answer nicely.

In posts that describe how I am exposing calotypes, I now use LV to describe the light in the scene, and aperture + exposure time to describe my exposure. I'm using LV to mean EV@ASA100.

For example, with this calotype I made earlier this month:

Bennett Valley Grange Calotype par Ned, on ipernity

LV ranged from 11 in shadows under trees on the right up to 16 with sunshine reflecting off the white wall. I chose to base my exposure on LV 15, and exposed my calotype for 3.5 minutes at f/16. All this information might be useful for someone else working with the same calotype process: a "standard" exposure for LV15 at f/16 would have been 4 minutes, so this describes how much I backed off, and explains why the development went longer and how I ended up with more contrast and a denser negative. So the LV is important to be able to describe how the choice of exposure was made.

Hope that makes sense!

Describing brightness with EV

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