Talk:Exposure value

message: I have been trying to understand this page completely for some time now.  I have a strong math/physics background and the math is no problem.  The concepts are very confusing, so I could be off base here.  If I am, I will consider any corrections a teachable moment.  The bright sunlight provides a measurement (I have performed myself) of approximately 10,000 footcandles.  I have also read that in several places that is the correct value.  EV15@ISO100 would be the correct settings on the camera for a good exposure of an average scene under these conditions.  As you know -- it is the sunny 16 rule.  However, Table 3 has the illuminance of EV15@100 as 7611fc.  This is 1/3 of a stop away from the value I expect to see here. Comments? Kq6up (talk) 17:21, 11 June 2013 (UTC)
replies: text: One-third of a stop is generally considered a negligible difference in photography rules of thumb.  Dicklyon (talk) 17:25, 11 June 2013 (UTC)
replies: text: Granted, however the table should represent scientific data derived from calculations or empirical measurements.  33% error would indicate that either an instrument is crude, miscalibrated, or broken.  If the data was derived, then there is a calculation error some where.  This could lead to someone trying to get a deep gut understanding of how all the pieces fit together to bang there head needlessly.  Back to the salt & pepper notebook and head scratching Kq6up (talk) 18:21, 11 June 2013 (UTC)
replies: text: 7611 fc is only 24% lower than 10000; if the rule of thumb gives the right exposure for 7611, it will be slightly over on your typical sunlit scene, which is exactly the direction that you want your rule of thumb to be a little off.  Maybe it's that simple?  Dicklyon (talk) 19:15, 11 June 2013 (UTC)
replies: text: The concern I raised was not addressed by the last comment.  Moreover, the table is also ambiguous as it stands.  The illuminance is very straight forward since there is no consideration of placement of tones photographically.  It is simply luminous flux per unit area.  However, there is no clue as to what shade of grey the luminance values would be rendered as photographically (what zone are we talking here? -- zone V?).  The ratio of illuminance to luminance is 20:1 for the metric side of table.  I can understand a factor of 4*pi for the units to line up, and then there is the whole lambertian defuse reflector cosine factor.  When this is integrated over a hemisphere throws in another factor of pi some how.  All very confusing even for a huge science nerd as myself.  This is hard enough to comprehend without the ambiguities in the table.  A paragraph explaining the luminance values especially.  Sorry for the rant.  I just hope my critique will make for a clearer article.  Thanks Kq6up (talk) 20:29, 11 June 2013 (UTC)
replies: text: Well, it's all rules of thumb.  As the article says of luminance metering, "Values for the reflected-light calibration constant K vary slightly among manufacturers."  The problem is that scene luminance, or illuminance, is not enough to determine a "best" exposure.  Both reflected and incident light meters, and the sunny 16 rule, give you a guideline, but you can adjust it based on what tonality you're trying to achieve.  The history of standards around metering is complicate; ask Jeff Conrad, iirc he's the expert on this.  Dicklyon (talk) 00:04, 12 June 2013 (UTC)
replies: text: I understand it is all a big ol' mess.  I am just trying to get my head around the photometry involved.  Once that makes good sense, I can sort it all out later.  That being said if one sticks to the modern formulas and definitions, it should all be internally consistent.  I doubt the standards themselves are er.  Just that most people don't really understand them.  Just look at some of the replies on Yahoo Answers.  They are horrendous.  One final question.  How do you get notified that there has been a change made to this page?  You responded very quickly.  Also how would I get in touch with Jeff Conrad? Kq6up (talk) 01:39, 12 June 2013 (UTC)
replies: text: Unfortunately, Jeff seems to have left Wikipedia quite some while ago: User:JeffConrad. You could try to email him, perhaps he'll answer. --Matthiaspaul (talk) 01:54, 12 June 2013 (UTC)
replies: text: Indeed, I miss him.  Here are some of his relevant edits to Light meter. Dicklyon (talk) 03:37, 12 June 2013 (UTC)

text: I don't get notified except by checking my watchlist, which has a few thousand articles on it.  Dicklyon (talk) 03:37, 12 June 2013 (UTC)
thread_title:  Table 3 Confusion 

message: In the section "Relationship of EV to lighting conditions"  EV15 is stated to be correspond to a luminance of approx 4,100 *lux*.
Yet in "Table 3. Exposure value vs. luminance (ISO 100, K = 12.5) and illuminance (ISO 100, C = 250)" EV15 is given as 4096 *cd/m^2*
From the Wikipedia article on luminance, cd/m^2 seems to be the correct unit for its measurement.
Are the units given under "Relationship of EV to lighting conditions" correct?  If so an explanation might be added as to why.
IanWorthington (talk) 15:57, 6 August 2016 (UTC)
replies: text: I have changed the units for luminance to the correct ones (cd/ft2 and cd/m2). I changed the illuminance relationship to use the common value () for a flat (cosine-responding) sensor, which is the only way illuminance can be meaningfully measured (and which the manuals for most incident-light meters indicate); I added a sentence to that effect. Though I did not mention it, the relationship of reflected-light measurements to luminance is meaningful only when measuring a single, uniform luminance. Accordingly, I wonder if giving these values here is actually useful, especially since the topic is already covered in EV as a measure of luminance and illuminance. I also think reference to the camera settings adds nothing but confusion. I would recommend dropping the material from this section. JeffConrad (talk) 05:14, 23 November 2016 (UTC)
thread_title:  Relationship of EV to lighting conditions: units wrong? 

message: All too often, edit comments don’t leave enough space for a proper explanation. I removed the subscripted v from the equation for luminous exposure for two reasons:
* The sources we cite do not use the subscripts; for whatever reason, the same is true for most photographic texts.  I doubt it’s a matter of currency; the subscript v has been used for decades to indicate photometric quantities. The difference may not be fatal, but it may still confuse the reader who bothers to check the source.
* Because we also refer to the original APEX symbol Ev, the nearly identical symbol Ev is asking for confusion; the implication that the quantities are logarithmic arises only in this context. The note indicating that this is not the exposure value may confuse as much as it clarifies; perhaps a more expansive explanation would address this, but I think the greater problem is needing an explanation at all.
The astute reader can probably sort this all out, but the reader should not need to do so. 
To me, there would seem little chance of confusing radiometric and photometric units in the context of this or most photographic articles; perhaps that’s why most photographic texts omit the subscript.  NIST  appear to accept either using or omitting the subscript, so I’m not sure omitting it is bad practice.
It’s obviously desirable to have consistency among articles, especially those in the same category (e.g., photography).  Matters are complicated somewhat by the seeming inconsistency of categorizations; because this article is also included under Photometry, omitting the subscripts here leads to inconsistency in that category.  But I would think this article should be consistent with others such as Light meter; it’s probably feasible (with suitable explanations) to include the subscripts in that article, but I cannot imagine doing so in APEX system without driving the reader nuts.
In a sense, we are damned if we do and damned if we don’t. But all things considered, I think the best choice is to follow most photographic texts and omit the subscripts; this avoids two different meanings for the same symbol, and avoids conflict with the sources cited.
If others insist that the subscripts are the better approach, I’m not going to press the issue too far. But I think something more expansive than “(not EV, the exposure value)” would be needed so that the reader is not left scratching her head. And related articles should be revised to take the same approach, though APEX system might need to remain an outlier.
JeffConrad (talk) 10:35, 27 November 2016 (UTC)
thread_title:  Indication of photometric quantities with subscript ''v'' 

message: I offer the following initial thoughts on how to (somewhat) cover the Deckel Light Value System discussed under Talk:APEX system#Light value system ?:
:The EV concept was developed by the German shutter manufacturer  in the 1950s (Gebele 1958; Ray 2000, 318). Its intent was to simplify choosing among equivalent camera exposure settings by replacing combinations of shutter speed and f-number (e.g., 1/125 s at f/16) with a single number (e.g., 15).
:On some lenses with leaf shutters, the process was further simplified by allowing the shutter and aperture controls to be linked such that when one was changed, the other was automatically adjusted to maintain the same exposure.  This was especially helpful to beginners with limited understanding of the effects shutter speed and aperture and the relationship between them.  But it was also useful for experienced photographers who might choose a shutter speed to stop motion or an f-number for depth of field, because it allowed for faster adjustment—without the need for mental calculations—and reduced the chance of error when making the adjustment.
:The concept became known as the Light Value System (LVS) in Europe; it was generally known as the Exposure Value System (EVS) when the features became available on cameras in the United States (Arizona Republic 1957, 46).
:Because of mechanical considerations, the coupling of shutter and aperture was limited to lenses with leaf shutters; however, various automatic exposure modes now work to somewhat the same effect in cameras with focal-plane shutters.
:The proper EV was determined by the scene luminance and film speed; it was intended that the system also include adjustment for filters, exposure compensation, and other variables. With all of these elements included, the camera would be set by transferring the single number thus determined.
:Exposure value has been indicated in various ways.  The ASA and ANSI standards used the quantity symbol Ev, with the subscript v indicating the logarithmic value; this symbol continues to be used in ISO standards, but the acronym EV is more common elsewhere. The Exif standard uses Ev.
:* Camera and Imaging Products Association. 2016. Exchangeable image file format for digital still cameras: Exif Version 2.31 (PDF).
:* CIPA. See Camera and Imaging Products Association.
I would put this in the lead for now because I can’t think of a better place for it (I can’t really justify a section Light Value System on the basis of one sentence). The current first and last paragraphs there would remain as they are.
I rely mainly on Deckel′s 1958 patent for the new information. Ray (2000, 318) would probably support the comment about automatic exposure modes if a citation is thought necessary.
I haven′t included the full reference for the Arizona Republic article because I’m trying to figure out how to get a view of that page without starting a free trial or coughing up $20.
JeffConrad (talk) 04:20, 4 December 2016 (UTC)
thread_title:  Deckel Light Value System 

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thread_title:  External links modified 

message: I’ve slightly cleaned up the last part of this section, but it still seems awkward. And I wonder if this material—especially the archived version of the calculator at dpreview.com—even belongs. The explanation on that page states
:The exposure generated by an aperture, shutterspeed, and sensitivity combination can be represented by its exposure value "EV".
This is simply wrong. EV can be applied to either side of the meter calibration equation, but not both. EV can represent either a combination of f-number and exposure time or a combination of luminance and sensitivity (and meter calibration), but not both. In a footnote “for the purists”, the author (Vincent Bockaert) further states
:(1) Strictly speaking, the term "exposure value" is used to represent shutterspeed and aperture combinations. An exposure value which takes into account the ISO sensitivity is called "Light Value" or LV and represents the luminance of the scene[2]. For the sake of simplicity, as is the case in this article, Light Value is often referred to as "exposure value", grouping aperture, shutterspeed and sensitivity in one familiar variable.
The first sentence is correct; the rest isn’t. There is no such thing as a “Light Value” that has a universally recognized meaning, as the article Light value makes clear. I agree with Bockaert that, for digital cameras, sensitivity is just another camera setting. And there is no reason that f-number, exposure time, and imaging-system sensitivity could not be encoded in a single variable—but such a variable would not be EV unless EV were redefined. As confusing as EV seems to be for many people, a new, unofficial, meaning seems like the last thing we need.
If no one objects, I’m for getting rid of the last two paragraphs altogether.
JeffConrad (talk) 02:50, 2 January 2017 (UTC)
thread_title:  Tabulated exposure values: reverse conversion and dpreview calculator 

message: I am concernded about the relative aperture versus f-number confusion. In the article's Formal definition section, the symbol N is said to be "the relative aperture (f-number)". That's confusing because it cannot be both.
When a f = 50 mm lens, for instance, has its aperture set to f/4 then
* the absolute aperture, or entry pupil diameter D, is 50 mm / 4 = 12.5 mm, and
* the relative aperture is D/f = 1:4 (i. e. a quarter), and
* the f-number is f/D = 4, i. e. the reciprocal of the relative aperture.
So if you're wondering what's to enter for N in the formula EV = log2(N2/t) when the aperture is f/4 — 4 or 0.25? ... after reading that Formal definition you won't be any wiser. In fact, N should be 4 (= the f-number) and not 1:4 (the relative aperture). I'd appreciate a clarification of this little but crucial point.
-- Omzu Iko (talk) 19:20, 20 February 2020 (UTC)
thread_title:  Relative aperture vs f-number 

message: The current images at the top of the page (correctly exposed photos of moving water at slower and higher shutter speeds) isn't what is needed to explain the concept of EV.  How about a series of normally exposed, underexposed and overexposed images? Groogle (talk) 04:00, 12 April 2024 (UTC)
thread_title:  Replace images at top