Talk:Film speed/Archive 2

More digital focus
Film is dead from a perspective of most people. People want to find out what ISO means from a digital perspective and don't care about film. Any suggestions how to rearrange things so people don't have to go halfway down the article to find the information they really wanted? Daniel.Cardenas (talk) 20:13, 17 February 2008 (UTC)


 * Film is far from dead, Daniel. — Preceding unsigned comment added by 67.253.117.64 (talk) 18:18, 12 June 2011 (UTC)


 * So, let me get this straight. You're complaining that the "film speed" article has information about... film speed? And that this is before an explanation of how digital cameras emulate the film-based standard? Just mind boggling. --Imroy (talk) 17:46, 13 June 2011 (UTC)

Splitting the article
The article currently covers film and digital subjects but the title is 'Film speed'. Perhaps the section covering digital ISO sensitivity should be split into its own article as its a totally seperate subject. It's rather like having a section on Video in the article on Film stock; they are completely different media. What do folk think? Baffle gab1978 (talk) 21:06, 1 February 2011 (UTC)


 * I don't think it's a good idea to split them. Digital simply inherited the same speed concept, and they're best discussed together.  Dicklyon (talk) 01:10, 2 February 2011 (UTC)


 * I agree with Dick; the concepts are the same, and discussing them separately might be awkward and could invite inconsistencies. We do have a terminology issue; for many, “film speed” is a bit dated, though I’m not sure we have an acceptable term to cover both film and electronic sensors. In some cases, “imaging medium”/“imaging media” might be OK, but we need to be very careful about coining new terms, because that’s not normally our role. JeffConrad (talk) 03:08, 2 February 2011 (UTC)

Historical systems
I've updated the discussion of DIN (mainly). Much of it is straightforward, but the old representation (for example) 17/10° may not be. I've included one reference, which is genuine, but the book must be almost impossible to find. I would have liked to include a 1941 advertisement from IG Farben, showing such a film (Agfa Isopan F), but I'm not sure of the copyright status. You can see the advertisement on my home page. Groogle (talk) 02:57, 11 March 2011 (UTC)
 * I have added various infos on the DIN 4512 system as well. Your description of the old film speed representation (between 1934 and 1957) as 17/10° DIN is correct, however it was shortened to just 17° DIN with DIN 4512:1957, and with DIN 4512:1961, the degree symbol was dropped altogether (just 17 DIN), whereas it is still being used up to today in the ISO system. Note, that with DIN 4512:1961 the definition of black & white negative film speeds was changed (effectively doubling the nominal speed, similar to ASA PH2.5 1960, so that a black&white negative film sold as 17° DIN before 1961 suddenly became a 20 DIN film after 1961 without emulsion changes). Originally, DIN 4512 was only meant for black&white negative film (other types of film speeds were not formally measured at this time, vendors simply gave recommendations on how to expose them, such as "expose as if for ... DIN"). However, that's why you often see somewhat misleading statements to the effect that all DIN film speeds were increased in 1961. Actually, they were, but color and/or reversal films were not covered by DIN at this time. This changed when DIN 4512 was expanded and split into nine parts also covering color and reversal films in DIN 4512-1:1971, DIN 4512-4:1977, DIN 4512-5:1977, etc. --88.77.217.84 (talk) 12:02, 25 July 2011 (UTC)
 * Far too much use has been made of italics and quotation marks, cluttering the article. In particular, standards designations (e.g. ISO 12232:2006) are not italicized in the photographic literature or by the organizations that publish them; I cannot find any guidance in WP:MOS, but most style guides (e.g., CMOS and the Oxford Style Manual) show them in upright font. Practice varies for standards titles''; ISO put them in italics, so it’s probably reasonable to do so here.
 * I’m not sure the case is so clear for quotation marks, but I also can find little support for the extent to which they were added here; the common connotation of quotes on individual words is one of “so called”, which is definitely not the sense in which they were used here. Normal practice for Wikipedia is unless the MOS (or another widely used style reference) strongly calls for a particular style, we defer to the original style of the article.
 * In any event, I think that either a convincing case should be made for the added italics or quotation mark, or these additions should be removed. JeffConrad (talk) 23:26, 25 July 2011 (UTC)
 * Apparently, WP:EN and WP:DE have different policies here, special names such as ISO 12232:2006 or Nikon D3s are typically italicized there to make them stand out as "single words", but I'm perfectly happy with your edits here.--88.76.53.220 (talk) 08:56, 26 July 2011 (UTC)

ASA standards before 1960
The article mentions that the ASA standard was developed in the 1940s and that it underwent major overhaul in 1960 with ASA PH2.5-1960 (well, my words ;-). However, I could not find any reliable information on the actual development of the standard before 1960. What have been the exact names of these standards? When have they been revised? What was the exact scope of them? Have these revisions been backward compatible in regard to the film speeds?

I found one source stating that the ASA standard was based on earlier research work at Kodak which had led to a proprietary Kodak film speed system before. Can anyone give better details on this (the development as well as this Kodak system)? In particular, since we also have Weston (1930s - 1955) and General Electric (1930s - 1940s) scales which predate ASA and, whilst not the same, at least seem close enough (+1/3 EV and -1/3 EV in regard to the "old" ASA values before 1960). Just a coincidence?

I tried to explain the "ASA film speed doubling" with ASA PH2.5-1960 already, however, I could not answer the question why this doubling was apparently not applied to all black and white negative films at the time (and sometimes not by adding +1 EV but only by adding +2/3 EV). Perhaps, someone can also shed some light on what happened with other types of film at the time. (DIN 4512 did not define a method to determine film speeds of color and reversal films until later - those films were exposed by the vendor's recommendations only, basing their recommendations on the unsuitable DIN scale on exposure meters -, however, this might have been different with ASA.)

--88.76.53.220 (talk) 10:15, 26 July 2011 (UTC)


 * The only pre-1960 standard that I have is Z38.2.6-1948 for exposure meters, but it’s not of much help because its test procedure only includes speeds from 12 to 250. JeffConrad (talk) 10:58, 26 July 2011 (UTC)


 * So far I could identify (but not track down paper or electronic copies of) ASA Z38.2.1-1943, ASA Z38.2.1-1946 and ASA Z38.2.1-1947 (published 1947-07-15): "American Standard Method for Determining Photographic Speed and Speed Number.". This was apparently replaced by ASA PH2.5-1954 in 1954, which then evolved into ASA PH2.5-1960. I don't know, if I have missed any revisions. Has there been a related ASA standard before 1943? What's the issue with the name change, is this really just a name change (since the title has apparently not been changed), or is there more to this? --88.77.212.191 (talk) 19:40, 28 July 2011 (UTC)

ISO speeds > 10,000
The ISO speeds greater than 10,000 that follow the previous ISO progression (added by Skatebiker on 15 June 2011 to replace speeds assigned by camera manufacturers) are unsourced, and require a source if they are to remain. JeffConrad (talk) 23:20, 24 July 2011 (UTC)
 * Jeff, I see that the subject has been debated here for some while with no real consensus, nevertheless, I have objections here with your (almost immediate) removal of the "semi-ISO" speeds above 12500.
 * A value of 12500 is at least mentioned in ISO and ASA standards, so it should be undisputable to have it included here. Since it is not explicitly defined, I didn't emphasized it (as some of the other values, as much as they are known to be explicitly defined in the standards - however, this is still WIP anyway). Since you seem to have access to the old ASA standards, can you perhaps look up the range of values given there? (I'm not only interested in the top values, but also in the lowest values mentioned in any of the corresponding standards - I have seen ASA definitions down to 1 and DIN grades listed down to 0° (!) in reputable historic books, however, I would like to source this from the actual standards and then emphasize those values listed in there. Over time, we will get a feeling, which values were actually listed in primary sources, and which values were derived and calculated.)
 * While not explicitly mentioned in the standards (I don't have the latest editions here to look up, though), I think, the system layed out in there is pretty much obvious to derive values not explicitly mentioned by formula and then round/fit them into the existing repeating scheme of values.
 * I do think, the 1/3 EV values in between should be given as well in the table as it helps to illustrate the scale. After all, Wikipedia is not only to look up stuff, but also to teach people concepts, and having a full range table helps a lot here, IMHO.
 * Nevertheless, I see your point as well, but I don't think, the extrapolated ISO-style-values should become "suppressed" here (since you removed them, I have put them back in as HTML source code comments for easier editing at least). I consider them just as "valid" as those values found on some Nikon and Canon cameras. Basically, these numbers are not exact anyway, but arbitrarily assigned. ISO/ASA and Nikon/Canon obviously had/have different ideas how to name them. I am keeping my eyes open for usages of both styles in standards, books or actual products, so hopefully this issue can be resolved over time (months, perhaps years).
 * Matthias --88.76.53.220 (talk) 09:37, 26 July 2011 (UTC)


 * Though ASA apparently envisioned a value of 12500, values greater than 10000 were never assigned by ASA, ANSI, or ISO, so we really cannot include them here without getting into WP:OR. accordingly, I’ve commented out 12500. As you can see, we’ve had quite a discussion of this in the past, and the user who insisted on adding the unsourced material got blocked.
 * We don’t know what values ISO may assign; they may follow the original sequence, or, more likely, they may defer to what the manufacturers have already done. Because Wikipedia is not a crystal ball, we really cannot speculate.
 * I removed the material quickly because I know there is no citable source, and think it better not to clutter the chart and confuse the reader. This is well in accord with WP:V, which no consensus can override.
 * Yes, we can calculate extensions to the old sequence. But for good or for ill, Canon and Nikon have chosen not to follow that sequence. They have de facto standing to assign new values; Wikipedia editors do not, so we need to stick with what actually exists. JeffConrad (talk) 10:49, 26 July 2011 (UTC)


 * If for some reason another manufacturer specifies speeds greater than 10000 that differ from the values that Canon and Nikon have chosen (or we find a manufacturer who has already done so), we presumably could include those values with adequate sourcing. Quite honestly, I hope we don’t need to do so because we would have a mess, especially if the values differed from those for Canon and Nikon and from the ISO sequence. But it probably would be a good idea to see what manufacturers other than Canon and Nikon have done anyway.
 * Several have expressed disappointment that Canon and Nikon chose not to follow the established sequence; I suggested that Canon’s and Nikon’ choices are arguably defensible. But whatever the wisdom, they have done as they have done, and for now they are calling the shots. JeffConrad (talk) 11:08, 26 July 2011 (UTC)


 * I have again removed 12500 because it never has appeared in any ASA, ANSI, or ISO speed standard. It was mentioned in Table 2 of ASA PH12.2-1961 for exposure meters, but was removed from ANSI PH3.49-1971, so it hasn’t even been mentioned in any ANSI or ISO standard for 40 years. Note that WP:BURDEN states
 * The burden of evidence lies with the editor who adds or restores material. You may remove any material lacking a reliable source that directly supports it.
 * So please don’t add this again without a directly supporting source. Please, let’s stick with the facts rather than speculation, however reasonable that speculation might seem.
 * The Canon/Nikon progression is not as capricious as some here maintain—it’s a direct extension of Table 2, Preferred Exposure Parameter Numerals, in ANSI PH3.49-1971. In any event, Canon and Nikon have chosen to extend that sequence, and showing a different value that was never assigned needlessly confuses the reader. JeffConrad (talk) 18:16, 26 July 2011 (UTC)
 * I would just like to point out that I did NOT re-add 12500 after our discussion. Apparently you simply missed to remove it in the ASA column in the first place, Jeff...
 * Still, the very fact that the value is listed in ASA PH12.2-1961 (even if not explicitly defined) (and implicitly also in ISO by the noise upper limit) is more than enough evidence at least to me to feel some urge to include it in the table without fearing WP:OR or unverifiability. The NPOV maxime would support this inclusion as well, because otherwise the "Nikon/Canon way" gets too much weight IMO, if people looking at the table don't get the idea that there are two concurrent mindsets of how to build on the old system. The fact, that 12500 is not listed in more recent standards does not defeat this, IMO, since our table does not reflect only the current state of affairs, but represents an accumulation of values used (or intended to be used) in history.
 * BTW. While I prefer consistency, I have no issues whatsoever with the Nikon/Canon style of progression. It will be quite interesting to see how Sony and Pentax will handle this. Perhaps, in the end we will have to add another column for vendor specific values instead of adding them to the ISO scale. ;-)
 * Anyway, I'm here to share information and improve the article, not for disputes. --88.77.219.92 (talk) 19:22, 26 July 2011 (UTC)


 * Clearly my mistake . .. Please accept my apology; I shall read the edits more carefully in the future (and perhaps try to get some sleep before reading). You weren’t the one who added the unassigned speeds anyway—you simply preserved what had recently been done.
 * A few thoughts on including ISO 12500:
 * I don’t think we can reasonably base a table on what may have been intended. Suppose, for example, that we had meeting minutes from the technical committee indicating that they were considering ASA speeds as high as 25000—could we cite that as a basis for including 25000? I don’t see how we could.
 * I also don’t see how we could rely on a document that’s 50 years old, and whose ideas have not been replicated in any similar document in the last 40 years. Even if they had envisioned ASA 12500, the idea was withdrawn for all practical purposes.
 * ASA PH2.12-1961 dealt with exposure meters rather than film speeds, so it’s hard to see it as directly supporting a speed of 12500. That table is also quite a piece of work as regards speeds, seemingly full of contradictions—but that’s another issue for another time.
 * There may indeed be two mindsets about how to extend the table, but I don’t think we can base the table on mindsets without something more recent that we can cite.
 * I don’t think NPOV enters the picture; Canon and Nikon were cited because at the time they were the only ones to offer such speeds. A quick glance suggests that Pentax have decided to follow the same progression with the K-5, so they should be added. As I said, if other manufacturers have specified speeds that differ from the Canon/Nikon (and now Pentax), it certainly is reasonable n(and probably required by NPOV) to include those speeds as well, provided that they apply to announced products. In any event, the values should be based on what is rather than on what we think someone may be thinking about. For now, there really is no other POV to present.
 * Though ASA may have once envisioned assigning a speed of 12500, they did not act on it. And for whatever reason, neither did ISO, even in revising ISO 12232. The technology quickly outpaced the standard (as often happens), and the manufacturers had a decision to make—they could hold off on releasing a product for several years until ISO caught up, or they could choose their own speeds. The decision was pretty obvious . .. Whether they made the “right” choice is debatable, but they did what they did. And their choice was arguably more logical than following the ISO progression, which looks like a remnant of a scale based on 0.1 log10 steps that derived from sensitometry. If aperture and exposure time are indeed in power-of-two progression, it does not seem unreasonable to have sensitivity in the same progression, so that doubling sensitivity while decreasing aperture by one step would give the same exposure. Moreover, with Pentax apparently now of the same mind, the C/N/P progression has to be seen as the valid de facto standard. Because (at least to my knowledge) no one else has released a product with a speed greater than 10000, the C/N/P progression is unchallenged. Again, if ISO or some other manufacturer decide to extend the existing ISO progression, the issue can and should be revisited.
 * Like Wikipedia, I’m no crystal ball, but I would be surprised if ISO did not bow to the manufacturers, just as happened with getting SOS into ISO 12232:2006. Any any event, we’ll know what happens when it happens. Until then, I don’t think we should include on mere speculation a speed that well may never come to pass, de jure or de facto.
 * Clearly, I erred in the way I cited WP:BURDEN, but I probably would have mentioned it here anyway—it binds all of us, and I just don’t think we can reasonably claim that we have anything that “directly supports” an “ASA” speed of 12500.


 * Incidentally, what was the source for the assigned ASA speeds? ANSI/ISO 2720:1974 (R1994) had a table that went up to 10000, but I wasn’t aware that anything above 3200 ever made it into a film speed standard—ISO&nbsp:6:1993 stopped at 3200 as well. JeffConrad (talk) 00:43, 27 July 2011 (UTC)

Here’s what I have for assigned speeds:
 * ASA PH2.5-1960: 6–3200, 1°–10°&emsp;(monochrome)
 * ANSI PH2.5-1979: 6–3200&emsp;(monochrome)
 * ANSI PH2.21-1979: 4–2000&emsp;(color reversal)
 * ANSI PH2.27-1979: 4–3200&emsp;(color negative)
 * ISO 6:1993: 12–3200, 12°–36°&emsp;(monochrome)

JeffConrad (talk) 10:02, 30 July 2011 (UTC)
 * Let's have a look:
 * ASA PH2.12-1961: reportedly mentions 12500 ASA as next step.
 * I cannot verify this, as I don't have this standard to look at, but the article says: "ASA PH2.12-1961, Table 2, p. 9, showed (but did not specify) a speed of 12,500 as the next full step greater than 6400." as per your edit: http://en.wikipedia.org/w/index.php?title=Film_speed&oldid=337917151 --88.77.221.103 (talk) 15:26, 30 July 2011 (UTC)
 * Indeed, 12500 appears in Table 2, Values of Corresponding Exposure Parameters Both in Arithmetic and Logarithmic Systems. But this table was for markings on exposure meters. At that time, no speeds greater than 3200 had been assigned, and as nearly as I can tell, no ASA or ANSI speed standard ever has, and I don′t think we can attribute a speed shown in a 50-year-old ASA exposure standard to ISO. Moreover, all the APEX stuff, including Table 2 was removed from ANSI PH3.49-1971; it was included in Appendix A with the comment
 * The additive (APEX) system of exposure units included in American National Standard PH2.21-1961 has not been used on consumer products and is omitted from this revision. However, since it has been found useful in engineering, it has been repeated in this Appendix for reference (see Tables A1 and A2).
 * So I think it would be a stretch to cite this as a source for ASA 12500, let alone ISO 12500. JeffConrad (talk) 21:06, 30 July 2011 (UTC)
 * ISO 5800:1987: ISO 4/7° to 3200/36°
 * ISO 12232:1998: ISO 6/9° to 10000/41°
 * --88.77.221.103 (talk) 14:58, 30 July 2011 (UTC)
 * We’ve already cited the latter; the former could be mentioned, but only if the person making the addition actually has a copy (I don’t). JeffConrad (talk) 21:06, 30 July 2011 (UTC)
 * I do.--88.77.221.103 (talk) 23:20, 30 July 2011 (UTC)

Speed conversion table—another possibility
One possible approach for the speed table is to extend the ASA and ISO speed ranges, clearly indicating that this has been done. I think that this is essentially what you suggested, but I think the key is adding a note immediately rather than later—does this seem reasonable? And the typographical conventions also need to be explained—with the bolding to indicate speeds actually assigned, what is the purpose of the parentheses?
 * Well, parentheses were used for multiple purposes so far, usually to indicate some kind of alternative value. In the ASA column some alternative values were given in parentheses (at least in WP:DE such as "3 (3.125)", as they were mentioned in some sources including books this way, but they do not seem to be official. For the same reason I put the high semi-ISO values in parentheses to indicate that they are not truely from an ISO standard (and do not seem to follow one as well). In the GOST scale some of the values seem to have been (once officially?) associated with corresponding ISO values (although they do not perfectly match given the slight shift in the GOST scale) - at least there are Russian sites which seem to support this (I don't have the GOST standards to look at). However, there are more official GOST values which fall in between (apparently by 1/2 EV steps?), and they could be associated with either of the two 1/3 EV ISO values with good reasoning, that's why they are given in parentheses. I'm not completely happy with this scheme, since to me it seems as if each ISO value could be matched with two possible nearby GOST values (perhaps some of them officially), but that's what has been established in the German WP years ago, and for as long as I don't have better sources, I hesitate to change this. There are also two other GOST values in parentheses, which can be often found on other web sites, that's why they are given as alternative values as well for as long as we don't have the standards (or old equipment) to look at.--88.77.221.103 (talk) 14:01, 30 July 2011 (UTC)

If the extension is done, however, I think the speeds assigned by camera manufacturers should be in a separate column (hopefully, only one) to avoid having two different values in the same table cell and having to explain why they differ.
 * I actually like that idea, as it would clearly separate those new digital semi-ISO values from genuine ISO values (or values extrapolated from the standards).--88.77.221.103 (talk) 14:01, 30 July 2011 (UTC)
 * If no one objects, I′ll give it a try—we can worry about a space problem if indeed there is one. JeffConrad (talk) 21:06, 30 July 2011 (UTC)

This might result in a space problem, and if it did, I might ask if the APEX Sv is really needed—APEX officially died 40 years ago (it actually never lived). Although APEX has come back in EXIF, I’d be surprised if one photographer in 10,000 has any idea of the EXIF details. JeffConrad (talk) 10:02, 30 July 2011 (UTC)
 * Hm, to be honest, I find the Sv value to be very informative and I think its linear scale in EV steps helps a lot to get the "great picture" (as APEX does, anyway - even today IMHO). Also, the value was once used as "ASA grade" and could be found on film boxes (as well as on some - few - professional equipment). Actually giving Sv values in such a table might be a bit like providing a "missing link" in a bigger puzzle to some readers trying to better understand exposure, in particular since they are not normally used today any more. So, I really think, it belongs into the table. Perhaps we could change the font of the table to be somewhat smaller than normal if it becomes to wide? Otherwise, given that most people today have very wide screens (I'm not among them, yet, though), adding another column does not seem as if it would impose readability problems.
 * In the German WP, we have another table showing conversions between pre-1960 film speed systems. I would like to include that table into here as well at some (much later) stage, but some of the stuff still needs to be verified and cross-checked and more reliable first-hand sources need to be found, given all the often misleading and contradicting information found on web-sites today. So, this may still take a while, before I think it has matured enough for the English WP.--88.77.221.103 (talk) 14:01, 30 July 2011 (UTC)
 * In a sense, Sv is useful, but again, for practical purposes, it was stillborn, and was officially declared dead 40 years ago. The relationship between Sv and arithmetic speed was byzantine to say the least. Table 2 of ASA PH2.12-1961 (where would we be without it?) indicated arithmetic speeds were to be in exact power-of-2 progression, with ASA 25/3° “exact”, and the logarithmic value apparently being more exact than the arithmetic value. It then stated that “the precise value of Sx 25 = $$32/\sqrt[3] 2$$ = 25.4. But the relationship between Sv and Sx is given in Table 1:
 * $$S_v = 3.32 \log NS_x \,,$$
 * where N = 0.30. This leads to the “precise” equivalent of 26.7 given in Table 2. But that actually wasn’t very precise. Clearly, the precise formula would be
 * $$S_v = \log_2 NS_x \,;$$
 * but that’s not the end of it. The constant N derives from the relationship between arithmetic and logarithmic speeds given in ASA PH2.5-1960, which was so incomprehensible that the authors of ASA PH2.12-1961 felt it needed explanation, which they provided in Table 2 and Fig. 1 of the latter standard. Stated succinctly, the arithmetic and logarithmic scales matched at speed boundaries rather than midpoints of the ranges; further complicating matters, the arithmetic speeds were in cube-root-of-2 progression but the logarithmic speeds were in square-root-of-2 progression, so not all range boundaries were common. As a result, the midpoint values differed by the twelfth root of 2, and N had the exact value of 2−1.75, or about 0.2973. Even with the explanation in ASA PH2.12-1961, the derivation of this constant was still apparently so confusing that ANSI PH2.7-1973 gave its value as 0.316.
 * Substituting the exact value of N into the formula for Sv and solving for Sx gives
 * $$S_x = 2^{S_v + 1.75} \,;$$
 * for Sv = 3°, Sx ≈ 26.9. So Table 2 seems to somewhat contradict itself, and accordingly, I have no idea what the “exact” speeds really were. Now perhaps this all matters little because the speeds are rounded anyway, but the mess resulting from that explanation has never thrilled me.
 * In any event, I thought the ISO/DIN logarithmic progression made for a more convenient index. The APEX stuff is explained pretty well in that article for readers who are really interested. JeffConrad (talk) 21:06, 30 July 2011 (UTC)

I′ve extended the table as discussed, including the ⅓ steps above 10000. I didn’t include log speeds for the digital cameras because the manufacturers don’t seem to state them. I removed the parens from the maker-assigned speeds to reduce the visual clutter—with the separate column, this shouldn’t be a problem. We still probably need a date for the first maker-assigned speed greater than 6400. JeffConrad (talk) 23:28, 30 July 2011 (UTC)
 * This looks very nice.--88.77.216.217 (talk) 12:05, 31 July 2011 (UTC)

Edits of July 2011
On the heading: I didn’t mean to have you change the internal links—you managed to save your links changes before I could save mine. ..

Had the heading been Current systems, I’d have asked first. In any event, revert my change if you plan to add other sections in the near future—the changes I made to the table are easy to restore. JeffConrad (talk) 09:24, 29 July 2011 (UTC)
 * I think I found a neat solution to this problem by introducing visible anchors to this article. It will make linking easier and give us more freedom in rearranging unless we change the anchors themselves. As a guideline I gave a recommendation on the prefered #anchor to be used for linking in the future, which is not necessarily the same as the first (visible) anchor. In some cases I also gave invisble alternative anchors, which may help establishing future section headers or external article names. For example, "#ISO 6" is the same as "ISO" for now, but perhaps there will be a seperate ISO 6 section in the future, so that all links to the specific topic would already be grouped under that name.
 * Regarding your change from "Historic" to "Historical". I had to smile, because I felt "historic" to be faulty from the moment I first read the article and was tempted to change it, but then I thought, it can't really be wrong given its very exposed position in the article and the thousands of native English readers who didn't change it to the better. ;-) --88.77.221.103 (talk) 12:42, 30 July 2011 (UTC)
 * Yes, Visible anchor seems a good solution.
 * The English skills of many non-English Europeans would put those of many native speakers (at least in the US) to shame. The distinction between historic and historical is less in UK BrE than in some other varieties and in AmE. If the SOED is to be believed, the distinction in UK BrE is minimal. Whatever the case, it seems better to go with what works in all EngVars. JeffConrad (talk) 01:14, 1 August 2011 (UTC)

A few other comments: A lot of good historical information has been added. But I question a couple of things:
 * 1) There is no reference for the assigned ASA speeds, and as I mentioned, I can’t find one greater than 3200 that was ever assigned. In any event, the source should be stated—it could be just another table note below that for the ISO speeds.
 * 2) Several of the ISO standard have the month appended to the designation—I can’t find any instance elsewhere that does this. Is there such an example? In any event, I think we should not alter the designation given by the authoring organization—if nothing else, it can confuse a person looking for that standard. For example, a Google search for  got only three hits, and even those were because Google ignores punctuation. The dates of issue could simply be added to the references. JeffConrad (talk) 09:19, 29 July 2011 (UTC)
 * Actually, appending the month (in ISO 8601 format) is the official standard format how to specify this (at least for ISO and DIN standards, apparently also for BSI - I'm not sure for the very old BSI standards where they seem to have used a "-year" appendix (as wth ASA) rather than the modern ":year" form), however, it can be abbreviated to just the year or even no year at all (if not known or meaning "any revision"). However, I often find it very useful to give the full spec, in particular when trying to put together pieces of history and identify each and any slight revision of a standard (as we'll have to do here in order to track down the various slight changes in methods to determine of film speed over the many decades). So, giving the month of publication in this notation we don't alter the official designations at all, and anyone can trunc this if Google does not give enough hits. --88.77.198.150 (talk) 09:58, 29 July 2011 (UTC)
 * You obviously speak with greater authority than I on DIN, but I can’t find the month appended to ISO standards on the ISO Web site or in any of the ISO standards I have. The Google search was more to illustrate the infrequency of appending the month—without the month, the search gets 23,000 hits. And of the three hits with the appended month only one (this article) actually shows the standards with the month appended. And the search doesn’t even find the ISO Web site (which incidentally shows only ISO 8601:2004—no month). 				JeffConrad (talk) 10:35, 29 July 2011 (UTC)
 * I tried to identify sources for these conventions. In the case of the DIN standards, the format (including the month) is clearly described in this German DIN-Norm (WP:DE) article, and defined in some of the DIN guidelines (perhaps also in DIN 820, DIN 1505, DIN 5008 or such?). However, to my surprise I could not find any such information for ISO standards. Instead I found this (ISO/IEC Directives part 1/2: and, where they describe the format without months. ISO 690 seems to support that dates in references can be extended to months using the ISO 8601 date format, but I could not find it mentioned explicitly for ISO standards. So, I would like to thank you for spotting this, and I will change the ISO stuff to not include the month any more soon. I would like to move all the inline references to the references section anyway, in order to improve maintainability and make using a reference in multiple places easier. However, this will be several hours of work and I have to schedule this.--88.77.221.103 (talk) 12:42, 30 July 2011 (UTC)
 * We seem to have reached the same conclusion. The only hits I got other than this article were on the Beuth Web site, where the ISO standards are apparently filed according to DIN practice. JeffConrad (talk) 21:17, 30 July 2011 (UTC)
 * I removed the months from the ISO and BSI BS standards, but left them intact in the DIN and DIN ISO standards (as this is the official format for them). Where known, the months are now appended as publication dates in the ISO 8601 format (yyyy-mm[-dd]) in the references section, so anyone interested in this can still find the info. At some stage the individual references will probably become actively linked to from the article section, but I will first have to move all the inline references into the references section and devise proper "ref name" attributes for them or it will become unmaintainable. Since this will probably "block" the article for several hours, I will announce it, when I find the time for it.--88.77.216.217 (talk) 12:18, 31 July 2011 (UTC)

Comment on BSA/ASA
Something which doesn't come out in the article, but certainly up to about 196odd, the "ASA" standard was a joint ASA/BSI standard, but film speeds were commonly known as BS or ASA only because the arithmetic index was used in USA and logarithmic in the UK. The point being that a conversion was exact as both indices used the same test method, but "DIN = (BS - 10) " say was a good rule of thumb only. — Preceding unsigned comment added by 88.97.9.181 (talk) 12:01, 26 August 2012 (UTC)
 * Can you provide reliable information on this? When I significantly reworked the article, I tried to get more information in regard to the various film speed systems used in the UK as well, of course, however, I found so much incomplete and often contradicting information (and information clearly just copied from other sources without verification) in regard to the apparently several systems of BS and BSI film speeds, which have been used in the UK in the past, that I hesitated to add this to the article and left this task to someone with better knowledge of the UK specifics or better access to historical UK sources. If you have more information and can further elaborate on this, based on reliable sources (not hearsay), this would be highly welcome, I think. --Matthiaspaul (talk) 14:13, 26 August 2012 (UTC)

Hurter & Driffield system bug
It says "In their system, speed numbers were inversely proportional to the exposure required. For example, an emulsion rated at 25 H&D would require ten times the exposure of an emulsion rated at 2500 H&D." Does is mean the inverse square of the exposure required? Or should the 2500 be 250? Can someone check the Sowerby ref? Dicklyon (talk) 06:53, 1 August 2011 (UTC)
 * Since I added that information, that'll be me. Unfortunately my scanner is currently broken and I can't scan the referenced 'Fig.3' at this time. The entire paragraph (H & D Speeds, p.583) sayeth:

"The first scientific method of measuring emulsion speed was that of Hurter and Driffield. They ignored any effect of the printing paper and laid down that the minimum correct exposure was the least that would give accurate tone-reproduction in the negative. They based their film-speed, fundamentally at least, on the point A of Fig. 3. (My note: Fig. 3 is a graph showing negative density over exposure time). But partly owing to the difficulty in determining the exact point at which the 'toe' of the curve began, and partly to find a speed-value that did not greatly depend on gamma, they continued the straight line part of the curve backwards as shown dotted in Fig. 3, and took as a measure of the H & D speed the the exposure indicated at the point where this extension cut the line indicating fog-level. This exposure they called the 'inertia'; the speed -number was found by dividing the value of the inertia by 34. Thus the H & D speed numbers are inversely proportional to the exposure required; a plate of speed 250 H & D requires ten times the exposure needed by a plate of 2500 H & D."

I hope that's useful. Baffle gab1978 (talk) 18:15, 1 August 2011 (UTC)


 * Yes, thanks. I have made the indicated correction (changed 25 to 250). Dicklyon (talk) 18:22, 1 August 2011 (UTC)


 * 250 is correct - my typo on the article! :-) Baffle gab1978 (talk) 18:36, 1 August 2011 (UTC)


 * Hi from Russia! I'm editing this page in Russia Wiki and I can't find some information. Does anybody know what else countries except SU used H&D system? Does the USA used it? Unfortunately, our domestic sources of that historical period are not credible for obvious reasons. And, if you interested, I have a link for Soviet photo book with the table of GOST into H&D units accordance. Runner1616 (talk) 08:17, 10 November 2012 (UTC)
 * H&D speed accordance is in the table 32 (Таблица 32) Runner1616 (talk) 08:32, 10 November 2012 (UTC)

Photons/area at saturation?
It seems that film speed, at least for an ideal linear sensor, is a measure of how many photons (of a given wavelength) per sensor area it takes to saturate the sensor. Is that right? That seems like the most natural units in which to reason about film speed and noise given that an ideal sensor will still have shot noise, and so the number of photons matters. Beyond that you do have quantum efficiency and pixel size (or grain size) which will affect how noisy an image appears, but isn't photons/area at a wavelength at saturation really the fundamental measure of speed for an ideal sensor? If so, it would be nice to see that on this page. It seems like an approachable mental model. As it is, the article goes on and on about arcane systems without giving a straightforward definition. —Ben FrantzDale (talk) 11:57, 12 August 2011 (UTC)


 * Film (and sensor) speed ratings are for the use of the photographer, to obtain desired exposures. ISO 12232:1998 contains a saturation-based method of determining ISO for digital cameras, and that option was carried over to ISO 12232:2006. However, it's rarely used because it doesn't mean much to the photographer, and it's based on the camera-generated sRGB TIFF file, not the behavior of the sensor itself. Early on, Kodak did attempt to adapt the older ISO specifications for use on the sensor in isolation: http://www.kodak.com/global/plugins/acrobat/en/business/ISS/supportdocs/ISOMeasurements.pdf ... I should note that the current SOS technique is essentially saturation-based, giving an ISO that's 0.704 times the ISO obtained by the older saturation-based technique; other than the multiplier, the big difference is that SOS can be applied to JPEG output files as well as TIFF.


 * As for a straightforward definition of "digital ISO," I'd suggest the section entitled "The ISO 12232:2006 standard". The reality is that today, digital camera ISO values are almost universally determined using the REI technique, which is basically "whatever the manufacturer thinks gives good results." Doug Pardee (talk) 15:38, 9 October 2011 (UTC)


 * Mostly true, but the SOS method is not saturation based. It is used to define how the output image brightness relates to the ISO EI setting on the camera; it's not a sensor or a camera spec, since the sensor and camera have many different ISO settings, and the SOS definition does not constrain their range.  Dicklyon (talk) 00:05, 10 October 2011 (UTC)


 * Interesting. So looking at the formula on page 2 of the Kodak PDF,
 * $$\mathrm{ISO} = \frac{15.4 N^2}{L\cdot t}$$,
 * where N is the f number and L is the luminance of an 18% reflector in the scene, and I think t is the exposure time to achieve 18/106% saturation. Then $$L \cdot t$$ is a measure of luminous energy per area per solid angle. The numerator is dimensionless so the units of ISO in this expression are area times solid angle per luminous energy, I think. If it weren't 8 in the morning and I used photometric units more, I could make sense of that. But it seems like that plus the photometry curves should be able to work out to at least a ballpark value for the conversion between ISO and photons/area at saturation. This also seems to give a conversion for using a camera as a crude light meter (assuming the manufacturer was honest):
 * $$L = \frac{1.54 N^2}{t \cdot \mathrm{ISO}}$$
 * Does that sound right? —Ben FrantzDale (talk) 12:47, 12 October 2011 (UTC)

Alternately, it seems like the sunny 16 rule could be inverted to compute an ISO:
 * $$\mathrm{ISO} \approx \frac{1\,\mathrm{s}}{\text{proper exposure time of sunny scene at f/16}}$$

With a precise definition of "proper exposure time", this should be pretty precise. That is, use a prescribed gray card and say that it should be exposed to some percent of saturation. This could also be pushed through to find photons/area/second at saturation. Thoughts? —Ben FrantzDale (talk) 13:33, 7 May 2013 (UTC)


 * Yes, when I was an image sensor designer we explicitly used photons per area in our sensor noise models and sensitivity calculations. But the ISO rating is usually defined based on noise, not on saturation.  So you can actually calculate the maximum ISO rating for a given pixel size with 100% quantum efficiency and no readout noise (you have to assume a light spectrum, too, which may be affected by the filters used, if any).  Probably some of the books I showed in PhotoTechEDU number 5 cover this well.  Dicklyon (talk) 22:16, 7 May 2013 (UTC)
 * Hi again, Dicklyon. Wait, are you saying that by measuring ISO in terms of noise that if I have a sensor that has an extra-noisy ADC you would measure it as having a higher ISO? That doesn't seem right. (Incidentally, my interest in this at the moment is in comparing CCD/CMOS image sensors to my DSLR, just to get a ballpark sense of a sensor's performance compared to a high-production high-quality sensor. For many sensor chips I know QE*FF and can compute noise and I am interested in comparing that to an SLR at, e.g., ISO 100.) Thanks. —Ben FrantzDale (talk) 13:10, 9 May 2013 (UTC)
 * A noisier sensor needs more signal to get up to the criterion SNR, so it has a lower ISO rating (not higher). When you set the ISO setting on your DSLR, that bears no relation to either the noise-based or saturation-based ISO speed definitions; rather, it controls something called "standard output sensitivity" iirc.   Dicklyon (talk) 00:41, 10 May 2013 (UTC)

ISO Examples
Just now, experimenting with the same shot with a digital camera at different ISO settings, I have a series of five pictures with the ISO settings captioned in the corner.

Would it be a good idea for me to add them to the bottom for a visual example?

PS: Here's what they look like http://youngwilliamthe.tumblr.com/post/83167569926/realizing-i-had-no-clue-what-iso-settings-do Youngwilliam (talk) 04:22, 19 April 2014 (UTC)


 * Please don't. Get a clue first.  If you just change the ISO setting, but leave the exposure time and aperture fixed, which is what it appears you did, then it will be pretty much like adjusting the white level in Photoshop:  just a gain variation.  But that's not how the ISO setting is normally used.  Usually, you'd set the exposure to make the image as bright or dark as you want, for whatever ISO setting you're using; or let auto-exposure set it for you.  Then the images would all look nearly alike, except that high ISO ones would be made from many fewer photons, so would have more noise, which you would not notice in small thumbnails like those anyway.  Dicklyon (talk) 04:48, 19 April 2014 (UTC)
 * ps. There's no such thing as ISO 159. Dicklyon (talk) 04:49, 19 April 2014 (UTC)
 * Okeydoke! I was basing the 159 off of what what Flickr was reporting post-upload. I was guessing it wasn't such an odd number, either, but was instead their setting detection trying to make the best of the default setting. Youngwilliam (talk) 04:52, 19 April 2014 (UTC)
 * How odd. Also odd is the fact the ISO is only defined for a discrete set of values; 160 is one and 159 is not.  Dicklyon (talk) 04:54, 19 April 2014 (UTC)
 * As for "what ISO does" on a digital camera, the section you want is Film speed. It tells you (inversely) how many lux seconds of light the sensor needs to make a medium gray, and it adjusts the camera's processing gain to make it so.  Dicklyon (talk) 04:54, 19 April 2014 (UTC)

Simpler examples/language
You know what this page needs? Some basic, simpler examples in plain language. I am a Super8 hobbyist (speaking of the conversation you had concerning "Film is dead," there are a LOT of us out there), and it seems like every time I sit down to buy more film from my favorite supplier, http://www.pro8mm.com, I have to try to remind myself what sort of ISO I need, and what it means. Is a small number more sensitive to light, or less? What looks best in bright light? What works fastest in low light? These are real and pressing questions for those of us shooting on film, and frankly, YoungWilliam's lo-tech example of the same picture in low light at different settings was exactly what I was looking for. It told me that my ISO 200 Reversal film was going to be OK in low light before I even pulled the trigger, which is why I came by, worried about wasting yet another roll. Having basic stuff like this alongside all the charts and graphs and gobbledygook would be swell. Playerpage (talk) 04:47, 7 December 2015 (UTC)


 * YoungWilliam's example is particularly useless. It doesn't tell you how the scene was lit. It may have been a dim bulb or a 500 W photoflood. Thus you do not know how bright the scene was to start with. Also, it doesn't tell you the aperture he used nor the shutter speed. My guess is the camera was on a tripod with a shutter speed too slow to handhold, and too slow to be usable on a Super 8 cam. But it's only a guess... Worse of all, it gives the false impression that 200 ISO is the right ISO for this particular kind of scene, which seems to be your conclusion and is 100% bogus. If this is what you take from his example, he did you a disservice by publishing it. Normal photography practice would be to adjust the shutter speed in order to get the same brightness at every ISO.
 * Personally, I find this Wikipedia article pretty clear: everything you need to know is in the lead; the rest is only encyclopedic content, for those who are curious. If you came here to get a practical tutorial on selecting film speed, you probably came to the wrong place. There is, however, a table of exposure values that could help. It tells you, for example, that home interiors are typically around EV5 – EV7 at ISO 100. This means that if you have ISO 200 film and require 1/60 s exposure, you would need a lens that opens up to somewhere between f/1.0 and f/2.0.
 * Now, if you are willing to take a film photographer's advice: buy an exposure meter (unless your camera has a built-in one) and learn how to use it. Not only will you waste less film, you will also be able to determine yourself whether a particular film speed is suitable for a particular lighting situation, taking into account the speed of the lenses you plan to use.
 * — Edgar.bonet (talk) 09:38, 7 December 2015 (UTC)

Can we have an article without film?
Film is dead from a perspective of most people. People want to find out what ISO means from a digital perspective and don't care about film. Any suggestions how to rearrange things so people don't have to go halfway down the article to find the information they really wanted? Daniel.Cardenas (talk) 20:13, 17 February 2008 (UTC)


 * Film is far from dead, Daniel. — Preceding unsigned comment added by 67.253.117.64 (talk) 18:18, 12 June 2011 (UTC)


 * So, let me get this straight. You're complaining that the "film speed" article has information about... film speed? And that this is before an explanation of how digital cameras emulate the film-based standard? Just mind boggling. --Imroy (talk) 17:46, 13 June 2011 (UTC)

Can we get an article that doesn't start out about film? I want to read about ISO on digital cameras as do most people. They don't want to be bothered about film that has been dead to most people for 10 years. Daniel.Cardenas (talk) 19:33, 7 December 2013 (UTC)
 * Daniel, two years ago I thought about splitting the article to separate film speed and digital sensitivity articles; consensus came up against this idea—see the discussion here. Strange you should say that film is "dead"; that's certainly not my perception. I wonder how you know what "most people" want to read about. Cheers, Baffle gab1978 (talk) 17:59, 8 December 2013 (UTC)
 * Dead to most people. Do think most people consider film?  If you mention film to a young adult they will think you are talking about some slimy substance. :)
 * If splitting the article is less than ideal than perhaps putting the digital aspect more prominently would be better solution. Rename the article, ISO / film speed?, and put the digital stuff in the intro.  Daniel.Cardenas (talk) 18:20, 8 December 2013 (UTC)
 * Yes I agree there should be some digital info in the header; which should be a summary of the main points of the article, per WP:LEAD. I may get around to doing a full c/e one day (but not soon), but in the meantime you can always fix it yourself. I find your sweeping assertion about the ignorance of young people rather amusing. Cheers, Baffle gab1978 (talk) 23:06, 8 December 2013 (UTC)


 * The description of historical systems is mostly "dead", even to those of us that still use film. I would have no problem with moving most of that section to a separate "historical film speed systems" article. Just leave DIN, ASA, ISO, and perhaps GOST. And the conversion table is large while serving little purpose.
 * I like the idea of moving most of the digital stuff into a separate article too and have ISO (disambiguation) point to it so people can find out what this "ISO" thing is. And have the two articles link to each other for historical completeness. --Imroy (talk) 06:33, 9 December 2013 (UTC)
 * I don't agree with splitting out any of the film speed related stuff (in fact, there's quite a bit more, that could and should be added).
 * If anything, the contents of chapter 4 ("digital camera ISO speed and exposure index") is the only stuff that does not directly belong into an article about "film speed". So, if this article would become too long somewhen in the future (it isn't too long at present), this digital camera related stuff is the info, that could be moved elsewhere, not the film-related stuff. --Matthiaspaul (talk) 16:49, 3 June 2015 (UTC)
 * The historical part is important as it leads to the later systems. Most of the changes were small refinements, not fundamentally new ideas.  It does seem to me that separate film and digital articles might have been nice, but I won't argue the point.  Film is more complicated, as it depends on developer and development time, two parameters that don't appear in digital cameras.  — Preceding unsigned comment added by Gah4 (talk • contribs) 03:17, 20 January 2016 (UTC)
 * It's not as different as you say. The film has an inherent speed, and can be "pushed" by modifying development; similarly, electronic sensors have a fundamental speed and can be "pushed" by processing.  Some of the alternative standards for speed measurement get at the differences.  Dicklyon (talk) 03:28, 20 January 2016 (UTC)

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Speed of Kodak T-MAX p3200
T-max p3200 is listed as 1000 along with delta 3200, but the Kodak T-MAX page says that it is a 800 speed film (this is my understanding a well). 73.173.14.14 (talk) 20:46, 5 August 2016 (UTC)


 * As well as I know, 1000 is closer, but 800 is within the uncertainty. The actual ISO value depends on which developer you use.
 * See: http://www.kodak.com/cluster/global/en/professional/support/techPubs/f32/f32f.jhtml
 * and: http://imaging.kodakalaris.com/sites/prod/files/files/resources/j86.pdf
 * even more, note that there are two different films with almost the same name, and both with the TMZ code. (This is true for TMX and TMY, too.)
 * But mostly, the characteristic (D-H) curves for TMZ (both of them), and Delta 3200 are not usual. They don't have a real straight line section, and so the ISO measurement isn't quite as good as you might hope.
 * Even more, this film has exceptionally poor keeping qualities. Even frozen, there are enough cosmic rays to fog it. If you have any to use, EI 400 is probably the best choice.  Gah4 (talk) 17:45, 11 October 2016 (UTC)

Unsourced?
There is an unsourced tag for the section Digital camera ISO speed and exposure index. Seems to me that it cites, among others, the ISO standard itself. Now, it isn't so convenient in that you have to pay for the ISO standard, but I don't see how it can be called unsourced. Gah4 (talk) 17:02, 11 October 2016 (UTC)
 * That ref is in the 'The ISO 12232:2006 standard' subsection. I intended the unsourced template to relate to the section before that, but did not know how to indicate that using such a template. -Lopifalko (talk) 17:31, 11 October 2016 (UTC)
 * Yes, the subsection is within the section. The part before the ISO 12232:2006 standard subsection is, as well as I know, the introduction to the section. That is, an overview of the following subsections where the actual details are spelled out and referenced. I am not a Wikipedia expert, but I believe that is reasonable.  As above, though, the fact that the ISO standard isn't free to look at is inconvenient.  (There are some standard sites that now allow free access for non-commercial use.) Gah4 (talk) 17:57, 11 October 2016 (UTC)

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ISO-Invariance
Could somebody add a sentence or two about the topic of ISO-Invariance, please? Thanks! Bonomont (talk) 12:09, 21 March 2017 (UTC)

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ISO in digital cameras
It would be good to have a separate article on ISO in digital cameras, as it is so widely misunderstood mainly because of its heritage and meaning in film. — Preceding unsigned comment added by Chrisvdberge (talk • contribs) 12:07, 5 May 2017 (UTC)

As a start, I changed the description in the first paragraph, relating to ISO in digital cameras, which said 'A closely related ISO system is used to measure the Digital signal gain of digital imaging systems', which is simply wrong. Hopefully this will help avoid promulgating some of the misunderstandings mentioned. Bobn2 (talk) 22:37, 10 August 2017 (UTC)

The ISO capabilities of the Nikon digital cameras has been misrepresented. For example, the REAL maximum ISO of the D5 is 102400 (see it's own article), however it is recorded here as the 'expanded' number, which is a misleading figure. 51.6.244.129 (talk) 20:31, 22 October 2017 (UTC)


 * Given the five different ways the ISO standard allows computing the ISO value, this isn't so obvious. It might be, for example, that the 10240 is using the 40:1 S/N ratio, and the higher one is with the allowed 10:1 ratio. Camera companies don't want to claim too high an ISO value, such that the noise level is high, and people get disappointed with image quality. On the other hand, in cases where there is no choice, you can get some amazing pictures with the expanded value. Gah4 (talk) 22:06, 22 October 2017 (UTC)