Talk:Film speed

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[edit] Graininess

Hi, all,
This is too much to just change in the main entry. May I have some comments so I can fix the proposed text up? My own comments are in [bracketed italics] 2B removed later. (I know there is an  !-- Invisible Note to editors -- mechanism, but these comments should be seen on the TalkPage. I'll hassle getting them out later.)

PROPOSED TEXT

Individual silver halide crystals suspended in a film emulsion aggregate into clumps ("grains") of random size. [Grains are not as regular and orderly as the crystals which lie at their heart, and at the heart of the energy storage mechanism that makes it possible to store and later develop a latent image] Even when these are not individually resolved in an image, a texture ("graininess") remains. Higher film speed brings more graininess. [nice direct statement from original more or less] Fine-grain stock, such as film used for portraiture or copying, is "slow", meaning that the amount of light used to expose it must be high or the shutter must be open longer. Fast films, used for shooting in poor light or for shooting fast motion, produce a grainy image. [Easily grasped contrast of different practical situations, also from original, more or less]

Since each grain of silver halide develops in an all-or-nothing way, photographic images actually consist of a mosaic of developed and undeveloped areas. In this sense, film is a threshold detector rather than a linear detector. [This is a delightful insight to present, at a time when so many of us are making the historic transition from "analog" to "digital". However, it didn't have enough of a "compare and contrast" discussion to clarify differences between the two ways of conceptualizing film's function.] If the subject has an edge between light and darkness and that edge falls on a grain, the result will be an area that is all light or all shadow. Fine gradations of grayness are also quantized, so that graininess interferes with the perception of shape from shading as well as with object contours (edges). [As the brain imposes structure on sensation to achieve perception, "shape from shading" has emerged in recent decades as an important mechanism of shape encoding from surfaces, just as contours and their elaboration in the brain is an important mechanism of shape encoding from edges, and of figure/background segmentation. Also, it makes for beautiful b/w photos :-) ] Photographers sometimes exploit film's quantization with high-contrast derivatives ("orthos") that really are only black or white, [These are typically made with photolithography film like Kodalith, hence the name. I put this in to be sure readers understand that it's hard to get even grainy shots to lose their grey-ness, unless special steps are taken. Perhaps it can be dropped to keep everything brief. Opinions? ] but the issue of quantization is moot in most photos, because grains are random in size, overlap, and are not individually resolved in the image. Under such typical circumstances, slow films have higher contrast, and faster films have not only lower contrast, but a much longer gray scale, beloved of available light photographers in journalism and movie making. [There was a problem in the original on this point. Maybe you can say it better, but we need some kind of clarification. An ASA 400 b/w film has what they call a "longer grey scale" than an ASA 25 film. Subjectively, I've always thought the grays of fast film "looked nicer", but technically it means that the negative film goes deeper into highlights before blocking/saturating, and it can throw a few grains into shadows before falling to baseline density at low image intensity.]

[Original: "Fast films are also relatively contrasty, for the same reason. That is, an area of the image will consist of bright areas and dark ones with few transitional areas of midtones." This statement is misleading at best. Slow films have a higher gamma. ]

END proposed text.

Please don't clobber me. If there are better ways to handle a suggested revision, just say. As for the revision itself, entries on technology are of necessity always a work in progress, so this won't be the last change, and not every change has to be made.
Thanks!
Jerry-va 17:09, 27 February 2006 (UTC)

Does anyone know how films speed and the ISO ratings relate to digitalo cameras? I think this would be useful to add.

[edit] Delta 3200

A while ago, I removed Delta 3200 from the chart, and today an anonymous user, in what I assume to be a well-meaning edit, added it back (at 3200). The reason that I removed it is that Delta 3200 does not have a true ISO speed of 3200; according to the data sheet, the true ISO speed is 1000. Shooting it at the recommended speed of 3200 is actually "pushing" the film, and will result in higher contrast and less shadow detail than if it were shot at the ISO speed. For this reason, I don't think it's appropriate to list it on the chart. Listing it under 3200 is inaccurate, and listing it under 1000 would be confusing without a lengthy explanation. Similar arguments apply to Kodak's Tmax P3200. -- Coneslayer 18:00, 2005 Apr 17 (UTC)

That depends on what we mean by nominal film speed. The nominal speed of a number of popular films is different from the true ISO speed (which already contains a safety factor). Kodak TMZ and Ilford Delta 3200 are marketed and labeled as ISO 3200 films and can be shot as such. For that reason, it makes sense to list them here and provide more detailed explanation in separate articles about these two films. Your reasoning is not wrong, but by the same token you could challenge the inclusion of Fuji RVP 50, which has given rise to endless debate about whether it should be rated differently than its labeled speed, with recommendations ranging from ISO 40 to ISO 80. I'd say it's simplest if we stick with what's on the box (yes, that may be marketing hype) and explain what's really going on in separate articles for each film stock. --MarkSweep 20:25, 17 Apr 2005 (UTC)
Mark, to put it simply, I would say you're using the word ISO where it doesn't belong. The ISO specifies a method of testing film speed. The 3200 speed does not come from this testing methodology, and you won't see the word ISO near that speed on the packaging or datasheet. The ISO speed of Delta 3200 is 1000, period, no matter what you set the dial at, or how long you develop it. In contrast, RVP 50 is an ISO 50 film. You, and other photographers, might like the results better when it's shot at 40 or 80, but that doesn't mean the ISO speed is wrong, or that the speeds you like better are the true ISO speed. It doesn't make sense to say I'm shooting an ISO 50 film at ISO 40--that's a misuse of ISO, because I'm not using the ISO methodologies. The correct term would be EI 40 (exposure index). If you want to list Delta 3200 under ISO 1000 on this page, that's fine with me, but I would strongly object to listing any film under a speed other than the ISO speed. -- Coneslayer 21:23, 2005 Apr 17 (UTC)
Good point. I don't disagree with your assessment of the facts. My only concern was that it would be better to explain this in the article, since these issues are generally relevant here and likely to come up again. So how about listing Delta 3200 under ISO 1000 in the table and adding a note explaining what's going on? --MarkSweep 23:33, 17 Apr 2005 (UTC)
I have added a paragraph on this topic to the article. -- Coneslayer 21:35, 2005 Apr 17 (UTC)

[edit] f-number and aperture diameter

I have edited the article slightly to remove the common misconception that the f-number is equal to the ratio of the focal length to the aperture diameter. It is not. The f-number is equal to the ratio of the focal length to the diameter of the entrance pupil of the lens. The latter is proportional to the diameter of the aperture. It is true that doubling the f-number halves the diameter of the aperture but it is not true that the aperture diameter is equal to the focal length divided by the f-number.--Srleffler 04:29, 14 February 2006 (UTC)

[edit] No mention of ISO 6 etc?

The description of ISO film speed method refers only to that for still colour negative film. Wouldn't it be more thorough to mention the ISO 6 method for B&W film; why there is a difference between the methods for B&W and colour film; why chromogenic B&W film doesn't quite fit with either; and the existence of a separate standard for colour reversal film? It might also be worth mentioning that there is no ISO for motion picture colour negative film. I would be happy to write the aditional material, as I have all the relevant standards.

--Helen Bach 15:50, 31 March 2007 (UTC)

Yes, please do. And if you can share copies of the relevant standards (just as fair use to help other editors, you understand), that would be fantastic, too. Dicklyon 16:23, 31 March 2007 (UTC)

[edit] Fallacy in illustrating digital sensitivity

Images of a flower taken at ISO 100 and ISO 1600 on a Canon 400D digital camera. Both images were shot under similar lighting conditions, varying only the ISO setting and shutter speed.

I can understand how they were shot under similar lighting conditions, but the illustration is incredibly fallacious, as the ISO 1600 shot would be overexposed compared to ISO 100. Shutter speed would need to be 16 times faster to achieve the same exposure, ie. 1/5600. This is a 2/3 stop of a difference, and that's assuming that the 1/4000th setting (fastest on that camera) is exposing correctly. Tests (in magazines) show that even shutters in professional cameras overexpose by as much as a whole stop at their highest speed, the problem is even more pronounced in amateur cameras (such as 400D). This test would be a good candidate to be repeated (possibly with the same camera), at shutter speeds of 1/100th and 1/1600th or slower. —The preceding unsigned comment was added by 217.153.194.14 (talk) 21:01, August 23, 2007 (UTC)


[edit] Use of Lux as a means of illustrating sensitivity of a digital video/still camera

I have a Sony HVR-A1J HDV camcorder with a 1/3" CMOS sensor which can be used as a still camera with images saved to a memory stick. The sensitivity of the camera is defined as: 7 lux at +18db with a normal shutter. Let's take this apart: 7 lux is a little less than one foot candle - sounds great, but that 18db is telling us that the noise level is going to be horrendous. Normal shutter probably refers to something between 1/30 and 1/48 second (25 or 30 frames/sec - this camera doesn't actually scan fields). If we move the gain back down to 0 db, sensitivity is more likely to be in the 400 to 1000 lux range. (Well you can do the math to get an exact number. I'm not going to bother.) This actually puts the camera in a fairly standard professional video camera sensitivity range - ISO 160 (or using our old friend Ektachrome 160 in the Bolex), where you can push the film in processing or turn up the gain as needed.

What would be muchly appreciated is a Wikipedia entry that incorporates a cross reference table comparing all these different units of sensitivity to each other. Competitive manufacturers product literature rarely uses the same standards so very little makes sense - like mixing RMS and EIA watts! --Mccainre (talk) 07:32, 7 January 2008 (UTC)

[edit] Definition of digital ISO speeds

According to light meter, the ISO film speed S is given by S=Kn^2/Lt, where L is the luminance of a medium-brightness area (candela/m^2), n the aperture number, K a constant (usually between 12 and 14), and t is the shutter speed. Usually, medium brightness is taken to be an 18% reflective card. However, this doesn't say anything about the headroom. Should a sensor with a given ISO number be at exactly 18% of saturation for a given luminance L? Or is there a standard amount of headroom? I've searched a bit and I found numbers of 106%, 170%, and 141% for the saturation level. What does the ISO document say about it? This information is missing. See e.g. [1], [2], [3]. Han-Kwang (t) 15:21, 10 October 2007 (UTC)

(copied from Talk:Light meter) Solving for S doesn't mean the meter is telling you that that's a definition of S, or a recommendation for S. I mean, yes, given a luminance and a meter calibration, etc., you can back-solve for S. But there's nothing there that says the L value is taken from a "medium-brightness area", is there? It's from wherever you aim the meter. Now, there is actually a saturation-based digital camera ISO speed definition that works something like you say, but it has its own constant, not dependent on any particular meter calibration of course, and leaves about a half-stop of headroom above a diffuse white when average scene is something 18%, if I recall correctly. But nobody rates their cameras by this definition anyway, so don't expect to find any such relationship in practice relative to any ISO setting or rating on a digital camera. If you want to get technical ISO 12232 says "The saturation based speed, Ssat, of an electronic still picture camera is defined as: Ssat = 78 / Hsat, where Hsat is the minimum focal plane exposure, in lux seconds, that produces the maximum valid (not clipped or bloomed) camera output signal." This may not be trivial to interpret as you want, but compare this to the noise-based ISO definitions of the form Snoise40 = 10 / HS/N40 where that H level is in some sense a "mid gray"; the ratio of saturation to this mid-gray is thus 7.8, which is more than 1/0.18 by a factor 1.404, or about a half stop. I hope this helps. Dicklyon 18:53, 10 October 2007 (UTC)

(copied from Talk:Light meter) I see, so the equation n^2/t = LS/K is a simply a definition of what the reading that a light meter should produce for a given luminance, even though K is somewhat variable. But as a photographer, of course I would want to know how much headroom I will get if I point the light meter at a 18% card. As you say, officially the saturation level should be 141% (1/2 stop above 100%), but in practice YMMV (e.g. my digital compact camera seems to aim for 18/100 rather than 18/141). Maybe this subject really belongs on film speed, where I also asked this question. Anyway, I think the focal plane exposure is given by H=pi L t/4 n^2 (for objects far away from the lens), so Ssat = 78/Hs = 312 n^2/ (pi*Lsat*t) where Lsat is the luminosity that just saturates the sensor. I guess that 78 comes from 100*pi/4, so Ssat=100 n^2/(Lsat*t), which seems to be an elegant equation -- would it be appropriate to mention on film speed? Han-Kwang (t) 23:43, 10 October 2007 (UTC)

From Talk:Light meter: apparently, the saturation-based iso number Ssat is defined as Ssat=100*n^2/(Ls*t), where Ls is the luminosity (cd/m^2) that is at the threshold of sensor saturation for a given n and t. This may be nice to add to the article, but I'm not yet 100% sure that I understood everything correctly. Moreover, are there any statistics on to what extent digital cameras follow this equation? Do they typically inflate the ISO speeds or are they rather more conservative? Han-Kwang (t) 23:54, 10 October 2007 (UTC)
Interesting how you found that 100; I had not seen that before. Perhaps you're right; perhaps it's WP:OR. Anyway, in typical good DSLRs you have a fair amount of headroom at ISO 100, meaning the saturation ISO is lower than that. For example, the Sigma SD14 had so much headroom that Sigma recently introduced an ISO 50 mode via a firmware update; at ISO 50 it probably has not much headroom; I don't know what the saturation ISO is, but like I said, nobody ever specifies that. Dicklyon 01:18, 11 October 2007 (UTC)
Do you actually have the ISO documentation or are you like me dependent on secondary sources? Instead of 100, I could write 312/pi (=99.3), in which it's a straightforward derivation from the Ssat=78/Hsat equation. Would it still qualify as OR then? I read in some policy (can't remember which) that straightforward mathematical derivations are OK. The question is whether this one is as trivial to us as saying that 11 out of 40 is equal to 27.5% to others. :) (The reason that I'm interested in this is that I want to use my camera as a luminosity meter, but it seems that I need to calibrate it against a known reference.) Han-Kwang (t) 07:18, 11 October 2007 (UTC)


This is the story behind Ssat = 78/Hsat, according to ISO 12232:
The exposure index value (I subEI) is 10/Ha where Ha is the arithmetic mean focal plane exposure. The constant 10 is chosen to be consistent with 2721 and 5763.
Hsat is the focal plane exposure that would result from a 141% reflectance object (ie half a stop over a 100% reflectance object). Therefore the focal plane exposure resulting from an 18% reflectance object is Hsat * 18/141. Put that into the EI equation and you get IsubEI = 10*141/18/Hsat = 78/Hsat. The speed is the EI for an 18% grey card, hence Ssat = 78/Hsat Helen Bach 17:30, 11 October 2007 (UTC)


(copied from Talk:Light meter) I've posted something on Talk: film speed. Now that I have read Dicklyon's posts here I see that my post there is a re-write of the end of his previous post - ie that the 78 factor in the Ssat formula comes from 141/18. The formula for focal plane exposure used in 12232 (Eq 2) takes flare exposure (Hf), cos^4 loss, lens transmission factor (T) and vignettng factor (v) into account. The pi/4 combines with the other losses (T v cos^4theta, with Hf << H) to produce 65/100 (which is 0.83 pi / 4), so the formula for arithmetic mean focal plane exposure is 65 La t / (100 A^2) where La is the arithmetic mean scene luminance and A is your N. On axis the focal plane exposure would be 0.88 pi L t / (4 A^2). Helen Bach 22:47, 11 October 2007 (UTC)

OK, for off axis there's a factor cos^4(theta). I always thought that was the main cause for wide-angle pictures to be dark in the corners, but if I understand vignetting correctly, there is also a contribution from physical obstruction. It doesn't seem logical to me to assign an absolute value 0.83 to the combination of T, v, and <cos^4 theta>, since these are dependent on the quality of the objective lens (T and v) and the focal length/sensor size (cos^4 theta). I think it would be nice to use the equations as discussed here in the article, although I'm not sure that film speed is the best place. I'm thinking of the general equation, H=T v pi L t cos^4(theta)/ n^2, the saturation-based ISO calculation, plus mentioning some typical values for v, T and averaged cos^4(theta), plus a few examples for the actual values of H for common photographical conditions (e.g. indoor 200 lux = 200/6pi nit (white surfaces), t=1/60, n=3.5, 38 mm lens (relative to a 35 mm sensor size), outdoor 10000 lux. More information about the noise-based ISO would also be nice, and conventions about the ISO numbers as indicated by digital cameras would also be nice. I did some experiments with a couple of compact and DSLR cameras and a calibrated lux meter. Using theta=0, T=1, v=1, and assuming that a saturated jpeg means that the sensor is saturated, and that the jpeg pixel values are with gamma=2.2, I calculated the saturation-based speed Ssat and compared that to the nominal speed as indicated by the camera. I find ratios Ssat/Snom between 1.5 and 3.2; even with the same camera different numbers depending on the nominal ISO speed setting. I really don't get how it is possible that something that is supposed to be a standard can be interpreted so freely by camera manufacturers. Han-Kwang (t) 11:25, 12 October 2007 (UTC)
A few comments. 1) The cos^4 falloff does not take physical obstruction into account. Cos^3 may apply to lenses that have tilting exit pupils - typically wide angle designs like the Super Angulon, but that is a subject for another page. 2) It is not correct to assume that a 'saturated' JPEG means that the sensor is saturated. Examining a RAW file will show that the JPEG may be at 255,255, 255 before the sensor is saturated. 3) From my own tests on various cameras I have found that the conversion to a JPEG does not happen at constant gamma, particularly at the shoulder, so there is a danger in assuming that it does. I'm just flagging this as a potential problem with your assumption, not saying that it is universally applicable. 4) ISO 12232 sets conditions that determine whether the noise-based speed or the saturation-based speed is reported as the camera's ISO speed. By the way, it also tells manufacturers to call the EI user control the 'exposure index' or 'exposure setting' control, rather than the 'ISO speed' control. Helen Bach 01:02, 13 October 2007 (UTC)
Helen is absolutely right. You can't begin to get at the question of sensor saturation by studying a rendered JPEG out of a camera; the relationship is too distant, and not at all standardized. Furthermore, the ISO speed or E.I. setting on a camera bears no relationship whatsoever to the ISO speed as specified in the ISO standard; well, maybe SOME relationship, like all the settings you can choose are hopefully between the highest noise-based ISO and the low saturation-based ISO, but even that is not specified or guaranteed. You'd be better off studying raw data and raw converters if you want to find out where the headroom is, and you won't need any standards for that. The latest ISO speed standard for digital cameras, ISO 12232:2006 I believe it's called, has added a new hack called "standard output sensitivity" (SOS) that tries to specify a bit about how a photo should be rendered as a function of exposure and ISO settings, but even that has no relationship to the ISO speeds specified in the same document, except that it's measured on the same scale and is a recommended exposure index; it's defined as 10/H for H being the exposure (lux-seconds) corresponding to an output code of 118 out of 256 (in an unspecified but presumably sRGB or gamma 2.2 color space). The processing gain can of course be anything, so any SOS value is possible, unconstrained by the different definitions of ISO speed rating. It's really a bit of a complicated mess. —Preceding unsigned comment added by Dicklyon (talk • contribs) 06:06, 13 October 2007 (UTC)

(unindent) To Helen: 1) OK for the vignetting, but after some thinking I don't see why it is cos^4 rather than cos^2. One cos(theta) comes from the angle of incidence onto the lens, and the other cos(theta) from the angle of incidence onto the focal plane. Derivation:

                     D    ,-| b
            o         |,-'
  --------------------+-----
                  ,-' |  f
               ,-'
o/cos(theta),-'
         ,-' spatial angle dOmega
      ,-'
  |,-'
a |

a is a small surface with a luminance L; the surface has an intensity I=L a cos(theta) [candela] and sees the lens (at a distance o>>f) with a spatial angle dΩ=D^4 cos(theta) pi/4 o^2 . The flux as captured by the lens is

F = I dΩ=L a D^2 cos^2(theta)/4 (o/cos(theta))^2 [lumen].

The image in the focal plane has a surface b=af^2/o^2. The illuminance E at the focal plane is then

E = F/b = pi L D^2 cos^4(theta) / 4 f^2 [lux]

With D=f/N,

E = pi L cos^4(theta) / 4 N^2.

Of course, you can add extra factors for vignetting v(theta) and a lens transmission T,but that doesn't explain the cos^4.

2) and 3) - OK, that's the difference between gamma 2.2 and sRGB, but that's not going to be a big effect at 1 stop below JPG saturation.

4) It looks like (consumer) camera manufacturers are ignoring that part of the ISO standard.

To Dick: aha, 118/256 is 18.4% of saturation in gamma=2.2 and 18.0% in sRGB. (Are you sure it wasn't 18/255 by the way?) And then we are actually back to where I started: SOS rating S (100, 200, 400, 800, etc.) is equivalent to a ISO saturation speed, except that the SOS number refers to saturation of the output JPG image and the ISO number refers to saturation of the sensor.

If one of you can explain the cos^4 factor to me, I think it's time to expand the article.

Han-Kwang (t) 07:16, 13 October 2007 (UTC)

cos4 is a common approximation to the physics, but can't be even approximately correct for a super-wide or fisheye lens design. Here are some sources; the Doug Kerr paper is a good one. Dicklyon 07:30, 13 October 2007 (UTC)
Aahh, I forgot that the distance to the lens is o/cos(theta) rather than o. Thanks. I don't have time today, but I'll update the article then tomorrow, unless one of you feel like doing that now. I will mention that 0.83 is a typical value for on-axis transmittance. (Seems rather low, aren't AR coatings much better than that?) Han-Kwang (t) 08:29, 13 October 2007 (UTC)
0.83 is not a typical value for transmittance, it is the combination of cos^4, v and T. The individual values used in the derivation of Eq 2 in 12232 are cos^4 theta = 0.94 (theta = 10deg); v=0.98 and T=0.9. Helen Bach 12:23, 13 October 2007 (UTC)

[edit] Arithmetic to logarithmic conversion formula different from that defined by ISO

How time flies. I'm still working on the draft I promised. Meanwhile, how about changing the arithmetic - logarithmic conversion formulae to the one implicit in the speed definitions given in ISO 6 and ISO 5800, and stated explicitly in ISO 2240; and the derived inverse?

This is the conversion method derived from the two speed definitions in each of ISO 6 and ISO 5800, and stated explicitly in ISO 2240: S° = 1+10 log S

This is the inverse of the above, which is not specifically mentioned in the Standards: S = 10^(S°/10) / 1.26

All base 10 logs.

Helen Bach 16:36, 10 October 2007 (UTC) —Preceding unsigned comment added by Helen Bach (talk • contribs) 16:33, 10 October 2007 (UTC)

How strange. I thought speed was measured in thirds of stops. 10log10(x) is close, but 3log2(x) would be exact. What is that particular standard? Is it still in force? Dicklyon 01:22, 11 October 2007 (UTC)

It is stated explicitly in ISO 2240, and can be arrived at by simple substitution in the speed formulae given in ISO 6 and ISO 5800. Its ancestry goes back further than that, but those are the three current standards. The relationship is based on the definitions of arithmetic and logarithmic speeds, not on a purely mathematical correlation between the integer pairs 100/21, 200/24 etc.Helen Bach 03:59, 11 October 2007 (UTC)

Interesting. I thought the numbers were tied to powers of two, and more specifically defined by tables such as those in ISO 12232. But now that I examine the tables, the break points do follow powers of 10, just like decibels, with 10 one-third-stop steps per decade. I guess that makes sense as a way to keep the decimal numbers nice. Thanks for clueing me in. Dicklyon 04:48, 11 October 2007 (UTC)


Will the formulae be changed? What happens next? I'm new to all this. By the way, which table in 12232 are you referring to? Thanks. Helen Bach 22:11, 11 October 2007 (UTC)

WP:Be bold; WP:SOFIXIT. Table 1, section 8.2, "Method of Reporting" in the DIS; I presume this made it into the final. Dicklyon 22:26, 11 October 2007 (UTC)

[edit] Pencil sharpener images

I removed this:

Images of a pencil sharpener taken at ISO 100 and ISO 3200 on a Nikon D40x digital camera. Both images were shot under similar lighting conditions, varying only the ISO setting and shutter speed.
ISO 3200, f/20, 1/160 s
(click on image for larger version)
ISO 100, f/20, 1/5 s
(click on image for larger version)
Comparison between 100% crops of the above images. Both are approximately the same brightness, but the one at ISO 100 is less noisy and has motion blur from the lower exposure time.

Reasons:

  • The images suffer from motion blur - use a tripod for 1/5 s shutter time;
  • The thumbnailing process makes it even harder to compare the images. Crop the photos in the original resolution (i.e. the native resolution of the camera) to e.g. 250x150 size and save as jpg with sufficiently high quality setting.
  • What do you exactly want to illustrate with these images that isn't already illustrated by the existing image (the yellow flower)?

Han-Kwang (t) 00:19, 7 January 2008 (UTC)

The problem with the flower shots was that they had unequal exposures; see Wikipedia:Reference desk/Science#ISO setting verus shutter speed. -- Coneslayer (talk) 15:10, 7 January 2008 (UTC)
(1) The motion blur was deliberate. I needed to show both the longer exposure time and the lower noise on ISO 100, and the motion blur in no way affects the noise. The noise is caused by the sensor, and will exist even if the photo's subject is blurred.
(2) Is this what you mean? --Bowlhover (talk) 01:37, 8 January 2008 (UTC)
Not to put too fine a point on it, but the images suck. The inclusion of blur due to camera motion totally complicates the comparison, and it wasn't mentioned in the caption. If you want to show the tradeoff between noise and blur, make it blur due to subject motion. Take pictures of something that rotates, so you can see a sharp unblurred part as well as a clearly motion-blurred part, and compare that to a frozen but noisy picture of the same. Dicklyon (talk) 03:40, 8 January 2008 (UTC)
Can you explain how including blur complicates the comparison if there's a white featureless piece of paper in both photos? Viewers can compare the amount of noise on the paper and also on the featureless surfaces of the pencil sharpener. Also, the photo gallery cut and pasted above by Hankwang contains the caption, "Both are approximately the same brightness, but the one at ISO 100 is less noisy and has motion blur from the lower exposure time."
Ah, yes, I was remembering the original caption. But the motion blur was from camera shake, not something that necessarily goes with exposure time. The fact that nothing is sharp makes the photo look a lot worse than such an ISO comparison should normally be expected to show. The featureless background and camera shake contribute to the problem.
You and other users are welcomed to post high-quality photos at any time and insert them into the article. However, readers need to see what photos look like when shot at different ISOs. --Bowlhover (talk) 05:19, 8 January 2008 (UTC)
Readers need to see these photos? I don't think so. Dicklyon (talk) 05:32, 8 January 2008 (UTC)
Most people are not photographic experts. They do photography pick up a camera, put it on the full auto setting, and take their photo. It would be very useful to these people to show that the fact some photos are unacceptably noisy is because of the high ISO. Explaining increased ISO causes increased noise is not helpful if the person doesn't know the meaning of "noise". --Bowlhover (talk) 23:58, 8 January 2008 (UTC)
While there's some doubt in my mind that this needs illustrating here at all, the above isn't the best way to show increased noise and the benefits of increased ISO in the same example. Motion blur is a perfectly fine way of illustrating what happens when you don't use higher ISO in reduced light, but it also makes a direct comparison of noise much more difficult for the casual observer. We might know that noise occurs, blur or not, but it would be easy to (wrongly) infer from this example that the lack of noise was due to blurring, and not lower ISO. It's not "scientific" enough; there's no control. If we want to show the reason for higher ISO as well as the noise penalty, I agree with Dick that a moving subject, like a vehicle or sports shot, would be much better. The caption could then point out a static camera and the static background would provide the control with which noise levels can be directly compared. --mikaultalk 09:33, 8 January 2008 (UTC)

I think the article would benefit from a photo comparison of different ISO settings. I like Dicklyon's suggestion to have a picture with something that moves against a steady background. It would be nice, though, if the picture had some aesthetic value as well when cropped (not scaled) to 250x150 px. Han-Kwang (t) 09:40, 8 January 2008 (UTC)

I'll try to do that, but if you think you have the necessary equipment, please take the photos yourself too. --Bowlhover (talk) 23:58, 8 January 2008 (UTC)

[edit] 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)

[edit] ASA 6

Where does the information that the original Kodachrome was ASA 6 come from? I've read in some sources that it was 8 and in some that it was 10, but never 6. —Preceding unsigned comment added by 130.232.17.50 (talk) 09:23, 6 May 2008 (UTC)

[edit] Readability

Parts of the article seem to be written more to convince the reader that the author knows the subject than to explain the subject to the reader.

Could it be simplified - perhaps by adding more explanations and links? Perhaps by adding very short summaries to each section?

One thing I had problems with was "clipped or bloomed". To me they are not well defined terms. If it is standard terminology, it would be good to explain them, either here or in separate articles. Mlewan (talk) 07:12, 31 May 2008 (UTC)