Why is Zone System EI often about half rated ISO/ASA?
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A few years ago 3 of us from APUG were sat on the Cornish coast we'd just been photographing the Crowns at Botallack on a nice sunny day. We discussed metering and compared our findings, we were all within a third of a stop of the same exposure (taking into account our different film speeds), that was using Spotmeters and Incident meters. I was using a Gossen Lunasix and a Pentax Spotmeter V.
I'm confident of getting correct exposures with any of my meters within half a stop.
Ian
You mean you all ended up using the same exposure or all your meter readings were identical. I could understand the former after placement of zones but not the latter unless al were using the same reference for metering from with their spot meters.
You mean to expel Ian for violation of rules?
http://m.lordsandladies.org/craft-guilds-in-the-middle-ages.htm
Yes we were all ending up with essentially the same exposure. In my case I metered using the Zone System with the Spotmeter and then checked with the Lunasix in Incident mode.
Ian
I'm struggling a bit here, not quite sure I understand what you are trying to get at.
He's saying its better to use an incident meter if there is a danger of another type of meter, such as in camera meter, being unduly influenced by light surrounding the main subject when you want the exposure to be correct for the main subject and sod the surrounds.
I don't know about anyone else, but I have never seen RobC and Xmas in the same room at the same time.
It is due to the two points being 1.0 log-H apart. This ratio and the one for reversal material is important to speed determination, meter calibration, and the placement and distribution of scene luminance.
Remember that two types of photographic materials use a single meter. Speed constants make it possible to have the b&w speed point in the shadow and transparency speed point in the mid-tone and still be able to use the same ISO scale for exposure. Black and white's speed constant is 0.80 and transparency film was a one time 8 (same as Eg). They fell 1.0 log-H apart but could use the same ISO setting with the same meter. Color reversal's speed constant changed from 8 to 10, but the speed point didn't change. This increased transparency film speed by 1/3 of a stop even though the speed point remained in the same place.
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Zone System and ISO speed methods for calculating black and white negative exposure also use that same meter.
Seems obvious, but I think it will help clear things up if we keep that in mind.
You need to be more specific because the ISO speed allows for one of two different testing methods the ASA/BS or DIN, and also use a controlled light source as manufacturers used to publish two ISO speeds one for Daylight the other Tungsten, all but EFKE (that I've come across) used the Daylight ISO speed on the box.
The Tungsten speed is more critical with films with reduced red sensitivity, the slower EFKE films and Ortho films like Ilford Ortho Plus. Ilford give an ISO of 80 for Daylight and 40 for Tungsten.
So this is why you have the anomaly that TMax100 needed to be shot at 50EI to get the same tonal range as APX100 at 100EI, that's from the manufacturers own data and practical Zone system tests. The Tmax speed is the newer modified ASA method (brought in for Tmax films), the APX the DIN testing.
The outcome is that with some films there's a need to use a slower EI than on the box but with others it may be higher and it's a variation between manufacturers methods of determining the ISO they publish/print on their film boxes.
However I'll reiterate that the 50EI for Tmax100 that John Sexton recommended in many article around the time of the films release, matches my Zone Syten testing and Kodak's own recommendation in the films datasheet if you wanted better tonality. I'll scan the relevant section of the Tmax datasheet in the next few days.
Ian
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Ian, the daylight and incandescent EIs I believe ended in the 1960s. Now, I'm not sure they were part of the ASA standard, but they were used mainly because of the type of photocells used with exposure meters and the color temperature the exposure meters were calibrated to. An Interpretation of Current Exposure Meter Terminology. I have an old Kodak Reference Handbook and they have different recommended daylight and incandescent EIs for Weston and GE meters.
DIN and ISO (ASA) have been in agreement since (I believe) the 1960 ASA standard, and if not exactly in agreement then, they were with the ISO standard. If the ISO prefix is listed on the box, the manufacturers have adhere to the conditions of the standard. It's comparing apples to apples.
The almost universal 1/2 to 1 stop difference seen in Zone System speed testing from the ISO film speed comes from the use of different ratios between the metered calibration point and the speed point. The Zone System uses four stops. Meter the card and stop down four for Zone I. ISO uses 3 1/3 stops. Hg = 8/Eg and S = 0.80/Hm. The reason why prefixes such as ISO and CI are used is to communicate the testing methodology used. CI 0.58 means one thing and G bar 0.58 or Gamma 0.58 another. Zone System EIs and ASA speeds were in agreement before the 1960 b&w film speed standard which eliminated most of the safety factor effectively increasing film speeds by 2/3 to 1 stop. Now ISO speeds and Zone System speeds are off by that same amount.
You wouldn't expect the same speeds as the ISO from Scheiner speeds or Hurter and Driffield's inertia speeds, or the old DIN and old ASA because they use different testing methods. Why expect it from Zone and ISO?
If you are looking for a spot that's 3 1/3 stops down from the meter reading at 4 stops down, then you will need to adjust the EI by 2/3 of a stop to find it. This can be considered the same thing as changing the speed constant as it changes the ratio between the speed point and the metered exposure point.
As for Sexton, he found his EI to be lower than the ISO of T-Max 100 just like he did with all other films. Why? Because he uses Zone System testing and its methodology is different from the ISO methodology. Sexton A few ideas on using Kodak T-Max Films Successfully, "As with most black and white negative films I used an Exposure Index (El) that is less than the manufacturers' suggested film speed."
Stephen
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In 1961 they did not change the colour negative speed only the mono.
The hype was everyone is using a meter nowdays.
Well I did for colour slide but not for mono negative.
But I thought they changed the ASA/BS toe only standard so it was a part ASA part DIN compendium.
So if a zonie does a toe test he won't get the same offset for different film.
I've never bothered much about the new fangled box speeds.
I didn't say the change to reversal film was in 1961. I think it was in the late 70s or early 80s but I don't follow color that closely. The standards come up for review every five years. Most changes, if any, are small. Two of the biggest for B&W were in the 1960 and 1994 standards.
The change from the fractional gradient based method to the fixed density method using the Delta-X Criterion for the 1960 standard was in part an attempt to create a international standard. The testing difficulties of fractional gradient testing tended to have experimental error with less than meticulous practitioners. The decision was made to also reduce the safety factor because exposure meters were more commonly used and were more accurate and to accommodate the growing number of 35mm users.
From Safety Factors in Camera Exposure, "The fractional-gradient criterion was originally chosen because it has the desirable feature of giving speeds that correlate closely with speeds obtained by practical picture tests. It has the objectionable feature, however, of being somewhat inconvenient and difficult to use. Consequently, a simpler and more convenient criterion, such as that based on a fixed density above fog density, is often desired. Fortunately, as shown by the recent data of Nelson and Simonds, a good correlation exists between fractional-gradient speed and speeds based on a density of 0.1 above fog, provided the development condition's are controlled so that a fixed "average gradient" is obtained.
Another important advantage to be gained by adopting the fixed-density speed criterion as part of an American Standard is that this step would encourage eventual agreement on an international standard for photographic speed. The fixed-density criterion has for many years been a preferred criterion in a number of countries. The use of this criterion in the DIN system," for example, is particularly well known."
The mention of Nelson and Simonds was to reference their paper Simple Methods for Approximating the Fractional Gradient Speeds which proposed the Delta-X Criterion which was adopted and is currently used in the ISO standard.
For those speed constant fans out there, here is a one of my favorite excerpts from Safety Factors in Camera Exposure, "The reduction in the safety factor could be accomplished simply by changing the constant in the ASA formula for deriving the ASA exposure index from the ASA fractional-gradient speed of the film...If the constant of ¼ were replaced by a constant of ½, a new type of "exposure index" would be obtained which would provide the proposed lower safety factor of about 1.2."
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I'm sorry I did not mean to run slide and negative together as you have interpreted.
They really only changed the mono standard the colour negative was left as is in '61 changes.
Their hypothese that most people were metering for mono cause they needed to do so for colour was imaginative.
If you were a zonie and had a EI for HP3 did you need to change it by a stop?
So that is the answer for the OP.
The document you cut and paste from was never independently peer reviewed?
In 1920s it is said they did not have a real standard the film manufacturers used bragging rights... But that was before my time.
While I always carry a meter it is rare I use it instead using sunny side f/8 unless it is a static scene that I can spot meter.
If the groom offered the bride a hanky for running makeup that was the shot of the day on Kodachrome 25.
If you are asking about an ASA and ZS speed comparison pre 1960, the results would be close to the same. Today, they will be around a stop off. I'm not suggesting any action needs to be taken only that the two methodologies are different and people should keep this in mind when comparing their test results.
However you do it you can not get away from the fact that both spot and incident meters start from how much light there is and subtract from that to place exposure on curve. They do that based on hard coded information which uses assumptions about effective SBR. The greater the SBR the further into the highlights the bias will be. i.e. meters are biased to expose for the highlights and not the shadows except where you are photographing low contrast subjects ( < 6 stops SBR ).
The point I'm making is that meters DO NOT say here is the speed point of the film and place the exposure up so many stops from there. They say here is the amount light and move down the curve from there. i.e. they are biased (keyed) towards the highlights, especially when you have longer SBR as you do in many landscapes. Just saying thats all. I know its not scientific enough for some but for others it helps understanding what your meter is doing and why incident meter users will tend to get far more consistent negative densities than spot meter users will when they expose for the shadows.
The point I'm making is that meters DO NOT say here is the speed point of the film and place the exposure up so many stops from there. They say here is the amount light and move down the curve from there. i.e. they are biased (keyed) towards the highlights, especially when you have longer SBR as you do in many landscapes. Just saying thats all. I know its not scientific enough for some but for others it helps understanding what your meter is doing and why incident meter users will tend to get far more consistent negative densities than spot meter users will when they expose for the shadows.
Yes I do the same. I calibrate for 10 stop SBR and where its greater than that I expose for the shadows instead of a highlight.
Meters certainly don't. That's what the film speed is for. The film speed gives the meter information about the film to factor into the exposure calculator. The reasoning why a test is done in a certain way is incorporated into the result. Such concepts as scene luminance range, luminance distribution, and what part of the curve is the most critical (remember transparencies it's the mid-tone and b&w it's the shadows) were considered when designing how film speed is determined. And it's all rolled up into a single number. The ratio between the speed point and the metered exposure is a key component in determining exposure placement with exposure theory. How do you think the same meter is able to exposure for both black and white negative film and color transparency when their speed points are in different parts of their curves? A better explanation can be found in Calibration Levels of Films and Exposure Devices.
For an average scene shadows fall around 4 1/3 stops below the metered exposure point (metered exposure point is also considered to be Hg). I've pointed out that the ISO speed point is 3 1/3 stops below Hg. Anybody wonder about this?
Incident meters don't interpret the scene's luminance range. They just place whatever the illuminance is at the same film plane exposure depending on the film speed. This is why they are so consistent with exposure, but determining exposure placement without considering luminance can lead to lost shadows in scenes with longer luminance ranges or depending on the distribution of the scene luminance. Phil Davis' Beyond the Zone System addresses how to use incident meters and still incorporate luminance ranges.
You are giving meters way too much credit in this process, determining the EI is where the math you are talking about is done.
Meters compare "the luminance value they see/measure" to "the EI we chose" and spit out "a value for us to consider"; that's the whole enchilada as far as the meter is concerned.
IMO the reason incident metering, not incident meters, is more consistent in practice is that incident readings are objective and reflective readings are typically subjective.
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