What is EI?

[ErinHilburn]

I recently had someone mention the EI of a camera to me. This was an older photographer. I'm still a student and was wondering what it was, I immediately thought of this sight and knew someone on here must know. It could be refering to film and not the camera. It was a very brief discussion and I shall not likely speak to him again, so I couldn't very well as him.
Thanks to anyone who knows,
-erin

 

[David A. Goldfarb]

EI refers to "exposure index," which is the speed rating of the film in combination with a developer as determined by the user, as opposed to the official ISO speed rating of the film.

For instance, the ISO speed of 400TX (Tri-X) is ISO 400 under official standardized testing conditions, but in some developers it might only be EI 200, and in some it might be EI 640 or more.

 

[ErinHilburn]

So do developers come with this information or is it some sort of formula you follow as you switch developers and films and what not?

 

[David A. Goldfarb]

Most films have this kind of information on their technical data sheet (go to www.ilford.com and download some of their film sheets for some of the best examples), but even this is just a starting point, and you can do your own testing for best results.

There are a number of approaches to film testing. I like the method that Ansel Adams describes in his book, The Negative, but you can also just start with the manufacturer's recommended speed and adjust based on your results. Adjusting the EI will change the amount of shadow detail that can be recored on film in general, and adjusting the development time will change the amount of contrast. If your shadows are always blocked up, lower the EI, and if your highlights are blown out, reduce the development time. Alternately, if your highlights are flat, increase the development time.

 

[Konical]

Good Evening, Erin,

1--Both film and developer manufacturers usually have data available, either packaged with their products or on a web site.
2--For an overall view, try to obtain a good general introductory book on photography, one which is a few years old may be devoted entirely to chemical photography rather than digital.
3--Do a search on APUG using the name of any particular film or developer; there'll probably be information available here.
4--Post questions in the Forum about particular film or developer combinations and you'll probably get answers (opinions??) rather quickly.
5--Do a Google search for specific films and developers. There is, for example, an entire site devoted to Kodak's HC-110 developer.
6--Practice and experiment!

Konical

 

[roteague]

I agree with David. I've always thought of EI as a personal index of what to rate film speed. I know a lot of people w ho use Velvia 50 rate it at 40, so that would be ISO 50 but EI 40.

BTW, this is not a strickly B&W rating, although I imagine that is where you will see it mostly used; you can also use it for color.

 

[ErinHilburn]

So is it a bit like calibrating film in your camera only taking it a step further and including developing time as well?
Also thank you for the response. We were taught a b&w course, but 6 weeks is just not enough time to learn all there is to know. I don't recall my first professor mentioning this at all, however I do now remember my second professor performing this test for us, however I guess since I didn't recall it until now I didn't pick up on it well enough (tues, night class 3hrs long seemed to last forever) He will be teaching it again so I will ask for a refresher. Thanks again.

 

[Bob F.]

So is it a bit like calibrating film in your camera only taking it a step further and including developing time as well?
Also thank you for the response. We were taught a b&w course, but 6 weeks is just not enough time to learn all there is to know. I don't recall my first professor mentioning this at all, however I do now remember my second professor performing this test for us, however I guess since I didn't recall it until now I didn't pick up on it well enough (tues, night class 3hrs long seemed to last forever) He will be teaching it again so I will ask for a refresher. Thanks again.

Ah well.. this is the old "Give someone a fish, he will eat well tonight, show him how to catch his own fish and he will eat well forever" (or at least, until the E.U. Fisheries Commission dictate a total ban on fishing in his area)...

To translate ( ).... To understand something fully, you have to do it yourself. Watching someone else do it, or reading about it, only gives you a fraction of the story and you are certain to forget the details. After you see it done again, pick a different film and have a bash at it yourself - it's very enlightening.

Have fun! Bob.

 

[Woolliscroft]

Are you sure it was the EI of the camera, rather than film? If so, it might be the lowest light level the meter can record accurately.

David.

 

[ErinHilburn]

No I don't know which. I had not previously heard EI of anything, and I wanted to know what it could be refering too. So yes it could be either or.

 

[pentaxuser]

I agree with David. I've always thought of EI as a personal index of what to rate film speed. I know a lot of people w ho use Velvia 50 rate it at 40, so that would be ISO 50 but EI 40.

BTW, this is not a strickly B&W rating, although I imagine that is where you will see it mostly used; you can also use it for color.

This is an interesting point. As a colour neg user and home processor, I don't think I have ever seen it mentioned in any colour photography book I have read. Mind you colour workers( transparency and neg) seem to be the poor relations in terms of good books. There's no equivalent of Les McLean's " Creative B&W Photography" or "Way Beyond Monochrome" etc. All colour books are about taking photos with little about processing other than to say follow manufacturer's instruction to the letter.

Given that there's no leeway with the developing times, how would it work? Presumably overexposing a little affects colour saturation but what other less desirable effects does it have? I have never seen any film testing routine to establish EI. If I can increase saturation and improve shadows by a lower ISO than the stated by the manufacturer, what are the downsides?

I would appreciate information on this and which books cover it?

Thanks

Pentaxuser

 

[Lee L]

Are you sure it was the EI of the camera, rather than film? If so, it might be the lowest light level the meter can record accurately.

David.

If it is the lowest light level the meter can read, it would be referred to as EV (exposure value), and not EI (exposure index).

Lee

 

[Gerald Koch]

You will also see the term EFS, Effective Film Speed.

 

[Donald Miller]

This is an interesting point. As a colour neg user and home processor, I don't think I have ever seen it mentioned in any colour photography book I have read. Mind you colour workers( transparency and neg) seem to be the poor relations in terms of good books. There's no equivalent of Les McLean's " Creative B&W Photography" or "Way Beyond Monochrome" etc. All colour books are about taking photos with little about processing other than to say follow manufacturer's instruction to the letter.

Given that there's no leeway with the developing times, how would it work? Presumably overexposing a little affects colour saturation but what other less desirable effects does it have? I have never seen any film testing routine to establish EI. If I can increase saturation and improve shadows by a lower ISO than the stated by the manufacturer, what are the downsides?

I would appreciate information on this and which books cover it?

Thanks

Pentaxuser

Since this was brought up by another poster earlier, I will weigh in and say that yes color materials are routinely rated differently then the ISO rating.

I can't direct you to specific places where this has been published but suffice it to say it has been published many, many times over the past twenty five years.

The norm is to under expose color transparencey materials to achieve better color saturation and to over expose color negative materials.

Color transparency materials have a much narrower latitude...thus it is fairly common to depart from the ISO by 1/3 stop...example of ISO 64 Kodachrome rated at EI 80.

Color negative materials are commonly wider latitude and departures can approach one stop, much the same as black and white film. Example ISO 200 rated at EI 100.

 

[pentaxuser]

Since this was brought up by another poster earlier, I will weigh in and say that yes color materials are routinely rated differently then the ISO rating.

I can't direct you to specific places where this has been published but suffice it to say it has been published many, many times over the past twenty five years.

The norm is to under expose color transparencey materials to achieve better color saturation and to over expose color negative materials.

Color transparency materials have a much narrower latitude...thus it is fairly common to depart from the ISO by 1/3 stop...example of ISO 64 Kodachrome rated at EI 80.

Color negative materials are commonly wider latitude and departures can approach one stop, much the same as black and white film. Example ISO 200 rated at EI 100.

Thanks Donald. I have settled on Fuji Superia 100 as my standard colour neg film in reasonably bright conditions. This film has particularly good saturation in normal light so pretty happy with its performance but I have noticed that my negs are thinner and colours paler in poor light conditions such as the inside of buildings.

As processing time is standard, I presume that I could treat the film similarly to Ilford XP2 and rate it at 50 in poor light, reverting to 100 again in brighter conditions.

Second question:Rating 100 at 50 can give problems with exposures handheld. What are the losses of using Superia 200 and rating at 100 in poor light compared to using 100 and keeping it at 100. Do I get the best of both worlds of extra saturation in low light with easier handholding exposures and negligible quality loss compared to using 100 at 100?

Anyone out there with experience of rating Fuji Superia 100 at other than 100 or indeed using Superia 200 at 100? If so I would appreciate your opinions on the effect.

Unless the quality of neg begins to suffer appreciably at 200 then it may pay me to switch to 200 and rate at 100 where extra saturation and avoidance of thinness in the neg is desired. I am unlikely to want to enlarge greater than 8 x 10.
Thanks

Pentaxuser

 

[Helen B]

In general colour neg film responds very well to 'overexposure'. I'm not sure about Superia, but Kodak Ultra 100 (a misnomer - it isn't ultra-saturated) has about 13 stops of useful range and the new Fuji Pro 160S seems to be very similar in many respects. Setting your meter to half or even a quarter of the box speed tends to place your exposure closer to the middle of the film's response curve, improving shadow detail, lowering the graininess and helping with light temperature mis-match. The more exposure you give dye-image negative film, the lower the graininess. In mis-matched lighting (eg shooting daylight film in tungsten light) 'overexposing' allows all the layers to have full exposure. In the 'daylight film in tungsten light' example, the blue-sensitive layer keeps from being a horrible grainy mess while the film's overexpose latitude keeps the red-sensitive layer from being blown out in the highlights. This could be one reason for the quality difference you see between outdoor and indoor photos, and why you should set a lower EI indoors than out.

As an aside Pro 160S is available in 220 and 4x5, which Ultra 100 isn't, as far as I know. They are both superb films.

Best,
Helen

 

[Nick Zentena]

One more thing. EI tends to be a function of your equipment. Maybe your shutter is off 10%. Or your meter reads high. Using an EI instead of the box speed will give you better results. The downside is you have to put the effort into finding your EI.

 

[pentaxuser]

In general colour neg film responds very well to 'overexposure'. I'm not sure about Superia, but Kodak Ultra 100 (a misnomer - it isn't ultra-saturated) has about 13 stops of useful range and the new Fuji Pro 160S seems to be very similar in many respects. Setting your meter to half or even a quarter of the box speed tends to place your exposure closer to the middle of the film's response curve, improving shadow detail, lowering the graininess and helping with light temperature mis-match. The more exposure you give dye-image negative film, the lower the graininess. In mis-matched lighting (eg shooting daylight film in tungsten light) 'overexposing' allows all the layers to have full exposure. In the 'daylight film in tungsten light' example, the blue-sensitive layer keeps from being a horrible grainy mess while the film's overexpose latitude keeps the red-sensitive layer from being blown out in the highlights. This could be one reason for the quality difference you see between outdoor and indoor photos, and why you should set a lower EI indoors than out.

As an aside Pro 160S is available in 220 and 4x5, which Ultra 100 isn't, as far as I know. They are both superb films.

Best,
Helen

Helen. Thanks for taking the trouble to do a detailed reply. Can you indulge me a little more. Looking at those of your photos which included sky has reminded me of another problem I have on some prints but not all. I am sure that on some, the sky was blue at the time of taking but has shown up as a disappointing grey/white on the print rather like that of a B&W print with no filter and clear sky.

I had assumed that this was due to the in-camera meter metering for the foreground which was the bulk of the picture and the exposure effectively burning out the sky. I don't recall this happening ever with a polariser. This should tell me something, I feel but not sure what except that the blue sky is darkened to an extent that prevents burn out even where the sky is over exposed. If I am right about sky over exposure(no polariser) then am I also right that those negs which were OK for foreground before reducing box speed will now have an even more burned out sky in return for better saturation in foreground colours and I can expect even less blue skies by reducing film speed.

I had assumed that the cure for grey skies when there should be at least a hint of blue is either a ND grad at the taking stage or dodging the sky at the printing stage. I have seen examples of increasing sky exposure at the print stage by 50% and printing through extra yellow while dodging the rest.

Dodging and burning in colour has been more miss than hit to date and I'd rather avoid it.

The strange thing is that sometimes in negs which exposurewise seem to have been taken in almost identical circumstances, the sky has turned out OK.

So to summarise, what effect can I expect on skies if I lower box speed?

Nick. Thanks. Yes I must try and set my own EI some day for both colour and B&W as you may very well be right about a meter problem. I have a Pentax MZ7. No separate meter and I don't know how good the in-camera meter is.

Pentaxuser

 

[Mick Fagan]

Firstly, Helen I think your replys to technical questions are brilliant, this current reply is no different.

Pentaxuser, I use Fuji Reala, now called Superior Reala or something like that. I've found it's most useful true speed to be 80 ASA externally and 64ASA internally.

If you wish to push process C41 you can, it's not the greatest but it can be done, I have done it and it gets you an image. If you wish for the best possible colour reproduction then push processing isn't the go.

To push C41 1 stop, add 15 seconds. To push it 2 stops add 30 seconds and hold your breath for the results.

I have used this procedure quite a few times over the years, it's reasonably successful. In mixed lighting the colour accuracy isn't going to be brilliant so the push processing isn't noticed.

For Erin, this has been knocked off of Wikpedia and possibly is the real answer to EI (Exposure Index)

Film speed is found by referencing the Hurter & Driffield curve for the film. This is a plot of density vs. exposure (lux-s). There are typically five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. Following the curve to the point where it exceeds the base + fog by 10%, find the corresponding exposure. Dividing 0.1 into that yields the speed.

The speed is used in the Exposure Index equation to find the appropriate exposure. Four variables are available to the photographer to obtain the desired effect: light, film speed, f/#, and exposure time (shutter speed). The equation may be expressed as ratios, or, by taking the logarithm (base 2) of both sides, by addition. In this form, it was easier at the time it was proposed to put into a nomograph (slide rule) so non-scientists could obtain good results. As a result, every increment of 1 is a doubling of light intensity, known as a "stop". The f/# is the ratio between the lens focal length and aperture, which in turn is proportional to the lens area by the square root. Thus, a lens set to f/2 allows twice as much light to strike the focal plane as a lens set to f/1.4. Therefore, each increment of the square root of two (approximately 1.4) is also a stop, so lenses are typically marked in that progression: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc.

Or you can go here to see the whole article, it's short but interesting, and, presumably, reasonably accurate!

http://en.wikipedia.org/wiki/Film_speed


Mick.

 

[Mick Fagan]

I've just read the above thread in which I inserted some Wikpedia information.

"Thus, a lens set to f/2 allows twice as much light to strike the focal plane as a lens set to f/1.4".

The above sentence is to my understanding completely wrong.

It should read:-

Thus, a lens set to f/1.4 allows twice as much light to strike the focal plane as a lens set to f/2.

Somehow the figures were put in back to front, unless I'm very much mistaken.

Anyone else care to comment?

Mick.

 

[Trond]

Thus, a lens set to f/1.4 allows twice as much light to strike the focal plane as a lens set to f/2.

Should be correct now. First time I´ve edited a Wikipedia article. It´s amazing that it can work...

Trond

 

[markbb]

We were taught a b&w course, but 6 weeks is just not enough time to learn all there is to know. I don't recall my first professor mentioning this at all, however I do now remember my second professor performing this test for us,

Wow!! you get not one but two professors teaching a 6 week B&W course! That would be like Stephen Hawking running a class on wiring a plug. What college are you at?

 

[Ed Sukach]

Another way to understand the concept of "f/stop" is to calculate the AREA of the aperture. An aperture of f/1.4 ("f" is the standard symbol for focal length; divide that by the aperture diameter) has an area twice that of an aperture of f/2 -thus allowing twice the amount of light to pass.

Let's see .. mathematics:

Area of a circle = pi (radius squared)
Given a focal length of 50mm:

(3.1416 ((50mm /1.4)/2)) squared = 3147.2 sq. mm
(3.1416 ((50mm / 2.0)/2)) squared = 1542.1 sq. mm

3147.2 / 1542.1 = 2.04086 : f/1.4 lets 2.04086 times as much light through as f/2.

Same way as calculating water flowing through a pipe of "x" diameter.

 

[ErinHilburn]

No, not just two professors in six weeks its sixteen(sorry about the six rather large mistake ) weeks. The beginning photography is b&w and all photography contracts are required to take it. We only have one professor here as it is a small school in Alabama. But I also believe its one of the only schools here that offer a BFA in Photography other than montevallo. After that we take studio two which is a colorslide course, but we don't do any of our own processing or print making for that, so I am currently trying to learn how to do that on my own. After studio two I realized that it would improve my color work if I improved my b&w. The single professor we have feels that having only one professor leads to poor teaching, so he gets all these other photographers to teach classes under his name, so they aren't actually employed by the university. It was one of those photographers that I took a finite black and white course under which focused more on printmaking that the actual exposure of the film. I atted troy University. I think they just put up a design/art website if you care to see it. The photography examples are rather poor since they just threw what they had on there.

Dead Link Removed

It's really not a bad school and one of the few here in alabama that still require you to start in the dark room. I know the professor in Auburn got rid of all the darkroom equipment and they all do digital now. I recently was in their gallery and so many of the photographs were just a poor picture with bad composition that had been highly photo manipulated, so that it would appear faintly interesting.

Sorry about the mistake with 6 instead of 16 next time I'll be sure to read over what I type (; I just don't feel that's enough time. I'm in my third year at the university and still I hesitate to call myself a photographer I am never satisfied with my work and the more I see it the less I like it. I feel that I know little to nothing about my chosen field andI want to know everything. Sometimes I get irritated with the classes and the fact that they must reiterate the same things in regards to fstop, shutterspeed, ISO, and proper exposure just because so many students are so lazy and dont' want to learn and instead shoot on automatic. I've purchased several books (some of which were suggested from apug), but without the equipment to try different techiniques I dont' really know them, I just know of them.

But now that I've gone on a really long tangent and talked forever. It's two professor in two different sixteen week sessions.

-Erin

 

[Mick Fagan]

Erin, you must be doing something right if you won an award!

Mick.