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Connor Adam

Difference between EI and ASA/ISO?

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Hey,

 

I was reading through Kodak's 'The Essential Reference Guide for Filmmakers' and came across the following:


A word about film speeds

You probably know that motion picture films use exposure index (EI) to indicate speed. Although similar, EI is not the same as the ASA or ISO speed used for still films. EI denotes a somewhat conservative figure related to the higher quality requirements of motion picture film that must be projected onto a large screen. Typically the EI speed is about one stop lower than ASA or ISO. EI 500 film, therefore, is the equivalent of ASA/ISO 1000.

 

Is anyone able to develop further on this? It is the first time I've come across the concept that EI is not the same as ISO. If I take what is written literally, does this mean that I should be setting my light meter to read at 500 instead of 250 (assuming I am shooting on say 250D stock) to get correct exposure?

All the best,
Connor

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exposure index means the actual speed where you rate the film. You can rate for example ISO500 film to EI 1000 by under exposing 1 stop and push processing ( EI is "speed setting" as opposed to ISO which is "speed rating" ) .

 

You can also rate for example a 200 ISO film to EI 400 and process normal, then you would lose some shadow information and gain some highlight information because you would underexpose the film by 1 stop. If you correct it later in scanning/printing/color correction to normal brightness (pushing one stop in printing) you would have more visible grain and maybe lost more or less one stop of shadow information

 

if the film manufacturer rates the 1000 ISO film EI500 it means they recommend to expose it to that speed to get well balanced image (desired color/grain, shadow/highlight balance, etc. if normal processed) . you can rate the ISO1000 EI500 film to which ever setting you want but that affects hugely the film's response .

If you want the basic image the film manufacturer intended you will set the meter to the EI they recommended, if for example EI500 then you have to set your meter to ISO500.

Edited by aapo lettinen

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Well that is exceedingly confusing. The short answer is no. If you look up the technical information for 250D (http://motion.kodak.com/motion/uploadedFiles/Kodak/motion/Products/Camera_Films/Color_Negative/tech_data/TI5207.pdf), under Exposure it reads:

Exposure Indexes

Daylight (5500K): 250

Tungsten (3200K): 64 (with 80A filter)

Use these indexes with incident- or reflected-light exposure meters and cameras marked for ISO or ASA speeds or exposure indexes. These indexes apply for meter readings of average subjects made from the camera position or for readings made from a gray card of 18-percent reflectance held close to and in front of the subject. For unusually light- or dark-colored subjects, decrease or increase the exposure indicated by the meter accordingly.

 

 

Further down it has a table of exposure corrections for color balance and clearly lists the Exposure Index at 250. So I don't know! I do know that box speed for 250D is 250, but hopefully someone else has an idea about what the deal with everything else is.

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Many thanks for your help. I think I understand the concept now, although still a little confused as to the statement they make saying 'EI 500 film, therefore, is the equivalent of ASA/ISO 1000'.

Perhaps Kodak are referring to a recommendation to overexpose film by a stop?

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Many thanks for your help. I think I understand the concept now, although still a little confused as to the statement they make saying 'EI 500 film, therefore, is the equivalent of ASA/ISO 1000'.

 

Perhaps Kodak are referring to a recommendation to overexpose film by a stop?

 

ISO is the modern standard, ASA was the older standard, and the standard states 'thus and such' about how to determine the speed.

 

An 'exposure index' is the value one uses for setting the meter. It can match the ISO/ASA value, but can be used to 'change' the camera settings, such as 'under expose', or 'over' depending.

 

So, if I use a film with an ISO rating of 400, and I set my Exposure Index to 800, I have 'under exposed' the film by 1 stop. Or if I notice that my meter yields exposures that are 'too thin', I can set my Exposure Index to 200 and compensate for the apparent underexposure.

 

Underexposure could be due to a creative choice, or just because the f-stop on the lens or the shutter speed is off, and heck, the meter could be off as well... if each item is off by 1/3 stop in the same direction I could end up with a full stop of 'underexposure' due to that.

 

In 'creative choices' one can chose to 'underexpose' and push the development process, yielding a specific effect. Likewise one can 'over expose' and 'pull' the development by one stop, yielding a different 'look'...

Edited by John E Clark

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Josh, of course. Typo on my part!

 

Thanks John - a clear explanation. I just wasn't aware that exposure index describes where the exposure is set, opposed to the sensitivity (or ISO/ASA rating) of the stock/sensor.

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Exposure Index is more or less the same as ISO except that the value has been tweaked by the manufacturer so that the customer will get optimal results. In other words, E.I. freed the manufacturers from listing the actual measured ISO value so that they could suggest a rating that they thought would work better for that stock.

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At the end of the day, if you use the tungsten or daylight ratings on the film can as your reference and compensate (for filtration, overexposure, etc.) from there, you'll be fine.

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At the end of the day, if you use the tungsten or daylight ratings on the film can as your reference and compensate (for filtration, overexposure, etc.) from there, you'll be fine.

 

I use to rate Tri-X at ASA 200... but I always shot color at the manufacturer's rating... I never developed color, except as a school exercise. With color there were just too many variables, chemical temperatures, then in the printing dialing in different amounts of color correction, with out the benefit of a analyzer... for the few prints I did do, it was hours of waving filters of various strengths over the test print... ok... I'd burn up 20 sheets of B&W paper on a print... but color struck me as more tedious...

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I recently found this out. I shot a roll of Plus X a few months back and the scan they did came out extremely hot or brighter then it should be. I used my 35mm film camera for the meter and I thought the EI was the same as ISO, so I exposed for 80 ISO. Since the film was B&W, should I have set the film camera to 160? Its funny as the still film is 125.

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I’m going to discredit the pamphlet cited. It contains an image of a box of EASTMAN KODACOLOR SAFETY FILM, dated 1923, on page 5. Kodacolor was not presented earlier than 1928. On page 6 we read that Reverend Hannibal Goodwin should have made his epochal invention in England. Goodwin never set foot to England.

On page 7 comes a blatant lie: “Eastman purchased the right to use that patent in 1888, and introduced the Kodak Brownie camera the following year.” Exactly not, it took a decision of the U. S. Circuit Court of Appeals to end the legal battle between Eastman and Goodwin’s successors, that was in 1914. And so the text goes on full of untruth. The film Dickson received from Eastman was not perforated. Eastman films were sold perforated for the first time in 1900. Until 1910 the EKC was on constant search for good perforating equipment.

“A hand crank drove the Kinetograph camera. It was determined that a frame rate of about sixteen images per second would yield satisfactory moving pictures when viewed.” Wrong and wrong again. Kinetograph and Kinetoscope were both driven by electric motors. The taking speed and reproduction were at the pace of 46 frames per second. The Kinetograph camera does not make eight exposures per turn of a crank since there is no crank and there is no 8-to-1 ratio shaft.

“On May 20, 1891, Edison demonstrated his projector for the first time when delegates from the National Federation of Women's Clubs visited the company’s research laboratory.” The Kinetoscope isn’t a projector.

“1894 Chicago Exposition” should read World’s Columbian Exposition of 1893.

I’m stopping here. Exposure index is another Eastman-Kodak pomposity. Unnecessary. What you want to know are the developer formula and the processing method, basically manual or machine. There are a number of standard developing methods, brush, immersion still, immersion agitated, hangers. If you want to learn about them, read up on Hurter & Driffield, DIN, Scheiner, Weston, Jones-Russel ASA.

 

Although our information is false we do not vouch for it.

Eric Satie

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14 hours ago, Scott Pickering said:

I recently found this out. I shot a roll of Plus X a few months back and the scan they did came out extremely hot or brighter then it should be. I used my 35mm film camera for the meter and I thought the EI was the same as ISO, so I exposed for 80 ISO. Since the film was B&W, should I have set the film camera to 160? Its funny as the still film is 125.

B&W stock is 1/3 faster in daylight balance but the truth is that if your negative is denser than normal, that could easily be due to processing, not the sensitivity of the stock.  Especially if the b&w stock was processed with a formula optimized for a different b&w stock. Or you overexposed by accident. Or the scanner was misadjusted.  That's the issue with film, there are so many steps where something could be done wrong, from manufacturing to exposing to processing to printing to scanning, etc., before you see the image.

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As far as I know there are no ISO standards for motion picture film speed, except for non-professional colour reversal camera films, that are treated in ISO 2240 (Photography — Colour reversal camera films — Determination of ISO speed), which in the 'scope' section says: 'It also applies to 8 mm and 16 mm motion-picture films used in non-professional applications. This International Standard is not applicable to professional motion-picture films regardless of their applications'.

The standard for determining film speed for colour negative film is ISO 5800 (Photography — Colour negative films for still photography — Determination of ISO speed), which in the 'scope' section says: 'does not apply to colour negative films for motion-picture and aerial photography or for making intermediate negatives', and for black-and-white negative films is ISO 6 (Photography — Black-and-white pictorial still camera negative film/process systems — Determination of ISO speed), which in the 'scope' section says: 'does not apply to motion picture, aerial photography, graphic arts, radiographic or micrographic applications, nor to negatives produced in diffusion transfer systems'.

And AFAIK there's also no ISO standard for black and white reversal.

So that's why is correct to speak about EI in cinematography, and not about ISO or ASA (which was the old american standard).

ASA speed is numerically speaking, basically the same as ISO speed: only the way of determining it changed a little. 

Simply speaking, when a stock is rated EI 200, I set my lightmeter to ASA 200. It is because mine it's an old one: if it was newer it would have an ISO scale, and I'd set to ISO 200/24°.

And since ISO 2240 applies for non-professional colour reversal, here's why on old super8 K40 cartridge you could read ASA speed (and maybe, on more recent Kodachrome also ISO speed - who remembers it?). On modern Super8 E100 speed is rated in EI, probably because today is considered a 'professional' stock.

You can search (and read) ISO standards here: https://www.iso.org/obp/ui/

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