Re: EI question

[Ben Kreunen <ben@xxxxxxxxxxxxxxxxxxxxxxx>]

At 02:45 AM 11/16/99 -0500, you wrote:
>In a message dated 11/15/99 4:10:07 PM Pacific Standard Time,
>mlevin@xxxxxxxxxxxxxxxx writes:
>
> > what is El?
>
>Doesn't look like anyone answered you yet... EI is Exposure Index.
>If you see a film speed on the box that is the ASA....  EI is what you shoot
>it at if you like to shoot it at a different speed.
>
>Like for 200 ASA (on the box) you might shoot it at 100 but you would call it
>EI 100 instead!  Since IR has no rating... I guess you should always call it
>EI  ;-)

Must have missed it...

Exposure Index = 3 more syllables than Film Speed, big words to impress 
people, another term to confuse the hell out of amateurs.

ASA, ISO and DIN are units of Exposure Index...

You can't quote the EI of a film without giving the units of ASA,ISO or DIN 
as well.... e.g "I expose my film at EI 20."   ASA or DIN?, there's a 2 
stop difference between them.

What you see on the box is an Exposure Index for *****a given set of 
conditions****. Since processing your own film offers more control and 
variability then it is inevitable that many people will get a different 
figure to what is on the box.

Unfortunately Kodak's product information sheets are not very consistent in 
the use of their terminology and the infrared film page could possibly be 
worded much better than it is. Some data sheets use only ASA, some use ASA 
and DIN. Most (including HIE) give recommended EIs for different conditions 
(particularly different developers for BW films).

As for HIE being unrated.... "We cannot give exact speed numbers for this 
film because the ratio of infrared to visible energy varies" Which is 
partly true and if they gave us an exact film speed then we'd all complain 
when it wasn't right.. but essentially it's a big cop out, since 
technically speaking a BW negative's film speed is measured from the shadow 
detail and there is less variation between visible and infrared reflection 
in lower light.  They also provide a table of suggested film speeds for 
some of the main filters so they do 'rate' the film, they just say that's 
their numbers are not legally binding  ;-)

EI EI O

Cheers

Ben

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