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What is Exposure Index

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And then there's DIN, which stands for DAS IST NORM or possibly Deutsches Institut für Normung.
 
How about DIN = Deutsche Institut für Normung = German Institute for Standardization ... http://www.din.de/en

ISO film ratings include both the older ASA numbers and the DIN numbers in degrees, for example, here's how Kodak publishes the ISO for TMY: "ISO 400/27°"

These above values are determined by rigorous standardized tests. Any deviation we photographers make from this when setting our meters becomes our E.I. or personal exposure index. As PE mentions above, overexposing by 1/3-stop or a bit more (depending on the developer used) gives the photographer a bit of a safety factor and results in more usably-exposed negatives.

Doremus
 
Last edited by a moderator:
Stephen Benskin said:
No. It was the testing methodology of B&W film that changed, not the meters. The same meter needs to be able to represent B&W negative, color negative, and color reversal film. From C.N. Nelson's Safety Factors in Camera Exposure, "There are no plans for reducing the safety factor by means of a change in the calibration formula or exposure meters because there are too many meters in existence with the present calibration and because the meters are also used for color film for which no change in exposure level or film rating is required or desired."
Click to expand...

The early Weston's calculators were calibrated in 'Weston's' and are 1/3 stop away from ASA (and ISO). All II and earlier some III maybe!

Yes they changed the testing but also removed a stop of safety factor.

HP3 in your camera magically changed from 200 ASA to 400, if you thought that was a good idea...
 
Xmas said:
The early Weston's calculators were calibrated in 'Weston's' and are 1/3 stop away from ASA (and ISO). All II and earlier some III maybe!

Yes they changed the testing but also removed a stop of safety factor.

HP3 in your camera magically changed from 200 ASA to 400, if you thought that was a good idea...
Click to expand...

You say magic. I say scientifically reevaluate.
 
Xmas said:
The early Weston's calculators were calibrated in 'Weston's' and are 1/3 stop away from ASA (and ISO). All II and earlier some III maybe!

Yes they changed the testing but also removed a stop of safety factor.

HP3 in your camera magically changed from 200 ASA to 400, if you thought that was a good idea...
Click to expand...

Stephen Benskin said:
You say magic. I say scientifically reevaluate.
Click to expand...

Xmas said:
Removing a safety factor to ensure more negatives would be underexposed seems like magic to me, YMMV.
Click to expand...

Rather than under exposed, more like the sensitivity range was expanded and developers were changed to help effect it.
 
Good, because that is what was done.

With the new sensitizations, the same emulsion could gain 1 - 2 stops. If you do that, you can extend the range or you can keep the range and improve sharpness using acutance dyes. If you extend the range, then grain goes down and you move all 3 parameters up the speed, grain and sharpness ladder. This is virtually impossible to do without control of the emulsion itself. In other words, a process change does not move all 3 except under very special circumstances. So, there is no magic bullet.

PE
 
Xmas said:
The early Weston's calculators were calibrated in 'Weston's' and are 1/3 stop away from ASA (and ISO). All II and earlier some III maybe!

Yes they changed the testing but also removed a stop of safety factor.

HP3 in your camera magically changed from 200 ASA to 400, if you thought that was a good idea...
Click to expand...

This got me to thinking... it's not that Weston film speeds are 1/3 stop away from ASA... even Wikipedia explains in footnote 21, Weston speeds are measured well up on the curve... They do not directly relate to ASA speeds and never did because of the significant difference between the speed determining methods.

But if you want to use the calculator dial on a meter calibrated in Weston film speeds, with ASA film speed numbers... you will get the f/stops and shutter speeds for the Candlepower indicated on the needle (assuming the Candlepower reading is correct)... if you take 1/3 stop (or 2/3 stop on my sample Weston Master II - there must be different variations) off the ASA numbers.
 
Why don't you guys read Hanson (revised edition) or Haist?!

It reminds me of people debating brain surgery! :D

PE
 
I always find it impressive when in response to an observation, someone is able to point to a relevant reference - and one where page 711 is just past halfway through!

Thanks for the link to Mees​ - bookmarked!
 
Thanks MattKing,

I cheated a bit. I have the book. Flipping through a real book is a lot easier than navigating an electronic edition.

As for my thinking I see Weston speed of 80 for TMAX 100, I think I was too hasty and should double-check my sensitometer calibration.

Looking at other historic film speeds in Weston and ASA terms, it seems the Weston speeds were close to pre-1960 ASA speeds.

http://www.prc68.com/I/Images/Weston650-03b.jpg
 
Bill Burk said:
This got me to thinking... it's not that Weston film speeds are 1/3 stop away from ASA... even Wikipedia explains in footnote 21, Weston speeds are measured well up on the curve... They do not directly relate to ASA speeds and never did because of the significant difference between the speed determining methods.

But if you want to use the calculator dial on a meter calibrated in Weston film speeds, with ASA film speed numbers... you will get the f/stops and shutter speeds for the Candlepower indicated on the needle (assuming the Candlepower reading is correct)... if you take 1/3 stop (or 2/3 stop on my sample Weston Master II - there must be different variations) off the ASA numbers.
Click to expand...

The II and III are usable if you adjust the ISO by 1/3 of a stop dependent on serial number of III as late III are calibrated in ASA though they still say Weston!

I'll check this later.

Yes Weston's were measured different but the calculator is merely a circular slide rule with log calibrations.

Invercone on brides nose with kchrome 25 always worked!

My Weston meters are within 1/3 of a stop of a dissimilar reference.
 
Photo Engineer said:
Good, because that is what was done.

With the new sensitizations, the same emulsion could gain 1 - 2 stops. If you do that, you can extend the range or you can keep the range and improve sharpness using acutance dyes. If you extend the range, then grain goes down and you move all 3 parameters up the speed, grain and sharpness ladder. This is virtually impossible to do without control of the emulsion itself. In other words, a process change does not move all 3 except under very special circumstances. So, there is no magic bullet.

PE
Click to expand...

Hi Ron

Yes I've read about eg the Ge sensitising around WWII and later Trix to Tx.

But in 1961 the photo mags said the ASA standard has changed (only) for mono and eg Ilford HP3 will now be metered at 400 ASA (ISO) instead of 200, but stocks in shops will be still 200 for a while.

So you should set your meter to 400 even if it says 200 on carton.

I had a cassette on HP3 in camera and a meter I only used for kchrome, so I did not change, I like silver in shadows.

The ASA pre and post 61 was and is predominantly toe speed based.

If I'm taking a static scene I'll meter for zone1... Very rare.

Noel
 
I'm having to assume that there was a time of change over to new stocks with new emulsions. IDK for sure. I know that what we shoot today puts us pretty much on the same curve as before at the same point with either ASA or ISO.

But, with better pictures.

PE
 
Welcome to APUG
 
Sorry, that was a 'typo". Although Hanson has a book (Evans, Hanson and Brewer) it is all color photography.

What I meant was Mees or Mees and James. Mees is the Revised edition. There are no inexpensive copies of Haist AFAIK, but it can be found in libraries.

Sorry.

PE
 
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