Understanding EI???

[Kirk Keyes]

Sorry Kirk,
I must have passed out.
(Did someone fart?!)

Obviously, Haiku also isn't my "Forte"

I... S... O... Yes? No?
Film, Camera, Lens Data -Why?
Art's in the E... I... !


Hope you are not too dissapointed, Kirk.


Ray

Ray - that's good!

Sorry about the fart, that could have been me....

 

[Sirius Glass]

Ray - that's good!

Sorry about the fart, that could have been me....

What?? Hoof hearted. Ice melted!

 

[Stephen Benskin]

Here are two excerpts from Phil Davis' book Beyond the Zone System, that are pertinent to some of the points discussed in this thread.

Page 94 Beyond the Zone System, fourth edition

“Because the fractional-gradient method of speed point location is difficult to implement in practice, it was important to find some simple calibration procedure. Finally, researchers concluded that when a realistic safety factor of about one stop is included in the fractional-gradient measurement procedure and when the film is developed to an average gradient value of about 0.7, the fixed-density and fractional-gradient are in close agreement. The current ANSI and ISO standards approximate this condition by specifying an exposure range of 1.3 and a density range of 0.8, with the sped point, or IDmin, located at the 0.1-over-B+F level. The average gradient of this standard curve is approximately 0.62.

It’s important to understand that the ISO speed point is only a point of reference from which the official film speed number is calculated.”

Page 95

“This final adjustment is necessary because you curve data are based on a no-flare test condition, but you’ll be applying the data to camera exposures that invariable involve significant amounts of flare.”


Steve

 

[Bill Burk]

Everyone knows that the average reader
can trust ISO on their camera meter

For average scenes the statistics are right
odds say your pictures are cheery and bright

The science is sound, you can't argue with curves
or folks who picked pictures of thousands of nerds

The standards are keyed to those excellent pictures
so the loop through psychology and science returns

The folks in the studies didn't care much for shadows
but you do, you're looking for details in blackness

So your EI is what you tested and dial into your meter,
it's beneath ISO but you know it will make your pictures better

With spotmeter you measure the dark for exposure
then the bright for the range and time in the developer

You're not pointing at gray, your scene isn't average
and you develop for times that aren't recommended

You justify this because you have something to say
you want granite that sparkles and flesh that's light gray

You want that point real black and this point nearly white
and let everything else fall where ever it might

You tested and threw out the standards all right
and pointed your camera right into the light

Now flare is your hobo, he joined for the ride
Your picture is ruined, you're buried alive

Bill

p.s. Steve, I just got the Mark VI, thanks

 

[Kirk Keyes]

Wow! How do you guys come up with these things? I'm way to analytical to think of stuff like that...

 

[markbarendt]

Good job Bill Burk!

 

[stradibarrius]

Wow...I posted this question so long ago that I had almost forgot about it but now with m flurry of questions of late this comes back into focus.
Bill you said, "With spotmeter you measure the dark for exposure then the bright for the range and time in the developer". The part of this statement that interest me is the , bright for time in the developer. How does the meter reading of the highlights correlate to a time in the developer? I understand that you expose for the shadow and develope for the highlight but how do you calculate a "development time" for a "meter reading"????

 

[Kirk Keyes]

You determine a development time based on the difference of two exposure meter readings. The meter readings give you the contrast of the scene, and the development time is based on that.

Did you ever find a copy of "Beyond the Zone System" by Phil Davis or any of the other books mentioned in this thread? They will go into more detail than you will get here...

 

[markbarendt]

How does the meter reading of the highlights correlate to a time in the developer? I understand that you expose for the shadow and develope for the highlight but how do you calculate a "development time" for a "meter reading"????

This is essentially the "Zone System" see Ansel Adams "The Negative" or a similar book for the long version.

First, you would spot meter the darkest point where you want detail on the negative, let's say the reading is f5.6@100.

That spot reading is not your camera setting, this reading is normally defined as Zone II or III. (Personal preference and metering style is the difference)

The camera setting is actually supposed to be Zone V, which is the middle gray/mid-tone of the photo you are trying to shoot. (Side note, Zone V is what incident meters are designed to read directly).

To find the camera setting, you need to offset the spot meter reading (stop down) roughly 2 or 3-stops. (I say roughly because Zones are not always equal to f-stops, that's why Ansel and his buddies used roman numerals.)

In this example the spot meter reading of f5.6@100 would be adjusted to a camera setting of say f5.6@400 or 800.

The Brightness Range is what determines development.

To find the Brightness Range you now need to spot meter the brightest point where you want detail, this is Zone VIII.

In a normal scene, and only a normal scene, f-stops and Zones are equal.

If your shadow spot reading is F5.6@100 and your highlight spot reading is f5.6@6400, a 7 stop Brightness Range, you would use normal development.

If the high reading was f5.6 at 12500 you may want to shorten your development time. If your high reading was f5.6 at 3200 you may want to increase your development time.

This method works best for sheet film because each sheet can get it's own time based on the high and low readings in a scene.

With roll film, it is tougher. Adjusting development to make one shot better affects all the other shots on the roll and not always the right way.

 

[stradibarrius]

Good explination.

 

[Chuck_P]

How does the meter reading of the highlights correlate to a time in the developer? I understand that you expose for the shadow and develope for the highlight but how do you calculate a "development time" for a "meter reading"????

Strad,

Here is an example (albeit not a great one), but an example of the use of a spot meter. From the camera's position, I metered my "important" shadow that was the trunk of the dead tree. It's reflective (luminance) value raised the needle to 9, I placed that luminance value on Zone IV.

Then I read various "important" highlight areas throughout the scene and found that the sunlight on the leaves of the forest floor and the sunlight on some of the trees had a luminance value that fell on 14 or Zone IX, 5 zones i.e. 5 meter scale numbers higher in luminance than where I placed the luminance of the shadowed tree trunk. Any other small areas that had a luminance value higher than a reading of 14 were ok with me, but I wanted the sunlight on the forest floor and that on the tree bark to be no higher than a Zone VIII print value. About the middle-left of the image there are two white dots, that's the ridge where there is a sign along the trail, I failed to see that while composing.

This is a SBR of only 6 zones. However, my high shadow placement on Zone IV pushed the luminance of the important highlights to a Zone IX negative density, where they would print without the desired texture. Therefore, I developed the negative for N-1, so that those important highlights would develop to an effective Zone VIII negative density. So, although the SBR of the scene was 6 zones from IV to IX (32:1), I developed the negative to an effective 5 zone range from IV to VIII(16:1) to accomodate those areas of the negative I want to print with the desired shadow and highlight detail.

The development time of N-1 is relative to what one determines as their "normal" time. My "normal" for this combo (TMY and D-76 1:1) is 8 min that puts the curve reaching a Zone VIII density of 1.3. So, N-1 dev would be the curve reaching a Zone IX density of 1.3----in other words, any area of the attached picture that has a luminance value of 14 (Zone IX) is developed to a negative density of 1.3. Continuing on with the example, for N-2 the curve reaches a Zone X density of 1.3-----the idea is to develop the film to the same density range.

I used an orange #21 Lee filter that brought the shadow down a bit, this is why I placed the shadow high on Zone IV----to account for an anticipated loss of some shadow density. Placing it on Zone III would have meant the filter would have brought the shadow down too low with more loss of detail than I wanted. The film was TMX with the basic exposure of 4 sec at f/64, accounting for the filter factor of 2.5x, the adjusted exposure was calculated to be 10 sec at f/64, then acounting for reciprocity, the actual exposure given was 25 sec at f/64.

I hope this helps in some way.

Chuck