help understanding ISO settings?

[stradibarrius]

I am a recent convert from digital to film and am trying to learn and understand some of the discussions I have been reading.
In B&W circles it seems that people of comments about the speed rating of film and shooting it at some ISO other than what is on the "box".
EX. shooting ISO 100 at 50 or 64.

Can you please explain what this means and how is it determined?
Thanks
Barry

 

[Steve Smith]

If you shoot ISO 100 film at EI 50, you are overexposing by one stop. In other words, giving it twice as much light as it would get at ISO 100.

To compensate, development time is usually cut by 25% to prevent the negatives from getting too dense.

This can have the advantage of increasing the shadow detail. The downside is that a longer exposure is needed.

This is often the result of 'finding your personal EI' for a film. i.e. working out what film speed works best for you.

I often use Ilford HP5+ at EI 200 for this reason.

There is a good article here: Dead Link Removed

And my nowhere near as good explanation here: http://www.freewebs.com/stevesmithphoto/personal.html


Steve.

 

[John Koehrer]

ISO is the manufacturers tested film speed. Many people think they tend to be optimistic or fast.
What you are talking about is adjusting the film speed to give better exposure with your particular developing techniques. When you change from the mfrs. rating the speed is no longer ISO but becomes your EI/exposure index.
Some simple tests are required to determine this speed. There's another thread discussing this same topic just below.
Wh

 

[JBrunner]

When tested PlusX for example doesn't reach 125 in PMK. Comes in at about 80 for me, in PMK with my agitation, temp, paper, etc. On top of that I prefer dense negative because of how I print, so I rate it a 64, one stop less than box speed. In a Kodak developer with proper agitation it may well deliver 125. It never hurts to slightly overexpose B&W film anyway, and if you are going to error, overexposure is the way to go, quite the opposite of the other technology.

There are various ways to test for a film speed/paper combination, some more complex than others. It can be as simple as reducing the speed rating of the film for individual frames across a roll of the same subject and lighting and deciding what negative you like the best, or as complicated as shooting grey cards and using a densitometer and printing tests, Zone System or BTZS (Beyond the Zone System).

 

[naeroscatu]

I have just completed the tests for Kodak Tri-X 400 Pro tailored to my camera/ lens/ light meter/ film developer/ enlarger/ paper deveolper...etc and my EI came out to be 160. I also got a personal development time different than the one recommended by Kodak.

 

[Jeff Searust]

A. The box lies.
B. You can move speed up or down in development.
C. Sometimes you want over or under exposure.

 

[stradibarrius]

If, for example if I were shooting Tri-X 400 and set the ISO in the camera at 200 would I still meter the same and set the shutter speed the same as if I were actually shooting at ISO400?

 

[JBrunner]

No, because you are rating it at 200. 400 is out the window.

 

[Thomas Bertilsson]

The film is tested in lab conditions, and under those conditions the negative will yield sufficient shadow detail and excellent tonal rendition all the way to the highlights and without blocking up the highlights. Basically, a 'technically' perfect negative.
This is when the Exposure Index (EI) is the same as the box speed, or ISO rating.
When you develop film, the conditions are almost invariably different than those in the lab setting, and if you expose the film at an exposure index you may, or may not, get sufficient shadow detail. If you don't get enough at EI 400, you need to feed more light to the film. So in this case you would change your EI to whatever 'speed' would yield the appropriate amount of shadow detail you want/need for your ideals.

Many things dictate this:
1. Light meter variations
2. Use of light meter variations
3. Lighting conditions
4. Camera shutter accuracy
5. Camera lens aperture accuracy
6. Your water quality
7. Chemistry used while developing
8. Developer temperature
9. Developer agitation technique
10. Any random factor in between those steps.

Look at the ISO rating as a recommendation. Then find out what works for you and shoot the film at that exposure index.

For me and the developer/technique I use, I actually can shoot Kodak Tri-X at an EI of 400 with results that are perfect for my use. Many other photographers will shoot it at 320, 200, 160. I've heard of people shooting it at EI 50 - because it yields a negative that works for their process.

I hope that helps in explaining it. Have fun with this, it is a real joy to work with film.

- Thomas

If, for example if I were shooting Tri-X 400 and set the ISO in the camera at 200 would I still meter the same and set the shutter speed the same as if I were actually shooting at ISO400?

 

[stradibarrius]

So with the given example above, how would you determine exposure? 200 is one stop slower than 400 so would I overexpose by 1 stop?

 

[Thomas Bertilsson]

Yes. EI 200 is one stop slower than EI 400. If you have a separate meter, set it to 200 and shoot away according to its reading. If it's built into the camera, there should be a setting where you can change the film speed to 200 manually. If not - do as you say, just open up a stop, or double the time.

- Thomas

 

[stradibarrius]

I'm shooting a Nikon F-100 and I manually set the ISO value. So if I manually set the ISO to 200 then the meter in the camera will work accordingly??? I shoot everything manual. I set my ISO, Shutter speed, F/stop. I never use any of the auto settings.

 

[naeroscatu]

Yes, basically that is what you do, overexpose one stop if shooting Tri-X at ISO 200. Depending on the subject contrast you may develop the film at manufacturer time or even less. For high contrast scene I would cut development time by 20-25% (that is more than 3 stops between your shadows and highlights). This is a general recommendation that may improve your results but however to get consistently good exposures you need to do some film tests.

 

[JBrunner]

So with the given example above, how would you determine exposure? 200 is one stop slower than 400 so would I overexpose by 1 stop?

Your film isn't 400 speed film anymore, because you are rating it at 200, so you shoot it as a 200 speed film, setting your meter or the camera meter to 200. If you rate it at 200 and overexpose it one stop, you have exposed it as 100. When you change the speed rating of a film, thats what you have done, giving it a new number. It's the same as rating 400 and over exposing one stop, but it is just easier to call it 200 and expose correctly for the speed.

 

[stradibarrius]

Thanks everyone! I know a lot of this will be learned by experience, but I am trying to cut the learning curve and needless wasting of film...
The novice folks ask a lot questions that are tedious for the experienced guys.

 

[Thomas Bertilsson]

But wasting film is what keeps film alive! Please dumb yourself down instead and shoot lots of film to learn!

And, we all had to learn it one way or another at some point. A lot about photography is acquired knowledge. Very little is automatic.

 

[removed-user-1]

"Wasting film" is the best way to learn! Get a bunch of rolls of film and accept that you'll make some mistakes. If you keep notes, you'll soon know what works for you.

 

[naeroscatu]

Amen to what Thomas said. I tried all kinds of shortcuts not because I'm lazy but because I have a 9-5 job and have limited time for my hobby. I wasn't happy until I started serious testing following the book workshops. Ultimately there is no substitute for experience and that you get by burning film/ paper. cheers

 

[removed account4]

hey barry

ask as many questions as you want !
a lot of people learn from whatever questions are asked.
(and you may even get a retired pro to cross swords with another! )

the whole thing about box speed is that the companies that make film
have a lab with perfect conditions --- real life isn't as perfect as a lab
another way you can figure out what speed you and your camera and your processing likes best
is to bracket your exposures. still shoot it at 400 asa, but over expose all your exposures by 2 stops, 1 stop, expose right on, then under expose by 1 stop and then 2 stops.

after you process your film, you will be able to see what works best for you, and then whenever you use that particular film
you will set your asa in camera to whatever asa you chose to be best for you.

bracketing can be your best friend!

 

[stradibarrius]

I agree with the real experience thing. I am a violin maker and on some of the forums that I frequent the folks that are trying to learn ask lots of questions, but there is a point that you have to make some sawdust to find out how to use the information you were given.

 

[MattKing]

Film with an ISO of 400, doesn't change because you use it in a different way. It will always be ISO 400 - i.e. it will always have the same sensitivity to light.

What you are doing when you change the setting on your camera to EI 200 (or EI 640) is adjusting how your camera and film respond to various lighting situations. You are tailoring how you use the meter, to:
1) how you see things (because that affects how you meter),
2) how your meter reads thing,
3) how your camera's shutter and aperture performs,
4) how your developing routine works, and
5) how you print (or scan).

In other words, the EI you choose relates to all the factors external to the film itself, as much as it relates to the film itself.

This is not to say that different films don't respond in different ways to those external factors. That is why you need to determine individual EIs for individual films.

Matt

P.S. By the way, I try not to refer to film "speed" when I have these discussions. I think it tends to confuse those who haven't been shooting for quite a while, and therefore don't automatically correlate light levels and appropriate shutter speeds. Sensitivity to light is a literal alternative that I prefer to use.

 

[Steve Smith]

P.S. By the way, I try not to refer to film "speed" when I have these discussions. I think it tends to confuse those who haven't been shooting for quite a while, and therefore don't automatically correlate light levels and appropriate shutter speeds. Sensitivity to light is a literal alternative that I prefer to use.

That's a good point. I tend to use ISO for the film's stated speed and EI for any other speed assigned to it. This may be even more confusing for beginners.


Steve.

 

[Anscojohn]

Thanks everyone! I know a lot of this will be learned by experience, but I am trying to cut the learning curve and needless wasting of film...
The novice folks ask a lot questions that are tedious for the experienced guys.

******
Hey Strad, Those violin makers didn't just start hacking and glueing and come up with a decent-performing strad: as others have said, there IS a learning curve and you are absolutely, positively, on the right track with your approach--keep at it.
Someone in the group (or perhaps more than one) told you a vital, necessary fact: please inscribe it on your consciousness: an ISO rating and an EI (Exposure Index) are usually different numbers.

Rest assured, this harrumphing darkroom dinosaur will send curses, hexes, and plagues upon you if you ever write something like: "I am shooting TRI-X at ISO (whatever number other than 400)."

If you do not set your meter at the box rating you are not shooting at the ISO rating, as others have said. Good luck and good shooting at whatever EI you establish for your work.

 

[markbarendt]

Hey Barry,

Good to "see" you here at APUG!

I had a tough time with this concept when I switched back to film too, a couple of things helped me.

First was coming to understand that film and digital were truly different.

Please don't consider this a patronizing statement, the simplicity of the difference is easy to miss!

Digital is an electronic process; film is a chemical process.

Second was understanding that the ISO rating of a film is determined by the Film/Developer combo.

This is straight from Kodak's data sheet for P3200

KODAK PROFESSIONAL T-MAX P3200 Film is specially designed to be used as a multi-speed film. The speed you use depends on your application; make tests to determine the appropriate speed.
The nominal speed is EI 1000 when the film is processed in KODAK PROFESSIONAL T-MAX Developer or KODAK PROFESSIONAL T-MAX RS Developer and Replenisher, or EI 800 when it is processed in other Kodak
black-and-white developers. It was determined in a manner published in ISO standards. For ease in calculating exposure and for consistency with the commonly used scale of film-speed numbers, the nominal speed has been
rounded to EI 800.

Since film is chemically based the rating, EI, can be manipulated by changing the process we can manipulate our film's results.

Third was a practical issue. With digital I was taught to protect the highlights and let the shadows fall where they may because of digitals limited range.

Negatives are different, protecting the shadows you want when your shooting becomes the priority because there is normally plenty of headroom for the highlights. Controlled overexposure is protective, not destructive as it is with digital.

Forth, "Rating" your film is simply adjusting to the way you and your camera see things and to the process you are using. The goal here is being able to produce consistently the desired results.

 

[Stephen Benskin]

Mark,

Don't let the terminology fool you. Exposure Index can mean one of two things. It can be referring to the effective film speed which is the speed of the film under the conditions of use (ie developer/film combination). It can also be referring only to the setting of the camera. With TMZ (P3200) and in most cases, it's the latter.

Steve