Determining ISO - Adjusting 'Box Speed'

[adamc]

I am wondering about rating film at an ISO other than 'box speed'. Am I correct in assuming that this is a simplified version of the zone system? Do you gain more contrast control? If I was to determine that my box of ISO 4oo is to be rated at 200, do I then set the in-camera meter at 200 and go about metering as normal while adjusting my development times?

Thanks,
Adam

 

[dpurdy]

Yes. Normally a person comes to that decision from using a meter that allows reading zone 1, or threshold of exposure. Or by judging subjectively whether there is sufficient shadow detail in prints or scans on a regular basis. Lowering the ISO rating should give more shadow detail.

 

[zenrhino]

Adam, if you get the chance to take any classes from Peter Latner (not sure if he still teaches at MCAD anymore), he'll have you do just that first thing. As I recall, he made it a big enough pain that switching film/camera/meters was no longer a fun distraction.

 

[bdial]

Testing your film speed in itself is not a simplified version of the zone system. While it is part of making use of the zone system, the point is to determine what the the film speed is given your equipment, metering technique, and processing methods/chemistry, since that is different than what the manufacturer used to determine the speed.
Once you know the proper speed for your equipment and methods, you can make use of the rest of the zone system or not. But having done it you should achieve more consistency in your exposures.
To answer your other question, yes, once you determine that film x is speed y, then you set your meter to speed y, regardless of what the box says, as long as you're using the same film, developer and methods you used to determine the speed in the first place.

 

[ic-racer]

I am wondering about rating film at an ISO other than 'box speed'. Do you gain more contrast control?

No.

If I was to determine that my box of ISO 4oo is to be rated at 200, do I then set the in-camera meter at 200 and go about metering as normal while adjusting my development times?

Yes

 

[Anscojohn]

I am wondering about rating film at an ISO other than 'box speed'. Am I correct in assuming that this is a simplified version of the zone system? Do you gain more contrast control? If I was to determine that my box of ISO 4oo is to be rated at 200, do I then set the in-camera meter at 200 and go about metering as normal while adjusting my development times?
*******
Adam,
One cannot go wrong getting a bit more exposure on a black and white negative than is called for by settings at "box speed." In my experience, the key is then developing your film so to bring on the shadow detail; give well-separated mid-tones, so as not to block up the highlights.
Some film developers are more "forgiving" than others in this respect.
Regarding "zone system:" there is no doubt in my mind that a complete control of negative exposure and development results in the greatest number of "good" negatives. There is, equally, no doubt in my mind, that the amount of testing needed for that complete control is beyond my interest. Each lens I own has slightly different transmission characteristics; each camera has shutter speeds with variations between itself and it's litter mates.
As I am not a compulsive personality, I refuse to spend the time and effort necessary for that kind of complete testing. What I learned early on with some of that testing is that Eastman's old notion of the "safety factor" in it's box-speed ratings has considerable merit. There are others around APUG who remember when Eastman rerated all it's films back in the late 1950s, or so. Tri-X went from being an ASA 200 film to an ASA 400 film.
For this shooter, Tri-X is still a "200 speed" film. To keep my life simple, I routinely use an Exposure Index of one half the ISO rating; and I soup in a soft-working film developer: D23; Rodinal; extra dilute HC110; Edwal FG-7.
Thoreau had it right: "Simplify; simplify."

 

[Q.G.]

I am wondering about rating film at an ISO other than 'box speed'. Do you gain more contrast control?

No.

You do, if you adjust development times as well.
Which you may need, whether you want to or not, when you start changing the ISO speed.

So i would say: yes.