Film test results

[macandal]

Mario, I'd be very cautious before choosing EI 160 for a 100-speed film.

Yes, Bill, I know. That's why I don't want to go any further with the testing until I'm certain I got it right.

So, Bill, what do you suggest I do? I don't want to keep experimenting with this film because it is not cheap, so I want to make sure that the next time I test, I get it right. My professor in a zone system class I took a while back used a Zone II method (as opposed to Ansel's zone I method) of testing.

So what could I have done wrong? Did I develop too long? However, that's what Ilford recommends for this film/developer/temperature combination. I thought that was the starting point of any zone testing: the recommended time for the combination.

Hmmm? What to do?

Thanks.

[macandal]

1. place a black card in shade
2. meter it
3. close down 4 stops (zone 1)
4. focus at infinity
5. make the exposure
6. develop normally
7. read the negative on the densitometer
8. note where the reading is in relation to film base plus fog
9. If not .10 above interpolate by 1/3 stops (remembering that .30 on densitometer equals 1 stop - exposure is recorded in terms logarithms and the log of 2 is .30)

This sounds like the testing I did.

[Leigh]

1. place a black card in shade
2. meter it
3. close down 4 stops (zone 1)

Solid black is Zone 0, not Zone 1.

If you make that correction, the OP's speed works out to be 80, not 160.

- Leigh

[Leigh]

Hi Leigh,
I'd be very cautious before choosing EI 160 for a 100-speed film.

Hi Bill,

I would be suspicious also.

That's why I made the correction in post #23, which puts the ASA right where it belongs at 80.

However, as I said earlier, the only real test is to go out and shoot stuff, and evaluate the results.

- Leigh

[ic-racer]

This sounds like the testing I did.

If everything checks out your personal EI is what it is. You, of course, did not do an ISO test. The reason one tests for EI is to take into account the way you meter and slow shutters, and meters that are off etc.

I'd just double check it with your next batch of film before you do your development tests. That is, shoot a few different uniform objects in different lighting conditions and place them on zone I. See that you densities are still around 0.1 log d on the processed film.

[Bill Burk]

Solid black is Zone 0, not Zone 1.

If you make that correction, the OP's speed works out to be 80, not 160.

- Leigh

No, that's not it, anything you meter becomes Zone V.

[Bill Burk]

Leaf shutter speeds are calibrated to include the whole bell curve of illumination that happens during opening and closing fully. At f/29, your shutter speed is longer than the shutter speed would be at f/5.6, because the entire aperture at f/29 is opened very quickly.

Maybe your shutter speed is effectively 1/40 second at f/29... If so, the exposure index you found, EI 160, compensates for the exposures you make at the shutter speed and f/stop combination of 1/60 and f/29. This would be a valid interpretation of your test results. I say you have good test process but the test steps you followed lead to results that are valid for that specific shutter speed and f/stop only.

I recommend that you use EI 100 for other f/stop and shutter speed combinations when you develop for 12 minutes. If you develop for less than say, 10 minutes, to pick an arbitrary cutoff, use EI 80.

[macandal]

Maybe your shutter speed is effectively 1/40 second at f/29... If so, the exposure index you found, EI 160, compensates for the exposures you make at the shutter speed and f/stop combination of 1/60 and f/29. This would be a valid interpretation of your test results. I say you have good test process but the test steps you followed lead to results that are valid for that specific shutter speed and f/stop only.

I recommend that you use EI 100 for other f/stop and shutter speed combinations when you develop for 12 minutes. If you develop for less than say, 10 minutes, to pick an arbitrary cutoff, use EI 80.

Bill I used neither f/29 nor 1/40 of a second?

[konakoa]

Mario, just re-run the film speed test with a single sheet of film and your meter rated at 160. If you get 0.1 on the densitometer, the test is valid.

For what it's worth, on my medium format Mamiya RZ camera I also rate ISO 100 films at 160.

[Kevin J. Kolosky]

Solid black is Zone 0, not Zone 1.

If you make that correction, the OP's speed works out to be 80, not 160.

- Leigh

solid black is film base plus fog. zone 1 is .10 above film base plus fog. Thus, solid black is zone 0, and zone 1 is .10 above film base plus fog, and is the speed point for a determination of the ISO speed. Basically, zone 1 is about 1/3 of a stop above film base plus fog, although down on the toe the film doesn't behave in a linear fashion. (you'd need calculus to calculate the derivative instead of a linear slope)

closing down from zone 5 (assuming the meter is properly calibrated for a true middle gray and one is using a 10 zone system) for 4 stops is 4, 3, 2, 1. Zone 1.