Over exposing C-41 film question

[Sirius Glass]

From another thread:

... It is always best to overexpose any color negative film (or B&W film for that matter) by about 1/3 stop. I use ISO 100 for Portra 160 and ISO 320 for any 400 film. This goes along with the charts that I posted a few months back regarding the first acceptable good print and which was taken from Haist.

PE

Something is not consistent here:

For 400 film, one stop would be ISO 200 and half a stop would be ISO 280. Therefore ISO 320 sounds like it would be about 1/3 stop.

For 160 film, one stop would be ISO 80 and half a stop would be ISO 112. Therefore ISO 100 sounds like it would be more than 1/2 stop over exposed! Should the ISO be around 120 to 130??

Steve

[Diapositivo]

I noticed myself the "inconsistency" and interpreted that Ron meant that 1/3 is some kind of a general rule as a minimum (any 400 exposed at 320, regardless of specific considerations). If the film requires/stands/benefits for more underrating, one underrates more, so the Portra 160 at 100 is one specific case where Ron would underrate by more than 1/3.

But that's just the way I read it. Maybe Ron meant it differently.

[Ian C]

Exposing a 160 speed film at 100 is a 2/3-stop increase.

All of the standard film speeds are 1/3-stop apart so there is no STANDARD film speed corresponding to 1/2-stop increments from one to the other.

A 2/3-stop exposure increase of a color negative film won’t hurt a thing, but it will record more printable shadow detail.

Due to the at least at least 2-stop (some sources say up to 3 stops) overexposure latitude of color negative films some uses like to routinely overexpose from 1/3 to 1 stop over to ensure a negative with plenty of printable shadow detail.

[Greg Davis]

ISO 125 is the generally accepted 1/3 stop between ISO 100 and ISO 160.

[Photo Engineer]

So I rounded!

Sorry, but that is what I expose these films at for best results. I have posted the scans and the prints here for you to see in another thread. This places the usable image in mid scale on the straight line and fits on the best part of the curve representing the maximum number of acceptable images in all scenes as published by Haist and by Mees. I've posted their graphs here as well.

And the reason I do this is because my cameras have detents for those values on the meters, and because it works. I have no detent for 112.......

There is some leeway you know!

PE

[B&Wpositive]

From another thread:


Something is not consistent here:

For 400 film, one stop would be ISO 200 and half a stop would be ISO 280. Therefore ISO 320 sounds like it would be about 1/3 stop.

For 160 film, one stop would be ISO 80 and half a stop would be ISO 112. Therefore ISO 100 sounds like it would be more than 1/2 stop over exposed! Should the ISO be around 120 to 130??

Steve

Though PE has already answered the question of why, here's another take on it:

Higher speed film traditionally was marked higher than its EI, moreso than slower film, and it often has a wider latitude as well. So overexposing higher speed film slightly more than slower film is not so far-fetched, especially if you want shadow detail. Not to mention, higher speed film tends to lose sensitivity faster and to a greater degree when it ages, compared to slower film.

If you want totally black shadows, then don't overexpose your film, period.

Personally, I tend to go by the ISO, the age of the film, and the storage conditions when guessing what EI to rate it at. Superia 1600 that's 2 years out of date and frozen gets rated at EI 500. The same film, when fresh, gets rated at EI 1000. That's one stop of plus compensation for the older film. On the other hand, Superia 200 that's fresh gets rated at EI 160, and when it's been in the fridge for a couple of years, anything lower than EI 100 seems to be overkill. So that's 2/3 stop. If I had really old high-speed color neg film I was going to shoot for artistic results (like that roll of Royal Gold 1000 I'll someday get to) I would give it more like 4 stops of plus comp, not to mention bracketing +/- 1.5.

[Sirius Glass]

So I rounded!

Sorry, but that is what I expose these films at for best results. I have posted the scans and the prints here for you to see in another thread. This places the usable image in mid scale on the straight line and fits on the best part of the curve representing the maximum number of acceptable images in all scenes as published by Haist and by Mees. I've posted their graphs here as well.

And the reason I do this is because my cameras have detents for those values on the meters, and because it works. I have no detent for 112.......

There is some leeway you know!

PE

PE,

The use of the Haist and by Mees curves is what I figured, but the inconsistancy kept me churning on this for a while.

Well as long as we can continue to discuss such questions without arguing whether or not magenta is a color.

Steve

[Sirius Glass]

Higher speed film traditionally was rated slower than marked more so than slower film, and it often had a wider latitude as well. So overexposing higher speed film slightly more than slower film is not so far-fetched, especially if you want shadow detail. Not to mention, higher speed film tends to lose sensitivity faster and to a greater degree when it ages, compared to slower film.

Well using that logic ISO 400 film should be ISO 220 and ISO 160 film should be 125. But that is not what had been suggested by PE and others. Therefore the original question.

Steve

[michaelbsc]

...I have no detent for 112.......

Bah! Cheap modern meters.

I'm gonna calibrate my eyeballs.

[Photo Engineer]

Well, not to spoil things, but early 400 speed films were actually slower than 400 and some were off balance for daylight as well. It was hard to make a 400 speed film back then! The slower you went, the closer to ISO the film was AAMOF. And, all Kodak color films were pretty much made to the same aim curve regarding latitude with the division being between professional and consumer products not between speeds. IIRC, one manufacturer actually made a 300 speed color film that was sold as 400, and the color balance was about half way between daylight and tungsten due to speed problems in one of the layers. This goes back to the 70s and 80s.

The first 400 speed film that Kodak made was in the mid 60s and used the C-22 process. It was only used internally and was never sold. It was actually about 320 - 380 and we only had it for test purposes. It used a totally different form of emulsion type than any other film before or since and no product was sold using this rare Iron sensitization. The inventor was a very good friend of mine and got a huge promotion out of the invention even though it was never used.

PE