"True film speed" vs just developing the film more?

[m00dawg]

Something has been bothering me a bit as of late - comments like "X film is a 400 ISO film but really it performs like a 200 ISO film". Example include Fomapan 400 (I've heard things like it is better at 200 or 320) or Pancro 400 (which to me in 4x5 tends to give me thinner negatives using stock times if I rate it at 400). I'm also confused at the notion of "full speed" developers - that feels like a function of development time to attain the rated speeds. It's a question irrespective of just erring on the side of over-exposing the film a bit or intentionally pushing and pulling film.

I guess stated another way I'm not sure the relationship in development times when developing at box speed. If I'm buying a 400 ISO film I kinda expect I should judge it, at least initially, by its box speed. So if my negatives are thin, I feel like I should add time until they are the density I'm looking for then then, if desired, I might push or pull?

Or stated a third way, what is the difference in shooting, say, Fomapan 400 at 200 over just developing it longer and expose it at the box speed? Why is one better than the other (if it is)?

Hopefully that makes sense. It's been bugging me a bit because while I like the look of Pancro 400 for instance, in the 400 range I tend to lean on speed a bit more, especially in 4x5. If I don't have to worry about speed, I tend to use TMX (which I know looks very different from Pancro). If I want to take photos of flowers and it is slightly windy for example, having to loose a stop of speed before dealing with filters and what not changes things. HP5 I feel like I know well enough to be comfortable with it at box speed and pushed (I've gone as far as 1600 in 4x5 but I suspect I could go to 3200 and get good results with my process).

This is a general question but for what it's worth I tend to use XTOL (1:1 though lately I'm experimenting with replenishment).

[mrred]

All developers will exhibit the same properties, but there is a standard developer they use to test for box speed. That said, the toe of a film curve (shadows) becomes non-linear at a certain point and will not develop more when development time is increased. That is effectively the box speed. You can develop more and the mid to higher part of the curve will increase, but the toe will always stay at that box speed.

Some developers have different levels for the toe, as such, they are called speed-increasing or speed-reduction developers.

Effective Index (or EI) is not the speed of the film, rather just what the user shot/developed the film at.

[Bruce Watson]

You seem to be confusing exposure and development. They control different things, but they do interact somewhat. Exposure controls shadow density on your negative film, while development controls highlight density.

A film's "box speed" is determined under laboratory conditions using a specific developer at specific times, temperatures, and agitation techniques. Since this is just about impossible to reproduce by any of us without the required laboratories, equipment, and controls, what it is, is a guide. A place to start.

What the Zone System (Adams and Archer) addresses is how to find your personal exposure index (PEI, or just EI), and your personal normal "N" development time for your preference of developer, time, temperature, and agitation style.

If you'll put in the work reading, understanding, and then testing, you'll end up with a system customized to your equipment and techniques that allows you to control both your shadow detail and highlight detail, accurately and (more importantly I think) repeatably.

If you don't like the Zone System, there are dozens of variants out there. There's likely a method that fits the way you want to work if you'll look for it.

BTW, there's really no such thing as "pushing" a film. Exposing the film less records less shadow detail which you can not recover in development. What you get from the increased development is mostly an increase in highlight density. This can make the film easier to print in the darkroom, and it's also responsible for the increase in "graininess" of the "pushed film". But if you look hard at the shadows in the print, you'll find them lacking shadow details. Because you underexposed the film. Pushing is more accurately described as "under exposure + over development".

[Jac@stafford.net]

Rule of thumb with B&W: over-exposing a stop is better than under-exposing. Due to variables in processing (and in my case inaccurate LF shutters), it's all revealed after processing. (My shutters are all a little slow. So am I. ) ... for processing I begin with the manufacturers' recommendation. I'm stuck in my ways and use only D-76 and Rodinal and leave exotic developers to my heroes on this forum.

[Leigh]

So if my negatives are thin, I feel like I should add time until they are the density I'm looking for...

Negatives being thin has nothing to do with EI. It's controlled entirely by development.

Shadow detail is a function of exposure and EI, and cannot be changed by development.
If information is not in the latent image, no amount of development can create it.

- Leigh

[Pere Casals]

rated speeds.

Read Beyond The Zone System book, ebay $4

Read this: https://en.wikipedia.org/wiki/Film_speed


Definition of speed:

Any film speed (with certain non ISO processing) tells you that film toe is at 3.3 stops underexposure from what an "standard" meter says, so with an spot meter you know what scene spots are in the linear part of the curve, or underexposed enough to be in the toe. It is important to understand this because this is absolutely basic.

This is becasue speed is useful: you know what scene spots will be in the toe and what spots will be "acceptably" captured because of being in the linear share.


Definition of ISO speed:

As always, if using D-76 (or equivalent in speed) and using recommended standard development time you have the toe at -3.3 from what meter recommends, but you also have the ISO standard contrast.


If a rated speed (with certain processing) don't places toe at -3.3 this is not a film speed, this is a way to say how you expose.


FOMA 400 is not a ISO 400 film, it is 400 (non ISO) speed if developed with an speed boosting developer, but it has lower ISO speed with D-76. Datasheet says that 400 speed can be reached, but they should mention with what developer.

If using a "speed" the toe is not at -3.3 then this is not a film speed, but a way to say how one exposes.

[Jac@stafford.net]

All these posts regarding nuances are largely distractions.

[Pere Casals]

All these posts regarding nuances are largely distractions.

Jac, no distraction, the speed term is used around very bad, IMHO.

In the massive development chart (with some errors) and in datasheets we have development of TMX to obtain 50, 100, 200 and 400. Only the 100 is a ISO speed. The 50, 200 and 400 are non ISO EI because contast is not standard, and film toe may not be at -3.3 stops, one thing is pushing and another one is modifying film speed.

When someone says "I rate TMX at xxx speed" he usually says nothing about film speed, if he has calibrated his process then may be he is talking about film speeds, if not he speaks about his film usage.

[m00dawg]

WOW this was a ton of good info in a really short time. Thank you thank you thank you everyone! Great things to think about. I've working my way through The Negative right now but it's a dense book and I may need to re-read it hehe. It sounds like the specific piece of the puzzle I was missing was the relationship between the toe and the box speed. That didn't click until now.

[Pere Casals]

WOW this was a ton of good info in a really short time. Thank you thank you thank you everyone! Great things to think about. I've working my way through The Negative right now but it's a dense book and I may need to re-read it hehe. It sounds like the specific piece of the puzzle I was missing was the relationship between the toe and the box speed. That didn't click until now.

Let me insist, read Beyond The Zone System, a flawless explanation about how the thing works.