Shooting "at" a Higher ISO

[JustinB]

I'm not sure if this is the right forum, but I am a little confused by the terminology. How do you know the limits of what you can do by shooting at a higher ISO. If i shot Ilford Delta 100 sheets "at" 400, I would be photographing the scene as if I was shooting ISO 400 speed film, then pushing the development 2 stops worth.

What are the practical limits to this? How fast will I just lose my highlights/shadows? How bad/good/natural does the grain structure look? Could I push Delta 100 sheets all the way to 1600? 3200?

Thanks!

[William McEwen]

Keep in mind that there's no magic to "pushing" film speed -- all you're doing is underexposing and overdeveloping.

I recommend you just commit a couple of sheets to the concept and see what happens.

[Roger Cole]

Technically you are exposing at a different EI (exposure index) not ISO. The ISO is a very specific rating.

While it's true to some extent that you aren't really "pushing" some film/developer combinations will yield somewhat (note, somewhat) different true film speeds than other developers with the same film. The practical limits depend on the film and, to a great extent, on your needs and tolerance for loss of shadow detail.

My all time favorite push for 35mm for example is Tri-X in Diafine, which yields good negatives for most of my purposes where such speed is needed when shot at EI 1600. The densitometrically minded can and have debated this at length, but the bottom line is that the speed is "real enough" (as I read someone else call it) for my purposes for candid shots and such on 35mm. If I need yet more speed it's TMAX 3200 and T-Max RS developer.

As far as I know in LF the fastest native speed available is 400. I'd definitely start with a 400 speed film rather than pushing a slower one to 400, unless long exposures bring reciprocity failure into consideration in which case some slower films (particularly Fuji Acros and TMX 100) can allow shorter exposures, even without push processing, than native 400 speed films.

[CG]

A couple of random responses to your queries.

This is the right forum.

Any change of exposure will change the amount of information that can be recorded in the deepest shadows. If you have a low contrast scene, you have the greatest chance that nothing significant will be lost.

Conversely, if you are shooting a scene with important information located at a very great range of brightnesses, you will probably lose important detail immediately if you cut exposure. In fact, with such a contrasty scene, you will possibly need to add exposure to retain important detail.

If you push film very far, the look of the film will be altered quite a bit and either you will like the look or you won't. You'll have to just try it to see. The absolute limit to the process is where there is no exposure left to be developed. Reasonably, the limit is found at some point where the destruction of the image just makes you stop. Very individual.

Grain will get big and the look you get will tend to the soot and chalk look that AA railed against. Nonetheless, the look suits some work. Check out Bill Brandt's work. Some of his images look like possibly pushed film (or darkroom printing manipulations that attain similar looks.

[Ken Lee]

If you're going to push, why not 20,000 ? Why not 100,000 ?

[CG]

Some developers are better for getting the greatest shadow detail out of a given exposure. Xtol for one. A couple of Crawley's FX series are supposed to get just a little more out of a negative.

Mind you, the most one can get from selection of a developer is on the order of one stop or less. That's it. You are talking about several stops, and with that, loss of shadow information is inevitable.

[CG]

If you're going to push, why not 20,000 ? Why not 100,000 ?

I once shot something - unintentionally - at some 10,000 or 20,000 or some similarly stupid underexposure. There wasn't a heck of a lot of anything on the neg, let alone shadow detail.

[Revolucion Artistico]

I don't have much experience with pushing sheet film but have had good luck pushing 35 and 120 Ilford films with Microphen which is basically what it was designed for.

[Roger Cole]

There isn't as often a need to push sheet film since it is almost always, in the last several decades anyway, shot from a tripod, and of subjects that are relatively stationary, though things like wind motion, moving water etc. could change that.

[ic-racer]

Shooting at a higher ISO causes under-exposure. In very simple terms, under-exposing your film will not allow enough light to activate the film in the lower intensity portions of your scene. In severe under-exposure there will be blank areas on the film where there is no image.

I suspect most people that under expose do it in cases when image tonal quality is less important than motion blur.