Finding the correct IE for film, changing film speed vs developing time.

I have been thinking and why do people that develop there self, change the iso of a film, like 400 to 250, instead of shoot at 400 and developing the film longer? This has always intrigued me. There is probably a simple answer, if there is I would like to know. You would still be getting the shadow detail.

Is it just 2 different ways to the same answer?

It seams to me like developing longer would be a better answer then changing the iso of the film.

Decreasing the EI you meter at increases the shadow detail.

Increasing the development time ("pushing") has little or no effect on the shadow detail. Instead, it increases the highlight detail and contrast.

Two very different techniques, with two very different results.

Ok thank you.

Matt answered your question very succinctly and simply. I would only add the old adage, "expose for the shadows and develop for the highlights."

Choosing to use an EI that is different than the box ISO rating is simply a way to "adjust your metering method" to fit "the processes and materials you use" so that "you get the result you want".

The shoot for the shadows and develop for the highlights method works well for some subjects and photographers but not everybody likes to spot meter every situation or develop each roll or sheet of film they shoot differently.

Development changes are not about the scene or the negative, they are used to make printing easier. You adjust your film development to make it easier to get what you want on a specific paper in a specific process.

Adjustment to development is not a required path. Normal development combined with variable contrast papers, or with using different grades of paper, does very much the same thing.

I personally meter to peg the mid-tones rather than the shadows because that works better for my subjects and my style. My personal EI is based on this method of metering and my development processes have been adjusted to fit my normal preferences and VC paper.

I often shoot ISO 400 film at EI 200 and develop shorter. I do it NOT because of shadow details but for controlling contrast. Say I'm out in very bright sunny day. If I shoot at normal EI and develop normally, I'll get very high contrast. By doing what I do, I can get more reasonable contrast so that it's easier to print.

Also, I take ISO 400 film and shoot at EI 800 or 1600, then develop longer. Sometimes I want grain. Sometimes I have no choice because there just isn't enough light. Works well too. This kind of shooting enhances contrast when there isn't enough contrast in the scene.

I also shoot at box speed if there is no need for such adjustment. That works, too. I don't do this just for sake of doing something different. When I do it, that's because there is a need. One stop of difference can make a lot of difference. I was amazed myself.

If I want to expose for shadow detail, I don't mess with ISO. I just measure the shadow area and set my exposure accordingly and then develop normally. I compensate at the printing time if I end up with dark negatives. If I'm changing ISO, that's because I want the same roll to be over or under exposed. Yes, it ends up being the same thing but this is my method.

The way film speed is measured, the rated speed gives pretty much the minimum exposure needed for a decent picture. The way meters are calibrated gives you a little extra margin, but not much and not always. Film usually responds well to slight overexposure. The highlights are still rendered properly even with one to one and a half extra stops of exposure. Rating the film at a somewhat lower speed than its ISO value gives you an extra margin of safety for the shadow areas, assuring that shadow detail will be preserved, with no real danger of blocking up the highlights, except in extremely contrasty situations.

Sometimes you also have to rate films at a lower speed because of the developer used. The rated speed is based on development with the usual commercial developers, like D-76 or HC-110. Some developers do not give the same sort of results and require more exposure. Microdol-X used to be an example. p-phenylene diamine developers are famous for requiring extra exposure. Even popular pyro and catechol formulas usually require slightly (maybe a third of a stop) more exposure.

thank you everybody. Can someone post a picture of a negative that has a density of .10. I have ran the test to see what the true iso of the film using Adams way in the back of THE NEGATIVE. The thing is i don’t have a densitometer to check it with, so i was hoping to check it off of a picture of someone elses. Thanks

Or if anybody knows a way to check with household items, that would be great.

Hi,

What people do is to use a different exposure index (EI) than the EI that matches the ISO film speed ("box speed"). They don't actually change the ISO speed of the film, because the term ISO film speed has a specific meaning. The ISO speed is always what the box says. It is how sensitive the film is to light according to International Organization for Standardization measuring techniques. An EI, on the other hand, is the figure for film sensitivity that you actually use when you are photographing. It is what you use to figure your exposure, with a meter or in your head. Even if you use box speed, you are not "using an ISO." You are using an EI that matches the ISO film speed.

People deviate from the EI that matches box speed because they want to make exposure compensations. They can do it to purposefully over- or underexpose the film, or they can do it for purposes of correcting exposure that they feel is incorrect due to a variety of possible factors. The latter is "calibration" of the light meter to the film to the process to the print.

Using box speed as your EI with an incident light meter will result in great exposures for the average shooter shooting the average shot in average light. Using an incident meter with knowledge of, and an eye for, luminance range to inform exposure and processing tweaks covers most situations that are not average.

In-camera meters complicate things by introducing endless variables, such as how the tones of the different subjects within the composition fall within the metering pattern in the camera. The weird variety of results that can be had by following in-camera meters is why I believe so many people initially decide to monkey with changing their EI. I think focusing on metering technique and equipment is a better way for most people to get better exposures than is re-rating the film. Use an incident meter, box speed, and dial in your development routine well, and things will be peachy most of the time. Add to that a knowledge of exposure and development tweaks that can be done to handle non-average lighting, and you are covered for all but the most odd and extreme of situations. Then you can really judge whether or not you need to re-rate a film for true purposes of calibration, and not just to cover up inaccuracies and inconsistencies in metering and processing.

As for not having a densitometer, try picking up a step wedge instead.

I was reading an old interview with Edward Weston, in which he says " I just expose for the highlights and let the shadows look after themselves". I kind of like his contrary thinking!

tony lockerbie said:

I was reading an old interview with Edward Weston, in which he says " I just expose for the highlights and let the shadows look after themselves". I kind of like his contrary thinking!

Click to expand...

It's not really "contrary" thinking, it's just a decision about what's most important.

See Dunn & Wakefield's Exposure Manual.

If I remember correctly, Weston used a form of extinction metering which can change the interpretation of the quote.