Film Speed Testing

If you are having problems with exposure (if a significant percentage of your negatives are either very dense or very thin, or both) it’s time to break your habit of buying and ruining film. Here is a reliable way to determine your own personal exposure index for the film you use, and for the way you expose and develop. Kodak devised a “ring-around” test which is more specific than this version; I have used it and benefited from it, but I think the version I describe here will be enough to tell you what you want to know. Essentially, you shoot the same scene at 3 different film speeds, develop each set at 3 different development times, and pick the best result.

***Use the lens you use most often and use one common shutter speed for all the exposures.

***Make a scene that is in part sunlight and part shade. Assemble a collection of well-known items of differing textures and colors. Place some glass, some wood, and some cloth in the scene. Be sure to get something dark and something light. Place things in the shade and in the sun. Also, place a standard gray card in the scene, in direct sun, and make sure that the card has no reflection, so that it represents neutral gray. Find a person to include in the scene; you can be your own model (use your timer or a long cable release). Take all the photos in a quick succession, so that the light is the same for each photo. If you want to test indoors, you can do that if you must, but you really want to test a natural scene, and come up with the film speed & developer time that looks most like natural light.

***Get some pieces of plain white paper and a broad-tipped marker, and make a set of 3 labels. For example, let’s say we are going to test 400TX film. Make a label that says “400TX”. Another will say “TX800”. Make another that says “TX200”. Make sure that the lettering is large, so you can read them when you make prints.

***On a roll of 24 exposures, set your light meter to a speed of 400 and take a reading from the standard gray card. Let’s say you get an exposure of 1/250 second at f/11. Place the label that says “400TX” in the scene, in a prominent location. Shoot a frame. Now stop down the lens by 1 stop, to f/16, and replace the label with the one which says “TX800”. Shoot a frame. Now open the lens to f/8, and replace the label with the one which reads “TX200”. Shoot another frame. Skip over 7 or 8 frames and repeat the exposures. Once more, skip 7 or 8 frames and finish the roll with a third set of test exposures.

We now have 3 sets of shots: one set for each film speed. We want to cut the film in the dark into 3 strips, and develop one strip of the film from each set for a different length of time. If we are using a developer whose recommended time is 10 minutes at 70 degrees, let’s develop one set for the recommended time of 10 minutes, another set for 8 minutes, and another set for 12 minutes. In the darkroom, make a set of contact prints on multigrade paper with no filter (or Number 2 paper), giving just enough exposure for the clear film edge to be as black as the paper allows. Use fresh chemistry, and develop each sheet for the same time, such as 2 minutes in LPD. Make a contact print, not an enlargement, because you want to eliminate the effect of the enlarger and the enlarger lens. It’s likely that your enlarger has a condenser head (a collimated light beam), meaning that high values could be blocked due to the Callier Effect.

Find the image which feels the most like light, throughout the entire range of tonality. You want the shadows to be dark, but still contain sufficient detail. You want the high values to look clean and white, but still have some texture. You want the model to look like a human. You want white paint in the sun to look like white paint in the sun, not bleached out. Gray clothing should look middle gray. That’s the film speed/developer combination you will use for normal lighting, and expect normal results. You will also find that one of the film speed/developing times looks best for a “minus-one” development time: The shadows will be normal, but the high values will still be one stop too low. Similarly, you will find a combination of film speed and development time that works nicely for “plus-one:” the shadows will look normal, but the high values will be a bit too high, by around 1 stop.

With these times, you can handle many lighting situations that arise: high contrast, and low contrast. If you want to perform more testing, you can determine the best times for N-2, N+2, etc. Be aware that when you under-develop film, you lose some speed in the process. So, to follow our example, you might have to shoot TMY at a speed of 100 when you lower the contrast by 2 stops, IE with N-2 development. In the same way, if you increase the development time enough to expand contrast up to N+2, you may need to shoot TMY at 300 or higher. Everything is… you know… interconnected.

You can use this same technique to compare the results of the same film in different developers, or different films with the same developer. They are not all the same. This is not only true in terms of densitometry and science, but subjectively. Some film/developer combinations are gritty, while others are smooth. Some are harsh, others are silky. Find the ones you like most; you’re the artist.

Bottom line, in a pinch: whatever the manufacturer claims for the film speed, just cut it in half. So if it’s T-Max 400, shoot it at 200. If it’s Ilford FP4+, which is rated 125, try it at 64.