Tipster: How To Measure Exposure Times For Pinhole Photos

For World Pinhole Photography Day we're celebrating the magic of pinhole photography with our community. Today we want to talk about exposure time when doing pinhole photography, more specifically how to take a metering if you find yourself without a light meter. For this tipster we used the Diana F+ Glass Lens Set paired with a roll of Potsdam Kino B&W 120 ISO 100.

If you are new to pinhole photography, the first question that will arise is, how can I accurately measure exposure times? The main characteristic to keep in mind is that it requires a long exposure time. When dealing with long exposure, one of the first obstacles you will face is getting acquainted with the law of reciprocity.

What is the reciprocity law?

The law describes the rules that govern the light hitting the film and the relationship between the shutter, the aperture, and the ISO of the film that determines a good exposure. The failure of this law is the term used to describe photographic film's non-linear response to low light exposure.

What it means is that once the light levels reaching the film drop below a certain threshold, the effective sensitivity of the emulsion decreases. This is because in chemistry, the longer time a reaction requires, the lower the power will be, until carried to the end of such process.

It is important to know the existence of such a rule if you are getting serious about long-exposure photography, as the time can be affected as early as 1 second of exposure time. However, it must be said that the quality of light is also important as the hour of the day.

But to what extent does the reciprocity law affect our film? Do we truly need to be worried from 1 second on? And what if you go out to shoot without a light meter that can tell you the exact exposure time needed? How can you calculate the compensation needed?

While browsing online, we found a useful chart designed by Richard Koolish that is an extremely handy tool to have if you need to know your exposure time but find yourself without a piece of technology to help you meter the situation.

To make this work, you must know the aperture size of your pinhole camera. That is the only mandatory piece of information. It is a simple wheel composed of three elements: shutter speed, ISO, and the f-number. Simply set the ISO of your film, with the lever point at the sun condition, and look at where your f-number is matching with the exposure time.

As we wanted to test how accurate this exposure was, we didn't apply any other compensation. The ISO of our film was low (100 ISO) and since the hour of the shooting was in the middle of the day we trusted the calculation, and waited to see the results. From the moment that we opened the tank and saw the negatives we knew that the exposure was correct, and we were happy with the scans as well. The glass lens had given a good overall sharpness through the picture and although with a pinhole image it is never absolute, in these pictures it's good enough.

We are happy that this chart has worked well for us and that we now know when the exposure is between one second and three seconds there isn't a need for a drastic compensation. The exposure was correct thus the failure of the reciprocity law is not compulsory at this stage.

Which one is you favourite metering system when doing pinhole photography? Share your work flow in the comments below.

written by eparrino on 2023-04-30 #gear #tutorials #pinhole #medium-format #balck-and-white #120-film #world-pinhole-photography-day #potsdam-kino #diana-f-glass