A Path to Consistent Results

By Ryan Gillespie

Some time ago, I thought I would try some different developers for my black and white film. I knew there would be some differences in the chemistry and developing times, but I figured "As long as my exposure was correct, I should have a nice negative to print from." Boy was I wrong!

The first roll of film in the new developer was a disaster. The negatives were thin and lacked detail in the shadow areas. I was confused because I had carefully metered and exposed the film exactly as I always had. What went wrong?

The ISO Revelation

After some research and discussions with other film photographers, I discovered the issue: different developers can affect the effective ISO of your film. The manufacturer's box speed is just a starting point. To achieve consistent results, you need to test and determine your film's true ISO with your specific developer and development process.

This was a revelation. I had been treating ISO as a fixed property of the film, when in reality, it's variable depending on your entire workflow - from exposure to development to printing or scanning.

The ISO Test

I decided to conduct a proper ISO test. Here's the process I followed:

1. Choose a scene with good shadow detail and a range of tones
2. Set up your camera on a tripod to keep everything consistent
3. Make multiple exposures of the same scene, bracketing around the box speed
4. For example, if testing ISO 100 film, shoot at ISO 50, 80, 100, 125, and 160
5. Develop all sheets together using your standard process
6. Evaluate the negatives to see which exposure gives you the best shadow detail while maintaining highlights

My Results

After testing several films with PMK Pyro developer, I found that most of my films performed best when rated about 2/3 to 1 stop slower than box speed. For example:

• Ilford HP5+ (box speed ISO 400) - best results at ISO 250
• Ilford Delta 100 (box speed ISO 100) - best results at ISO 80
• ADOX CHS 100 II (box speed ISO 100) - best results at ISO 64

These results were specific to my workflow: PMK Pyro development, contact printing on silver gelatin paper, and my metering technique. Your results will likely be different, which is exactly why testing is so important.

The Impact on My Work

Once I determined the true ISO for each film-developer combination, my negatives became much more consistent. I could predict how my exposures would turn out, and I had far fewer disappointments in the darkroom. Shadow detail improved dramatically, and I could push my work further creatively because I wasn't fighting technical problems.

Beyond ISO: Other Variables

ISO testing taught me a broader lesson about the importance of controlling variables in film photography. Other factors that affect your results include:

• Development time and temperature - Small variations can have big effects
• Agitation method - Consistent agitation is crucial
• Water quality - pH and mineral content matter
• Film storage - Age and storage conditions affect film performance
• Metering technique - How you meter significantly impacts exposure

The Path Forward

If you're experiencing inconsistent results with your film work, I strongly encourage you to conduct your own ISO tests. Yes, it requires time and film, but the investment pays off in dramatically improved consistency.

Keep detailed notes about your process. Record everything: film type, developer, dilution, temperature, agitation, and results. Over time, you'll build a knowledge base that makes your film work predictable and repeatable.

Conclusion

Film photography is both an art and a science. The artistic vision is what drives us, but understanding the science - the technical foundation - is what allows us to consistently realize that vision. ISO testing is one of those fundamental technical skills that separates casual film shooters from serious practitioners.

Take the time to test your materials. Understand how they respond to your process. Build that foundation of knowledge, and you'll find that your results become not just better, but reliably excellent. That consistency frees you to focus on what really matters: making meaningful photographs.