Wiki/F-stop Printing

F-stop Printing

F-stop printing is a method for determining exposure for a print by running test strips in increments of stops (halvings and doublings of exposure).

It's perhaps most easy to understand the benefits of the f-stop method by first understanding the limitations of the standard method of exposing in fixed increments.

Using the standard method you might notice that as your number of test strips increases the tonal difference between each strip decreases. This is because as we reach the tail end of the test we are adding only a small proportion of the total time each step. For example if we did 11 steps across a page, the first strip would double the exposure time where ase the final step would add only 10%.

With f-stop printing every step across the page will be a halving or doubling, as such we can map those changes directly to aperture stops and halving or doublings of exposure time on the timer. This can make it substantially easier to relate observations from the test strips to how we can to make adjustments to our print.

As an example if we had a fixed horizontal horizon shot with the sky in it, and made a 4 step f-stop print we might be able to capture our desired dodges in the lightest strip, while giving us information how how long to burn the sky by the darkest.

For me personally I do the following when I walk up to the enlarger:

  1. I set up my negative and easel, contrast filters, and focus, etc.
  2. After waiting for my eyes to adjust I set the len's aperture to a point where the light on the easel looks like a "20s" amount of light. (Note: This is the most wishy washy part of the process but I swear that if you have been practicing printing to 20s for a while this will easy to do within a stop!)
  3. I look at my scene and see if there is a direction that is better to make my strips in. Sometimes you know you have shadow or highlight information that you need and setting that up early is best.
  4. I make 4 exposures across my page: 20s, 10s, 5s, and 5s. The net result is a page with 40s, 20s, 10s, and 5s.
  5. At this point I usually know my base exposure, but if I don't it's easy to adjust and repeat.