EV Values for Zone III Calculations
EV Values for Zone III Calculations

A couple weeks ago I began to talk about my metering technique for the Zone System. I use exposure values for the shadows when metering and always adjust the metered value to Zone III. As I find myself using longer exposure times, I realized I needed to start adjusting for reciprocity rates of film as well as making a quick cheat sheet for using other meters for EV. I am only using Ilford Delta 100 and HP5 Plus right now, so they are the only charts I have added for my personal use and thought I would share them out. I actually have them bookmarked on my cellphone if you want to bookmark as well, or download these images below for quick reference.

The formula is Tc = Ti ^(t factor) all times in seconds.

Where:

  • Tc is Time correction
  • Ti is Time indicated
  • t factor is supplied by the manufacture per stock

Again, these are already adjusted to Zone III (closer to Zone IV for my taste). So simply meter the EV as usual, then use the chart to find your adjusted exposure time. If going over 1 second and using Ilford Delta 100 (t factor of 1.26), switch to the second chart. If using Ilford HP5 Plus 400 (t factor of 1.31), then move onto the third chart. Again, these charts are adjusted from Zone V (where you usually meter) to Zone III to save a step. The max exposure time I calculated out for is 13 hours, 46 minutes and 39.1 seconds.  After that, you're on your own.

In a nutshell, the times are pre-adjusted for Zone III.

Downloads (jpg)

I made a couple simple screenshots below that you can save to your phone or print off below.

Let me know if you find this useful, I'm curious. If there's a call for more film stocks to create charts for, I will. Just drop me a line.

delta 100 zone iii values
delta 100 zone iii values
hp5+ zone iii values
hp5+ zone iii values

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