Sunday, October 21, 2018

ISO in Digital Cameras

Doing some film photography here and there, my mind is often with the sunny 16 rule. This rule works for me big time.

However, I noted when using digital cameras, this is somewhat of a different beast. The Fuji X100S seems off by about 1 stop of light (see earlier tutorial), however, the basic principles are working here. With my Fuji X100T, this is a different story.
Today I tried some sunny 16 shots with the X100T @ ISO 200. Fully overcast by bright should have resulted in f/8 with 1s/250 (give or take). That was by far too dark. Auto-exposure brought it to 1s/30, or 3 stops darker. The ISO 200 of my X100T appears to behave like an ISO 25.

For comparison, I got my Leica X2 out at ISO 100. At f/8 with 1s/125 the image was slightly dark, but could be considered well exposed. Auto-exposure resulted in a shutter speed of 1s/80. Mind you, the next real stop shutter speed would have been 1s/60.

What do I learn from this?
  • I will trust the ISO settings in the Leica and snap away with the sunny 16 rule, giving me full control.
  • The Fuji sensor will need some calibration before trustworthy. The native ISO 200 might actually not be ISO 200 at all.
So why bother? It is all about speed and delays. I shoot with manual focus. The only shutter-lag can be created by some auto-exposure in aperture priority.
Operating in full manual control, one needs to be able to trust in some given parameters, e.g. film speed. I expect from digital cameras to actually reflect the correct film speed when I set the ISO sensitivity (aka amplification) of the light sensor.

With my Leica, it seems that I can trust the ISO settings.