Adjusting Exposure with ISO Settings

Another way of adjusting exposures is by changing the ISO sensitivity setting. Sometimes photographers forget about this option, because the common practice is to set the ISO once for a particular shooting session (say, at ISO 100 or 200 for bright sunlight outdoors, or ISO 800 when shooting indoors) and then forget about ISO. The reason for that is that ISOs higher than ISO 100 or 200 are seen as “bad” or “necessary evils.” However, changing the ISO is a valid way of adjusting exposure settings, particularly with the Canon EOS 5D Mark II, which produces good results at ISO settings that create grainy, unusable pictures with some other camera models.

Indeed, I find myself using ISO adjustment as a convenient alternate way of adding or subtracting EV when shooting in manual mode, and as a quick way of choosing equivalent exposures when in automatic or semi-automatic modes. For example, I’ve selected a manual exposure with both f/stop and shutter speed suitable for my image using, say, ISO 200. I can change the exposure in 1/3-stop increments by tapping the ISO-Flash exposure compensation button and spinning the Main Dial one click at a time. The difference in image quality/noise at the base setting of ISO 200 is negligible if I dial in ISO 160 or 125 to reduce exposure a little, or change to ISO 250 or 320 to increase exposure. I keep my preferred f/stop and shutter speed, but still adjust the exposure.