Canon 5D2’s Auto ISO setting

The Auto ISO mode sets ISO values between 100 and 3200 ISO. Compared to what I am used to (no auto-iso at all on a Canon 10D) this is pretty convenient. Some thoughts so far:

  • I noticed that Auto ISO has a strong tendency to go for 100 ISO. That’s nice if there is enough light to get a short shutter speed and a safe amount of depth-of-field. But the camera also used 100 ISO on a 28mm, 1/30 s, f/4 shot in the evening. Arguably this still adheres to the old 1/f-rule for shutter speed. But the quality (noise, dynamic range) difference between 100 ISO and 200 ISO is minimal (although visible in DxOmark ‘s measurements). I thus wonder how often that stop could be put to better use like having a 2x faster shutter speed or getting more depth of field.
    Update (16-Mar-09): a work-around to increase the minimum ISO from 100 to 200, is to enable “Highlight Tone Priority”. This, as a side-effect, sets the minimum ISO value to 200.
  • Maybe this is overoptimistic, but are the “only” conditions when one would overrule Auto ISO might be for either landscapes using tripods (where 100 ISO is a good idea) or sports photography (where increased ISO is a good idea).

See manual page 58.

This entry was posted in Photo Technology and tagged , , , , . Bookmark the permalink.

2 Responses to Canon 5D2’s Auto ISO setting

  1. Sakke says:

    I have also found auto-iso a very handy feature. I have been a bit irritated of it´s tendency to stick with 100 ISO. I tried your trick with highlight tone priority. I was shooting on a somewhat foggy day with snow on the ground. I was not correcting the exposure, but thought, that the highlight priority will shoot to the right, i.e. use the maximum available range of it´s 14-bit resolution. My logic might not have been right on how the highlight priority works, since all the pictures were roughly 1 stop underexposed. However, the lowest ISO was 200, which was the reason for trying this out. I have to do some experiments still, but it would be good to understand the highlight priority mode logic better. BR, Sakke

    • pvdhamer says:

      There is quite some info on the feature. See

      Summary and claim (Feb 2008, based on HTP on the Canon 1Ds Mark III): “there is a visible advantage only if you shoot JPEGs. In RAW, the Highlight Tone Protection setting has no effect other than underexposing by one stop.”

      I don’t know if this is true for the Canon 5D Mark II as well.

Leave a Reply

Your email address will not be published. Required fields are marked *