My Pentax K-5 comes with a "regular" low ISO setting of 100, but if you enable "expanded ISO" you can set it as low as 80 (plus go up to an absurd 51200!). I know that in general to reduce noise, lower ISO settings are better, but I'm wondering if that holds true for this "expanded" setting as well. If I'm outside and there's plenty of light and I can use 80 ISO without ruining my shot with inappropriate shutter and aperture settings, should I?
(I know there may be certain specific circumstances where the super-low ISO would be helpful, e.g. if you are shooting right into the sun and don't want the shutter at 1/8000 s. That's not the situation I'm talking about.)