View Full Version : Fossil-like photog seeks Auto ISO help

05-06-2005, 04:21 PM
I just picked up a D70S with 18-70 kit lens.

I once owned a film SLR more than two decades ago, so I have some passing acquaintance with the relationship between shutter speed, aperture, and film speed in terms of exposure.

But how does the Auto ISO function actually work?

Does it assume you want to shoot at the lowest ISO possible and only adjust to higher (and potentially noisier) ratings if your chosen shutter speed and aperture seem insufficient to get decent exposure?

Or does it make some general assumption based on available light and then require you (or the camera) to set shutter speed and aperture around that?

With DSLRs, it seems that ISO becomes a true variable—something that can potentially be changed with each shot as opposed to with each roll of film. I realize in the future I will likely choose specific ISO ratings myself, but I first wanted to see what the camera chooses to get a better idea of what happens at the different ratings. This is the same thinking that has me using some of Digital Vari-Programs in these early days—i.e., a tactic to give me a baseline from which to make my own photographic choices.

Thanks in advance for any help. I hope this query makes sense!

05-06-2005, 06:51 PM
Sorry, it looks like p. 142 answers most of these queries. It appears, though, that "auto ISO" is somewhat of a misnomer. That is, the camera appears to leave the ISO rating wherever you last set it, unless doing so forces the camera outside of certain parameters (too fast or slow a shutter speed for example). Is that right? So if you shot at 1600 the night before and then switched to Auto ISO the next day...you'd likely still be shooting at 1600 even though you might have chosen, say, 200 or 400 ISO yourself and would have thought the camera would have chosen that range too. Is that about right?

More confusingly, the "Auto" dial mode appears to set the ISO at 200, rather than on "Auto ISO," which is what I would have guessed.

I know, I know. I didn't get this camera for its point n shoot ability. It's just my last SLR had NO auto anything, so I'm just learning now about letting modern cameras do some of my work...like focusing



05-07-2005, 02:50 AM
Yes, you seem to have figure out what auto ISO does, although I've never used it myself. I wouldn't have thought that it would default to the last manual ISO you used though. So in your example if you'd shot at manual ISO1600 the night before then switched to auto ISO it would default to the lowest possible ISO that would keep the exposure correct. Not ISO 1600.

Don't ever use the dial 'AUTO' it takes far too much control out of your hands. If you want the camera to just 'point-n-shoot' use 'P' mode. it'll still automatically meter for you but you will get more control over ISO WB etc.