hypothetical digitalbISO question/thought

why is it that digital cameras still require you to set your ISO as

if you are still using film? Why cant it be as easily variable as

shutter speed and aperture? Wouldn't it be cool to have a third mode

(beyond AV and TV) where you could choose a shutter/aperture

combination and the camera would then adjust the ISO for a proper

exposure?

 

I've been shooting concerts lately and might change ISO a dozen

times (as the lighting changes) to keep the shutter and aperture

settings where I want them. Why can't that be automated?

Some digicams automatically adjust over a limited range, typically when in "idiot modes".

 

The range of available values is pretty limited. From ISO 100 to ISO 1600 (what a good DSLR can get) is only 4 stops, with a big impact on image quality.

 

If you're willing to let your camera choose whichever sensitivity it wants, you trust it to use the highest one. Why don't you set it to that value, and stop thinking about it?

 

Yes, it would technically be possible to create for each lens a custom map of sensitivity, shutter speed and aperture against the light level. That would add quite some complexity to the software.

Yes, my Nikon D70 will do that. Much of the time I set the ISO to 200, but in addition to the 'auto ISO' mode you're thinking of there's a menu function that will bump the ISO up if the light gets lower than about 'wide open' at 30. That's the way I have it set.

 

The 'feature' sneaks up on you in odd ways. I was travelling and wanted to do some backlight / deep blue sky stuff, so I switched to manual. I shot three or four frames biasing more towards underexposure with each, and couldn't figure out why I wasn't getting what I wanted. I finally figured out the auto ISO thing was countering my moves, completely unexpected in manual.

Jean-Baptiste--

 

I often use "idiot modes". You need to have your brain engaged and understand what the camera is doing for you. And four stops is a hell of a lot of light. Would you see a difference between a 300mm f2.8 lens and a 300mm f8 lens?

 

The reasons for not just setting it to high speed and leaving it alone are two: first, that ignores my desire to have a specific shutter speed and aperture for reasons that should be obvious. Second, that would default you to the worst quality, when I would prefer to use higher quality ISOs when possible.

 

Todd-- Interesting. Thanks.

Ward: If I really didn't want to think about it, I'd use a shifted P mode (standard P mode is too stupid), ISO 100 outdoors, ISO 800 indoors. But then I'd probably worry too much about it.

 

A matter of perspective, I guess.

That normally works fine but when I shoot concerts the lighting can change dramaticaly from moment to moment. Like I said, I need to change ISO constantly to keep my desired shutter/apperture settings. I was just saying that a third mode, to correspond to shutter priority and aperture priority, would be handy. As it is, I use aperture priority and vary the ISO to get the shutter speed I want.