Are there any "rules" for using ISO?

Started Apr 3, 2013 | Discussions thread
baloo_buc Veteran Member • Posts: 9,472
Re: Are there any "rules" for using ISO?

GreenMountainGirl wrote:

baloo_buc wrote:

There is certainly a rule:

Increase the ISO when other means of adjustment (shutter speed and aperture) could not be used anymore.

In most cases you can set the aperture as wide as possible and the shutter speed as high as needed and then increase the ISO speed.

This is what I do, but still tend to get some underexposures.  The photos are taken in early evening when the light is falling away.  For instance, took some photos at f/5.6, 1/250sec,  ISO 320 which turned out OK.  But when I raised to f/16 and 1/500sec, ISO 800 the picture was underexposed.  I think I was using shutter priority, but not sure.  Another underexposed photo was taken at f/5.3, 1/250sec, ISO 640, also probably shutter priority.

If the light was the same f/16, 1/500 s would have required ISO 5000 not ISO 800 to be properly exposed.

If you use Nikon you have a powerful tool in ISO Auto. You either use A mode and set the aperture while setting the shutter speed via the ISO Auto (the soft way) or use the M mode and set both the aperture and shutter speed and let ISO Auto to manage the exposure (the hard way).

My camera is a Nikon D7000 (sorry, forgot to mention that), but I have never tried the Auto ISO.  My reasoning is that I want to learn how to use the camera's functions, not let the camera do everything.  When I first started using my camera, I set it on manual all the time.

You have a powerful tool you paid for and not using it. I reckon you don't understand the aperture and shutter speed. The aperture f/5.6 will let you 8 times more light (i.e. 3 stops) than f/16. In order to compensate for such loss of light you should either reduce shutter speed 3 stops (to 1/30 s) or increase ISO speed 3 stops (to ISO 2500) or any combination of these two that gives you 3 stops.

Thank you Victor for your help.


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