Are there any "rules" for using ISO?

Started Apr 3, 2013 | Discussions thread
OP GreenMountainGirl Contributing Member • Posts: 684
Re: Don't worry about ISO !
Thinking about ISO is thinking about exposure from the wrong direction.  It's placing emphasis on something that should be secondary.

What causes noise in a photo ?  The noise you see is the result of low signal:noise ratio.  The noise is already there; how much of it you see depends on how much signal is present.  In other words: the more light you put on the sensor, the less noise.

So instead of worrying about whether you should shoot this scene at ISO 800 or that scene at ISO 1600, you should concentrate on what shutter speed and aperture you want to/have to use.

Dennis, Thank you for your explanation/description of the situation.  I realize I have been floundering around in the mire of details, losing my way in the forest of theories.

After owning my camera for over a year, and striving to learn how to use it (first DSLR), finally am beginning to see where I have steered myself in wrong directions.  At least I have figured out many of the right questions to ask!  And as you can see, I am getting lots of good answers!

But the basic idea is that you set your shutter speed and aperture with the intent of putting as much light on the sensor as possible (assuming low noise is the goal ... and in bright light situations, you obviously don't want to overexpose at base ISO).  If you do that, you don't need to think about ISO; it just falls into place.  On the other hand, setting the ISO manually requires constant monitoring of your exposure settings to see if they're acceptable, if you have to raise it to get acceptable settings, or if you want to lower it to avoid unnecessary noise.

You are correct - I do need to concentrate more on setting shutter speed and aperture for proper exposure.   Initially I was using aperture-priority, started trying to use shutter-priority, but have been shown the problems created by that.  So back to Av or M!

Looked at your website, very nice pictures.  There was an autumn landscape that reminded me of the kind of view we see here of the Pownal Valley (but without the lake)!

I appreciate your input, and have learned from it.


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