The exposure of the photo refers to amount of lighting. If a photo is overexposed, there is too much light; underexposed is too little light; and the photo with the correct amount of light is 'just right'. Sort of a Three Little Bears scenario.
There isn’t a single formula to achieve this ‘just right’ lighting in your photo. Bryan Peterson’s book (Understanding Photography Field Guide) mentions that there are at least 6 perfectly exposed combinations of ISO/aperture/shutter speed for each photo you want to take.
Let’s say the following settings produce a perfectly exposed photo:
shutter speed 1/80
You know what else will also be a perfectly exposed photo?
shutter speed 1/160
(double the ISO = twice the light sensitivity; therefore, halve the shutter speed = less time for light to get in)
Or how about?
shutter speed 1/40
(up one aperture f-stop = half the light; therefore, down one shutter speed = longer time for light to get in)
You can see that even with different settings, these photos look pretty much the same from an exposure point of view. So try not to worry so much when you're setting up your photos. There are a bunch of right answers and if you practise enough, you're bound to stumble upon a few of them.
This chart shows the relationship between aperture and shutter speed (with a constant ISO). Sometimes it's helpful to have picture to clarify ideas.
|Silver Strand Photo
I was thinking that next week, we could break out of auto mode and try some experimenting. What do you think? Yeah, I knew you'd be game -- see you then.
Silver Strand Photo - check out the demonstration of shutter speed
Scrappers Workshop - good use of photo examples
Bryan Peterson - Understanding Photography Field Guide (got this at the library, fyi)