There are three main elements which affect exposure. The first is Light, or the luminance which we call ISO. The second is the time it takes for the shutter to open and close, this we call shutter speed. And finally there is Aperture, as explained on another page, the size of the hole which lets in light.
I am not going to confuse you with a lot of maths, but you can work out if the shutter speed is slow, ½ as opposed to 1/400, then you know more light will get in. The reason shutter speeds are so fast is because of vibration. If the shutter speeds were slower there is more chance of vibration. Vibration can be overcome through image stabilisation, which some lenses and cameras have. Vibration can cause blur. We don’t like blur.
The Holy Trinity of Photography, in ISO, Aperture and Shutter Speed are things we will cover, and of course you’ll learn about them through trial and error, however without AutoFocus, getting the exposure exactly right can be tricky. Always remember to use your viewfinder to work out how the image main perform, and take some trial shots and go through them. What you think you can see, might not be what the lens understands.
I am not going to try and explain dynamic range, because when you are starting off this is irrelevant, but you have to understand what is too bright and too dark.
So now you ask yourself, where you are, is there a lot of light? If the answer is yes your ISO can be low. 100 etc. 12,400 being high for example. High would be noisy or your picture would be grainy. Now is your subject, yes in the case below, moving?
In my case the bubbles were, so I need a fast Shutter Speed. 1/1000 or whatever. Not ½ which would be click….click sound wise. The aperture here would be about F 5.6, this is good for us because we want a shallow dept of field. The wall is behind it and there is nothing in the distance we want to capture. If we were in a street, and I wanted to capture the faces of the people watching an entertainer, I would increase ISO and Aperture by 4 and 2 respectively. Play around with it and find what you like, nothing is certain when it comes to taste.
Here is an example of wanting to capture objects deeper in a photograph. We increase our ISO and Aperture.