ever wonder how professional photographers get shots with the person in focus and everything else encapsulated in a dreamy haze? it doesn't require any photoshop magic, but rather just a little understanding of aperture.
there is a part of the lens that is close to the lens/body junction, basically a hole, whos function is to let light through when a photo is taken. the amount that the hole opens is called the aperture. aperture is measured on a numeric scale where a smaller the number indicates a larger opening on the lens. the aperture control can be thought of as your eyelid and how much you open it. the wider you open it, the more light comes in. when it's real sunny, you squint. why? to reduce the amount of light intake. cameras are very similar except they can't wear sunglasses.
in isolation, the aperture's main influence on your photo will be the depth-of-field. here's a couple examples to explain depth of field. this first picture has an aperture of 1.8 (referred to as f/1.8) while the second photo is taken at f20. the object focused on is the garlic clove (the white thing that looks like a small alien spacecraft) in both photos.
above picture at f/1.8
above picture at f/20
notice how at f1.8, the objects in front of and behind the alien spacecraft get blurrier the further away they are. at f20, everything in the picture is relatively clear even though the focus point in both photos was the same. that's it. you want dreamy portraits? flip that camera into 'aperture priority' mode and start playing around with different aperture sizes. your camera will be gracious enough to adjust your shutter speed so you have perfect exposure every time. go crazy.
ummmmm, hang on. that's not the whole story. let me tell you one more thing before you go open a photography business and put me out on the streets with your newfound knowledge. the other thing that aperture has a big influence on is how quickly it can get enough light into the sensor to correctly expose a photo. you can think of this like holding a poland springs bottle out in the rain as compared to holding a trash barrel out in the same rain storm. which will collect more water quicker? the trash can. that's a larger aperture (remember - lower number, like our f/1.8 photo). ok, now you can go crazy.
here's a quick summary of aperture:
* smaller aperture, bigger opening, more light, shallow depth-of-field *
* larger aperture, smaller opening, less light, deeper depth-of-field *
dead horse beating section below (reader caution - could be considered rambling beyond this point):
still not clear on aperture? man, photograph puns are horrible. anyway - hold your arm out in front of you and put up a few fingers. close one eye. you are now a camera. now let's set you to a low aperture. open your eye all the way and focus right on your fingers. without shifting your focus from your finger, try to take note of how blurry the objects past your finger are. this is mildly difficult to do, but it is possible. in this mode, you've got a shallow depth-of-field. let's switch you over to f/16. keeping focus on your finger and one eye closed, squint so your eye is barely open. you'll notice that even though you're focused on your finger, the objects in the background are nearly completely in focus also. you've got a deep depth-of-field, but your sacrifice is the amount of light you're able to take in with your eye all squinted and bunched up. let that sink in, it'll all make sense, i promise. don't forget to open up your other eye before reading the rest.
each lens has its limit to the lowest you can go with the aperture. more expensive lenses can open up wider and are referred to as "fast lenses". low-light situations such as traditional church wedding ceremonies require fast lenses. the rule for wedding lenses is usually no slower than f/2.8, but that's going to hit your wallet pretty hard, take it from me.
next up: ISO