Your aperture. It's soooo important. It's the ring inside of your camera that narrows and widens to determine how much light you let inside of your lens to wait at the shutter - so it's the first element of the exposure triangle. And it gives you fabulous creative control over your images IF you understand a little thing called "depth of field" and how it relates to your aperture setting.
Depth of field is the amount of your photograph that will be in focus. How narrow or wide that area of focus is will be determined by two factors. 1) The aperture setting. 2) The distance between you and the point of focus
Because we're improvising moms, we're not going to use a measured field, we're going to use my bathroom rug (moved to my foyer) and three candles to show you what we mean. I'm not a chronic redecorator, it's just that my bathroom rug has a diamond pattern so we can get a feel for how much of each object is in focus as we get further away from my camera. Well, that, and I would have had to have crawled in my toilet to get these shots :)
First, the setup - my camera was all the way to the left:
Now, let's start with a WIDE aperture, an aperture of 1.4, focusing on the first candle, the middle candle and the far candle.
Look at how many diamonds are acceptably in focus based on our distance from the point of focus. The closest candle really only lets us have half of each of the diamonds it's on, so one. The middle candle gives us between 3-4. And though the far one makes it difficult to tell, when the photo is enlarged, it's about 5-6 diamonds in focus.
From this we determine that the CLOSER we are to the point of focus, the SHALLOWER the depth of field. The FURTHER away we are from the point of focus, the WIDER the depth of field. Take note of the middle candle. Look at the difference in it's blur (also known as bokeh) when the front candle is in focus and when the far candle is in focus. So, when our focal point is closer, the depth of field is going to be much more dramatic than when our focal point is further away.
Now let's look at the same candles shot at a much wider aperture - 5.6.
Because the depth of field is so much wider at 5.6, I added a 4th element to refer to - the mercury glass spindle at the end of the room. Look how much more of the rug is in focus at 5.6! In the first photo, focusing on the close candle, we get almost 3 full diamonds in focus. In the middle we get about 7. For the far exmple we get at least 10 because we run out of rug! So even though we start of with more in focus at an aperture of 5.6, the depth of field (or area in focus) still grows by the distance between us and our point of focus.
Need to see it another way???
Again at 5.6 - a narrower aperture.
One final note - these results are a little exaggerated on my camera because I have a full frame sensor (Merry Christmas to me!), but the same principal applies to all cameras.