Ok. I'm going to grab the bull by the horns and give us a new assignment.
It is my favorite aspect of photography besides light.
I think being able to control your depth of field separates the men from the boys, the women from the girls, the artist from a point and shooter.
Depth of field is created with the aperture on your lens. If you are lucky to own a lens that is a 1.4 or even up to a 2.8, it is pretty easy to create an image with a shallow depth of field.
Our aperture setting does 2 things. 1) It lets in more light (1.4 creates a larger hole in the aperture like the size of a quarter and lets in more light, opposed to, say f22 which creates a much smaller hole like the size of a pencil tip and lets in less light) and 2) creates DOF. The larger the aperture (f1.4), the narrower the area of focus the lens creates...it can be less than an inch; and the smaller the aperture (f22), the broader the area of focus, such as from the tree branch right in front of you to the mountains and infinity.
Being able to control your depth of field is how you are able to create images that "grab" the viewer. It is the photographers tool for directing the viewer to what you want them to see.
Once you get the hang if it, you never want to shoot without knowing what your fstop setting is. Initially I thought it was a phase I was going thru, but I have found it to be a way of life!
You can see here I tried a couple different things...Caitlin with her husband and baby... I took the second image first, and I liked that Charlotte was looking at her mom...but I didn't really care for Caitlin being out of focus in the front...so I moved them closer together to get a more "intimate" image, and by having the focus on Caitlin instead of her husband, the image tells a stronger story. Notice that they are about 6 feet apart, and I was able to select who I wanted in focus. Had I closed down the fstop( to a higher number), I could have had all 3 of them in focus.
Here you can see I was trying to decide which way I liked the image better. Is the photo about the medal? or about the girl? By changing the area of focus with a narrow DOF, I get to pick which I want to empasize. The area of focus is very narrow...you can follow her hand up to her wrist and see it begin to blur pretty quickly. This was taken with the 105mm f1.4 @60
I shot these like this to be able to use the images as a background on an album page. Not something you would use to hang on a wall, but effective to tell a story in an album with other images off to the side.
The other variable is where you stand when you are taking the photo. The setting on the camera and lens was the same in both these photos. 105mm f1.4 @60.
BUT
Where I stood when I shot the image makes the difference. The closer I am to the subject, the narrower the DOF.
In the image on the left, I was as close as I could get without laying on top of her. Notice the lashes are in focus, but the eyebrows aren't. In the image on the right, her lashes and the blanket, her hair and her mouth are in focus. Because I increased my distance from the subject, the DOF increased.
Here I used DOF to tell the story of the girl and her art...her eyes are in focus...the brushes help tell her story, but have the potential for being distracting if they were all in focus...so DOF blurred them some, and then the brushes lead you to her, instead of wrestling for attention.
So
The challenge here is to take photos of anything you want. Subject is up to you. But shoot it with different apetures and see what you come up with. And feel free to post more than once. I think we could all learn from this exercise.
Mostly
Have FUN with it!
This is the example Craig was referring to I think, where the gun is in focus and the shooter and targets are not...still tells a story, but the DOF directs what the viewer is looking at. Pretty cool, huh. 
This is a good example of a portrait with a blurred background. Makes you pay more attention to the actual subject. We might not have been able to see the casing being ejected from the chamber if the whole image was in focus. 
F/5, 1/20sec, iso-800, 36mm
F/8, 1/60sec, iso-100, 44mm
F/8, 1/60sec, iso-100, 42mm
As soon as I saw water was the topic, I knew exactly what I wanted to go capture...Sweat! But it is now two weeks, or more, we have not found the courage on the weekends (I say WE because my husband is going to provide me with beads of sweat for my photo) to go do one of my killer-sprint workouts at sunset. Alas, I will upload a few water-inspired pictures from my trip to Hawaii. I really have this great image in my head of sweatbeads pouring off someone's nose and forehead, the beads in focus and the person and background out of focus with great sunset lightling...so I may try to get it once the fear of the workout pass! 
