Sadie gives me the "eye"

This is a little example of setting the lens aperture yourself, and why you care.

I walked into our bedroom at lunchtime one day and saw Sadie and Katie lying on our bed. That was not unusual in of itself because they do this often. What was unusual was that they were right next to each other instead of having a bit of space separating them. And Sadie appeared to be peeking over Katie's back in order to keep an eye on me. So I got the camera and hoped she would stay in-place while I decided how to best photograph it.

I had the Nikon 105mm Micro-Nikkor f/2.8 VR macro lens on at the time because I love its sharpness and was trying to find excuses to use it. At the time it, and the Nikon 70-200mm VR f/2.8 zoom lens, was the fastest lens we owned (until I added the Nikon 50mm f/1.8 recently). Anyway, I decided I wanted Sadie's face in sharp focus but have Katie (lying in front of Sadie) and the blankets and pillows (behind Sadie) be blurred. In this way, your attention would be drawn to Sadie's right eye.

To do this, I set the D300 in aperture-priority (press the "Mode" button down and spin the rear command dial until "A" appears in the top LCD display), then selected the widest aperture on this (f/2.8) by spinning the front command dial until "f2.8" appeared on the LCD display. Now that I've set the aperture, the camera picked the appropriate shutter speed given the ISO I had set (800). (On second thought, I guess I could've set the exposure mode to Program Auto, metered the scene, then spun the rear command dial until the LCD display read "f2.8", but I didn't. For Canon users, I think aperture-priority for them is "Av" mode.)

Now the "why-you-care" part: setting the lens aperture to its maximum opening (like f/1.4, f/2, f/2.8) lets you put your subject in focus and blurs everything else in front or behind it, while setting the aperture to a smaller opening (like f/16, f/22, or f/32) lets you put pretty much everything in focus.

I'm sure I also set the focus mode to Dynamic-Area AF so I could set a focus point on her eye.

(Shot with the D300 using the 105mm Micro-Nikkor f/2.8 lens; aperture-priority; 1/30 sec @ f/2.8; ISO 800; normal JPG.)