And Holly, remember that depth of field is affected both by aperture and focal length. So, yes, if you want a larger amount of the scene in-focus, the easiest thing is to stop the aperture down (higher f-stop value) but you can also zoom the lens back to its widest setting (then move the camera position in) which will also increase the depth of field.

Sort of. Depth of field is determined by aperture, focal length, and subject distance (the format of the film/sensor is also a factor, but since Holly is only using one format, it's not relevant in this case), so if you move the lens closer to the subject, the depth of field also decreases.
In the macro range, things get a little more interesting, because if you were actually to calculate it, because of the factor of subject distance, depth of field will turn out to be effectively a function of magnification and aperture, regardless of focal length. So if you photograph something smaller than 10 times the size of the sensor or the film frame (for the D90, that would be something smaller than about 8 inches that fills up the entire long dimension of the frame), it doesn't matter if you zoom out and move the camera close or zoom in and move the camera back--the depth of field will be the same, if you are framing the subject in the same way.
Now I said the format isn't relevant in this case, but if you wanted to consider it for the sake of argument, here's how it would be relevant. Say that instead of zooming out and moving the camera closer you were to zoom out, keep the camera in the same place, and crop the image. This would be like using a smaller format, and would give you more depth of field, but since the D90 is already a small format camera, the loss in overall image quality from not using the whole frame isn't worth the increase in depth of field from shooting wide and cropping.
Another thing to consider is, if you're in a situation where you can't use a tripod easily, stopping down for more depth of field will give you a longer shutter speed, which will reveal more camera shake. With a digital camera you can turn up the ISO setting to give you a faster shutter speed. A higher ISO will give you more image noise, but this is usually less of a problem than camera shake. Another solution for camera shake is to hold the camera more steadily--left hand palm up cradling the lens, right hand squeezing (not jabbing) the shutter release, elbows in and braced against your body, relax, and shoot between breaths.
Edited by David A. Goldfarb, 27 August 2009 - 03:35 AM.