More on completing this Aperture/ DoF assignment

Originally, I suggested that you complete this assignment outside on a nice day. Well, the weather went downhill shortly thereafter. The idea of this assignment is for you to see the change in depth of field as you change your aperture. Of course, as you do so the amount of light that is allowed to reach the sensor changes which necessitates changes to the shutter speed and/or ISO as well. If you were to complete this assignment outside on a sunny day, you would likely be able to complete it by simply changing your shutter speed as you changed your aperture. The general rule of thumb is don't use a higher ISO unless you need to. When do you need to? When your shutter speed drops below 1/60 without the use of tripod.

You can complete this outside in overcast light outside or even indoors. You will just have to increase the ISO at the point that a shutter speed of less than 1/60 is required. Let's say you start out by determining that f3.5 @ 1/125 at ISO 200 is the ideal exposure (the histogram is as far to the right as possible without climbing the wall). You begin by taking that shot. Then you take a shot at f4 @ 1/ 100 at ISO 200. The next in the cycle would be f5.6 @ 1/50 at ISO 200; however, that means a shutter speed of less than 1/60 at which point you risk having a blurry image due to camera movement. So, you would instead go with f5.6 @ 1/100 at ISO 400 which is a reciprocal exposure (it results in an equivalent image in terms of brightness). From there, you would go to f8 @ 1/100 at ISO 800. Then, f11 @ 1/100 at ISO 1600. Then f16 @ 1/100 at ISO 3200. Of course, if you don't have ISO over 1600 available, then you would have to go with f16 @ 1/50 at ISO 1600.

Here is a short article that describes Aperture with a few examples.