Aperture - one explanation

I would like to show you why more and more people are moving away from a point and shoot camera and getting themselves a digital SLR. If you look at the prices of cameras you will see that a good brand SLR can be cheaper than a point and shoot. I am not writing to argue the "pro and cons" of the different types of cameras, there are plenty of articles to give you those. What I would like to show, along with three photos I have just taken, is something that can be done with an SLR with no complicated pressing of menu buttons.
Just as on a point and shoot camera there is a wheel on the top of all SLR cameras that gives different scene modes. (I have not found or heard of anyone with an SLR who ever used these scene modes!) This same wheel has three extra things written on it.
M - which means Manual mode - this takes the most skill to use and get good results.
A or Av (Nikon =A, Canon =Av) - the aperture can be set manually while the shutter speed is automatically adjusted by the camera.
S or Tv (Nikon =S, Canon = Tv) Here the shutter speed can be set manually and the camera takes care of the aperture setting.
The most usual setting SLR users employ (those that aren't using full "Auto"!) is A or Av, the aperture control. It is this setting I will show the reasons why.

With the camera set on A (I am using a Nikon camera - the D90 model) so I am in control of the aperture settings, I have chosen to set the camera at f/1.8 (Using a 50mm prime lens). The smaller the F number the narrower the field of focus. Its so easy to remember that connection!
Even without clicking on the picture to see it larger, you can see that the place mat under the pen is not in focus either nearer to the camera nor behind the pen. The depth of field is just enough to show the pen. If I used this setting to take a picture of a dog's looking at me, the nose would be in sharp focus but the eyes would be out of focus. Small F number, small range of focus.

This time the aperture setting was changed to f/9 and you can clearly see the flower pattern on the place mat in front of the pen and about the same distance behind the pen. The shutter speed has changed but I am not telling you what it is - the camera took care of adjusting the shutter speed to make sure the amount of light and shade was to the camera's liking. This choice of aperture setting is often used for such things as shooting wild-life and getting the animal in focus and the background blurred.

The aperture on this occasion has been set to f/22 and because the camera slowed the shutter speed to almost one second, I had to use my mini tripod to keep the camera still. The high f number has given a very wide depth of field and the entire place mat is in sharp detail.  (Large F number, large depth of field.)
I hope that my explanation has been simple enough for you to follow.
Really, the camera operator is still using the camera's automatic settings - the focus is set automatically and the shutter speed is set automatically - and yet there is far more control (with no real brain work needed) to get the sort of shot that is required.
The people who want "everything in focus" will always use full automatic settings and are really using the SLR as a "point and shoot" (but will get better results) however the more adventurous photographer can experiment with depth of field by choosing to use the Aperture Priority mode.
AJ