Photography tips

The Aperture of f-stop is a measure of "how big" the hole is that passes the light from the lens to the film (or digital Sensor). So, Adjusting the Aperture is really making the opening bigger or smaller in the Lens.

This is of course a very simplistic explanation, but That Is what we are going to explore and try and make sense of.

Changing the Aperture is one of several settings within your Camera that you might want to change depending on what you are wanting to photograph. We will explore how different settings affect the photo that is being taken.

The Aperture is measured in terms of an f- number for a given Lens.  All Lens' will have a minimum and Maximum. The Bigger the Aperture (smaller F-number) the More expensive the lens, and the more light it is capable of letting pass. So an f2.0 lens will let in more light than say an f4.5 Lens. Most lens' will have a minimum Aperture of around f22 for a DSLR. With Compact Cameras, the Aperture range of the Lens is probably very small - it might be something like f2.8 - f4-8 - which is a very small range., while a "Prosumer" model is likely to be around f3-f8.

By using a larger Aperture, (a smaller f-number) you are letting in more light to the sensor. So far so good.

Now, this is where things start to get a bit tricky, the Lower the F-number the shallower the depth of field. The Depth of field is the "depth" of the scene that is sharply in focus in a given picture. A smaller f-number will give you a smaller depth of field, while a large f-number gives a greater depth of field.

Now, there are certain instances where you would desire either a small or wide depth of field. The best example where you would desire a wide DOF is a landscape type photo. You would typically desire that close and distant objects all be sharply in focus. An instance where you might desire a shallow DOF is when you are taking a photo of a single person in a crowd. You would use a shallow DOF (big F-number) to have the focus only on your subject, and closer and more distant people in the crowd would be out of focus - thus emphasising the subject of your photo.

A couple of Examples that highlight the DOF can be found in my Photoblog - Example 1 and Example 2

Example 1 is taken with an Aperture of f2.8, and the subject is fairly close (approx 15 cm) to the Camera. You can see that there is only a very small part of the picture that is in focus, and the closer and more distant parts are OOF (Out of Focus).

Example 2 is taken with a Larger Aperture setting of f22. The main subject which is close to the Camera is clearly in focus and the Distant object is clearly OOF. You might at first ask why such a small Aperture was chosen to demonstrate this. The answer is simple, A large Aperture was required so that the whole of the Near object was in Focus, as object was once again only about 30cm away from the Camera, but around 20cm in length. The DOF at 30cm distance and f-22 for the lens is approx 5cm, and you can see in the picture that an area of about this size is what is in focus.

You can get a chart that allows you to calculate the Depth of field for any given aperture. The best resource I have found for this is the DOFMaster site.

As noted, Compact Cameras only have a very small range of adjustment in this area, and this is one of the big trade-offs you get with a very small lens in almost all P&S - you simply don't get a large Aperture range. 

Now, grab your Camera and experiment for yourself. With this small amount of theory, put it into practice and take some creative photos.