Choosing an Aperture:

What Aperture should I use?

What are the factors affecting my choice?

Answer:

All of these considerations may affect your choice of aperture in some way. Let's discuss them.

 

Shutter Speed:

The relationship between the two has been examined in depth.

If you are still unsure it might pay to go back for a little revision.

 

Depth of Field:

Depth of field is a big subject and a little tricky to get a handle on.

At this stage we only need to know how to get the results rather than why it happens.

But here are the basics:

If a person standing two meters away is in focus but a bus ten meters behind is barely recognisable because it is out of focus, then this photo is said to have a shallow depth of focus.

If the same person is in focus and the bus is in focus and the mountain range in the distance behind the bus is also in focus, then this photo has greater depth of focus or depth of field.

The whole concept is discussed in terms of depth of field.

 

 

The rule to remember is - the wider the aperture, the shallower the depth of field.

Depth of field is also affected by lens length. For example, a photo taken with a 14mm lens has almost infinite focus (at f22), from the pebble six inches away to the mountain 20 kms away.

On the other hand, a 200mm lens at f2.8 could have a person's eye in focus while his ear is not.

Which brings us back to Artistic Effect.

 

A narrow aperture - f8 on an 18mm lens - gives depth of field - that is, the foreground and distant background are equally sharp. click on the image to enlarge

Artistic Effect:

When deciding to choose aperture and letting the camera or light meter dictate the shutter speed, we do so mainly for artistic reasons.

But don't forget the relationship between the two. You may not be able to do what you want.

Depth of field is what we're after.

 

Greater Depth of Field:

For example, landscape photography is best done with greater depth of field.

Some foreground detail is a good idea to add interest to the otherwise boring background.

This foreground detail needs to be in focus.

To achieve this effect a narrow aperture is required, for example, f22.

 

In this case, a wide aperture - f2.8 on a 200mm lens - kept the subject sharp while throwing the background, which was a white car anout 4 meters away, out of focus. click on the image to enlarge

Shallow depth of Field:

Portraiture is best done with a shallow depth of field to separate the important subject from a cluttered or uninteresting background.

To put the background out of focus - a shallow depth of field - a wide aperture is required, for example, f2.4

 

Of course there are exceptions to every rule. That's what artistic effect is all about.

And besides, none of these are rules, they are all just guidelines to help us understand the principle.