photography: 2 - lens sizes and depth of field

Lens sizesDepth of Field

Camera lenses come in different sizes:

The longer the lens the more it enlarges the object being photographed

Lens are measured in mm… 50mm is roughly the same as what we see

with the human eye:

Less than 50mm (typically 24-30mm) gives wide angles:

And more than 50mm (typically 70mm+) zooms in on a subject:

A zoom lens is a jack of all trades lens that can change its length from, say, 30mm to 70mm:

Many digital cameras do not have a CCD sensor that is as big as a 35mm film frame so some cropping occurs

GEEKGEEKALERTALERT!!

Depth of Field (DOF) refers to how much of a photo is in focus

Suppose you have focused on a person you want to photo:

The DOF is the distance you could move the object towards or away from the camera without having to re-focus:

Everything outside of this zone will be blurred and out of focus

>>> DEMO <<<

>>>DOF with zoom lens<<<

There are three (four counting Photoshop) ways to create shallow Depth of Field:

1.Use a long (70mm+) lens or a zoom2.Set a smaller aperture setting (f2.8 / f4)3.Put a Neutral Density filter on your lens

There are various setting on an SLR camera:

ISO Shutter Speed Aperture

They all adjust different aspects of your photo…

Aperture adjusts the Depth of Field by changing the size of the hole that light travels through to get to your film/CCD:

Basically, the smaller you set the f number to, the smaller your Depth of Field:

Changing the aperture means changing the shutter speed to compensate (more next week), for now…

Set your camera to aperture priority mode (usually marked ‘A’ or ‘Av’on the control dial)

Narrow DOF

Wide DOF

>>> TASK <<<

Put an a few objects on along a table Step back as far as you can and zoom in to create DOF Then get closer and take two identical photos – one on f2.8

and one on f16

If you don’t have these setting on your camera try using Macro mode and getting really in close…

…and/or take some photos that you can add DOF to later using Photoshop

On a bright summer’s day you will have to set your aperture to a high number (f11 / f16) to avoid over exposure…

So setting a small f-number toget a small Depth of Fieldwill not work

The solution is to put aNeutral Density filter on yourcamera…

Using an ND filter is a bit like putting sunglasses on your camera

What this means is that you can open the aperture a bit more and get more Depth of Field

ND filters do not effect the colour, only the amount of light reaching the film/CCD

And, of course, Depth of Field can be faked using Photoshop selections and a blur filter:

>>> END <<<