Thursday, May 1, 2014

The Newbie - Aperture

So this month we are having a look at aperture.  We talked about pictures with fuzzy backgrounds and pictures with sharp backgrounds.

I want to make it clear that I am not necessarily going to say things that are accurate here, but I can tell you what helps me remember aperture settings.

My friend in the garden

Here is a picture that I want to take.  My friend is standing in front of a garden.

The important thing to consider here is that the lens of a camera is not flat.  It is curved.  Light is bent when it comes through the curved lens.

The aperture setting controls the size of the hole that lets light into the camera and onto the lens. When I look at the lens of the camera and turn the aperture dial I can't see anything.  But the experts tell me that changing the number on the aperture dial and moving it from its lowest number 5.9 to its highest number 22 is changing the width of the lens that is going to capture the image.

Lens cross section showing the aperture gates that can close
I am going to imagine that when I set the aperture to 6 then 6 little circular gates click across the lens to block off part of the lens.  When I set the aperture to 22 there are 22 little gates blocking the lens so the hole is much smaller.
Six gates closed

What difference does this make? Now we have to look at the lens side on so that you can see the effect of blocking off part of the lens.

f6 - person in focus, background fuzzy
If we choose an aperture of 6 - f stop 6 - then six little gates are closed and there is a lot of curve on the lens that is open to receive the image.  When the picture comes in to the camera there is a lot of fuzziness because with all the curve not much of the photo is captured by the centre of the lens where the image would be sharp. So if I have focussed in the area around my friend I have a sharp image of my friend but a fuzzy background.

f22 - all the image in focus
What if I now choose f stop 22.  There are now 22 blocks on the lens and only a small amount of the lens to capture the photo.  This means that there is a small amount of curvature on the lens. So all the image is captured through the narrow lens opening and all the image is in focus.

So I tried a few photos to test this out.
Of course with photography nothing is this easy.  There are lots of factors that affect a shot, but at least I have an idea of the effect of this one setting!

f6 fuzzy background - wide lens, maximum curvature
f22 - mostly clear background - narrow lens, minimum curvature

This series shows how the background is more or less clear when the only thing that is changed is the aperture

Some useful websites discussing aperture settings:

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