Monday, January 10, 2011

The Basics of Manual Settings–Part 3–Aperture

Now that we know ISO and Shutter Speed, it’s ready to move on to Aperture.  Aperture can be confusing, but let me let you in on a secret, it’s only the jargon that is confusing.  When you come right down to it, aperture is the size of the hole in your lens that is letting light through during a photo. 

You know how your pupils get bigger or smaller depending on the ambient light?  The aperture basically does the same thing.  Only, instead of having your own super smart brain to do it automatically, you have to tell it what to do.  We do this by setting F-stops.

What’s an F-stop.  Well, it’s a mathematical calculation of the focal length divided by the diameter of the aperture opening, but you don’t need to know that right now.  All you need to know, is the smaller the f-stop number, the bigger the hole and visa versa.  F1.4 is a very big hole.  F22 is a small hole.  If you get into pinholes, sometimes those are F300, but that’s a whole other story.

So, what is the point of aperture?  Well, obviously a bigger aperture (f1.4) will let in more light.  This means you can shoot at a higher shutter speed and/or lower ISO than at f22.  Example: if you are shooting at 200 ISO at f4 and your shutter speed is at 1/30th, but you need it at 1/60th, change to f2.8.

Now for the fun part of aperture, it controls your depth of field.  Depth of field refers to the amount of stuff in a scene in front of or behind your focal point that will be in focus.  When you shoot at a wide aperture, your depth of field will be really short.

In this photo, my dog’s eyes are in focus, her ears are sorta in focus, but the focus drops off at her nose and in the background.


This can be a nice feature because you can use depth of field to focus on a subject and blur out the background. 

Or, on the other hand, you can shoot at a smaller aperture, such as f22 and get more depth of field.  Or take it one step further and use a pinhole and achieve almost infinite depth of field.

This is my mailbox and street at f22.


Some other things of note about depth of field, the closer your subject, the shorter your depth of field.

Some of the older cameras even had depth of field guides on the focusing ring.


In this photo, the top 2 lines of numbers are focal distances, the 3rd line down shows where the focus is (orange line).  It also shows, with the mirrored f-stop numbers, what distances would be in focus at that particular setting.

If the above settings were used at f22, everything from 1.5 to 10 meters would be in focus.  At f 11, everything from 2 to 4.5 meters would be in focus and so on. 

This can be handy for having complete control over depth of field.  Do you want more in focus in front of your subject than behind it?  Using the guide numbers, you might not actually focus on your subject to control where the depth of field lies.

Finally, depth of field is controlled by how much your focal subject fills the frame.  If you zoom in (or get close), you will have a shorter depth of field than if you shoot at a wider angle.

Those are the basics of aperture!  Now we can see how the 3 settings come together… tomorrow we’ll talk about stops… and there will be a handy craft project!!

Shasta Betty

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