2 out of 3 for my technical DSLR tutorials, hopefully this one helps. This does lead on a little from my one about
Shutter Speed so try and understand that first then read this one. Any problems, just post up
I want to focus on the Aperture size, it's affect on the amount of available light and what is called 'Depth of Field' (DOF).
Using Aperture to control lightThe aperture serves the same function on a camera as the pupil does in the eye. You can make it bigger or smaller to control the amount of light hitting the sensor while the shutter is open.
The aperture size you are using on the camera will be denoted as
Fsomething for example, F4.5 or F11. My standard kit lens ranges from F3.5 to F22. What makes this slightly confusing is that
the bigger the number, the smaller the hole.
If you know you need a set shutter speed for the picture you want to take, being able to change the aperture size is invaluable as you can make the hole bigger or smaller until the picture is exposed correctly (not too dark and not too bright). You will find that there are times when you still cant make the aperture big enough to allow adequate light but as this is only a basic guide I'll discus that in the next tutorial. I just want people to understand the basic principles here.
So, generally if you are shooting during night time or in low light areas you'll need the biggest/widest aperture of F3.5. During a sunny day you may to be using F6.3 or slightly higher as the light is much stronger. Remember that F6.3 is a smaller hole than F3.5.
A different way of thinking about it, if you are shooting sports you'll want a big aperture (small number) to compensate for the fast shutter speed. (Remember that a fast shutter speed doesn't allow a lot of light through because of the short time it's open)
Depth of Field, or DOFDepth of field can be used as a creative tool, and it's controlled directly by the aperture size.
The bigger the aperture (eg. F3.50)
, the shallower the DOF. This is an excellent way of isolating your subject and drawing attention to the main focal point of the picture. Putting this into practice can be quite confusing so I've made a few examples to demonstrate its effect.
The point of focus for all these images was the little cloud on the blue wooden thingy.
Shot wide open at F3.5. Notice how the subject is in focus but everything is very blurry and you cant really tell what's on the picture at the back.
This next picture was taken at F11. Take notice in this one how the writing on the first battery becomes slightly distinguishable, the wall tiles are slightly less blurry and you can see some planes forming on the card in the background.
The last picture was taken at F22, the smallest hole the lens can go to. In this picture see how everything is much clearer including the writing on the battery etc.
Looking at them like that the difference may not seem so dramatic but look at this slightly bodged comparison. I know it's not perfect but it does demonstrate DOF well
.
In the last tutorial I mentioned focal length and it comes into play here as well. How dramatic the backrgound blur is can be exaggerated by the focal length. As a general rule,
the longer the length, the more blur will form.
To have a go at seeing DOF change set your camera to Aperture priortiy, AV on Canon and use F3.5, F11 and F22. (Make sure that you are using the shortest focal length of the kit lens, around 17-18mm, otherwise you wont be able to use F3.5
)
Hopefully some of this makes sense, please ask any questions as there are probably several people wondering the same thing
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