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I was reading my camera manual last night and playing with the apature setting but if I have to be honest I am still not completely sure what the apature does and how if effects the photos and when one should use what setting. Is there anyone that can explain it to me in absolute simple terms, idiot prrof explanation please?
I look and the diagrams / phots explaining it etc but I am still left with a "so what are they talking about?"

Aperture controls the amount of light which reaches the film (or chip) in a given unit of time, and it also determines the depth of field. The relationships are as follows:

Big aperture (small f-number) allows faster shutter speeds, and causes small depth of field.

Small aperture (large f-number) requires longer shutter speeds, and causes greater depth of field.

Matej thanks,
does a "small depth of field" mean you can see things closer clearer and then with "big depth" of firld things further away will ALSO be as clear as the things close?

Alison, not quite. Small depth of field means that you see sharp only those things you have focussed to, while big depth of field means that more stuff around the point you focus to is sharp (or "clear" as you put it).

Maybe a little sketch will help. See attached image (sorry for the bad quality, I don't have much time right now, and am lacking the right tools on this computer). Look at the top half ot the image to start with. It's a rough sketch of your lens to the left, and the black lines indicate light rays coming from your object (the film/sensor would be to the left of this image). Where the black lines cross is the focus point - where you focus your lens to. That is the only point that will be 100% sharp in the image.

Now, viewing an image with the human eye allows for some tolerance, i.e. points a little bit in front or a little bit behind the focus point will appear sharp. In other words, even if the black lines do not actually cross, but are very close together, that's going to be still sharp. I've tried to indicate that with a red bar - all the points inside it will appear sharp. The length of this red bar would be your depth of field. It's a range of distances around the focus point inside which objects produce a sharp image.

Let's now change the aperture. Note the little thick black lines on the top and bottom of my "lens"? That's a cross-section of the aperture, being wide open. If you turn to the lower half of my sketch, there I've changed the aperture to a narrower opening - "stopped down" in photographic slang, which means increased the f-number. So, the top half could be something like aperture f/2.8, while the bottom would be something like f/11. (I may assume your manual explains these numbers?)

What happens is, that we are blending out some of the light rays, so the ones that determine which points are still sharp form a narrower cone - see how my black lines have changed. Now, if I take the same tolerance for the dof as above, the red bar becomes much longer, since the black lines meet at a smaller angle, i.e. stay close together for a greater distance. This means that the dof has increased by stopping down.

Credit where credit is due: the web site (www.)flaschenboden.de has a sketch like this, with explanations (in German). You might also want to try out photozone.de, click on "Technique" and then on "Depth-of-Field" under "Lens Technology" - there's a little JavaScript on that page that allows you to play around with aperture settings and observe how that changes an image. Of course, the best way is to try it out on your own camera!

Please note that this simple sketch misses a few important points, but it should explain the close-up you are concerned about: what happens if you keep the aperture fixed but move the focus point closer to the lens? I'm sure you can figure out why the dof will be very, very small then.

So much about how aperture affects the depth of field. I assume you've read in the manual about the link between aperture and exposure time: obviously, if you increase the f-number, less light comes through the lens, so you need to expose longer, and vice versa. The most tricky bit if you're new to this probably is to remember that increasing the f-number makes smaller apertures...

Hope this helps,
Thomas.

Think of depth of field as being what is in focus from front to back.

If you want a flower to be in focus with the back ground out of focus you would use an fstop with a low number, large opening. i.e. f2.8

If you want everything to be in focus; with the flower in focus as well as the background, use an f stop with a high number, small opening. i.d f16

A helpful way to understand DOF, take your camera and go out and find something that has repetitive lines, i.e. telephone poles, fence, etc.

Take a picture using each fstop, be sure you focus on the same point for each shot. Also, remember , you will need to change the shutter speed if you are in manual mode. If you are using Aperture priotry, the camera should mke the ajustment for you. DO this on a day with good light, so you will not drop below 1/60 of a second in shutter speed,as a blurring photo may confuse you with what was camera movement and what is DOF.

Examples:

Landscape photographers use large DOF, so everything is sharp from front to back. I.E. fstops of F64 and above.
On the other hand, sports photos show short DOF, so the player is in focus and everything behind them is out of focus, I.e/ f 2.8

hope this helps

Thomas, eureka!!!! I see the light. Thank you so much for an simple understandable explanation. I have printed it and keep referring in moments of doubt. Thank you.
Ann's further explanation just put the cherry on the cake. Thank you Ann. Wow I feel bright lmao. Thank again.

Ann Thank you so much I replied to you and Thomas together. A wonderful simple explanation. Thanks again.Alison

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