Beginners question, please! - F-stop/aperture and exposure?

Viva · Beginners question, please! - F-stop/aperture and exposure?

Right!!! Where shall I start?

Please could someone explain aperture and f-stop to me! I sort of understand that a longer exposure means keeping still :

: , but what about depth of field if light conditions are nice and bright? I am lost.

dtalbot

Right,
F stop setting and aperture are the same thing! As you adjust the the f stop setting what you are doing is making the the hole that light can pass through the lens to the film (or ccd in a digital camera, doesn't matter) bigger (as you move to smaller f stop numbers) or smaller (as you move to bigger f stop numbers). And this means that for a given exposure time less light will get to the film at a bigger f stop than a smaller f stop number. To get the correct exposure you need the right total ammount of light hitting the film so as f stops get bigger you need a longer exposure to get the light you need.
As to the keeping still a good rule of thumb is you can hand hold a phot and get a clear picture for an exposure of about 1/(focal length of the lens) seconds. So say 1/50th sec for a standard SLR 50mm lens or 1/300 for a 300mm telephoto.
So it might look like the best bet is to use nice low f stop settings to get fast shutter speeds and avoid camera shake. (Low f + big hole for the light to get through so less time taken to get the ammount of light you need). This is where depth of field comes in. At a low f stop value the length front to back that is actually in focus (thats more or less what depth of field means) will be very short, possibly only a matter of mm or cm if you are doing close up work. On the other hand at a big f number the depth of field may extend from a few feet away out to the horizon.
So as well as being a trade off of more depth of field = slower shutter speed you have a load of creative possibilities opening up. For a landscape you need lots of depth of field so a big f number. But if you are shooting a portrate or closeups of somthing you might want to thow the background out of focus for the best effect. In that case go fith a low f number, focus tightly on your subject and let the depth of field effect blur the rest. If your camera has a depth of field preview feature click it on to check the effect.
Hope this helps, any more questions just ask and I'll do my best to answer!

Viva

I'm getting there, just hopeless as learning without actually being shown

, will try again soon .... and possibly ask another question

Tanks!