newbie question

[boxer82003]

is the apature and the f/stop the same thing ?

from what i understand an a apature or f/stop of 4.5 the focus will be on the main subject and the background will be blurred and a apature or f/stop of 8.0 means more of the background will now be in focus

is this correct

sorry for the dumb question

[forrest64]

F-stop and aperture is the same thing. Smaller apertures (larger F-stop numbers) increase the in focus range in front and in back of the object in which you are focused.

Mark

[Andy_T]

Boxer,

what you write is *basically* correct.

Aperture or f/stop measures how much light reaches the sensor or film, regardless of the exposition time. The lens has a diaphragm inside that can be opened or closed, leaving a big or small hole for the light to pass through.

The 'out of focus' effect is both a function of a large aperture and focal length. The larger the aperture AND the longer the focal length AND the further the background is away from the main motive, the more the background/foreground will be out of focus.

If you shoot at 100 mm focal length, 4.5 might be sufficient to blur the background, if you shoot at 28 mm, you'll most likely get a somehow sharp background.

Look at some interesting thread with pictures for the Canon 85 mm lenses: http://photography-on-the.net/forum/showthread.php?t=34632

Best regards,
Andy

[EugeneK]

If you have a digital camera you can do some test shots and see for yourself the effect. Try this:
Use a tripod if you have one, but go to Av mode on the camera and take a series of pictures of a garden or something that has a wide range of things at differant distance. Focus on on subject nearby and take a series of shots at say f/4.0, 5.6 ,8 ,11... - every other f/ stop. Bring them up on the computer and see the differance. The wider open settings ( the smaller numbers) will have a more narrow "depth of field", the area that is in focus. The amount of depth of field is also related to the distance of subject and the lens size.

-Eugene