Aperture Question

[sbug_adam]

So the lower the aperture number (ex. F/2.8 ) the more distorted the background becomes.. Is that the case also if the object you want distorted is the foreground?

Adam

[Abel]

Shallow depth of field = smaller f number

Deep depth of field = larger f number

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SMALLER f number means the aperture will be open much WIDER which will allow MORE light in which in turn will require you to SPEED UP the shutter so that your photo is not OVER exposed. this is what people refer to as "fast lenses". a "fast lens" is one that allows a maximum amount of light in (lower f number ex f1.4 or f2.8)

LARGER f number means the aperture will be open much SMALLER which will allow LESS light in which in turn will require you to SLOW DOWN the shutter so that your photo is not UNDER exposed.

[chloew]

Originally Posted by sbug_adam

So the lower the aperture number (ex. F/2.8 ) the more distorted the background becomes.. Is that the case also if the object you want distorted is the foreground?

Correct, but rather than using the term "distorted", it is more correct to say "out-of-focus" or "blurred". Distortion is a different behavior of a lens.

For a wider aperture, anything in front of or behind the plane of focus will be more out-of-focus or blurred than for a smaller aperture.

http://www.photozone.de/3Technology/demos/depth.htm

[Hogleg 44]

Originally Posted by sbug_adam

So the lower the aperture number (ex. F/2.8 ) the more distorted the background becomes.. Is that the case also if the object you want distorted is the foreground?

Adam

This question is subject to a lot of variables...If the object you want Blurred at f2.8 (out of focus) is in the foreground, you need to carefully focus on the background object you want to be in focus, or behind it somewhat if possible. And it also really depends on how far the two subjects are apart, and how close you are to them. Wide shots where you are closer will produce less DOF at 2.8 (more out of focus in front and behind the subject) than zoomed way out.
In another respect, short DOF is desirable, and in portrait pictures called brokeh, where the background behind the subject is deliberately 'soft'.

[Abel]

also something i learned the hard way, many smaller point and shoot cameras can not produce a shallow depth of field...

their f2.8 may seem like a f8 on a dslr etc etc

[chloew]

Here is another good resource and description of boke (or bokeh), the property of a lens of how nicely it puts a point light source out-of-focus (circle, octagon, etc.) For example, if you use a mirror reflective lens (500mm f/8 are common), a point light source out of focus will look like a donut (bad bokeh).

http://www.luminous-landscape.com/essays/bokeh.shtml