Short Description
Wide aperture lenses let in more light, letting you take shots with less blur or in more dimly lit situations. Shooting at wider aperture also narrows your depth of field, allowing you to focus selectively on your subject and blurring the background. The aperture setting is rated in f-stops (also known as f-number and focal ratio), each increment in f-stop lets in half the light meaning you must expose the photo for twice as long.
The average digicam has an f-stop of 3.2 and DSLRs can get lenses with an f-stop of 1 although those are rare and extremely expensive, affordable DSLR lenses with a 1.8 f-stop are common.
F-Stop Scale
The standard full-stop f-number scale is:
f/1.0
f/1.4
f/2
f/2.8
f/4
f/5.6
f/8
f/11
f/16
f/22
f/32
More Light
Each time you step down the f-stop one stop you gain the ability to expose the photo for the half the time. Although you can modify the ISO to achieve the same, unlike changing ISO modifying the f-stop does not degrade the image quality. Typically the lower minimum f-stop on a lens the more expensive it is and that is why most compact digital cameras do not utilize very low f-stop lenses. For example the average f-stop for digicam is around 3.2 vs say f1.8 on a reasonably priced fixed lens for a DSLR - at f1.8 vs f3.2 you need only expose the photo for about 1/3 the time which can make the difference between a blurry photo and a crisp one.
Shallow Depth of Field
Selective Focus Portrait
The following portrait shot at f2.8 / 24mm on a
Canon 5d Mk2 DSLR demonstrates using the benefits of selective focus.
One of the trade offs of using a wide aperture is the depth of field is narrowed significantly, this means that a portion of the photo will be in focus and the objects in front and behind that focal point will be out of focus. The larger the aperture the smaller the plane that remains in focus. Although this is a disadvantage if you want everything in focus many find the results desirable providing a means to draw attention to portions of the image. The photo to the right uses selective focus to capture a portrait, you can see behind the man is out of focus and his hand in front of him is also out of focus. Although most portraits would attempt to get rid of distracting detail using simple backgrounds this photos uses selective focus to capture the individual in an environment without visual distraction. The photo was also taken at night and the larger aperture allowed a relatively lower ISO speed to be used.
Big Aperture Digital Cameras
The following compact cameras have larger than usual minimum apertures.
Discussion
/panasonic-lumix-dmc-lx10-(lumix-dmc-lx15)_front_thumb.jpg "Panasonic Lumix DMC-LX10 (Lumix DMC-LX15)")
Although most digicams do not have very wide apertures, the Panasonic Lumix DMC-LX10 (Lumix DMC-LX15) has the widest aperture available of f/1.4.
Showing 6 comments
This is surely incorrect - and the other way round?
Sourav
(twinkle_littleheart@yahoo.com)