Canon 50D vs. Canon 500D

[Big Mike]

Since you prefer to use your feet for zooming, what about prime lenses? A 50mm F1.4 and maybe something in the 24-30mm range?

I'm not much of an expert, so for what exactly do I need a wide aperture? I'd like to take pictures at night and at daylight, lets say for landscapes..

Photography is about exposure. The exposure equation has three main things that you can control. The shutter speed, the aperture (size of the hole through the lens), and the sensitivity (ISO).

The shutter speed is pretty simple. The shutter opens then closes. The longer it's open, the more light it can let in. The shutter speed affect how movement is recorded. A longer shutter speed will show motion as blur. Part of that motion could be the motion of the camera because it's never fully still while you are holding it. So if your shutter speed drops too low (open too long), your shots will be blurry because of the camera movement (unless you are using a tripod etc.)

The 2nd part is the aperture of the lens. The bigger the aperture, the more light that can get in. Aperture also controls the Depth of Field (DOF). Aperture is represented by the F number...lower number is a bigger aperture, higher number is a smaller aperture. The number on the lens is the maximum.

Shutter speed and aperture work in together to regulate the amount of light that gets into the camera. So if the light is the same, the setting can trade off with one another. If the aperture gets bigger, you would need a faster shutter speed, in order to keep the same amount of light (same exposure).
This becomes important when the light levels are getting low, be cause you probably wan to avoid having to use slower shutter speed (because of the blur)...so a lens with a larger maximum aperture will be able to let in more light, thus letting you use a faster shutter speed...thus getting less blur. That is the main advantage to a lens with a larger max aperture (usually called fast lenses). Also, some people like shooting with a shallow DOF, so a large aperture is good for that.

So that is why someone would choose a lens with a large maximum aperture.

 

[johnj2803]

i would still go for the 17-55mm f 2.8 canon.

they say its a hidden "L" lens