when Buying a lens for your dSLR

zaramuni · Jan 28, 2007

When you buy a lens for the dSLR, the lens usually has a few numbers associated with it. One of these numbers I think is the aperture, for example, a lens that I bought said 3.5. Does this mean 3.5 is the widest my lens will go? What does it mean when they say a lens is 2.8?

just x joey · Jan 28, 2007

yep, if its a 3.5 thats the widest the aperture can go.

shingfan · Jan 28, 2007

just different aperature capability.....the smaller the number...the larger aperature it can provide.....the faster the lense

Mike_E · Jan 28, 2007

2.8 means that it is more expensive! lol

With an f3.5 you can take a picture of some one walking at just after sunset with a medium lens (70-85mm 35mm film equivalent).

At f2.8 you can take the shot between sunset and dusk.

And at f1.4 you can take the shot at dusk (not quite dark).

The faster and more expensive lenses will give better color rendition and will last longer as a rule but a tripod works wonders too.

mike

GilTphoto · Jan 28, 2007

There are 3 main reasons for having or using a more expensive f/2.8 lens rather than a middle of the road f/3-f/5 lens.

1. Optical superiority. Brighter visually through viewfinder.

2. A larger aperature will allow faster shutter speeds. This comes in handy for shooting distant wildlife, or fast moving sports, or night scenes, when using a tripod is more difficult. The ability to get a shutter speed fast enough to handhold the camera and still get sharp pictures.

3. A large aperature gives limited DOF which is good for isolating a subject from the background. A lens with a f/4 maximum aperature may not blur the background enough and make for a distracting or busy image.

It boils down to considerations of budget, and what you need the lens for. If you do mostly landscapes on a tripod, fast shutter speeds are not an issue, and you usually need maximum DOF so a small aperature is needed.

If you do wildlife or sports, you might need the faster lens.