Johnny Loc: Shreveport, La

I here people saying that you want faster lenses, but not quite sure what that means. I have a Canon 50D with an EFS 18-200mm lens. Is that a fast lens?

DanielB Loc: San Diego, Ca

Lenses have ratings for "f" stops or how much light your lens will let in at maximum aperture. A lens at f1.8 let's in twice as much light as a lens that is at f4. look at your lens usually at the end it should show you what your lenses "f" stop rating is. It will look something like f4-f5.6. The lower the number the faster the lens (more light it let's in).

notnoBuddha

also a faster lens will cost more and fixed lens is more likely to be bought as a faster lens than a zoom. A zoom lens will have a variable f-stop in that the longer range will not be as fast as the lower mm setting.

Dame

And if it's unclear; A bigger aperture (smaller F #) requires less open shutter time for correct exposure. Therefore, it's faster.

Leopold Lysloff

My thoughts about fast lenses is that: The wider or more open a lens is, the faster it is. The fastest lenses have the largest open area. Today a lens that opens as far as f=0.95 is considered among the fastest lens. Most lenses we use are marked f=1.8 or f=2.8 or 3.5 etc. The larger the f number, the slower the lens. Fast = more light get in, Slow means less light get in. In darker situations it is good to have a faster lens. In Bright situations you can do fine with a slower lens. Faster lenses are also more difficult to build and therefor can be more costly.

DanielB Loc: San Diego, Ca

Wow... Talk about redundant answers.

Leopold Lysloff

Hey, some of us need them. What can we say?

sinatraman Loc: Vero Beach Florida, Earth,alpha quaudrant

Complain to the department of redundacy department!!!!! One point not brought up the smaller f stop numbers have the smallest depth of field allowing you to make those great shots were the subject is in focus and all the background is not.

PhotoArtsLA Loc: Boynton Beach

Here's something not so redundant:

F-stops are not an accurate measure. Each lens element absorbs a certain amount of light. The actual amount of light hitting the film/sensor plane is the T-Stop, or transmission stop. As the photographic stakes rise, such as in film production, you mainly see lenses marked in T-stops.

T/0.65 has been the theoretical limit for lens design for a long time, but the lenses of this spec have been one-offs and never mass produced.

That said, this thread is basically correct. Fast lenses are always more expensive, and fast zooms with uniform f/2.8 or faster performance are also often of prime (single focal length) lens quality at most of the zoom range. These lenses are often more expensive than the camera used.

I've seen people errantly posting about their 500mm f/1.8 lenses. These are f/8 catadioptric lenses which confuse the user by their common 1 : 8 designation on the barrel. It means f/8. The olde Perkin Elmer 600 f/8 solid cat sold by Vivitar a generation ago was a fine little 600mm lens.

DanielB Loc: San Diego, Ca

Excellent information PhotoArtsLA -Thank's

Victor

The term fast lens refers to the shutter speed. With more light you can use faster shutter speeds and with less light you will need to use slow or slower shutter speeds. A lens that lets in a lot of light (f1.4) allows for faster shutter speeds (desirable). A lens that lets in less light (f5.6) needs slower shutter speeds (and/or high ISO). That explains the "fast" and "slow" words regarding lens speed. The indicator of the light that a lens allows is the "f" stop number as in f1.4. Today's high ISO digital cameras partly make up for slow lenses (f5.6).

jerryace1

see i told you i was here to learn thanks guys

Johnny Loc: Shreveport, La

Thanks fellows that certainly answers my question, and gives me a better idea for my next lenses.