What does something like 'f/2.8' on a camera lens indicate?

Question

I know about shutters and apertures. I also know that f/2.8 is an f-stop number. But it is unclear what this indicates. Is it the best aperture to shoot at ? Or is it the lowest f- stop number ? Or is it something else ?

Answer 1

2.8 is the largest aperture that the camera has. if it is a point and shoot, you will not be able to control the aperture (unless it has some manual features like the Canon A series).

Answer 2

The above posters are all correct, but has anyone mentioned this?
Most lenses are not as sharp at the widest aperture. If you need the light, by all means, so ahead and shoot wide open. If not, stop down a bit. Lenses are usually sharpest in their mid-range.

Here is something else to envision.

Consider your picture is a bucket of water you want to fill. The aperture is the diameter of your hose pipe. The shutter speed is how long you leave the faucet on. So you can use a big hose (wide aperture) and turn on the faucet for a little bit (faster shutter speed) Or, you can use a small hose (small aperture) and leave the faucet on for a long time (slower shutter speed.) Either way, your bucket will get filled (the image properly exposed)

Aperture also controls depth of field, so f2.8 will have less in focus than f11.

Hope this helps.

Answer 3

The f stop rating on the barrel of a full auto SLR/DSLR lens indicates the "lowest" f stop that lens can handle, i.e., this is the largest that the aperture will open. Remember that a higher f stop indicates a smaller aperture opening.

A lens with a low f stop is often referred to as "fast glass" because a larger aperture will allow for a faster shutter speed. f2.8 and lower would be in the "fast glass" range, while an f4 rated lens would be consider "slow glass".

The relative speed of the galls has an impact on how much you pay for it also. Faster glass costs more.

Answer 4

http://www.megapixel.net/phpBB2/viewtopic.php?t=11239

I think I'm getting the hang of all the basics of cameras and photography, but there is one thing that keeps hovering just outside my grasp: aperture and f-stop. I understand that the f-stop is a fraction related to the lens length and the openning for the light, but what is the formula? Further, what does it really mean? If it was just a matter of light gathering ability I would think every shot should be taken with the lens wide open, but I've heard caution against this? Why is that?

Also, is this related in some way to why some photographers prefer fixed lenses instead of zoom lenses? All other things being equal the ability to change the zoom of your lens would obviously be an advantage, but I know some prefer the former. In my brief reading online I've noticed that fixed focal length lenses tend to have lower f-stop values, though considering my sample size I could be way off.

I'm considering a new lens for low light photography, but don't just want a good suggestion on what specs to look for; I want to really understand what all the specs mean. I guess what I really need is a primer about lenses and the specifics of how they work. Could anyone help me out? Maybe a good link or two?

GO TO THIS SITE AND THE ANSWER WILL BE THERE.

Answer 5

The Maestro and HouseMom are correct, but I'll provide some insight. This is not a "best answer," since they have already answered your question.

Aperture is the ratio of the size of the opening to the focal length of the lens. The diameter of an f/2, for instance, is 1/2 the focal length. If it is a 50 mm lens, the opening is 25 mm. (50/2=25 mm) f/2.8 on a 50 mm lens would be about 18 mm in diameter. (50/2.8=17.8) f/2.8 on a 200 mm lens would be a whopping 71 mm in diameter. (200/2.8=71.4) This is why large aperture telephoto lenses are so big and cost so much money.

Answer 6

F/2.8 will also let the most amount of light in; an F/22, the smallest amount. It kind of goes backwards - the higher the number, the smaller the aperture and the less light is let in through the shutter.

Answer 7

F/2.8 is an aperature size. There is no one best size, it all depends on what you're shooting and how you want to picture to look. If I remember correctly (took high school photography years ago) F/2.8 is a large aperature, best for shooting objects close to you, like a bowl of fruit on the table or something. The larger F-stop numbers indicate a smaller aperature, best for shooting far away objects or landscape type shots.