What do "1/250" and "f/4.5" stand for?

Sleepy_Sentry · May 15, 2007

I've been reading over this HDR tutorial, but don't know what "1/250" and "f/4.5" stand for. I know they must stand for a camera setting, but don't know which ones (does f mean focus?).

Are these setting changeable on must digital cameras?

tr0gd0o0r · May 15, 2007

The two terms you mention are referring to shutter speed and aperture. 1/250 is the shutter speed. It stands for 1/250th of a second. A faster shutter speed will prevent motion blur from a faster moving subject. Conversely, if the shutter speed is too slow, then the subject will be blurry b/c it is moving too fast or the camera shakes.

f 4.5 is referring to the aperture, or how wide the lens is open. The wider the lens is open, the more light is able to get into the lens and onto the sensor. The smaller the actual number the wider the lens is open (there is a complicated formula someone else will have to explain for this.) Both of these are changeable on many digital cameras? Which model do you have specifically?

YoungPic · May 15, 2007

1/250 is the shutter speed and the f.4.5 or what ever it is, is the aperture value

Iron Flatline · May 15, 2007

The aperture is the hole through which the light comes into the camera on to the sensor or film. F/4.5 is a certain aperture, it designates how far open your aperture is. 1/250th means the shutter speed, it denotes how long your shutter is open - and subsequently for how long light is allowed to hit your sensor or film.

A well-exposed image requires a certain amount of light. You can open your aperture to a smaller size and then keep your shutter open longer, or you can open the aperture wider (thus allowing more light to flood in) but then you'll want to keep it open for a shorter period of time to limit the amount of light.

You can drive a car at 20 mph in 1st gear at 5000 rpm, or in 2nd gear at 2500 rpm, or in 3rd gear at 1000 rpm. They each have their own advantages and disadvantages. 1000 rpm is quieter and uses less gas, but you have lower responsiveness.

With photography it is the same thing - a smaller aperture but longer exposure means greater depth of field (more things in focus near and far) but the longer exposure means you have to have really steady hands or better even, a tri-pod. A quicker shutter speed and wider aperture means you can freeze action and don't have to worry about camera shake, but you'll have a shallower depth-of-field, meaning some parts will be in focus where as things in the background and/or foreground might be blurry.

These are creative choices, as well as environmental choices, as well as ultimate limitations of the equipment that you can use to your advantage, or that will force you to work around themselves.

Hope that helped.

Big Mike · May 15, 2007

Are these setting changeable on must digital cameras?

These setting are variable on just about any camera these days...but whether or not you can directly set them depends on the camera. Simple cameras just have settings with pictures, for landscape or portrait...while more advanced cameras let you adjust the settings directly.

Iron Flatline · May 15, 2007

Oh yeah, and just to add to the confusion: the smaller the aperture number, the wider open it is. F/2.8 is pretty wide, where as f/11 or f/16 is much narrower. Others here will be able to explain why, but what you really need to know is low = wide.

Digital Matt · May 15, 2007

Those refer to shutter speed and aperture, which are two parts of the exposure forumla which states Exposure = Aperture + Shutter speed + Film speed (ISO). A good basic photography book might be what you need.