photography exposure?

Question

what does it mean "exposure" in photography

how do you do the technique?

@ ALT my other question didnt make sense when i read through.

Answer 1

Exposure is getting detail in everything in the scene - highlights and shadows. From the blackest black to the whitest white and every gradation of tone between those extremes.

Cameras with built-in meters (99.9%) "read" a scene as 18% gray. 18% gray is the reflectance of an average scene, such as a sunny day with a field of yellow flowers and a blue sky with white puffy clouds.

Exposure becomes more difficult when our scene consists of an area in bright light with areas of dark shadows. Relying on the camera's meter will almost always result in the brightly lit area being over-exposed ("washed out", "blown highlights" are terms commonly used) with little or no detail and shadows that are very dark with little or no detail ("blocked up") and a poor image that we'll delete or discard.

I could continue but I'd rather suggest a book for you to read: Object & Image: An IntroductionTo Photography, Third Edition" by George M. Craven.

These are also worth considering:

"How Digital Photography Works, 2nd. Edition" by Ron White

"Exposure & Lighting for Digital Photographers Only" by Michael Meadhra & Charlote Lowrie

"Hands-On Digital Photography" by George Schaub

You can read reviews of these books at shutterbug.com

Answer 2

Edwin's got a good answer.

The biggest thing I'd like to add is that exposure is somewhat subjective. Part of the reason for this is that no film or digital medium (with the exception of some HDR effects) can effectively expose the entire dynamic range that you can see.

In laymen's terms, your eyes can see bright-brights and dark-darks at the same time. The camera can't always handle these extremes all at once. So in some situations, exposure MAY mean sacrificing the highlights for the shadow detail you want, or vice versa. A prime example is a brightly backlit subject (without the use of flash): you may well need to accept "blowing" the highlights to properly expose the subject... and this may even be a desired artistic effect.

Answer 3

You deleted your question before I was able to edit my answer. Here is what I was going to say:

Exposure time on a camera does affect the lighting and it also effects the sharpness of the subject. When the exposure time is long, it is letting more light into the camera, making the final picture brighter. When you have a short exposure time, it is letting in less light (use this on a very bright day). If you are trying to capture a night scene, like fireworks, you want a longer exposure time to capture as much of the movement as you can. If you are taking a picture of a sport where there is a lot of fast movement, use a short exposure time to get a clear picture.

Here are some examples of fast and slow exposure (it is really called shutter speed):

Fast:
This was taken on a bright day:
http://www.flickr.com/photos/21805952@N08/2104430613/

This captured the movement of the horses (it was a overcast day so the photo is not the best quality):
http://i28.photobucket.com/albums/c215/myleshowling/horsesrunning.jpg


Long:
All of the lights are off except the tree's:
http://www.flickr.com/photos/21805952@N08/2105397879/

Notice how the cat's face is blurred? He moved when i took the photo:
http://i28.photobucket.com/albums/c215/myleshowling/IMG_2903.jpg

Hope this helps!

Answer 4

Exposure is a combination of light intensity and time, imaged onto a sensor or film.

There is an entire science around it (sensitometry) and while the scientific value of exposure is something like Joules per Square Centimeter (at a specific freqency of light) the modern measure of exposure for photographers is called EV (exposure value).