22 July 2011

Exposure

22 July 2011

Exposure is how much light is absorbed into your cameras sensor.  If the shot is exposed for too long, the image will be “washed out”, by letting too much light exposed to your film or digital sensor.  If the image is too dark, then the exposure was too short.

Most cameras have a “light sensor” with a meter inside of your camera that you can see when you look through the lens.  This meter will tell you how much light is being exposed to the sensor.  Normally, there is a middle line which is telling you that the exposure is just right, if it is to the right, then it is too much, or to the left, there is not enough exposure.

If you learn how to control your exposure, you can create some beautiful images.
To do this, you will need to control your shutter speed (The amount of time that your shutter opens to expose the light) and your aperture (The size of the lens opening to let the light in)

Example:  Lets say you are near a fountain in a garden and the correct exposure is f/8; 1/250s with a ISO of 100.  You decide that you want to freeze the water coming out of the fountain, but you cannot make your image any darker (underexposed) or too bright (over exposed)  What do you do?
a) Change your shutter speed to 1/500s, this allows ½ of the amount of light in.  But you cannot stop there, because then your image will be underexposed.  You must compensate to do this
B) Change your f-stop to 5.6, which will give you a larger aperture to let in more light. 

Now you have the same exposure for the image, but your shutter speed is faster that will allow you to freeze the water!

Example:  You are inside and the light is too low to obtain the correct exposure but the problem is that you camera will not be steady and your image will be blurred.  Your settings are:  f/5.6; 1/60s and ISO 100. The largest aperture for you camera is f/4, one stop faster that will result in f/4; 1/125s/ ISO 100.  The shutter speed is still too slow and you will have camera shake.  Since you cannot change the aperture anymore you will have to change your shutter speed and ISO to compensate.  Change your ISO to 200 and up one step to f/250s.  This will allow you to take your image and be sharp enough to take a photograph.

See?  All three parts are related to each other the ISO, shutter speed and aperture.  If you change just one, then your image will be either overexposed or underexposed.  If you change both, you can keep the balance.
Instead of falling water, i included falling snow!  This was taken at f/7.1; 1/25s and ISO 640


Overexposure:

This occurs when the sensor is exposed to too much light.  The result will be white images or white around the areas of the light source.  Sometimes it is impossible to expose the image without any overexposed areas.

Underexposure:

This is the opposite of overexposure, the sensor does not pick up enough light creating dark and black areas.

Note if you are using a digital camera, it is always easier to bring back shades and color from an underexposed image, than the other way around.  (Using PhotoShop)


Related lessons:
Aperture and f/16 Rule
Shutter Speed Basics

Bracketing
Depth of Field
Focused Bracketing or Photo Stacking

4 comments:

lee woo said...

Exposure from a young age to the realities of the world is a super-big thing. See the link below for more info.


#Exposure
www.ufgop.org

Silvia Jacinto said...


I must say that you have a very good article.Continue to inspire your reader and Have a good day! You can also visit my site indicated below and share it with your friends.

n8fan.net

www.n8fan.net

sarah lee said...

I really enjoyed reading your article. I found this as an informative and interesting post, so i think it is very useful and knowledgeable. I would like to thank you for the effort you have made in writing this article.


edupdf.org

crossing borders said...

Thank you! I finally am reading these. ahah, I do not get notifications. must change that! Glad that I could be of some help.