Archive for July 2010
What is Exposure?
Exposure is the total amount of light that is allowed to fall onto the cameras digital sensor or film.
There are three elements that make up an exposure:
Aperture: The size of the hole that lets light into you camera.
Shutter Speed: The amount of time that the shutter is open to allow light in.
ISO sensitivity: How sensitive the digital sensor or film in a camera is to light.
Past posts have been written about each of these elements and I strongly suggest you read about each one to get a good understanding of how they work.
Putting it all Together.
In order to achieve the right exposure each element needs to be balanced out, raise the shutter speed and you might need to use a wider aperture or a higher ISO to compensate. This is called the exposure triangle.
One way you can think of it is that a camera is like a bucket being filled with a garden hose.
There are three variables to consider,
The size of the hose and how much water it lets out (aperture)
The time that the hose is left running (shutter speed)
and the size of the bucket (ISO)
In order to achieve the right exposure the bucket needs to be filled to the very top, if its undefiled you will under expose and if you over fill you will over expose.
Say we want to use a fast shutter speed to take a photo of a moving object, well if we run the hose for a short period of time the bucket will not be filled to the top, so we need to compensate, we can use a hose that has a larger opening and lets more water out (open the aperture) or we can make the bucket smaller so that it gets filled quicker (raise the ISO)
It takes time to master exposure, but its necessary to have an understanding of how it works to achieve turning an idea into a great photo.
You need to understand how each of the elements work and how they effect each other.
For further reading to better understand the three elements of exposure check out some of our past posts:
ISO – How it Works
Some times when we are taking photos we find ourselves in a low light situation where we cant get a fast enough shutter speed to get a sharp photo. You could try opening your aperture to alow more light in, or you could use a flash, but some times thats just not prefered.
One option we have to achieve a faster shutter speed is to increase the cameras ISO sensitivity.
What is ISO
The ISO sensitivity determins how sensetive the cameras sensor is to light. At a high ISO setting like 1600 the cameras sensor becomes more sensitive to light and thus does not need to be exposed to light as long.
You may remember when we used to shoot with film, there was certain film made for sports. What made that film ideal for sports was that it had a higher ISO sensitivity such as 400, so it could achive a faster shutter speed then normal film that might have a lower ISO such as 100.
The Negatives of High ISO
There are some negatives to using a higher ISO though. The higher you boost your ISO the more distortion or grain you can see in your images, sometimes this can be a good look but usualy you want to avoid this distortion. The distortion you get from high ISO is kind of similar to a radio, at a low volume the radios music sounds fine, but as you begin to turn it up louder you begin to hear distortion and imperfections in the audio. As you boost the ISO sensetivity you begin to notice distortion.
Now days alot of the newer, higher end digital SLRs have amazing ISO sensitivities that barely show any distortion or grain.
You should always strive to use the lowest possible ISO sensitivity to achive the best quality photos, here are some guide lines of what ISO to use in certain situations.
Bright Sunny Day, you will want to use your lowest ISO either 100 or 200
Overcast cloudy day, ISO 400 would be a good bet for an overcast day
Indoors low light, you would want to use an ISO between 400 and 800
Night Time, You can boost your ISO up to 1600 or 3200 but at this point you might want to look into using a tripod and a longer shutter speed to avoid harsh grain.