The Exposure Triangle

[ricktas]

Thanks to member Bigdazzler for this information:


The Exposure Triangle - Shutter Speed, Aperture, ISO

These three things will determine the exposure, ie. how bright or dark, of all pictures you take with your DSLR, and how they will ultimately look.

Shutter Speed - Shutter speed is the amount of time the shutter is open whilst taking a picture. Most entry level DLSR cameras offer shutter speeds variable between 1/4000th of a second (a very fast shutter speed) and 30 seconds ( a very long or slow shutter speed, commonly referred to as a " long exposure.") The time that the shutter is open when you take a picture determines how much light will reach your sensor. Think of your sensor as like a roll of film, the sensor records everything that the camera sees through your lense. Your chosen shutter speed, along with your chosen "aperture" and ISO ( see below ) will in part determine how bright or dark your picture will be.

Aperture - The "aperture" is an adjustable diaphragm, or hole if you like, inside your lens which can be opened and closed to different sizes. Different settings, or variable sizes of the hole are commonly referred to as "f-stops" and are indicated in "f numbers" on your LCD screen and/or in the viewfinder of your camera. For example, f2.8 , f3.5, f4 , f5.6 , f8 etc. The "f stops" or "f numbers" on your camera screen can be set at certain intervals or "stops" usually up until a "f number" of around f22 , and sometimes beyond.

These "f numbers" or "f stops" are indicative of what size the hole is set at within your lens.

IMPORTANT: Smaller numbers mean the lens "aperture" (ie. diaphragm or hole) is opened up to a larger size, allowing more light through the lens. Larger numbers mean a smaller "aperture", resulting in a lot less light travelling through the lens and reaching the sensor.

It sounds kind of backwards , large hole small number .. and ... small hole larger number .. but you will get used to it !! Think of it in terms of as you close the aperture or hole in the lens to a smaller sized hole, resulting in less light being allowed to travel through the lens and onto the sensor, you are "stopping" ( remember f-"stops" ) down the lens.

Lens apertures or f-stops can be chosen or set manually by the photographer to achieve different results in your final picture. Aperture settings not only affect the amount of light entering through the lens but will greatly affect a creative aspect of DSLR photography called " Depth of Field", or the amount of sharp focus within an image. But thats another discussion

ISO - ISO is an abbreviation of " International Standards Organisation ". Not important really but there you have it anyway !!

ISO is a measurement of how sensitive your cameras sensor is to light entering through the lens and/or shutter and is measured in these numbers. eg. ISO 100 , 200 , 400 , 800 , 1600 , 3200 and sometimes 6400 on much more expensive higher end cameras. Most DSLR cameras will also have an ISO AUTO setting.

You will notice the ISO numbers DOUBLE at each interval , this indicates that the sensitivity of your cameras sensor DOUBLES each time the ISO setting is increased. Increasing your ISO means that you will need to adjust either your lens Aperture and/or shutter speed to compensate for the increased sensitivity of your sensor.

REMEMBER: ISO , APERTURE AND SHUTTER SPEED ALL CORRESPOND TO AND WORK WITH EACH OTHER TO OBTAIN CORRECT EXPOSURE: That's why we call it the Exposure Triangle , they are all as important as each other !!

Now there is a whole lot more to learn about these three critical elements but I hope this has given you a good basic definition of what the Exposure triangle consists of and how each of the three important elements does their individual jobs in creating correct exposure for your pictures.

[Jcas]

Thanks for this info Bigdazzler, you have explained it in a really understandable way.

When i first started reading about aperatures in one of my books, the technical lingo made it sound so difficult to achieve.

Much appreciated.

[bigdazzler]

Welcome Julie .. Very quiet at work this morning

[clm738]

Thanks, thanks, thanks, this information is going to help in a big way.
Am I correct in saying - Large aperture, fast shutter equal slightly darker (exposure) photo as opposed to small aperture, slow shutter?

[bigdazzler]

if shooting in A mode .. you camera will change your shutter speed to match the aperture you have chosen , in theory your exposure should be identical , but ive noticed is not always the case .. i know where youre coming from because I just saw your post in the exercise thread ..

if you find that when stopping down the lense ( as you did to f22 ) to gain a deeper DOF and a larger field of sharp focus , that your exposure is now a little brighter due to the corresponding slower shutter speed , you can tweak this with your EV controls ..

in the case of your exercise with the little miniature guys .. i would step down the EV to -1/3 or -2/3. This will bring down the exposure of the entire frame.

The EV control is a very very handy feature and I use mine all the time

[ricktas]

Thanks, thanks, thanks, this information is going to help in a big way.
Am I correct in saying - Large aperture, fast shutter equal slightly darker (exposure) photo as opposed to small aperture, slow shutter?

Not really, its all inter-related. You can have a large aperture and a fast shutter speed and you will get a lovely photo with a shallow Depth of Field. If you say took a photo of a sunflower, with the above settings, the sunflower would be nice an sharply focused, but your background would be rendered blurry.

If you then changed to say F22, you would need a slower shutter speed to allow the same amount of light to hit the sensor, but your resultant photo would have the sunflower AND the background all in focus.

So as you go from a large aperture f2.8 to a small aperture f22, your shutter speed needs to be slower to compensate. You effectively create the same amount of light hitting the sensor each time, but the different aperture setting changes the Depth of Field in your photo.

So a correctly exposed photo at f2.8 and 1/1000th second, and a correctly exposes photo at f22 and 1/10th second, although both correctly exposed will look completely different due to depth of field (or area, front to back that is in focus in your photo).

[bigdazzler]

what rick said .... ^^^

my reply was more in terms of suggesting a technique in getting the brightness of the image to look simialr at both apertures and still achieving the desired DOF ..

[Boofhead]

While trying to expand my knowledge I did a google search about iphone apps for the exposure triangle and came across this: http://iphone.ambertation.de/lightmeter/

When using it in my iphone I am able to lock in either the f-number, shutter speed or ISO, adjust one of the other fields to see what setting the third part of the triangle should be to achieve the same exposure.

Just playing around with it is helping me see the inter relation and better understand.

[Kym]

The more detailed version is here: http://www.ausphotography.net.au/for...944#post238944

[Zac]

Noice explanation

[Zac]

Noice explaination... thanks

[sumanjay]

Phew... I finally got my head around the relationship between DoF and aperture. High school physics still has its uses. And tip of the hat to Kym's fabulous explanation.

[rwg717]

Well written and informative stuff, thanks for that
Richard

[kevinj]

While trying to expand my knowledge I did a google search about iphone apps for the exposure triangle and came across this: http://iphone.ambertation.de/lightmeter/

When using it in my iphone I am able to lock in either the f-number, shutter speed or ISO, adjust one of the other fields to see what setting the third part of the triangle should be to achieve the same exposure.

Just playing around with it is helping me see the inter relation and better understand.

Another useful iphone app is Photo Buddy,has a lot of useful settings.

[jksgoh]

thanks for the quick summary