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Exposure Triangle-Aperture,Shutter Speed and ISO

Updated on April 14, 2015

Exposure Triangle-Aperture,Shutter Speed and ISO

CC BY-SA 2.0
CC BY-SA 2.0 | Source

"In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical systemis the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise.

In photography, shutter speed or exposure time is the length of time a camera's shutter is open when taking a photograph.[1] The amount of light that reaches the film or image sensor is proportional to the exposure time.

Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system. A closely related ISO system is used to measure the sensitivity of digital imaging systems.

Relatively insensitive film, with a correspondingly lower speed index, requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a slow film. Highly sensitive films are correspondingly termed fast films. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality (via coarser film grain or higher image noise of other types). In short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the quantum efficiency of the film or sensor." Wikipedia

Many photographers,especially amateurs , simply choose to let the camera select all the settings (as in automatic mode) and simply worry about getting the subject in focus.

Professionals however, apply extra attention to every detail that will affect the shot.

They manually choose the aperture, the shutter speed and also the ISO which equals how much grain the final image will show when enlarged. They fully understand photography and the exposure triangle.

In other words, professionals never use the auto mode unless it is absolutely necessary always preferring to "make" the photograph" instead of just capturing it.

This brings us to what some refer to as the exposure triangle; aperture, shutter speed and ISO.

There are several things to keep in mind when choosing the each of these three settings. For example the larger the aperture the more light that is allowed to enter the film or sensor plane and this increases your chances of getting a good usable picture in less than ideal lighting conditions.

However, using a large aperture means that you will be sacrificing something. This is usually the depth of field.

A large aperture translates into the subject being in sharp focus but as you go past it, the elements (behind the subject) lose detail. This is great for some techniques like Bokeh and for macro shots but is not a one size fits all approach.

Let's say that you come upon a lovely patch of flowers which are set against an even lovelier mountain range. Using a large aperture will deny the view of the mountain range but will keep the flower patch intact.

Sometimes this works but the flowers will probably look much better when viewed against a nice looking mountain backdrop.

If you want to purposely isolate a subject then it's fine but sometimes you might want to show what is behind the subject and then a large aperture will not fit the bill.

Bottom line is that if you want a sharp scene from beginning to end you usually need a small aperture.

Depth of field

CC0 1.0
CC0 1.0 | Source

Kind of get the idea of why you need to understand how shutter speed, ISO settings and aperture work together?

See results

Shutter speed is basically how fast the shutter opens and closes thus limiting or rather controlling how much time the light is allowed to hit the film/sensor plane. Nothing guarantees a sharp picture more than the speed of the shutter.

However if you want to combine a small aperture then you also have to take the speed into consideration.

A really fast shutter speed does not always work in conjunction with a small aperture. You need to find the balance.

Taking several shots with different shutter/aperture combinations is the best method to determine what settings work best with what light conditions.

Also when you want to show some movement as when photographing moving water, a slower than normal shutter speed is required. Here you can play around with different apertures depending on what you want to isolate or how much depth of field you want to show.

A slower speed means that you can use a smaller aperture. If you use a slow speed and a large aperture then your images may be overexposed. Here is when knowing what combinations work well together pays off.

Slow shutter speed

CC BY-SA 2.0
CC BY-SA 2.0 | Source

ISO to put it simply, is the sensitivity index of film or a digital sensor. The higher the ISO number the less light that is required to make a good picture.

With that said, the higher the ISO number the more grain/noise that will show on the picture and this is incremented dramatically the larger the photograph is made. An 8X10 will not show, i.e will not be readily visible to the naked eye, as much grain as an 14X16 and so on.

Films usually came in ASA/ISO of 64 (Kodachrome), 100,400 and 1000. Most professionals used to use either Kodachrome or Fuji-chrome with a rating of 64 or 100 ASA/ISO.

Digital cameras do not have an ISO requirements per say. But the sensor can be set to accept a "pretend" ISO number when manually selected by the photographer. This nevertheless yields basically the same results as if you were using film; the higher the digital ISO selected the more "digital noise or grain" that will be shown in the final photograph.

"Image noise is random (not present in the object imaged) variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the sensor and circuitry of a scanner or digital camera. Image noise can also originate in film grain and in the unavoidable shot noise of an ideal photon detector. Image noise is an undesirable by-product of image capture that adds spurious and extraneous information." Wikipedia

Digital Noise

CC BY-SA 2.0 DE | Source
Image on the left has exposure time of  10 seconds in low light. The image on the right has adequate lighting and 0.1 second exposure CC BY-SA 2.5
Image on the left has exposure time of 10 seconds in low light. The image on the right has adequate lighting and 0.1 second exposure CC BY-SA 2.5 | Source

All in all, you need to know your settings and how each member of the "triangle" is used as well as how it affects the image.

Experimenting with various combinations is what is going to give a good idea of what to select when faced by less than ideal photo ops or when you want to be creative.

To round things off because this can be confusing to some, me included, when you find yourself in need of adjusting the shutter speed, the aperture the ISO or a combination of the three, keep in mind that when you adjust one setting, you can balance it by adjusting one or more elements of the triangle to compensate.

The same thing applies if you just want to be creative like purposely capturing movement/blur, in a scene of moving people around a person who is standing still.

I have included two videos which clearly explain the Aperture Triangle and show samples to help you better understand how all of this works and comes together thus giving you the opportunity of making exceptional photographs.

Good use of the elements in the triangle.

CC BY-SA 2.0
CC BY-SA 2.0 | Source

Must watch!

© 2014 Luis E Gonzalez


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    • LuisEGonzalez profile imageAUTHOR

      Luis E Gonzalez 

      5 years ago from Miami, Florida

      Steff Tompkins: Thank you. Glad I was able to help.

    • Steff Tompkins profile image

      Steff Tompkins 

      5 years ago from Quakertown, Pennsylvania

      This article was very helpful and informative! I do photography as a hobby and I took some classes on photography but it seemed that there were details left out even in a college course that you have mentioned in this article! Thank you for laying down the facts with this.


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