How is the exposure triangle INTERRELATED?

[Cad0587]

And yes...I have Googled the subject haha. I am just starting out learning about manual mode. I am sooooorta getting it. But when it comes to reading about the exposure triangle on different websites all that's exlpain is aperture, shutter speed, and ISO individually. I get what they are individually. But I want to READ about how they are INTERRELATED. The triangle thing itself isn't clicking with me, I don't want to look at the triangle lol I want it in words. I want to know that if having a large aperture is what is most important to me then this is where I should go to compensate with my shutter speed and ISO. Sometimes when reading what settings someone choose for their picture they say something along the lines of well I decreased this therefore had to increase/decrease this, THAT'S What I want to know. How they work together, how they relate together. Can anyone help out? I don't want a diagram, just words!

[ScottyP]

The apples and oranges thing is why they invented "STOPS".

There is an equivalence between doubling/halving shutter open time and doubling/halving sensor sensitivity, and doubling/halving the opening size made in the lens aperture blades to let light in.

Each of the halving/doubling moves can be swapped between the 3 factors (shutter, aperture, ISO).

Read Bryan Petersen's book "Understanding Exposure". It is 1/2 pictures so itt is a quick but useful read. There are at least 6 possible CORRECT exposures for any shot, but you SELECT the one you want for artistic reasons.

[ScottyP]

Artistically, it works like this:

Aperture: A wider aperture lets in more light but narrows your depth of plane in-focus. Narrowing the aperture gives a deeper depth of field in-focus but shuts out light.

Shutter: fast ones freeze motion; both subject motion and camera shake, and slow shutters let more light in. Slowing the shutter lets more light in.

ISO: Doubling the ISO doubles the sensitivity of the camera to light. It allows for compromises in shutter or aperture but it introduces nasty noise and grain and loss of detail as you raise it. On a Rebel you really don't want to go above maybe 400 ISO.

Under the equivalence idea, you can juggle the 3 pieces of the triangle to get the look you want.

[TCampbell]

Matthew Gore made a video that you may find helpful:

[Skirball]

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@TCampbell wrote:

Matthew Gore made a video that you may find helpful:

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That would have been easier.  Nice find.

[Skirball]

I wouldn't pay much mind to the triangle.  It's just a visual example showing that all three variables are interrelated when it comes to exposure level.  If you move any one variable down a "notch" you can move either of the other two up a "notch" and you'll have the same exposure level.  That's really it for the triangle.

As Scotty mentioned, the "notches" are called stops.  One stop represents a doubling or halving of the amount of light that hits the sensor.  But our eyes perceive light logarithmicly, so doubling the amount of light doesn't have as great an impact on the brightness of the photo as you might imagine.  Working in stops allows all the 3 variables to be comparible.

Shutter speed is easy.  If you double the amount of time the shutter stays open then you went up a stop.  Your camera will most likely adjust shutter speeds in 1/3 stop increments.  For example 1/15, 1/20, 1/25, 1/30 sec...   You'll note that 1/30 is half the amount of time as 1/15.

The confusing one is the aperture (commonly referred to as F Stop).  The F Stop is proportional to the diameter of the aperture that lets light through the lens.  Since we need to double the area of the circle (to keep consistent with stops), not the diameter, we end up getting funny numbers (it's more complicated than that, but I'm keeping it simple).  These numbers you just have to memorize:

http://en.wikipedia.org/wiki/F-number

Or, keep in mind that every three 'clicks' on your camera will double or half the F-stop.  It's further complicated because the F-stop is a ratio with diameter as a denominator.  So, the larger the Fstop the smaller the aperture.

Lastly is ISO (or ASA), which represents how sensitive the sensor is to light.  Also easy.  They use an old system that was developed for film, so it starts at 100 (more or less), and doubles each time you double the sensitivity.

The part that I think you're looking for is, how do they all play together.  Each one has its benefits and drawbacks.  Every time you raise ISO you introduce more noise.  So as a general rule you keep ISO as low as possible.  Shutter speed doesn't matter much so long as it's fast enough to freeze the subject (artistic 'movement' aside).  So this gives you some flexibility so long as you have enough light.  Fstop/Aperture affects the sharpness of an image.  If the aperture is too big (low F STop) then only a sliver of the image will be in focus.  This is called depth of field and will take some research.  If the aperture is too small the entire image will be soft due to diffraction.  Learning what aperture to use, for what effect you want, for what lens you're using...  just takes experience.