Exposure triangle explanation please.

Started Jul 9, 2013 | Questions thread
Gerry Winterbourne Forum Pro • Posts: 14,487
Re: Exposure triangle explanation please.

AnthonyL wrote:

Lots of references to the exposure triangle (ISO/Shutter Speed/Aperture). Now, I am comfortable with the relationship between the 3 elements,

I've read the whole thread to this time.  I recognise that you don't need a lecture on how the three parameters interrelate.  However ...

but has anybody got a good explanation of how to use the triangle to define the relationship and how to use the triangle?

... none of the ideas suggested actually provides an answer to the specific point of this question "how to use the triangle" if you mean for any practical use.  There are several attempts, including your diagram, but what they all do is add some complexity to the conceptualisation of the three-way relationship.

The truth is that I can't imagine any way of actually using the triangle.  To do so you'd have to put a scale on each parameter so that as you shorten shutter speed by one stop you have to widen aperture by one stop - assuming you keep ISO constant, of course.

You would actually need some sort of scaling that allowed you to move any pair (in unequal steps if that's what you want) in response to a change in the third.  And you'd need to determine those scales according to the amount of light available.

In other words, the people who have said that the only use of the triangle is to show that there are three related parameters have got it right.  The way to use it is to demonstrate this relationship.

The way to use it to define the relationships doesn't exist in any form simple enough to put into a straightforward diagram.  Someone skilled in graphics and maths could no doubt build an interactive model that would move the three parameters as the light changed but it would be useless without a light meter built into it.  Take away the interactive diagram and use scales instead and that's what a good old-fashioned light meter does.  But it doesn't have any triangles.

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