Lots of references to the exposure triangle (ISO/Shutter Speed/Aperture). Now, I am comfortable with the relationship between the 3 elements, but has anybody got a good explanation of how to use the triangle to define the relationship and how to use the triangle?
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Exposure triangle explanation please.
- Thread starter AnthonyL
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Tan68
Veteran Member
I think the best way to build a model of this sort would be a loop of string around the three points.
As the aperture corner is pulled out, the other two are pulled in. If someone locks down shutter by putting their finger on the string, then only the ISO side is drawn in.
If the aperture corner is brought in by using a smaller aperture, there will be slack in the string. Don't want slack so either the shutter or ISO points need to be moved to take up the slack.
This is really a physical model of what I described so I am not impartial.
As the aperture corner is pulled out, the other two are pulled in. If someone locks down shutter by putting their finger on the string, then only the ISO side is drawn in.
If the aperture corner is brought in by using a smaller aperture, there will be slack in the string. Don't want slack so either the shutter or ISO points need to be moved to take up the slack.
This is really a physical model of what I described so I am not impartial.
confyushis
Senior Member
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i suppose the loop of string could represent the amount of available light (?) ... a super bright sunny day could be a big loop (i suppose an ND filter could be a cinched-off section of the loop) and a indoor/night shot could be a small loop ...
Tan68
Veteran Member
yeah. in my verbal example i used surface area to help visualize the triangle but then used length of arm in stops to show how the triangle grows.
thing is, i don't think surface area will scale properly with the changes in length. so, surface area probably isn't the best thing to key on. arms betting longer or shorter in increments of stops is a thing to key on.
thing is, i don't think surface area will scale properly with the changes in length. so, surface area probably isn't the best thing to key on. arms betting longer or shorter in increments of stops is a thing to key on.
It's probably best to ditch the triangle. Forget you ever saw it. I agree, as you're learning these things from scratch, the incessant online references to the lofty-sounding "Exposure Triangle" leads you to think there MUST be something more to this than a simply analogy of three parameters = three sided object. It's as if the concept of three of something is so hard to comprehend that we need to add a geometric analogy into the mix.
If you want to stick with the triangle, maybe start with the vertex lines and the center point as you've drawn, but delete the sides of the triangle. Then think of it as a 3-prong balance with the balance point in the center: ISO, aperture, and shutter are baskets of "stops," hanging at the end of each respective prong of the balance.
If you're in balance (i.e you have the "desired exposure," which may be intentionally over or under exposed so it's not always strictly/literally in balance), and let's say you remove 1 stop from the aperture basket. Then the scale goes out of balance, and to get back to balance you have to add 1 stop to one or the other of the ISO or shutter baskets (or you could even add 1/2 stop to each). You have to think of this strictly in a conceptual sense of balancing stops though. If you try to put numeric weights on it or think of it like a normal scale, it doesn't work.
Or maybe the 3-prong balance is a goofy idea. I dunno. I'm sure someone will let me know if it is
If you want to stick with the triangle, maybe start with the vertex lines and the center point as you've drawn, but delete the sides of the triangle. Then think of it as a 3-prong balance with the balance point in the center: ISO, aperture, and shutter are baskets of "stops," hanging at the end of each respective prong of the balance.
If you're in balance (i.e you have the "desired exposure," which may be intentionally over or under exposed so it's not always strictly/literally in balance), and let's say you remove 1 stop from the aperture basket. Then the scale goes out of balance, and to get back to balance you have to add 1 stop to one or the other of the ISO or shutter baskets (or you could even add 1/2 stop to each). You have to think of this strictly in a conceptual sense of balancing stops though. If you try to put numeric weights on it or think of it like a normal scale, it doesn't work.
Or maybe the 3-prong balance is a goofy idea. I dunno. I'm sure someone will let me know if it is
Yes there's an explanation out there somewhere which does it by pie-charts.
It occurs to me that in my model the size of the triangle represents the EV. So less light, squeeze the triangle in forcing higher iso, slower shutter and wider aperture, conversely expand the triangle in good light.
It occurs to me that in my model the size of the triangle represents the EV. So less light, squeeze the triangle in forcing higher iso, slower shutter and wider aperture, conversely expand the triangle in good light.
Tan68
Veteran Member
i think with the ND, part of the triangle would not be tightened up or synched down.
the length of the arms represent the light we want for the light available in our scene. if we toss on a 2-stop ND then we have decreased light available to strike the sensor.
the arms are set up for a good exposure on a sunny day. if the light is dimmer (with either ND or twilight) the arms need to get bigger to gather more light.
a 2-stop ND could be offset by adding 2-stops of length to the loop of string. this way there is additional slack in the string to lengthen the shutter 2 stops.
in a physical model, caribiners could be used to secure the loop. to add an ND, a length of string could be clipped in. this makes the triangle/net bigger to catch more light.
maybe that is stretching the analogy... :^)
the length of the arms represent the light we want for the light available in our scene. if we toss on a 2-stop ND then we have decreased light available to strike the sensor.
the arms are set up for a good exposure on a sunny day. if the light is dimmer (with either ND or twilight) the arms need to get bigger to gather more light.
a 2-stop ND could be offset by adding 2-stops of length to the loop of string. this way there is additional slack in the string to lengthen the shutter 2 stops.
in a physical model, caribiners could be used to secure the loop. to add an ND, a length of string could be clipped in. this makes the triangle/net bigger to catch more light.
maybe that is stretching the analogy... :^)
Tan68
Veteran Member
No... it made me think of working with number lines in grade school. one line/arm/apex gets longer and another must get shorter. measuring in stops, add one here and take one away from there.will222 wrote:
... Or maybe the 3-prong balance is a goofy idea. I dunno. I'm sure someone will let me know if it is
i think of stops as length. your model would be using stones for stops. add a stop/stone here and take one out there.
i can't think of a way to rationalize adding an ND with weight as i did with with the string model.
if an ND is added to the weight model i suppose the springs tighten up and you have to add more shutter speed rocks.. make the shutter longer. but that doesn't make as much sense to me as 'make the triangle/net/whatever bigger to gather more light'.
still, weight works fine and by time someone decides to use an ND they probably don't need the triangle any more. not really...
Tan68
Veteran Member
happysnapper64
Veteran Member
Anthony. Methinks you are overanylizing this. :-D If you understand the relationship between the 3 ellements & know how to adjust for different light, then you understand the basics of the so called exposure triangle.
happysnapper64
Veteran Member
Again, with respect, I don't think any of us so far, understand your question! :-( It doesn't make sense to me personally. Hey that's just me, maybe I am thick or something. But if all the searching doesn't answer your question, then maybe the question is at fault, & there is no answer, I don't see what the question has to do with photography.
Calling it a triangle, is just an expression, like a love triangle. When 3 factors [or people] are involved, it often gets the title "triangle" :-D
You've come into this late, not reading the thread, missing some (good) attempts at explaining the triangle and then say I'm not explaining myself.
Many reputable sites show this picture of the triangle without any explanation as to what the sides mean or how one item varies with another. If you know then please put forward your ideas. 3 in a bed doesn't cut the mustard.
Many reputable sites show this picture of the triangle without any explanation as to what the sides mean or how one item varies with another. If you know then please put forward your ideas. 3 in a bed doesn't cut the mustard.
JTC111
Leading Member
taking a good picture!
Just because the numbers add up in this magic triangle you're trying to create doesn't mean you're going to end up with a good photograph. It doesn't even mean you're going to come up with the correct settings since some locals require other factors to be taken into account (the beach, for example).
Just because the numbers add up in this magic triangle you're trying to create doesn't mean you're going to end up with a good photograph. It doesn't even mean you're going to come up with the correct settings since some locals require other factors to be taken into account (the beach, for example).
I don't understand how this post helps with the question but thanks all the same.
If you understand the three factors -- shutter duration, f-stop, and ISO -- then the so-called 'exposure triangle' has done it's job. It is simply an explanatory device for introducing concepts, don't try to read too much into it.
In the end, what you're trying to do is create a final image with the desired brightness. Most often you're trying to create an image that more or less replicates the brightness you saw in the original scene. There are four factors contributing to image brightness
The light incident on the scene may or may not be controllable with flash or artificial light, depending on circumstances This is a complex topic, for now assume the incident light is a given.
Note that we're talking about light incident on the scene, not light reflected from the scene. That's because we want a black cat in a coal mine to produce a dark image, and a white cat on snow to produce a bright image. By exposing for the incident light we'll correctly capture those different scenes in the final image.
Using larger f-ratio (i.e, smaller f-number which is the number in the denominator of the f-ratio) means more light is gathered from the scene. It also decreases depth of field so this is a creattive control, too.
Longer shutter duration also gathers more light from the scene. It also controls the degree of motion blur, so it is also a creative control.
Finally, ISO is an indicator of the combined sensitivity of the camera's sensor and electronics to light. Higher ISO allows more latitude for creative control of lighting, f-ratio, and shutter, but comes at the cost of increased sensor noise.
While each of these four factors has its own units of measurements, it's very convenient to use a powers of two to express changes in each factor. Each doubling increases the image brightness by 'one-stop' ;
It's just that easy.
That was quick and off-the-cuff, but an approach that I find far more useful than an ill-defined 'exposure triangle'.
In the end, what you're trying to do is create a final image with the desired brightness. Most often you're trying to create an image that more or less replicates the brightness you saw in the original scene. There are four factors contributing to image brightness
- light incident on the scene
- the light gathered by the lens determined by the f-ratio (e.g, 1/2.8, 1/4, etc.)
- the length of exposure determined by the shutter duration (e.g, 1/200 sec.)
- the net sensitivity of the sensor determined by the ISO (e.g., ISO 100)
The light incident on the scene may or may not be controllable with flash or artificial light, depending on circumstances This is a complex topic, for now assume the incident light is a given.
Note that we're talking about light incident on the scene, not light reflected from the scene. That's because we want a black cat in a coal mine to produce a dark image, and a white cat on snow to produce a bright image. By exposing for the incident light we'll correctly capture those different scenes in the final image.
Using larger f-ratio (i.e, smaller f-number which is the number in the denominator of the f-ratio) means more light is gathered from the scene. It also decreases depth of field so this is a creattive control, too.
Longer shutter duration also gathers more light from the scene. It also controls the degree of motion blur, so it is also a creative control.
Finally, ISO is an indicator of the combined sensitivity of the camera's sensor and electronics to light. Higher ISO allows more latitude for creative control of lighting, f-ratio, and shutter, but comes at the cost of increased sensor noise.
While each of these four factors has its own units of measurements, it's very convenient to use a powers of two to express changes in each factor. Each doubling increases the image brightness by 'one-stop' ;
- Incident light is often measured in EV. Each EV is equivalent to one-stop.
- One click in f-ratio (e.g. f/4 to f/2.8) is an increase of one-stop.
- Each doubling of shutter duration (e.g., 1/400 to 1/200) is an increase of one-stop
- Each doubling of ISO (e.g., ISO 200 to ISO 400) is one-stop
It's just that easy.
That was quick and off-the-cuff, but an approach that I find far more useful than an ill-defined 'exposure triangle'.
happysnapper64
Veteran Member
Hey Anthony, OK, hands up, I appologise if I was rude. I simply didn't know what it was you were after. Maybe you are a person who likes things explained in a very technical way? I don't know. Nothing wrong with that. I am having a hard job getting to grips with the basics, then we have a thread about exposure compensation that left me a bit confused till one post got through to me. What I am saying is, we learn things in different ways, & I found myself getting rather condecending & rude with you. I appologise.
Well, if you're comfortable with this explanation, then the triangle is obvious. Get yourself a piece of triangular graph paper -- label each corner with ISO, f-ratio, and shutter speed, and label each grid line moving away from the corner with a one-stop change in the corresponding value.
For fixed incident light, every point inside the triangle results in the same image brightness.
If the corner for ISO is set to S = 100, and the other corners are labeled t for shutter duration, and N for f-number, then the exposure value (EV100) is given by EV = log2(N^2/t) which will be the same everywhere inside the triangle.
Did that answer your question?
Last edited:
I'm not and never said I was.
Yes, at first the sides of the triangle have little relevance and there is no good reason why the joining point can't move outside. However it could be considered that the size of the triangle represents the EV, so a big triangle allowing more manoeuvrability in good light and a small triangle representing poor light and a low EV.
It also becomes obvious that the longer the ISO the more it pushes Shutter speed/Aperture down representing a decrease in dynamic range.
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