The three salt shakers version of the triangle

The Three Salt Shakers Version of the Triangle

Okay. Last lesson we got into what ISO actually is and what noise costs you. Now I want to put all three settings, shutter, aperture, and ISO, in the same room together, because that's the part everybody's been waiting for and also the part that trips people up the most.

Here's the thing. You've been learning these one at a time on purpose. Shutter first. Then aperture. Then ISO. That's not me stalling. Everybody wants to understand the whole exposure triangle in one afternoon and you can't, not really, not in a way that sticks. It's slower to learn it in pieces but it's the only way I've seen work, for me or for anybody I've taught.

So now that you've got all three pieces, let's talk about how they actually work together.

Same amount of light, three different dials

Exposure is just light hitting your sensor. There's a "correct" amount for a given scene, and you can get there three different ways, or some blend of the three.

I used to explain this at the kitchen table with salt shakers. One shaker for shutter speed, one for aperture, one for ISO. Move any one of them and the total amount of salt, meaning the total exposure, stays the same as long as you move another one to balance it out.

Tami told me I was making it more complicated than it needed to be. She was right, honestly. The salt shakers are fine as a picture in your head but you don't need three actual salt shakers on your kitchen table to get it. Here's the plain version instead.

• Shutter speed controls how long light hits the sensor, and also whether motion is frozen or blurred.
• Aperture controls how much light gets in at once, and also how much is in focus front to back.
• ISO controls how sensitive the sensor is to whatever light shows up, and also how much noise you get.

Every one of those settings does two jobs. That's the whole reason this is confusing. You're not turning three separate dials for three separate purposes. You're turning three dials that each affect exposure AND something else, and the "something else" is usually what you actually care about creatively.

Working it out loud

Say you're shooting your kid's soccer game. You want the motion frozen, so you pick a fast shutter speed, something like 1/1000. That's a decision about the shutter's second job, freezing motion. But a fast shutter speed lets in less light. So now you need to let more light in some other way, either open up your aperture (lower f-number, letting more in at once) or raise your ISO (make the sensor more sensitive to what little light there is).

Or say you're shooting a landscape up American Fork Canyon and you want everything sharp front to back. You pick a small aperture, something like f/11, because that's aperture's second job, depth of field. A small aperture lets in less light too. So you either slow your shutter way down (fine if the camera's on a tripod and nothing's moving) or bump your ISO.

You're always solving the same puzzle. You decide which of the two jobs matters most for this shot, motion or depth of field or noise, set that one first, and then let the other two settings make up the light difference.

A practical way to practice this at home

Put your camera in full Manual (M on the dial). Pick one static subject, a plant on your porch, a bowl on the counter, whatever's around.

1. Set your shutter speed to something reasonable, say 1/125.
2. Set your aperture to f/5.6.
3. Adjust ISO until your meter reads correctly exposed. Take the shot.
4. Now change ONE thing. Drop your shutter speed to 1/60. Your exposure meter will show you're now overexposed. Fix it by raising your f-number (smaller aperture) OR lowering your ISO. Take the shot.
5. Compare the two photos. Same brightness, different look, because you traded one thing for another.

Do this for a half hour and it'll click in a way that no amount of me explaining it at you will do.

My grandson, who was maybe nine at the time, picked up my camera once in full manual and just guessed at all three settings with no explanation from me at all, and got a shot of our dog that's honestly better composed than most of what I've taken. I keep a print of it in the shop. I don't fully know what he understood and what he stumbled into, but he wasn't scared of the dials, and that's most of the battle. The camera doesn't punish you for trying something. It just gives you information back.

One real caution here: if you're outside practicing this and the light's changing fast, like sunset, don't get so buried in the dials that you miss the shot entirely. I've done that. I'll tell you about the moose another time. A slightly wrong photo you actually took beats the perfect one you were still adjusting for.

Before next time

Do the exercise above with at least three different subjects around the house, and write down in your notebook what you changed and what happened. We'll build off this next lesson when we start using the light meter on purpose instead of chasing the needle blind.