What Is A Stop Of Light?

Photography - 101 Basic Photography Concepts
6 minutes
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One of the terms that we've mentioned and that you're going to hear constantly throughout your photographic career is a full stop, or In short, a stop of light. What is a stop? You're gonna be hearing this a ton, especially when we talk about exposure. Well, a stop is simply a relative measurement of light, it means either double or half the amount of light. But what is that relative to? What are we doubling?

What are we having? Well, if I were to say a stop is relative to basically whatever we currently have, and where we want to go, and relative to everything, well, that makes absolutely no sense. And it's a terrible explanation. And if I were to ask you a question, Well, tell me this. How about you tell me how much light is actually in this scene? If you're starting out in photography, what would you say to that?

If I were to say, Tell me the exposure value of this scene where you're going to go, oh, there's 65 gallons of light in the scene or there's 242 liters of light in the scene. those terms make absolutely no sense and there really aren't any specific terms of measurement for measuring the amount of lightness seen. Well, actually, you know what I lied there are, we can measure in terms of lumen. Which is, again, kind of confusing, we can also measure in terms of a vs or exposure value. But if I were to tell you that this room has an Eevee of eight, or if I were to say shooting outdoors in sunny weather has an Eevee of 15. What would that mean?

That would mean absolutely nothing to someone just starting out in photography. So instead, we use terms like a stop. So a stop is simply going to be describing where we're at with our current exposure and where we need to go. So to show you all and hammer this point home, we're going to be using our same exposure triangle real world analogy. Well, this is our visual analogy, not real world. And what I want you to remember is that well, a stop is either double or half the amount of brightness, but we have three ways to control that.

So let's talk about it. Let's go ahead and first and what I'm going to do is just open up my faucet all the way to my widest open aperture, what we're going to say is that this faucet is our lens and it has a maximum aperture of F 2.8. That's as wide as it can go. So this is as much light as we're going to get. Now what I'm gonna do is go ahead and bring my ISO 100 Cup in and let's do this. I'm going to use My timer and I want, let's go ahead and get back to that.

Okay, so what I want to do is I want to three seconds shutter speed, or let's say that I'm at a three second shutter speed and I'm at my aperture of F 2.8. And I'm at 100 ISO. Well, if I were to start this at three seconds, we know from before that basically we're only going to get halfway so at three seconds, we fill the cup, halfway up, now filled halfway, this means that we're one stop underexposed, or I need to brighten my image by one stop, it's the same thing. So we have one stop underexposed. So what I want you to do as at three seconds, instead of using a three second shutter speed, I would need to double or increase the shutter speed by one stop of brightness, and that would mean that I double it to six seconds. So let's go ahead and reset that.

We're going to go again six seconds, and we're going to double it. We're going to get all the way filled up. And there we go. Okay, so at six Second, we doubled the shutter speed we increased the shutter speed by one stop to get one stop brighter to get to our proper exposure. Well, same thing with the aperture we can adjust the aperture to give us one stop brighter or one stop darker. One more thing I want to go over one last thing What if I leave it for a shutter speed of let's say 12 seconds?

Well at 12 seconds if this was again in the same scenario, what ends up happening, you guys can already guess we're going to end up over filling the cup. So if I over the field a cup and this doesn't actually go up to this point, but if I were to overfill it, I could say that I need to go with one stop darker so we can adjust the shutter speed and cut it in half to get back to that point. So this is kind of our overexposed image here. Now let's move on to our aperture. Okay, so with the aperture let's go ahead and open the faucet up to I'm going to say this is full. So this is f 2.8.

That's our widest open after. Let's say this is around f four. So that's one stop darker or half the amount of light as f 2.8. Okay, so now let's go ahead and we're going to use our same cup What I'm going to do here is let's use a six second shutter speed again, and let's see where we get. So I'm gonna hit start, we should get roughly around a half if that was indeed. And we do, we're at 5.85 seconds, and we basically got half of our exposures.

So you can see here, so it's not exactly we're gonna run a little bit, but we got basically half to where we need to go. So what we need to do is again, we need to increase the aperture by one stop in brightness, and that means a double it. So again, we would go back up to full life. Okay, so you can see how these are two different controls already in controlling the stopper and controlling our relative brightness. Now, let's say this I'm going to give you guys another example. And we're going to say that, for compositional purposes, I'm shooting water, I'm trying to get that wispy water effect and I find that at 1.5 seconds, that gives me the perfect look in the water.

It's not showing too much motion, it's not freezing it too much. It's just right. So I need to keep my shutter speed at 1.5 seconds. Let's also say that we're at F 2.8. So we've maximized the amount of light coming Through we can't go with any more. Now I need to go with 1.5 seconds for my shutter speed because that's for compositional purposes I don't want to change it.

But the problem is that well at ISO 100 if I go for 1.5 seconds, we get only a quarter of the cup filled up so we're two stops underexposed. Well, same thing if I go to ISO 200, which is one stop brighter than ISO 100 at 1.5 seconds, we only get halfway so we're one stop underexposed. So what I would need to do is go up to stops and then go to ISO 400 and ISO 401.5 seconds, gets me filled up right to the top. So 1.5 seconds we feel that we got to the exact exposure while maintaining our shutter speed we wanted to keep a shutter speed of 1.5 seconds, we used our ISO to increase by two stops and just one more time to reiterate. I'm going to put my phone now let's take a look at this. So ISO 100 we have roughly a quarter of the cup filled up at ISO 200 we have roughly half the cup filled up so we're one stop underexposed.

Here we're two stops underexposed, and then at So 400, we are correctly exposed with our desired exposure. So that is a stop. It's a relative measurement of light that's incredibly useful for describing where we need to go with our exposure. And I want you to remember what we discussed in the last video, which was when we go up in stops, we're doubling the amount of light. So basically, from 100 to 200, that's twice as much as 100 400 is actually twice as much as 200, which becomes four times as much as ISO 100. It's four times and it's not three times basically a lot of people confuse it as each step up is 300% 400%, so forth.

The easiest way to remember this that I didn't mention in the last video is basically each step up can be indicated just by the number itself. So 200 is twice as much as 100. Everything's in relation to 100. ISO 400 is four times as much as 100 800 is eight times as much as 100 1600 16 times and so forth. Okay, so that's it for a stoplight. Hopefully this video helps you all out.

Let's head on out to the next one.

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