As said, there may be some concepts that will not make sense immediately, but need to be understood in a larger context. The first of these “abstract” concepts is the notion of “double and half”.

We’ve all seen numbers on the camera, the aperture numbers, the shutter speeds, but what do they mean? As these lessons progress, we will look at each of these items on their own, but the concept we just need to get to grips with right off the bat is that the numbers on the shutter speed, aperture, and ISO settings, all represent either a doubling, or a halving, of the number preceding/following it.

The one thing to keep in mind here, is even though the numbers are worked out to be *photographically* double and half, they do not always *mathematically* follow double and half. I call these exceptions the “except sometimes” moments, because, as a general rule the numbers make mathematical sense, but sometimes, the double and half is “not quite”. The most obvious example here is on shutter speed, where a doubling-up of 30 is 60, but the doubling of 60 is 125, not 120 as one would expect. But this you need not know right now.

What you need to know is that these double and half increments are known as “stops”. For the purpose of these lessons, a “stop” is simply a quantity of light. Camera settings work in “stops” of light. Each time we adjust our camera, we let in exactly double, or exactly half, the light of the previous setting.

For example, shutter speed will usually have a base of 60 (more detail on this in lesson 107). A doubling of that is 125, then 500, then 1000, then 2000, etc. Going the other way, we get 30, 15, 8 there is that “except sometimes” thing again), 4, 2, 1, then two seconds, four seconds, etc.

We can follow the same formulas for ISO, where a camera has a base ISO of (for example) 200, and we can go 400, 800, into **stratospheric numbers**. And going the other way we get 100, and then, the “except sometimes” numbers of 80, then 64, then 50, and 32.

As for aperture, we get *f*/1.4, *f*/2, *f*/2.8, *f*/4, *f*/5.6, *f*/8, *f*/11, *f*/16, *f*/22, and *f*/32. These numbers make NO sense, but I explain them in detail in lesson 108 and delve deeper into the mathematics of this peculiar numbering system in lesson 311.

As said, right now, you do not need to know what the numbers mean, just know that each number is a double, and a half.

But this is where new, modern cameras tend to make things complicated for the beginner. When I was a student, my **fully manual camera** worked in full-scale stops only. I only had the scales above to contend with. Modern cameras—even entry level cameras—can make micro adjustments in half, third and even quarter-stops. This gives you a lot more numbers to play with, and is awesome when you know what’s happening, but can be a lot to deal with when you do not know what you doing.

So: “Double and half” and “stops of light” are the concepts you need to take with you from this point forward.

*Photo credit: George Becker from Pexels*

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