108 – Your Second Control: Aperture

Warning: this lesson is perhaps the most challenging and taxing one in this entire series. This one may bend your brain – it certainly bent mine writing it!  Take it slowly and we’ll get through it. 

Aperture is the second leg of our initial “exposure see-saw”. The basics of exposure is the play-off between shutter speed  and aperture, and in the next lesson, we’ll see how they play along together.

Aperture is also arguably the most difficult to understand concepts in photography – thanks largely to its odd naming system. This could get complicated but I’ll try to keep it simple.

The thing to remember here is that aperture is just a fancy name for “hole” or “opening”. Every lens (as distinct from the camera) has a hole in it that lets the light through. The size of that hole is adjustable, and how big, or how small, that hole is, will impact on your photograph.

The purpose of that hole is, as stated above, to let light in from outside your camera, to inside the camera. The first ever pin-hole cameras was a lens-less camera with a hole. The principle has not changed; we now have a lens covering the hole which gives us focus, and we can adjust the size of the hole, which gives us more control about the inflow of light, but the principles remain exactly the same.

The clincher here, the thing that makes aperture what is is, is a simple common-sense axiom: the larger your hole, the more light will enter your camera, the smaller the hole, the less light will enter the camera. Duh.

f 1.8 vs f 22

Thus: if you are in a situation  with is a lot of light, IE direct sunlight, you may want a small hole. When there is a little light, such as shooting wedding in a church, you may want a large hole. Does this sound familiar? It should, it’s the same example I used in the lesson on shutter speed.

Sounds simple so far? Well, hang on to your hat and pour a stiff one, things are about to get complicated!

What you do not need to know – for now

The f/number is a fraction based on the focal length of your lens to the diameter of its entrance pupil.

Phew, aren’t you glad I put that in the “do no need to know” part!? Well, “for now” later on we’ll delve into how f/stops work.  We shall look at exactly how aperture is calculated, and what the numbers mean, but all you need to know for now is that these numbers are the exact same thing of double-and-half as we saw on shutter speed. The crazy way the numbers work is not of importance now.

What is great, however, is that across all lenses, across all cameras, across all systems of photography, an f/number is a constant.  f/5 on one lens is exactly the same as f/5 on another lens is exactly the same as f/5 on a cheap point-and-shoot is exactly the same f/5 on Hasselblad. The same way that a second on a cheap wrist watch is the same as a second on an expensive watch is the same as a second on a grandfather clock, an f/stop remains constant.  But it’s not a constant size – the actual physical hole on a smaller lens will differ from the physical hole on a larger one – but the exposure value of f/5 will always be exactly the same.  Sorry, I know this is complicated – it will come clear as we move along.

What does it do?

When you set your camera to aperture priority (“A” on the P-S-A-M dial), it means that YOU tell the camera what the size of the hole, the f/stop will be. The camera will then automatically calculate the ideal shutter speed for your chosen aperture (in the given light conditions and ISO). In effect “A” is a semi-automatic mode.

Sound familiar? It’s EXACTLY the opposite of what shutter priority (Lesson 107) does.   In shutter priority you set the shutter and the camera adjusts your aperture, and in aperture priority, you set the aperture and your camera sets the shutter speed.

And, as said, like shutter speed, there is a “double-and-half” effect on your aperture numbers.

Larger Hole – more light – faster camera Smaller Hole – less light – slower camera.

The graph above shows aperture settings in their “double-and-half” configuration. f/4 for instance, is a full stop of light above f/5.6. This means that changing your lens from f/5.6 to f/4 will exactly double the amount of light coming in. And moving from f/5.6 to f/8, is another doubling.  (The numbers though, makes little sense, and again, these numbers are explained later, but for now, know that each of these numbers is a double-and-half of each other.).  Allow captain obvious to point out another feature here:  each time you close your aperture, your camera gets slower, each time you open the hole, your camera gets faster, as said in lesson 105.

An interesting way to remember the small-hole-large-number, is not to look at the hole, but at what is not the hole. Huh? Like this:

Sidenote:  The “problem” with modern cameras is, that like shutter speed, there are increments between the full-stops.  From half-stops, third-stops and even quarter-stops, which makes it difficult to learn the “natural” full-stop range. In my student days, we only had full-stop adjustments on both shutter speed and aperture.  This made the principles easier to learn, modern cameras which have tinier and tinier increments are actually more confusing.  One of those things that make great sense if you know what is going on, but will confuse the crap out of you if you don’t

It’s worth to note there that this line above is a theoretical/mathematical line, and can extend to the left to for example f/0.7 and to the right to f/64, but in reality, you will rarely lenses with these extreme-end numbers. Expensive, good off-the-shelf lenses may start at f/1.4, even f/1.2. Your average affordable kit-lens will start at f/4, or even f/5.6. On the other end of a scale, most lenses will go to f/22, maybe even f/32. I do not know of any off-the-shelf lens that can “stop down” to less than f/32. A common lens will typically have an aperture range between f/5 and f/22.

For interest sake, Zeiss made an f/0.7 once (Click on link to see the size of that sucker!), made for NASA and used famously by Kubrik in the 1975 film Barry Lyndon, and while f/64 lenses exist, they are rare and cost the same as a mid-range yacht. However, when you go smaller than f/64, diffractions happens and it becomes impractical, so to my knowledge, no lenses smaller than f/64 exists for dSLR cameras.

What does it look like?

Modern dSLR cameras will allow you to set the aperture directly on the camera, as there is a connection between the camera and the lens. In the old manual camera days, this setting was set directly onto the lens itself. We shall use this old-timey lens as an example of what an aperture ring looks like.

This is, as the picture says, a 50mm Nikkor (IE, Nikon) lens, and at the bottom of the lens, is the “aperture ring”. As you can see, it starts off with 22, and goes down in increments to 16, 11, etc, until it reaches 1.8.

So what do these numbers actually do? I’m glad you asked that, because I spent an entire day taking photos of my own lens, showing exactly what these numbers do!


This is my f/1.8 lens, and if you are astute, you would have noticed that f/1.8 is not on my line above.  f/1.8 is a half-stop between f/1.4 and f/2. Why do I use an f/1.8 lens and not an f/1.4 lens? Well, at nearly three times the price of the f/1.4 over the f/1.8 model, I’m was not sure half a stop was worth the price.

Anyway, what we see here is a progression of hole sizes, aperture settings, f/stops. At f/1.8, top left, you can see the lens is “wide open”. The next photo is f/2.8. You can immediately see that the hole-size is significantly smaller. With the naked eye you can see it’s about half the size. The next photo is f/4, half of f/2.8. The last one on the top line is f/5.6. On the bottom line, we have f/8, f/11, f/16 and f/22 – each one getting progressively smaller, letting in exactly half as much light as the opening before it.

Some popcorn to chew on:

Most new lenses does not have these aperture rings, as these settings are no longer controlled on the lens, but “in camera”. Lenses without an aperture ring usually has a “G” somewhere in the lens model, the “G” meaning “gelded”. Ask a horse: being gelded is not a good thing, and finding a lens with an aperture ring is usually a better lens than one without.


“But Gerry”, I hear you ask, “what are the implications of these different hole sizes?”

I’m glad you asked, and this is a subject for lesson 203- Depth of Field. This is a truly fascinating lesson, and is a separate lesson from this one because of two reasons: a) it’s a lesson more on “composition” rather than “exposure” and b) this lesson is long enough already. There is also an implication in image quality, which we will look at in lesson 307 – Zooms and fast primes.

Aperture Ratios Explained.

Your aperture is simply a ratio between the physical size of your lens diameter, and its focal length.

Say what?  Okay, every lens has a “focal length”, how long the lens is (more on that in lesson 307), and your aperture is a function of the width of that lens.  The f-stop is the focal length divided by the diameter of the entrance pupil – the front bit of your lens.

Okay, let’s make it easy, time for an analogy.

Take two cardboard tubes of the same diameter, but off different lengths – for instance, one from a roll of toilet paper, and the other from a roll of gift-wrapping.  Look through short one, and then look through the long one – you see less through the long one as from the short one.  In essence, the short one lets more light through.  If you want to see the same amount through a longer tube as through a shorter tube, you will need a wider tube!

So it is with lenses and their apertures.  The same physical size of your entrance pupil – the front end of your lens – will give a different aperture value depending on the length of your lens.  If you want a wide aperture for a long lens, it will have to be substantially “bigger” than one that has a smaller aperture.  This is why smaller, shorter lenses tend to have larger apertures than bigger, longer lenses.  Also why wide-aperture lenses are more expensive than smaller aperture lenses – you need a lot more glass to make them!

Need to Know:

What you need to know and understand right now at the end of this lesson is the interplay between shutter speed and aperture. When one goes up, the other goes down. When you increase your shutter speed by one stop, your aperture decreases by one stop.  But its not as simple as this.  Because there is a 3rd variable: ISO.  And in lesson 111 we’ll see how shutter speed and aperture interplay with ISO.


Try setting your camera on Aperture Priority, and see what it does to your shutter speed in the same given circumstance of light, as you change your aperture. In lesson 203, we will use aperture creatively, and that will be a fun one!


Its a royal pain in the butt to correctly type out the italicised f  in f/22 or f/5.6 every time! Just plain old f-22 would be easier, and read the same, but would be technically incorrect.

You may breathe a sigh of relief now, after this 2,000-word lesson, everything gets easier. For you, and for me!

Photo by Pixabay from Pexels

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on October 17 • by

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