What is an Aperture Anyway?


Shutter speed, ISO, aperture, quantum physics, what is it all about? Well, I can't help you with the last one, at all, but the former are the essential components that make up every photograph ever taken. Yes, even when snapping away on your phone casually, only in this instance it is all happening automatically without your knowledge.

We're going to dig a little deeper into the world of exposure focusing on (no pun intended (or is it?)) the most challenging of them all, aperture. Exposure isn't as difficult as many believe, and doesn't require any complicated formulae to conquer. Trust me when I say that math's is not my strong point, so you can leave that calculator at the door. Provided your happy to accept certain constants and principles you are good to go!

But what is exposure?

An exposure is every image ever recorded using a light source to expose an image to a light-sensitive recording media. This could be using light-sensitive film in a disposable camera pointed towards the holiday sunset, using x-rays to assess a bone fracture, or the most recent group selfie of mates on a tiny microchip (or sensor, depending on your preference).

Each exposure is a balance between three key factors:

📸 Shutter speed


📸 Aperture

A correct exposure is produced after careful consideration of these three elements which results in an image that clearly shows all the parts of the scene being photographed under the light conditions available at the time. That's not to say that under and overexposure are always wrong, and can be used to creative effect, but we'll just stick to the basics for now. 

Getting the exposure calculation wrong generally falls into one of two camps:

Under Exposure

The image has been exposed to let in less light than is required resulting in very dark areas with little to no detail. In these situations (provided they're not too extreme) details within the shadows can be rescued using photo editing software.

Over Exposure

The image has been exposed to let in more light than needed resulting in blown out highlights which are unrecoverable resulting in a loss of detail and patches of blank white space in the image.

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Deliberate under exposure to focus attention on the subject, but probably too much as a lot of detail has been lost  

The sky is overexposed blowing out details in the clouds, not intentional this time and irreversible

'But wait, you said there's isn't any math involved?'

Well, yes and I stand by that as this isn't a calculation as such, but more of a balance. Imagine an old fashioned set of weighing scales where you put the object to be weighed on one side and the weights on the opposite side, only this set of scales have 3 platforms that counter each other. This is referred to as the exposure triangle, which works by balancing one element with the other two sides of the triangle. Still with me at the back?

Like with most things in life, everything is a trade-off, so to make up your correct exposure you need to keep your exposure triangle in balance. This means that when you add to one side, you need to take away from the one of the other two, or both. This is the maths which beginners have to tussle, but with practice, it becomes as easy as breathing. Trust me on this, stick with it and one day it will just happen like riding your bike for the first time without stabilizers!

Briefly explained, the 3 exposure components can be described thus:


Shutter Speed


What is it?

The sensitivity of the sensor/recording media

The speed the shutter operates at when the shutter button is pressed.

The opening at the end of the lens which can be made larger and smaller.

How is it used?

This is usually a static item when shooting in fairly constant lighting conditions. If you are shooting in low light and require a faster shutter speed, or large depth of field this needs to be higher. Contrastly,  shooting on a bright day this can be a lower setting.

A fast shutter speed will freeze action and create little to no blurring, a slower speed will introduce blurring as the image being recorded to the sensor has time to move in the time the sensor is exposed.

A larger opening will let more light in and produces a shallow depth of field, whereas a smaller opening lets in less light and produces a deep depth of field.

What is the trade-off?

Shooting with a high ISO setting introduces image noise which is visible as grain that can be unsightly.

A slower shutter speed provides more light and so can be used in darker situations but produces blurring, whereas a fast shutter speed freezes movement but lets very little light in.

Typically the largest trade-off is keeping the aperture wide open and producing a shallow depth of field in order to keep the shutter speed high and the ISO low.

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As you can see from the diagram above, each of the 3 components is directly linked to the other two, so any adjustment made to one must have an opposite adjustment to one, or both of the others. An adjustment of any of the exposure settings is referred to as a stop, and you will see this effect by the marker on the exposure meter. This is the horizontal line across the LCD that has markers long it with numbers at various intervals such as -2 to 0 then up to +2 (some models may show -5 to +5, or -3 to +3). 

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This meter is your camera telling you how well the scene in front of it is exposed, it's doing the maths for you! All you need to do is tweak the settings to get the marker to show 0 which is the correct exposure for the scene in front of you according to your cameras in-built exposure meter. As adjustments are made thatthat let more or less light in, the needle or marker will move up or down the scale respectively.

Still confused?

Let's look at a quick example. Let's say you're taking a portrait of a friend outside on a fairly bright day, naturally, you don't want any image noise. There's plenty of light so you can maintain a low ISO setting of 100, so that's the image noise taken care of. You dial in an aperture of f18 and a shutter speed of 1/20s which hits the 0 on your meter indicating a correct exposure, so you take the shot. The result is pretty lousy because you're laughing and joking with your pal and their movements have blurred in the photo. What do you do now? Give up? Hell no!

As we have learned, the shutter speed freezes motion, but lets in less light. The aperture will let in more light if we open it up, so this will be the trade-off. Let's dial in again then by increasing the shutter speed by around 8 stops to 1/80s, this means dialing down the aperture to f9. Our meter shows 0 so crack off the shot. Now the image is correctly exposed and the movement has been frozen. Success!

Despite two of the settings being completely different from the first attempt, the amount of light hitting the sensor is exactly the same. By moving the settings through the exact number of stops in opposing directions we have managed to maintain the balance and hit the correct exposure.

Bigger Aperture, Smaller Number?

What?!? Look, I didn't make the rules here, and yes it is totally counter-intuitive, but it's this little hurdle that all photographers have to overcome when entering the world of full manual. Trust me, it's worth it.

Each aperture stop equates to double the amount of light hitting the sensor when stopping up, or halving the amount of light when stopping down. This process is achieved through blades at the end of the lens creating a hole, known as an iris,  which gets wider or narrower when stopping up or down.

A typical range of aperture settings are as follows:

More Light Enters

Less Light Enters

1.8, f2.8, 3.2, 3.5, 4.0, 4.5, 5.0, 5.6, 6.3, 7.1, 8.0, 9.0, 10.0, 11.0, 13.0, 14.0, 16.0, 18.0, f  20.0

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Image courtesy of https://commons.wikimedia.org/wiki/File:Lenses_with_different_apetures.jpg#filelinks

This range will vary between lenses, but the principle remains the same. The smallest number will give you the widest aperture and let in the most light, whilst the biggest number will provide the smallest aperture and let in the least amount of light.

So it's all about letting light in?

No, not exactly, and this is where the fun begins. (I promise!)

Aperture is the setting that enables you to control the depth of field (DoF) within your photograph, this is the size of your plane of focus within the scene. The focal plane can be made deeper or shallower and then moved laterally from your nearest to your furthest subject by adjusting the distance of the focus. The point at which you focus on will always be the sharpest part of the image, and with the aperture, you are able to control how much of the frame remains in focus based on the lateral distance between the camera and the subjects in front of you.

Using the minimum sized aperture (largest number) you will ensure a much larger plane of sharpness in your image, which means that objects near to the camera and in the background will be relatively sharp when focused in the middle ground. This is often referred to as a deep depth of field because you are creating a deep plane of sharpness within your image. Alternatively, this is also referred to as a wide DoF,  but I do find that this term is easily confused with shooting wide open which has the total opposite effect.

Smaller aperture settings are most commonly employed by landscape photographers who are seeking crisp images from the foreground to the background but it comes at a cost due to the amount of light entering the lens and hitting the sensor is significantly reduced. It's for this reason landscape photographers tend to shoot from a tripod to reduce their shutter speed and avoid camera shake. Remember, as we discussed above, everything is a trade-off, so the luxury of front to back sharpness does come at a cost.

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1/8s @ f16, ISO 200

So to get everything sharp, crank up the aperture then? Well no. Just because you focus to infinity using a wide/deep depth of field does not guarantee you front to back sharpness. This is down to various reasons which are far more advanced than this discussion, but if you are looking for further information search 'Hyper Focal Distance' or 'Focus Stacking'.

A word of warning when shooting with a deep DoF: because everything is sharp the exposure will capture pretty much everything it sees, including any dust particles on the lens of the sensor. This is an annoying fact of life but can be easily fixed in photo editing software, so do pay close attention to the final images before publishing.

A wide aperture is the complete opposite; here you can narrow your DoF to the smallest permissible by the restrictions of the lens and create a shallow depth of field. This means the area of sharpness is now much smaller and your sharpest part of the image will be the plane in which you focus, with the focus quickly dropping away and blurring subjects in front of, or behind the point in focus.  As a practical example of this effect, hold your finger about 20cm in front of your face, then focus your gaze to your finger. Hopefully, you will notice that everything in the background became blurry, maybe even unrecognizable. This is the same effect as a wide aperture on a lens (approximately a 50mm  lens if you want to be geeky about it) focussing on a subject with some distance from the background.

Need more convincing? Ok, here are some friends of mine to help:

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Here the figures are in the same focal plane as they are stood side by side. At this point, the aperture is fairly wide at f 5 and is blurring out the background but both figures remain in focus as they remain within the focal plane. So what if some distance were to be introduced between the subjects, the camera, and the background?

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With the aperture widened slightly to f 2.8 to exaggerate the effect, the focus remaining at the same point and asking the figure on the right taking a small step back from the figure on the left (such accommodating models) we can see the effect of the wide DoF. The figure on the right is now blurring slightly out of focus, but not too much as to lose detail because the focal plane is gradually dropping away into the background. 

Staying with the same settings, but increasing the distance between the models further, the blurring effect becomes even more profound:

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This blurring is described as Bokeh which can be used in many ways to enhance, or even create an image. When shooting portraits, you can use a wide aperture to isolate your subject by blurring out unwanted of distracting elements and draw the viewers attention to your subject. For more situational portraits you are able to isolate the subject with careful management of the bokeh whilst retaining enough detail to provide context to the shot.

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1/1000s @ 1.8, ISO 125

In the example above, a wide aperture has been used to blur out the background and foreground, whilst maintaining crisp focus in the mid-ground where my subject is placed. The careful placement of the items in the foreground and the distance between the subject and trees outside create a sense of depth within the image as if you are sat across the table sharing a coffee. 

Bokeh can be used as a subject in its own right as an abstract image such as out of focus street lights that produce a dreamy mixture of different sized colored shapes. In this example, the focus is given to the raindrops collecting on the outside of the window. Careful blurring of the background aids in directing attention to the water drops, but not enough to lose the form of the rush hour commuters on a busy New York avenue venturing through the freak torrential downpour which provides context and adds to the story of a rainy day.

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1/200s @ 7.1, ISO 4000

Wide = £££

When it comes to selecting a lens, the wider the aperture is the smoother and more pronounced is the bokeh that is produced. This brings us to yet another trade-off. 

Each lens is designed and produced with a unique aperture range from the widest to the narrowest setting. For prime (fixed focal length) lenses things are pretty simple, as what you see is what you get. A 50mm 1.8 lens will give you a wide aperture when opened right up. Because of there being less moving parts you tend to find that prime lenses offer wider settings than other lenses, as well as being cheaper, lighter and faster; the tradeoff being you only have one focal length. 

When you start looking at zoom/telephoto lenses things start to get a little more complicated. Premium lenses will have a constant widest aperture setting throughout the various focal lengths, whilst cheaper lenses will have a widest aperture setting for the shortest focal length which increases in size as the focal length is extended. I did say it was confusing! Let's look at an example:

Lenses are named after the focal length with the range of the widest apertures it can achieve, and for this example, I have selected the Sony FE 28-70mm f3.5-5.6 and the Sony FE 24-70mm f2.8 G Master. Straight away you can see a small difference just by the names of the lenses, aside from the small variant in focal length. The G Master lists only one aperture setting, this is because it will provide that widest setting when shooting at 24mm through to 70mm. 

The standard lens, however, will only provide it's widest aperture setting when shooting at 28mm, and as the lens is extended this number will increase (and aperture size decrease) as the lens is extended, so that when shooting at 70mm you will only achieve an aperture of 5.6, instead of 3.5.

The premium lens also offers a slightly wider aperture than it's more cost efficient counterpart. These premium lenses are referred to as fast lenses as they enable you to use faster shutter speeds. If we refer back to the above example we saw that opening the aperture meant increasing the shutter speed without increasing the ISO setting. It's these premium lenses that are employed by professional photographers, particular sports photographers who need all the speed they can get to freeze sports action.

As with our settings, the price of equipment is another tradeoff, so acquiring equipment at a more reasonable cost that has features that aren't quite as good as other market alternatives is to be expected. The price difference between these two examples is around £1,500. You should not feel discouraged, however, just because the equipment is not as good as some, doesn't mean you can't take great images, and as you grow as a photographer you can upgrade items of kit along the way.

Now you have the power!

The power to command your own blurryness! Not the most amazing superpower I know, but it will mean you can take control of the degree of Bokeh you can introduce into your images which opens up a world of photographic possibilities.

Time to put this power into practice. I found the easiest way to understand the effects was to start with objects close up in the foreground and blurring the background and work from there. If leap to full manual is far too great a void to span, there is always aperture priority mode. In this mode, you have full control of the aperture setting, whilst the camera sets the shutter speed for you. This is a great way to experiment with different aperture settings without having to worry about what else you need to adjust. 

Hopefully, you have learned something here and found some inspiration to explore further the settings on your own camera. If you found this useful, or have any questions please feel free to hit the comments below. Also, let me know if you have any other subjects that should be explored and featured here.


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