How do apertures work?

The aperture is one of the most important parts of a camera, but how does it work? Professional photographers know. In this article I’ll tell you what they do and how in order to illustrate how important photographers are.

A wide aperture gives a narrow depth of field throwing foreground and background out of focus.

It’s all very easy for a photographer, they just push a button and it works, right? Well, it can do and the flooding of the photo gear market with fully automatic cameras would make you think that. A computer can get everything right in a split second? Why do you need a professional to do it then?

There are a multitude of factors to take into consideration when taking a photograph. One of those is the aperture. The aperture is the small iris like hole inside the lens. Working like an iris, it widens and shrinks to allow various amounts of light in. Easy enough, right? Just close it down when you’re in sunshine? Well, no. Actually the aperture will work with three other critical components of the camera in order to get the best exposure and having a photographer behind the viewfinder who understands how light works and what the different settings of the aperture can do to your photograph is why it costs more for a professional and why you need one handling important events such as weddings.

The aperture is measured in F numbers, or F stops (if you ever hear a photographer say something like “I had to knock it down half a stop” then they’re discussing apertures). The number starts as low as f/1 and goes up to as much as f/32. The annoying thing is that the lower the number, the wider the aperture.F numbers move up in sequence roughly doubling in size (though not exclusively – because that would be easy). The sequence that you would find on a typical camera lens is: 2.8, 3.5, 4, 5.6, 8, 11, 13, 16, 22. There are many more settings than these, but these are arguably the most used in everyday photography.

Using a narrow aperture for creative purposes will tell a different story. Here I wanted to highlight what it would be like to stare down the barrel of a gun. Who is holding it isn’t important.

As well as letting more or less light in, the F stop also will widen or shrink the focal plane – that’s the area inside the photograph that is in focus – which you can use to your benefit when taking various types of photographs. The band of focus is called the depth of field. The lower the number, the wider the aperture, the more light comes in, but the narrower the depth of field. Therefore, taking fine detailed pictures where you want a thin point of focus requires a narrow band of focus in order to accentuate the item you’re shooting requires a narrow depth of field/wide aperture/low F stop. Portraits require a wider depth of field in order to get the tip of the nose to the back of the head in focus while casting the background out of focus so it’s not distracting. This requires an aperture of around f/5.6 – f/11. Incidentally, the lens is always sharpest in the middle of the F stop range, so use this as much as possible when shooting portraits; even if you have to use a flash.

There are a number of outcomes to consider when selecting the aperture:

Shutter Speed

The aperture works directly in collaboration with the shutter speed. The subject that you’re photographing will depend on which aperture and shutter speed you use. These can also be determined by the third party to join in the fun:


The ISO of a camera is an equation that determines how fast the digital sensor (or film if you’re quirky) reacts to light. The higher the number, the better it reacts. Unfortunately, you also get a loss of quality in the form of noise which I explain about when in the ISO article. The idea is to get as slow an ISO as possible in order to get sharp, smooth pictures.

Using these three factors together

There will be plenty of scenarios where you’ll be using your camera and taking these three factors into consideration will guarantee perfect results (which is why photographers are so important and cost so much). If the situation is too dark, you need to use a slow shutter speed to let more light hit the sensor to get a good exposure. By doing this, you open yourself up to getting blur from hand shake or movement in the frame. So to overcome this you can throw the aperture open which decreases the plane of focus and use a higher ISO which will allow quicker shutter speeds but also increases noise. To help further, let’s look at a couple of examples:


My favourite style of photography. The portrait is all about getting a message across to the viewer simply by looking at someone’s face. Technically, it’s about getting a sharp, well exposed image because portraits are usually examined close up. The lens you use can determine how sharp and aberration free the pictures will be. A zoom lens is extremely versatile, but a zoom lens loses it’s sharpness out at the extremes of the focal length. A prime lens (doesn’t have a zoom feature) is a lot sharper but generally costs more. I’ll go into lenses in another article.

An aperture of around f/11 will get a sharp portrait and out of focus background. Here I wanted the green to contrast the red hair but not to let the eye draw away from Constance.

The perfect portrait focal length is 90mm. You can use any lens around this length though, between 50mm and 150mm. I get great shots from a Canon 50mm lens when shooting both weddings and portraits. Using an aperture of around f/8 or f/11 will produce very sharp pictures of the face and head while throwing the background out of focus.

A small aperture means the sea and background are all in focus.


The idea of a landscape is that you generally want to get as much in focus as possible, from the foreground to the horizon. Using a smaller aperture will create this, but with a small aperture, images aren’t as sharp. You can help to minimise this by purchasing a better quality lens, using a very low ISO and a tripod to keep the camera steady while the camera exposes. The use of a tripod is essential in most cases because the small aperture and low ISO will cause a longer shutter speed which can, in turn, cause camera shake if hand held.

The difference between full frame and crop sensor. The smaller sensor fills the frame more with the boat, so it appears closer. This diagram isn’t mathematically correct, it merely serves as an illustration.

There’s a difference between film and digital and this is that the size of a digital sensor on a typical DSLR is slightly smaller than a 35mm film. It’s the same size as an APS film in the C format (remember APS? No?) Because it’s slightly smaller, the image that hits the sensor isn’t as wide. In fact in many cameras, it’s 1.6x the difference(1.5 on Nikon). That’s why digital camera lenses are so much wider – because you have to multiply them by 1.6 to get the 35mm equivalent focal length. The wider the lens, the more light you can get in and that’s what you want. This also creates more problems which I’ll go through when I cover the various types of lenses available the the problems they can cause.


This article doesn’t cover everything about apertures, but it gives you an idea what a photographer has to know and think about in order to get a sterling photograph. This is just one aspect of photography and they all work with each other to create a picture you love. The camera can produce technically perfect results automatically, but there’s no way it can be creative or break photographic rules like a photographer can.

The photographer is the most important person at a wedding, they will get your business seen, they will think out of the box about how the best way they can promote you through visual medium which is the most powerful one around. They do this by using the tools at their disposal from years of training, practice and passion. When you get married and think you only need to stick some cameras on a table, think about the difference a photographer can make. I can shoot an entire day of wedding photography for £350. It’s a snip for the quality of shots you’ll receive.


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