Let’s talk about Exposure and the trio or triangle, the aperture, shutter speed and ISO.  

The object of photography is to expose the digital sensor or film to the correct amount of light.  In order to get a perfectly exposed image, all three of these must work in perfect sync.  If you change one, then you will also need to adjust the others.  All three effect the way your image will look.  So knowing how changing each of these will effect your image is the key to perfecting your travel photography.   

Aperture.

Light passes through the lens opening to reach the digital sensor or film.  The aperture can be opened wide to let more light in or closed down to keep light out.

The F stop is the measurement used.  F stop refers to the ratio of the focal length to the diameter of the lens opening.  e.g an 80mm focal length at f/4 to look through the front of the lens, the opening of the aperture would be 20mm across (80/4).  This is all so confusing and you don’t need to solve a maths equation every time you take a photo, so instead we will work with the number the lens uses and how they relate.

The most common F-stops you will see on most lenses are:  f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22

Here is a diagram that shows

Sometimes this confuses people also because as the number gets bigger, the hole gets smaller.  So think of the f as a fraction, so think of it as follows f/2 = 1/2, f/4 = 1/4, f/8 = 1/8 etc etc. 

We know that 1/2 (one half) is larger than 1/4 (one quarter) so by that logic, the larger the F-stop number gets, the smaller the lens opening.  

Not all lenses have the ability to shoot at all of the f stops listed above, some shoot wider at f1.2 and some can go all the way through to f32, but others the widest f stop may be f4.  You may have heard the term “fast lens” and you think what the hell is a “fast lens”? Lenses that open to f1.4 are classed as fast lenses because they expose the digital sensor or film to light more quickly than a slower lens such as f4.  Which is beneficial for indoors or lower light situations.  Faster lenses for this reason are more expensive.  There are also zoom lenses that have a constant maximum f2.8 as the fastest aperture for every focal length but then other lenses change the maximum aperture depending on the focal length.  The constant maximum aperture are more preferred and are more expensive lenses.

The aperture also controls the depth of field which I will focus on in greater detail in another article but it is another thing that sounds confusing and directly effects how you view an image so think of it this way.

The depth of field is the distance between the closest and furthest part of picture that are relatively sharp.  The subject will be in focus but transitions from sharp to unsharp gradually.   An aperture of F16 creates a deeper depth of field or far greater image in focus than an aperture of say f2.8 which will be a shallower depth of field and less of the surrounds in focus.

A couple of examples of how to use each would be:

Portrait - Often a shallow depth of field f1.4-f4

Landscape - Often a deeper depth of field. f8-f22

So the two main reasons to change your aperture are to let more light in or to adjust your depth of field.

Shutter Speed.

The shutter is a curtain like object that protects the digital sensor or film from light, when pressed it opens for the time specified to expose the digital sensor or film to light.  As with Aperture, adjusting the shutter speed effects the look of the image, it is either to let more light in (slow the shutter) or to create or freeze movement in a subject (eg sport).

The photographer chooses when to expose the sensor or film to light by pressing the shutter button.

The amount of time the shutter remains open is crucial for getting the exposure right and is called the shutter speed.

Shutter speed is determined by the lighting conditions, low light conditions require the shutter to be open for longer therefore a slow shutter speed and bright conditions require the shutter to be open for less time therefore a faster shutter speed.

There are standard shutter speeds as follows:

1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000

1 being a full second, then the other numbers represent fractions (eg. 2 means 1/2 of a second, 125 is 1/125 of a second etc.)

These day, digital cameras means you can open your shutter for times outside those listed above, I have a canon Eos r5 so my setting allow me to open up to as slow as 30 seconds and as quick as 1/8000 of a second.  Other cameras may allow an even quicker time.  You may also see “B” which refers to bulb, which allows the shutter to stay open for as long as the shutter button is being held or “T” which is time, which allows you to press the shutter button once to open the shutter and then again to close it. (“T” is less common in modern cameras).

The shutter also controls how movement is perceived.  For example if you require your subject to be relatively sharp and the movement frozen, then a faster shutter will be required.  If you are trying to show movement in your image, such as a waterfall then a slower shutter speed will blur the water, creating or emphasising movement.   This is usually artistic expression so neither are wrong or right but knowing the difference is crucial to how your photo will turn out.  If your focal point is blurred (for movement) but the background is not relatively sharp, then the image may just look out of focus.  So the shutter needs to be fast enough to freeze the background but blur (or create movement) in the subject.  

How quickly the subject is moving also needs to be taken in to consideration.  For example a person strolling across the frame can be frozen at 125th of a second, but a car travelling across the frame will need a faster shutter speed to freeze it.  Also a subject walking across the frame from left to right or right to left will require a faster shutter than walking toward or away.  

Another creative way of showing movement in an image is by panning.  Panning is moving the camera during exposure in the same direction as the subject is moving.  This creates a sharp subject but a blurred moving background.  You will need to approximate the speed of the moving subject in order to create a successful panned image.

These days a lot of camera’s and lenses have inbuilt image stabilisation so we are able to handhold at a slower shutter speed than before without getting camera shake.  Previously we could only hand hold the camera for roughly the same time as your focal length, for example if your focal length was 50mm then you would be able to handhold at 1/50th of a second before you would get camera shake or if your focal length was 600mm then you would only be able to handhold for roughly 1/600th of a second etc etc.  Now this is not so much needed but I still use it as a guide.

A tripod comes in use for images that require a long shutter speed.  A good tip is to use the 2 or 10 second timer if using a slow shutter speed so that the act of pressing the button does not cause the camera to move slightly.

ISO.

Another important aspect to a well exposed image is the ISO.  In film photography the ISO (International Organisation of Standardisation) or previously ASA  (American Standard Association)   (The German system refers to DIN eg. 27DIN is equivalent to 400 ISO) relates to the film speed.  

Emulsions of silver crystals that when exposed and then developed clump together which create the films density.  You can see the clumps that look like fine particles of sand that is referred to as grain.   Faster films have emulsions that are larger than that of slower films, therefore you are able to see the clumps easier than that of finer grain film. The higher the ISO or ASA the faster the film.   The most common film photography ISO are 100, 200, 400, 800.  

In digital photography we measure the ISO by the digital sensors sensitivity.   We still use the same principles as film, so the higher the ISO the more sensitive the sensor is to light.  The difference instead of grain it is more defined as digital noise, higher ISO can create a shot that is less crisp with more noise.  Most newer camera’s have improved to allow you to shoot an image with far less digital noise than previously allowing us to shoot in lower lighting conditions with higher ISO’s.

So combining all three (Aperture, Shutter and ISO) directly effect how much light reaches the film or digital sensor.  Changing one of these setting on a digital camera will require you to update at least one of the other settings for a perfectly exposed image.

Each full stop aperture or shutter speed doubles or halves the amount of light let in (eg. f8 is double the amount of light than f11 and 1 second allows twice the amount of light than 1/2 second). So if you slow the shutter speed down 1 stop then you will need to close down the aperture by the same 1 stop to make the same exposure or reduce the ISO if digital by 1 stop. If shooting film then the film will be rated accordingly and set when you put the film into the camera, so only changing the shutter speed and aperture is necessary.  Remember a slower shutter speed lets more light in, so you will need to close down the aperture to a larger f-stop to compensate.  This is where artistic creation comes in and you create the image based on depth of field, movement and grain/noise wanted.

I hope this helped break down the different aspects of exposure so you can make better more informed decisions while shooting.