Understanding exposure – photography

The Very Basics Of Photography: Understanding Exposure

First, you want to take good images. Then you’ll want to take awesome images…

But if you do not understand the very foundations of photo creation, i.e. exposure, you won’t be able to fully achieve that goal.

Just relax, it’s a very simple concept. Yet very important! It’ll surely help you create fantastic images for long years to come.

 

The two basic elements of exposure: light and sensor

 

Right at the beginning I must clarify that, for the sake of simplicity, I will refer to film or plate or digital image sensor as “sensor” since their basic function is the same: “record the image” or “grab the light it is exposed to”.

A picture is properly exposed if the sensor gets the right amount of light. Although there is no universal standard for what the right amount of light is, we can say instead: the right amount for your purpose.

This means you have to master exposure to get what you really want.

Your sensor needs to get at least some light to be able to record an image. Without light, your image is pitch black. With too much light, your sensor is overexposed and in the worst case it will show a completely white image.

So it is the interaction of light and sensor that creates an image.

How well you can manage this interaction is key.

 

The three basic camera tools for exposure: aperture, shutter, and ISO setting

 

The simplest camera, which is capable of creating a photographic image, is the pinhole camera.

The pinhole camera has no lens at all. It is a lightproof box with a tiny pinhole in one side. As light passes through the hole, it projects an image on the opposite side, which holds the sensor.

 

Structure of pinhole camera
Structure of pinhole camera. This is how a pinhole camera works.

 

So the pinhole camera has

    • a fixed aperture (the hole),
    • a sensor (with an ISO value based on the film/plate type or digital ISO setting),
    • and its shutter is simply a piece of material (e.g. a flap) with which you can cover and uncover the hole manually.

 

In its core, a professional digital camera has the same “exposure tools”, however, with advanced features:

    • an adjustable aperture (usually between f/1.4–f/22),
    • a sensor with adjustable ISO speed (usually between 100–1600),
    • shutter speed (usually between a couple of seconds to 1/8000 sec.)
Simple build up of digital camera
Very simply, the three basic elements of a digital camera: aperture ring, shutter curtain, sensor

 

The exposure triangle: aperture, shutter speed, ISO

 

All three tools just mentioned are capable of helping you achieve the exposure you want, i.e. projecting the desired amount of light on the sensor.

Each of them can be adjusted separately and it is very useful to know how and why to do that.

Exposure Triangle

 

Aperture

It is the hole through which light is passing through. You can change the size of the hole so you can increase or decrease the area which light passes through.

The lower the aperture value, e.g. f/1.4, the larger the hole, and the higher the aperture number, e.g. f/22 the smaller the hole.

Note: It is denoted as “A” on your camera. If you shoot in aperture priority mode, your dial or display shows an “A”. This means that if you change the aperture number, your shutter value will automatically be adjusted for shooting with the correct exposure.
Warning: aperture will affect the depth of field and image sharpness!
  • Wide apertures and very small apertures cause a loss of sharpness.
  • The wider the aperture, the smaller the depth of field (DOF) and vice versa: the smaller the aperture, the greater the depth of field.

Depth of field: the range of distance (or zone) within which the image shows acceptable sharpness – objects in this zone appear to be in focus.

 

Understanding depth of field in photography
You see: depth of field is a range of sharpness, in front of and behind the focus point

This all means that if you can achieve the greatest sharpness (but not greatest DOF) by using aperture numbers in the mid-range of your aperture scale, typically, values of f/5.6– f/11.

 

Shutter speed

Shutter speed can vary from an infinite time (theoretically) to a tiny fraction of a second, e.g. 1/8000 depending on your camera features.

(In practice, most of the time you’ll use shutter speeds between 1/30 and 1/250, assuming you’ll do a lot of hand-held shooting throughout your travels.)

The longer the shutter speed, the longer the time light will project on the sensor and thus the lighter the image becomes.

Many times, especially as you become more and more experienced in photography, you’ll want to make a different exposure from what the light meter of your camera suggests.

In such cases the simplest way to change exposure is to change the shutter speed.

The very useful +/- setting on your camera lets you over or underexpose your image in ⅓ or ½ increments, which will most probably help you achieve the desired exposure quickly.

Note: Shutter speed is denoted as “S” on your camera. If you shoot in shutter priority mode, your dial or display shows an “S”. This means that if you change the shutter speed, your aperture value will automatically be adjusted for shooting with the correct exposure.

 

ISO speed (sensor speed or film speed)

Back in the early 2000s, when I was extensively using Fujichrome Velvia slide film, ISO 50, for my landscape photos, I often needed to use a tripod to be able to “give enough light” to this slow film (which meant longer exposures, many times 1-4 seconds, impossible to manage with a hand-held camera).

Film speed limited my possibilities for achieving the right exposure, especially when subject matters were in motion, e.g. wind-blown trees or moving animals.

Today’s state-of-the-art digital cameras give you a wide range of ISO settings without having to make a compromise on quality.

Basically, the higher the ISO number, the more sensitive the sensor to light. On the other hand, as you increase ISO speed, image noise increases as well.

Good quality digital cameras can now handle image noise very well up to about ISO 1600, which is very good news since you’ll be able to take your travel photos by just holding your camera—unless you have special long exposure ideas, but that’s another story.

 

How to check correct exposure?

 

Use your eye

If you can see your LCD screen properly (e.g. there is not too much ambient light), you can rely on your eye in most of the cases.

If you check your photos on your desktop monitor or tablet screen, make sure the screens are adjusted rightly in terms of lightness and contrast.

Now you can decide whether you like what you see or not.

With your image editor you can still make some adjustments if your photos are not very over or underexposed.

 

Use the histogram

If you have a little extra time when shooting, it’s worth checking the histogram on your camera’s LCD screen, right after you’ve taken your image.

The histogram gives you instant feedback on how balanced the tones are in your picture.

You should see peaks and valleys that are balanced all across the scale.

Ideally, all the tones are shown from left (dark) to right (light) and neither the dark tones nor the light tones are “cut off” from the scale.

 

Check exposure with histogram
Underexposure (dark image) – Correct exposure (normal image) – Overexposure (bright image)

 

I do hope this hasn’t been too overwhelming and now you feel you have a better understanding of the basics of photography and how to set the correct exposure for your images.

I’m sure as you take more and more photos it’ll become less and less a challenge to take the high standard images you aim for.

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The Very Basics Of Photography: Understanding Exposure #photography #exposure #photo tips

 

Text and images © Daniel Kerek

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