Understanding Exposure Settings - tutorial

Now your camera has some solid settings dialed in that will work for most situations, its time to look at the options available to you that you can use to help you capture a usable exposure for your photograph. In this blog post we will look at:

The Exposure Triangle
Exposure Modes
Exposure Metering
ISO Settings

THE EXPOSURE TRIANGLE

In photography, exposure is the amount of light hitting the cameras sensor (or film). There are three main tools on a camera that you use to affect exposure.

Lens Aperture – controls the amount of light passing through the lens onto the camera sensor and it also controls the depth of the area of focus.
Shutter Speed – controls the amount of time the sensor is exposed once light has passed through the aperture.
ISO – controls the sensitivity of the camera sensor to light. The higher the number is, the more sensitive it becomes and the more digital noise is produced.

To highlight the relationship between these three I will use the following examples:

Shooting a long exposure at night you would use a long shutter speed and a low ISO to reduce noise (subject dependent) and the aperture would be set according to how much of the photograph you want to be in focus.

Shooting a creative portrait during the day (high amount of light) you would use a narrow depth of field, a fast shutter speed and a low ISO. If the exposure is still too bright you would use a ND filter to balance the exposure.

Photographing indoor sports you would set your aperture to be fairly open if not completely open, and then set shutter speed to control the amount of motion blur. Depending on the amount of available light you would either adjust you ISO accordingly or set it to auto and define the ISO range the camera can use.

Photographing fast moving objects, for example racing, you would have a fairly open aperture, a high shutter speed and a ISO around the 500/600 mark if not higher depending on the generation of camera you are using.

It should go without saying, the best way to discover the best settings for the above is to experiment. Odds on you wont nail the shot first time. But the amazing thing with digital photography is the feedback you receive is instant and allows you to adjust camera settings as you see fit.

CHOOSE AND USE THE CORRECT EXPOSURE MODE

All worthwhile cameras come with the standard four exposure modes:

Manual (M)
Aperture-Priority Auto (A)
Shutter-Priority Auto (S)
Programmed Auto (P)

Exposure modes control the relationship between the lenses aperture blades (these control the amount and angle of light travelling through the lens) and the shutter mechanism. The action they perform is also directly affected by the ISO settings selected.

Manual – You set the shutter speed and the aperture. This gives you full control over how long the shutter mechanism remains open and the size of the aperture. Practically, it is good for studio work and conditions where light levels are consistent.

Aperture-Priority Auto (A) – You manually set the aperture, and the camera adjusts the shutter speed. This is used for any type of landscape/interior work, outdoor portraiture, sports, weddings…basically a lot of shooting situations.

Shutter-Priority Auto (S) – You manually set the shutter speed, and the camera adjusts the aperture. This is best suited to situations where your subject is moving fast, like sports, where you want the shutter speed to remain constant.

Programmed Auto (P) – Camera sets both the shutter speed and the aperture. I have still yet to find a practical use for this exposure mode, I’m sure there is one but it does sit lonely and unused on my camera. I suspect it is for complete beginners who just want to use their camera before learning all of the settings. Nothing wrong with that….as long as you learn the other settings!

The two modes I have only ever used in my work are Manual and Aperture Priority. I use manual shutter mainly in the studio where I am using controlled lighting from studio blocks and radio triggers. In the past I have also used the manual mode in the below two situations:

When i am using auto-iso. When I shoot events like a wedding or sports, I keep the aperture and shutter fixed and let the auto-iso do the job. You can define the range the iso can go to so you can prevent the camera from going above a certain iso level.
When I am shooting panoramas with a tilt shift. The tilt shift I own plays tricks with the aperture priority setting on my camera. So I work out my shutter speed on my central image and then keep that fixed along with fixing iso and aperture.

Aperture priority is the mode I use. It is absolutely perfect for when I have no control over the light intensity. If you are shooting HDR’s outside then you use aperture priority as it makes life a lot easier letting the camera workout shutter speed as opposed to shooting, checking, reshooting, rechecking. And the same goes for outdoor portraits. Whilst you can do most things with manual exposure, realistically you will not have time to keep checking the exposure meter to make sure your exposure is correct. You will need the camera to do some heavy lifting as you will be concentrated on your subject.

EXPOSURE METERING

Exposure Metering is the mechanism that allows your camera to work out the correct exposure for the scene you are photographing. There are usually four options: Matrix, Centre-weighted, spot and highlight weighted. For the purpose of this lesson, set the camera to Matrix metering as this setting calculates an exposure based on the overall scene and is usually accurate most of the time. If I’m shooting in aperture priority I use matrix in conjunction with the exposure compensation setting (the +/- button) to fine tune the exposure.

Centre weighted, whilst monitoring the overall scene, pays more attention to the centre of the frame. Spot metering meters a small circle in the middle of your frame and then calculates exposure. Highlight-weighted aims to reduce loss of details in highlights which is handy for unbalanced situations.

ISO SETTINGS

What is ISO and what is the appropriate level to set it to?

ISO (International Organization of Standards) is the sensitivity of your camera’s imaging sensor and it is one point of the exposure triangle. ISO was originally used to describe the sensitivity of photographic film and has been passed over to the digital world as an equivalent measurement system. A low number of iso 50 -200 equals low sensitivity, low levels of digital noise in your image, smooth gradients, accurate colour representation and fine details. A high number, iso 1200 – 6400+, will result in a high sensitivity, visible levels of noise, rough gradients, poor representation of colour and a loss in fine detail. Both have their advantages and disadvantages depending on the situation you find yourself shooting in which I will talk about later.

The degree of digital and colour noise present in an image with higher ISO settings is dependent on the generation of camera you are using. Each generation comes with an increase in the clarity of higher ISO cameras. When you are researching a new body to buy make sure you look at the high ISO test shots to see how that new body performs.

So what ISO levels should you use?

A very general rule to follow is: If you have strong light source set the ISO as low as possible (this includes good sunlight and any type of flash or direct lighting). As the light source gets weaker increase the ISO. This is all dependent on how the camera is supported and what speed your lens is.

To give you some situational examples:

Shooting a landscape…

…or a portrait (either with or without flash) then you would aim to keep the ISO low.

Photographing outdoor sports then raising the ISO to about 400 to 500 allows you to have faster shutter speeds. Depending on what sport you are photographing you can either have a wide aperture for slower moving sports…

…or for faster moving sports an aperture of f/5 – f/5.6 which should make your shots nice and crispy.

If you are shooting the milky way then you would use ISO 1600-2400 (or higher with a more recent generation body) with a 20 to 25 second exposure.

If you are in a situation where light levels are changing, but you want to keep the shutter speed and aperture the same then use auto ISO. Examples of this type of shot include indoor sports…

…and weddings.

All dSLR cameras will have this functionality so check the manual out to find out how to set this up on your camera.

I usually set the auto ISO range in the camera settings and then lock the aperture and shutter speed (although for weddings I usually flick between manual and aperture priority). I usually set a maximum ISO of 1000 ISO on my d750, or 2000 to 2500 ISO on my D780.

It goes without saying that you should always experiment with these settings on your camera. So use the above as a guide and develop your understanding from there.