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Starting with Off-Camera Flash in Photography: Techniques

Starting with off-camera flash feature image

In my last post, I showed you what equipment you needed when starting with off-camera flash. This time, I am going to be looking at the technical side and what you actually need to learn in order to take great photos using off-camera flash.

It’s hard

This is the part where you need to really get to grips with how this all works. When starting with off-camera flash, this will be something that frustrates you. I’m not going to lie, it involves hard work and practice to get right.

In order to start, you really should have a good idea of how to shoot in manual mode, or at least a good awareness of aperture, shutter speed and ISO.

For someone new to off-camera flash, the technical aspects are the part that is the most daunting. Not only are you working with the camera in manual mode, but you are also adding things such as flash power and flash-to-subject distance. Then there is a model for an extra layer of pressure. That said, a good model is vital.

Fuji camera close up showing dials and shutter button
It’s time to move to manual mode. It’s not that scary. Promise

Working with a model

Finding people to pose for you while you learn is always hard. For this article, I managed to get an awesome model. She is incredibly patient and did exactly what I asked her to do every time. Here she is:

A mannequin is great when starting in off-camera flash. This image is shot with a soft box against a blue background.
Always hits her mark perfectly and never complains. A great investment.

Honestly, a mannequin head is a great investment when starting with off-camera flash. I only paid £4 for this hairdressers mannequin on an Amazon flash sale. Using a mannequin really allows you to build confidence and test lighting setups without worrying about annoying friends, family or models. 

You can always use other inanimate objects, especially if you are not interested in portraits, but a hairdresser mannequin is one of the best investments you can make to help you master off-camera flash for portraits.

Learn the technical rather than letting the camera do it

With modern cameras, flashes and triggers, you can easily stick with letting the camera do all the hard work. Call me old school, but I think it is hugely important to learn off-camera flash manually. By doing this, it is easier to understand how everything works. It also means you are in total control of what is happening.

Just like learning to photograph in manual mode, using off-camera flash manually allows you to get the exact results you want every time. Even if you then go on to shoot in auto mode, you will have the knowledge to still get the shot when the camera plays up (which they tend to do when you need them to do it least).

As you shoot more, you will become more confident, so I would always suggest using an inanimate object whilst you practice. There is nothing worse for knocking your confidence than having your subject in front of your camera and having a total mental meltdown, because you changed the position of the flash but you can’t remember how to adjust the exposure in your camera to make it look right. 

CANON EOS RP PRESS IMAGE WITH 24-105 LENS
Modern Cameras are incredibly smart. But getting started in off-camera flash requires you to do the hard work.

The five variables

Unlike shooting in ambient light, where you only have three variables that can control the image, shooting flash ramps this up to five.

However, it is simply a case of working through them methodically. With practice, it becomes easier. However, your first few times, it may be trial and error (and possibly frustration). 

The five variables are:

  1. Shutter speed
  2. Aperture
  3. Flash power
  4. ISO
  5. Flash-to-subject distance

Let’s start with the two elements that are present in every photograph: shutter speed and aperture. 

1. Shutter speed

A model bride shot against a dark backdrop in a dimly lit venue.
The ambient light for this shot was awful, so I removed it. I left my shutter at 1/200th and found an aperture to kill the ambient light. I then set the flash power accordingly to create this.

The main use of shutter speed when using off-camera flash is that you can darken or lighten the ambient light. This includes your background and any other light sources, such as room lights and candles, etc. By using your shutter speed, you can alter the amount of ambient light in the shot without altering any other variable. 

The reason for this is that a flash will put out all of its power in the smallest fraction of a second (as quick as to 1/20000th second on some flashes). Your shutter speed will be less than this and, therefore, will not affect the power of the flash itself.

There is also one other thing that affects the use of shutter speed, the flash sync of your camera.

The flash sync is the maximum speed that you can shoot the flash at. This is usually around 1/200th of a second. There is a technical explanation for this and ways to shoot faster, but I won’t get into it within this article as I don’t want to overload you with information. Just remember, you cannot put your shutter speed faster than your flash sync.

Shutter speed in practice

When thinking about using the shutter in off-camera flash photography, the thing you need to decide is how much of the surroundings you want to include. If shooting portraits outdoors against a beautiful sky or backdrop, you may want to balance the exposure with the flash to make the most of the location.

However, if you are doing an indoor shoot with ugly or unflattering lighting, you may want to totally remove all ambient light. Shutter speed is your key to doing this. 

Let’s look at this with a series of images.

In all of the images, the only thing I will alter is the shutter speed. Everything else will remain identical. The Aperture is f/16, ISO 100. My flash power is 1/4.

For the first shot, I set the shutter speed to the maximum sync speed (1/200th). As you can see in this image, the background is underexposed for effect and the model is lit by the flash.

Starting with Off-Camera Flash in Photography: Techniques
The model is lit by flash. Areas where the flash does not hit are much darker (left side of her face)

As I slow the shutter, this time to 1/100th second, you can see the sky is lighter and the darker areas of the model that are not hit by the flash are less harsh. I have allowed one more stop of light into the camera, but only for the ambient exposure due to the speed of the light coming from the flash.

Starting with Off-Camera Flash in Photography: Techniques
See how the sky is brighter and the darker areas are not quite as harsh. This is due to the shutter allowing more natural light into the camera.

Finally, I slowed the shutter down to 1/60th to give the correct ambient exposure for the sky and using the flash as a fill for any shadows on the model.

A photo off a mannequin used to illustrate getting started in off-camera flash. The doll is shot against a cloudy sky.
With a balanced ambient and flash, the flash fills in any shadows on the model’s face.

Notice how the lighting from the flash has not changed. That is because aperture controls flash exposure.

You can also use your aperture or ISO to increase or decrease the natural light coming into the camera, but remember when you alter them, you will also need to alter your flash power too.

2. Aperture

When starting out. The easiest way to think about things is that shutter speed controls the ambient exposure and your aperture controls your flash exposure. I know it is a little more nuanced than that in reality, but when learning, you want things to be as simple as possible.

We know that your shutter speed controls how long your camera shutter is open. Your aperture, however, controls how much light enters your camera, not for how long.

As flash power is too quick to be affected by shutter speed, you control it by changing the aperture. If the image is overexposed, you need to close the aperture down, and if it is too dark, you need to open your aperture up.

Setting aperture in practice

To show this in action, look at the images below. In all images, I will keep the shutter at 1/200th of a second and my ISO at 100.

Firstly, I set the flash at f/4. As you can see, the image is overexposed. This means I need to close the aperture a little. 

A photo of a doll against a blue backdrop. The image is overexposed.
f/4 is overexposed. I need to change the aperture.

Next at f/8, you can see I have closed the aperture down too far. The image is too dark, so I need to open the aperture a little more.

An underexposed image of a dolls head against a blue background.
At f/8, the image is too dark. I need to change the aperture.

Finally, here is the shot at f/5.6. As you can see, this is the correct exposure.

A dolls head against a plain background exposed correctly
Finally, at f/5.6 I have the correct exposure.

As you can see, I have not changed any other exposure variable, just the aperture. Changing the shutter speed would have no impact because the flash discharges its power so quickly. Now I have locked in my exposure, my lighting will be identical every time.

Bonus round

Here is the same image shot with the same aperture and a shutter of 1/100th of a second. A you can see, the change of shutter speed has made no difference to the exposure.

Starting with Off-Camera Flash in Photography: Techniques
Changing the shutter to 1/100th has made no difference to the final exposure.

3. Flash Power

Flash power is simply how much power the flash can put out. This varies from flash to flash.

In terms of getting started, a Speedlite is more than fine. It will mean not shooting in the brightest part of the day (unless you are in shade), but it is super affordable, and the best way to start with off-camera flash.  

As with shooting in manual mode, you want to learn with your flash in Manual mode. This helps with consistency.

If you set your flash to 1/2 power, every single pop of that flash will be half power. This consistency is key to mastering flash. 

In terms of power, you start with full power, which is sometimes also known as 1/1. This is the largest amount of light that your flash can produce. Most modern flashes work in small 1/3 stops, but to simplify things whilst you learn, you really need to concern yourself with the following outputs:

  • 1:1
  • 1/2
  • 1/4
  • 1/8
  • 1/16
  • 1/32
  • 1/64
  • 1/128

Each of these settings equates to 1 full stop of light the flash produces. So changing the flash from full power (1/1) to half power (1/2) reduces the amount of light coming out by one full stop. Changing it from 1/1 to 1/4 reduces it by two full stops, etc. 

Remember, the stops it refers to are your aperture, as this is what controls flash exposure. If you look at the table below it will explain it more clearly.

FLASH POWER1/11/21/41/81/161/321/64
APERTUREf/16f/11f/8f/5.6f/4f/2.8f/2

As you can see, if the flash at full power gives you a correctly-exposed image at f/16, half power will bring you down to f/11 and so on. This relationship is the key to mastering flash. Half the power = 1 stop of light. 

4. Where does ISO fit into all this?

Shooting a flash at full power is less than ideal. There may be some circumstances where you cannot avoid it, but it will kill your batteries quicker, take longer to recharge between shots, and, in some cases, it may overheat the flash, causing it to not work at all. Ideally, you want to be working at 1/2 power or less.

ISO is where you can make that happen.

By doubling your ISO, you allow one more stop of light into the camera. Therefore, you can reduce the flash power and still get the look you wanted. For example, an image at ISO 100 and a flash power or 1/1 will be the same as an image at ISO 400 and 1/4 flash power.

ISO in practice 

I have decided I want to shoot at f/8 and ISO 100. To do this, the flash has to be at 1/1. To get to 1/4, it means I will lose two stops of flash power.

When starting in off-camera flash, your ISO is something you need to reduce flash power. Here is an example at ISO 100 and flash power or 1/1
Here is the image at ISO100 and flash power 1/1.

To keep the same aperture, I turn my ISO from 100 to 400, therefore, giving me two more stops of light into the camera. The image is virtually identical

Starting with Off-Camera Flash in Photography: Techniques
At ISO 400, the exposure and the flash at 1/4 power, the image is almost identical.

It is all a juggling act, and ISO is there to help you fine-tune. However, upping your ISO comes with more noise. But, most DSLR and mirrorless cameras can easily go up to ISO 800 and still be of great quality.

ISO can also help with getting the correct ambient exposure whilst keeping a required shutter speed – especially as light drops. A simple tip is – if you need to double your ISO to get more ambient light, drop your flash power by one stop to compensate.

5. Flash-to-subject distance

I have saved this for last. This is the most technical when it comes to understanding flash (and involves the laws of physics). 

The distance of your flash to your subject is governed by The Inverse Square Law. This law states:  

The intensity of an effect such as illumination or gravitational force changes in inverse proportion to the square of the distance from the source.

https://www.diyphotography.net/visual-approach-inverse-square-law-affects-photographers/

Now, I am sure you are reading this thinking, what the heck does that mean? Well it means the amount of light is reduced by distance. See the diagram below courtesy of Wikimedia:

Starting with Off-Camera Flash in Photography: Techniques
Every time the distance doubles, the power drops by 3/4.
Image: Borb / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

The easiest way to look at this in a photography sense is every time you double the distance between your light and the subject, the amount of light will be reduced to 1/4 of what it was.

What also happens is that every time you double that distance, you get more space to work in. This is really useful if you are doing a group shot. Again, whilst this is hard to explain with words, look at the diagram below.

A diagram of off-camera flash and how distance is affected by the inverse square law.
If you are doing a group shot, you want to get the flash further away from the subjects to avoid issues with exposure across the image

Flash-to-subject distance in practice

Now we understand the inverse square law, we can use it to our advantage. All of the images will be shot on the same blue background.

For both images, I will set the exposure at 1/200th, f/16 at ISO 100. I will keep the exposure the same by changing the flash power. The model is 1.5m from the background.

I start with the flash close to the subject (30cm). You can see the background is black. This is due to the light being close to the subject. Therefore, the difference in exposure between the subject to the background is huge due to the inverse square law. 

A dummy head showing the inverse square law in action. The head is close to the flash darkening the background
With the flash 30cm away from the model, the background gets virtually no light due to the inverse square law and light fall-off.

Now, as I move the light back, the difference in the power of light between the subject and the background is much less due to the inverse square law.

The distance between the model and the light is now around 2m.

To keep the exposure the same, I have had to increase the power of my flash a whopping 6 stops. In this example, it has gone from 1/128 power to 1/2 power to keep the same exposure. 

As you can see in the image below, the final model and background are both well-exposed due to moving the light further back.

Starting with Off-Camera Flash in Photography: Techniques
With the flash further from the background, the exposure covers the model and the background.

Let’s recap

So hopefully, you now have a good understanding of the basics for getting started with off-camera flash. But let’s recap the basic points to remember:

  • Aperture controls the flash exposure
  • Shutter speed controls the ambient light
  • Doubling or halving the power of your flash moves the power of the flash by one stop of light. 
  • When the flash is close, the light falls off incredibly quickly
  • As you move further away, the fall-off is much slower.
  • Get yourself a model that isn’t human to practice on. Try the model head or bottle of whiskey.
  • Practice, practice, practice. 
  • It isn’t easy to get your head around, but I promise that one day it will just click. The only way for this to happen is if you practice. So, what are you waiting for?

There are more variables you can throw in, such as modifiers, high-speed sync, etc. but right now, that isn’t what you need to learn.

Master these basics and then push things further. The only thing I would suggest to add is an umbrella to diffuse the light and give more flattering results.

Now it’s time to practice

An article about starting with off-camera flash that tells you to shoot fully manual. You might be thinking “I can’t do this.” You can – you just need to practice.

It may sound daunting to some of you, but I promise it is easier than you think. I always compare starting with off-camera flash to learning your time tables. When you are learning them, they feel really difficult. Then it clicks, you suddenly understand it and you wondered why it took so long.

All together class, sing along. Two times two is four…

Do you have any other tips or questions you’d like to share? Please do so in the comments.

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Carl Spring
Carl Spring

Carl is a Lincolnshire living, skateboard-riding, Rock N’ Roll listening, pet-loving, trainer-addicted photographer.
Along with his wife Lisa, they photograph weddings and portraits under the name 166 Photography
Carl has also spent many years photographing musicians and extreme sports. You can see more of this work on his website