Roie Galitz - Photographer Galleries Articles Courses Downloads About
Flash – Let there be light


Flash – Let there be light!


We all know that in situations in which there isn’t enough light, or that the natural light doesn’t work in our advantage, we use flash, that little bulb that sheds some light on the subject. But what is that mysterious flash, and how can we use it to our best advantage? In this tutorial I’ll discuss the flash and its qualities. I will concentrate on external flash for those of you who are more advanced and I am sure that many will want to further their knowledge after learning more about flash. A small warning, I incorporate some advanced terms and concepts and I’ll try to explain things as simply as possible.


This tutorial’s bright spots:

  1. Introduction to flash
  2. The first flashes
  3. How does the modern flash works?
  4. Measuring light with your flash
  5. What affects exposure?
  6. Guide number
  7. Synchronization speed
  8. Flash photography modes
  9. External flash  - advantages and options
  10. Bouncing – not what you think
  11. Diffuser – Mellowing the atmosphere
  12. Tips for flash photography
  13. Examples of flash photography
  14. Summary


1. Introduction to flash photography – Question - how a photograph is created? That’s right, by light emitting from an external source reflected off different objects. But what happens when we don’t have enough light where we are, for example at night or in a dark place? Right again, we use flash or a long exposure. The second option is in most cases irrelevant and this is why I’ll focus on the former. The flash’s role is to serve as a comfortable and available light source and to light the scenes the photographer wishes to capture.


2. The first flashes – Photography as we know it began in the 19th century, and right from the start early photographers thought about solutions to the problems brought up in the first clause. The first flashes were made of magnesium powders and other materials that when ignited created a short burst of light. Naturally, blowing up noisy smoky compounds for a photo was quite unpleasant. How did it work? The ancient photographer would open the lid off the lens (ancient shutter), held the magnesium ribbon in his hand, lit it and immediately cover the lens and run away before the people in the photo begin to complain about the smoke.


3. The modern flash – Thankfully, flashes today work much more efficiently and comfortably than 150 years ago. We shall now discuss the flash’s structure and how it operates:


a.     Batteries – The flash needs an energy source and in most cases it is 1.5 Volts batteries that we like to call “AA batteries”.

b.    Capacitor – In fact there are 2 capacitors, a main one and a secondary one, whose job is to store large amounts of electricity from the batteries. The power from the batteries is augmented from 1.5 Volts to about 300 Volts in the capacitors, while the capacitors charge you can hear a high-pitched sound that anticipates the flash’s fire.

c.     Transformer – This device augments the power from 300 Volts to thousands of Volts (!) and delivers the power to the flash’s light bulb.

d.    Light bulb – A glass cylinder filled with Xenon gas, which usually doesn’t conduct electricity. In the flash process, electricity is conducted from the secondary capacitor with voltage of thousands of Volts in order to ionize the Xenon gas and turn it into a conductor for free electrons. After that the main current is delivered from the main capacitor to the bulb, and is converted to photons, meaning – light! Naturally, This whole process happens in a flash (…). After the flash is drained, the process repeats itself.


4. Light measuring with the flash – When the camera measures light, it takes into consideration the light reflected off the subject. But how is it that the camera can measure light when the only light available is about to come from the flash? Good question… The answer is that the camera shoots a tiny flash right before the real flash and uses it to measure the light reflected off the subject. The real flash is determined according to this measurement. For a more detailed explanation, read about the differences between TLL and E-TLL in section 9.


5. Guide number and Working distance – Every flash has a guide number (GN), which measures the intensity of the flash, the number is stated in meters according to ISO 100. In order to double the GN you’ll need to increase the energy 4 fold.


Formula: To determine the relevant working distance (the distance the subject shoul be from the camera) with the flash the following equation is used: GN/F-number (Guide number divided by the aperture). For example GN 42 in F4 will permit a working distance of 42/4 or 10.5 meters.


6. What affects exposure with a flash? I see that you’re asking all the right questions. The relevant factors are:


a.     Shutter speed – The shutter speed doesn’t influence the subject’s exposure when flash is used because the flash is faster than the fastest shutter speed. This is why the shutter speed only affects the background’s exposure and ambient light.

b.    Aperture – The aperture is the main factor that affects the exposure with flash photography since it determines that amount of light that enters the lens. As a rule, use the widest aperture you can (the lowest F number) in order to use the flash most efficiently. If we close the aperture then either the flash won’t be strong enough (see formula in section 5) or it will be too strong and blind the subjects.

c.     Sensitivity (ISO) – The higher the sensor’s sensitivity is, so the efficiency of the flash will increase. Doubling the ISO will increase the GN by 1.4 and after ISO 100 will double the GN.

d.    Working distance – That’s an obvious one. The distance between the camera and the subject is one of the most influential factors on exposure in flash photography – you need to keep your subject within the flash’s range and is the case of several subjects it’s recommended to keep them in the same plane from the flash in order to guarantee equal lighting. 

e.     Flash compensation- In most advanced cameras there is an option of positive or negative flash compensation. This function gives us more control on the scene’s exposure by over or under exposing the subject.


7. Synchronizing speed – In reflex (SLR) cameras, when using high speeds, the shutter exposes the film in several stages and not just once. This is why the synchronizing speed of the flash is limited to the maximal single exposure speed of the film/sensor. In most cameras this stands on 1/250 when the usual range is 1/125 –1/500. In some of the digital cameras this problem was solved by using an electronic and not a mechanic shutter. See “Fast Synchronization” regarding synchronizing speeds higher than the camera’s maximal sync speeds.


8. Flash photography modes:


a.     Automatic flash – Automatic flash is the simplest mode for junior photographers. In this mode the camera decides when and when not to activate the flash. I recommend you use your judgment and not to use this mode.

b.    Red eyes – With on-camera flash we suffer by the phenomenon of “red eyes” which is caused by a reflection of the flash light which is close to the lens off the back part of the subject’s eyes (the retina) which is rich in blood vessels. In some animals, by the way, the eyes shine and reflect some of this light as part of a night vision mechanism they possess. Anti-red eye flash fires a preliminary flash that causes the pupils to contract so that when the main flash is fired the retinal reflection in minimal. Red eye effect does not exist with external flash (see section 9).

c.     Slow synchronization – is used in night photography when you want to activate the flash and maintain the low shutter speed in order to expose the background. The regular synchronizing speed is usually at a minimum of 1/60 and longer exposures permit enough light from the background to enter the lens. I recommend you use a tripod for this mode.

d.    Rear curtain – Unlike front curtain where the flash is fired at the beginning of the exposure, in Rear curtain the flash is fired at the end of the exposure.

e.     Fill flash – It is used in situations where the daylight is strong but you want to “fill in” the shadows created by sunlight. For this mode we use negative compensation flash to soften its effect but still leave enough of it to light the shadowy parts.




9. External Flash – almost every camera has in internal flash. We will now discuss the differences and possibilities of the external flash.


a.     Power – An internal flash is weaker compared to an external flash. This is because there is less room for the flash apparatus we learned about earlier, such as the capacitors, bulb, transformers and of course the batteries used are those of the camera and so an external flash will be significantly stronger compared to the camera’s internal flash.

b.    Red eyes – An external flash solves the problem of red eyes because the distance between it and the lens is great enough so that the angle won’t allow light to be reflected off the retina.

c.     Attachment to the camera – There are several ways to attach a flash to a camera, a common one being the “Hot Shoe”. This is a metal groove with several contacts on its bottom on which you slide the external flash on. Another way to attach a flash is using a synchronizing cable and a special flash adaptor.

d.    Through the Lens (TTL) – spares us the need to manually adjust the flash before every photo. There are several variations on the method such as A-TTL, I-TTL, E-TTL etc. The differences between the methods are the light measuring technique. What are the differences and how do they work? A flash working on TTL fires without a preliminary flash and measures the correct exposure while the flash is shooting and stops the flash when it has been achieved. E-TTL is a more recent method that has been developed by Canon and is carried out by shooting a weak preliminary flash through which the camera measures the light with a light sensor and after calibrating all the chosen data fires the main flash. This method exists in the advanced Canon cameras developed since 1996.

e.     Zoom Flash – Advanced flashes are equipped with zoom heads that adjust according to the lens’ focal length. In a wide lens the light is dispersed in the space and in a narrow lens it is focused on a narrow area in a more efficient way to enable it to reach a longer distance.

f.      Fast Synchronization – As stated in section 8, the synchronization speed of the camera is limited. But sometimes the need arises for faster shutter speeds, such as in strong daylight. This is why “fast synchronization” was developed. The flash emits a series of ultra rapid fires one right after the other throughout the exposure and by doing that exposes the film (or the sensor) to light in each stage of the exposure. The disadvantage of this mode is that the intensity of the flash becomes much weaker because instead of one strong flash there are a lot of short weak ones. This is also the reason why the shorter the exposure speed is in fast sync so will the flash intensity be lower (it flashes less times) until even from a distance of a meter at speeds of 1/4000 it will be difficult to achieve good exposure. In electronic shutter speeds you can use higher shutter speeds than in mechanic shutter cameras.

g.    Strobe – In this mode the flash fires several short flashes for about half a second. It is a good mode in case you want to see how shadows fall in the scene or achieve special effects such as motion of freezing it. In today’s digital world this is a less meaningful function because you can shoot a picture and see on the screen exactly how the shadows fall. Using this mode is mainly out of habit.

h.    Slave flash – Meaning flash that isn’t on the camera but is activated as a reaction to another flash. The firing mechanism is a reaction to the light emitted from the other flash or through a wire/wireless connection in more advanced flashes. The first kind of flashes fire in a predetermined intensity while the second kind fires according to the light measured by the camera as the data are transferred through the wires (or air in the wireless mode).

i.      Repeat – Ultra fast flashes are determined by the flash frequency per second and the length of the flash. For example, a frequency of 20 flashes per second for half a second will cause ten flashes. This is used mainly for creative effects in photography, freeze framing etc.


It is recommended to use a flash from the same manufacturer as the camera since the communication between them is best.



10. Bouncing - There are two main techniques with flash photography, the first is direct and the second is bouncing it off walls. It’s important these walls as white, otherwise the flash reflected will be in the color of the wall.

A. Direct Flash – The flash is directed straight forward towards the subject. It is characterized with harsh shadows and a little lighting from above (perfect for motor vehicle license quality photos)


B. Bouncing from above – The flash is aimed to the ceiling (the existence of a ceiling is mandatory for the success of this technique), and you take the picture. The advanced flash knows that it is pointing to the ceiling and will compensate for the long way it has to go with TTL. The end result if lighting from above that is also called butterfly lighting and it is soft due to the diffusing qualities of the ceiling.


C. Bouncing from the side – The flash is pointed to one of the walls, measuring the flash is done the same as bouncing off the ceiling and the end result is quality lighting from one side also known as window lighting or Rembrandt lighting.

As you see, you can achieve a studio light effect with an external flash.


D. Diffuser – A flash usually creates very strong contrasts in the lighting with sharp shadows because of the small size of the light source. A good way to improve this disadvantage in by the use of a diffuser. The diffuser is made of plastic and is placed on the external flash. Its Job is to soften the light and create gentler shadows and soft uniform lighting. It is highly recommended you use it in direct flash photography. Take into consideration that it's required to increases the intensity of the flash to get the same illumination with diffuser. In studio flashes other, more effective diffusing methods can be used such as umbrellas, soft box etc. whose job is to diffuse the light even more and to create very soft and pleasant shadows.



12. Tips for flash photography – Beyond what we’ve learned there are some other tips that will probably come in handy:

a.     Shooting in the fog/smoke – A lot of photographers that use flash can be found in smoky environments, such as parties. In these situations the flash is bounced of the particles of the smoke and the camera is “blinded”. This is why a diffused flash is recommended in these situations, or even not using a flash at all. Also, try and not to get too close to the subjects.

b.    Shooting from long distances – When using flash in long distance photography you should try and close the aperture as much as you can, take the diffuser off and point the flash forward. Increase the ISO a level or two and adjust the conditions so that the working distance is maximal using the GN formula.

c.     Taking the flash off the camera – You can take the flash off the camera and work with it by pressing the “shoot” button on the flash. Automatic flashes will shoot with full intensity but manual flashes are more flexible. In this way you can achieve interesting exposures.

d.    Several flashes per scene – Define the camera to the longest exposure possible, take off the external flash and start flashing a lot, really painting with light. The shutter should be set to around F5 to prevent light from being smeared and to prevent flash over exposure.


Examples of Flash photography – I am adding some examples for different applications of the flash photography guide for demonstration.

A. Shooting models on the beach – An example of external flash Nikon SB800 on a tripod while shooting a model (my ex-girlfriend) on the beach in Netanya. The flash was on full intensity, the camera was set to F/8 and the shutter speed to 1/500 at ISO 200 when the camera wirelessly controls the flash.


Actual implementation of the photo – Nina was jumping and I was shooting from a low angle while the flash fired wirelessly like in the previous demonstration and is not shown in this frame. Aperture F/7.1 Shutter speed of 1/320 ISO 200. The background is deliberately under-exposed in both photos to make the photo more powerful and to bring out Nina, which is lit by the flash. Without the flash she would have appeared as a silhouette. More examples can be views in my portfolio.


Macro photography – in macro photography we use extremely closed apertures to add depth of field to a difficult scene (I recommend you read the depth of field tutorial and the macro photography tutorial). Because the aperture is so closed, it is almost mandatory we use flash to light the subject. In real macro photography we are so close to the subject the lens is blocking the flash, so we have to take the flash off the camera and work with it wirelessly or with a synchronization cable. The results are breathtaking. The first photo is lit from the upper-left side and the second from the left.



14. Summary – The flash is a unique and advanced device that enables us, the photographers, to shoot in situations where the available light is working against us. We’ve learned how it all began, how the flash is built and how it works, what an external flash is and its advanced functions and how to make the most out of flash. The possibilities are endless. As always, the best way to learn is to put the theory into practice.



Roie Galitz


All rights for this article and photos are reserved to Roie Galitz

You're welcome to read more Digital Photography Articles


© All rights reserved Please do not use without explicit and written permission. You are always welcome to link to this page :)

צילום .. מאמרים צילום .. קורס צילום .. צור קשר .. Photography .. Articles .. Photography Course .. Bookmark