The big flash equipment tutorial
This tutorial is meant as an introduction to flash equipment. It describes the basic knowledge required to understand the tutorial on the creative use of flash that will be posted shortly (stay tuned for more! ). Its content might be interesting for those that want to buy a new flashgun too.
Disclaimer: some of the information presented in this tutorial may be specific. If you use another brand, your camera and flash combination might react differently. I've tried to minimize the brand-specific stuff except for chapter 4 which really is brand specific.
On to the contents...
1. Various types of flash and their features
1.1 The internal / popup flash thingy
1.2 The system flash or flashgun
1.3 Studio flash
1.4 Exotic miscellaneous
2.1 The guide number
3.1 The minimal synchronization time
3.2 Synchronize on rear curtain
3.3 High-speed flash
3.4 Stroboscopic flash
4 Main versus fill
4.1 Fully automatic mode (P)
4.2 Half automatic mode with user-set (Av)
4.3 Half automatic mode with user-set (Tv)
4.4 Fully manual (M)
A. Frequently Asked Questions
1. Various types of flash and their features
Some typical flash equipment (click for larger image)
In this tutorial, I (admittedly completely arbitrary) distinguish the following categories: the internal flash, the system flash, the studio flash and last but not least the repository of "exotics".
1.1 The internal / popup flash thingy
Probably everyone is familiar with it: the internal or popup flash. Treated by most as "useless", it sometimes can save the day. Features: it is built in so you can't leave home without it (duhhh... ), you can't aim it anywhere but straight ahead, it is not so powerful (guide number varies per body, but usually somewhere around the 12 or 13) and it uses power provided by the body (which is both, an advantage and a disadvantage!). I guess this thing doesn't really need any more introduction.
1.2 The system flash or flashgun
Flashguns are available in several sizes and types. calls them "speedlight", varies on that and calls them "Speedlite". Other manufacturers give 'm a type number only. these days makes three different types: the 220EX, the 430EX II and the 580 EX II, makes five: SB-R200, SB-400, SB-600, SB-800 and the largest of the pack: the SB-900. Other manufacturers like Metz and make excellent and often relatively cheap alternatives for all of the top brands. In addition, some manufacturers (Metz specifically) make external flash systems that do not sit on the flash shoe of your camera but instead are hand held.
System flashes in general provide more than the internal flash, the flash head swivels and turns and they use their own set of batteries. You often can get a couple of accessories like external power packs, gels and other modifiers for them too. In short, system flashes are becoming a viable alternative to studio flashes these days
1.3 Studio flash
A whole different category of flash contains the studio flash systems. Basically, there are two different types: the flash heads that connect to a big external generator pack and the so-called "monoblocks" that usually hook up directly to a wall socket. These things typically sit on top of a special stand and a triggered from the camera either by a cable hooked up to the X-sync terminal on your camera, a remote control (either radio or infrared) or they can be used in a slave configuration where they act on the from another flash.
The the smaller studio flashes generate often can be compared to that of a system flash; the bigger studio flashes however generate a lot more . They usually are used in combination with some type of modifier (an umbrella, softbox, snoot, beautydisc or whatever).
1.4 The exotics
Now, this is a totally arbitrary category; I put all the flash types not mentioned earlier in this category: ring flash, macro flash, slave flash, you name it. Flashes in this category usually provide a mix from the above types: they often (but not always) connect to a hotshoe, the can or can not be aimed etc. etc. The flashes in this category fall outside the scope of this tutorial (even though some information is valid for them too!).
On first sight, one of the most important features of a flash is the amount of it can produce - the more , the better. How much often is expressed in one of two units: the guide number ("GN" for short) and energy (in Joules).
2.1 The Guide Number
The maximum amount of an internal flash or a system flash can produce usually is expressed using the Guide Number. This number is the outcome of the formula RG = x distance, specified at 100 . Distance can be expressed in meters or in feet (the latter is somewhat strange and in reality used in the USA only - Yanks specify focal distance in mm as does the rest of the world and set the sensitivity in , but use feet to express subject distance with... now that is plain silly, isn't it?). For the sake of simplicity, I assume all distances and GN's in the remainder of this tutorial to use the metric system.
The internal flash on a typical camera body has a GN = 13, meaning you can use it up to a distance of just over 3 meters if you use f/4 and 100. If you close the to, say, f/8, this distance is reduced to 1.5 meters.
When using an external flashgun, chances are you can derive the GN from the type identifier (Nikonians: you're out of luck here!). 's Speedlite 580EX has a GN of 58, the 430EX has a GN of 43.
Caveat... check the specifications of the GN carefully since things can be deceiving. To re-use George Orwell's words: all guide numbers are equal, but some guide numbers are more equal than others. Modern system flashes adjust the opening angle of the reflector to the focal distance of the used and some even take the sensor size into account. The idea is that you don't need to the same area when shooting at a longer focal length than you’d need when using shorter . The longer the , the smaller the area, the smaller the angle. Of course, the covered area is different for smaller sensors too. If you don't have to spread out the , you can concentrate it and thus get more on the same area. The bundling of is done by moving the reflector in the flash backwards when shooting at longer focal .
In the end, this means guide numbers are depending on the focal length you’re shooting on. Some manufacturers specify the GN at 105mm ( , Metz and ), others at 80mm ( ), 50mm ( /Minolta) or 35mm ( ). Be sure to check the manual for a table representing the GN's at different focal length. For example: here is the table from the 's 580EX's user manual:
Guide numbers for a SpeedLite 580EX as specified in its manual (click for larger image)
Except from the focal length, the settings are important too. After all, if you increase the sensitivity of your sensor by a factor 2 (going from 100 to 200 ), you can take 1 back in your settings. This means that the guide number increases if you increase the sensitivity; each time you quadruple your setting, the guide number is doubled.
When checking the specification of studio flashes, you will notice production hardly ever is specified as a guide number. Instead, they specify power in Ws, Watt Second (note: Watt x second, not Watt per second!), also known as "Joule". The idea is that a 100 Ws monoblock generates the same amount of in a fraction of a second as a "standard" (whatever that may be) 100 Watt household bulb generates in 1 second. The reason for expressing " power" in this unit instead of a GN is that studio blocks hardly ever are used bare bulb (it usually is modified using softboxes, umbrella's etc), plus typically the distance between camera and subject is very different from the distance between studio flash and subject.
Now, it is not easy to compare different brands based on their specifications in Ws. Some brands are more energy efficient than others and thus effectively generate more from the same amount of power. There also are differences in attributes that make it hard to compare brands. An increasing number of manufacturers actually specify a guide number in addition to the power rating (LinkStar specifies a 400 Ws monoblock with GN = 65, Elinchrom specifies 64.5 for the same power), but how this is measured and under what circumstances is not clear.
- Guide Number GN = distance x at 100
- The GN increases by a factor 2 if the increases by 4
- Modern system flash units change GN with focal lenght and sensor size
- Studio flashes are specified in power x time => thus WattSeconds, not Watt / second as is often written
3.1 Minimal flash synchronization time
Modern single reflex camera's use a known as a curtain- or focal plane . The mechanism used in such a consists of two "curtains", consisting of metal fins. When at rust, the sensor is covered by the first curtain. When you trigger the , the first curtain opens. After a set period of time (close to the time), the second curtain (also known as the "read" curtain) closes, after which both curtains are moved to the original position.
The speed at which the curtains move is not infinite; it takes a curtain some 4 milliseconds to move from completely closed to completely travel from "closed" to "open" and vice versa. If you dial in an time that is less than those 4 milliseconds (1/250"), the rear curtain already starts closing whilst the first curtain is not even completely open. Thus, a split of moves across the sensor and there is no time at which the sensor is completely exposed. If you would generate a flash in this case, part of the sensor will be shielded from the .
This problem exists with all focal plane cameras with times shorter than 1/200 or 1/250 of a second. The minimum time at which the whole sensor is visible is also known as the X-sync time or the minimal flash synchronization time. If you do not use any tricks, it therefore is not possible to use shorter than X-sync in combination with a flash.
3.2 Rear curtain synchronization
Instead of taking a short , you could dial in a longer time too, for example to show movement. If the flash fires as soon as the first curtain is open, the subject is nicely lit at the start of the movement. Take, for example, a car that runs from left to right through the image area. The car is "frozen" at the beginning of the movement. After, say, 1/1000", the flash is gone... but the curtains remain open and the car is moving. Thus, a ghost trail due to the subject's motion is generated. The effect: the car seems to drive backwards.
First curtain synchronization (Click for larger image)
This may or may not be what you want. A rally car that seems to drive backwards is a strange thing to see. The solution is rather simple: make sure that the flash fires just before the second curtain closes and the frozen action follows the trail. This feature is known as "read curtain synchronization" (or variations thereof). Be aware that on some camera / flash combinations you need to set this feature on the flash. The EOS system for example provides settings on the camera body to control this feature, but in combination with some flashguns the settings on the flash overrides this setting on the camera.
Example of rear curtain sync (Click for larger image)
Caveat: rear curtain synchronization needs time. In theory, you could use it on any speed less than X-sync. However, where X-sync on bodies is around 1/200", rear sync won't work with time shorter than 1/40"!
Note: this use of flash with longer times to create an action blur is a balancing act. If you don't expose long enough, hardly any motion might be visible (depending on the speed of the object). In addition, if your flash generates too much in comparison to the ambient , chances are the trail is just barely (if at all) visible, but if the flash does not generate enough , you will see the motion blur but the freezing point won't show).
3.3 high-speed flash
Sometimes, for whatever reason, you may want to use very short times, maybe even shorter than X-sync. Most manufacturers offer a special feature for this purpose known as "High Speed Sync" ("HSS") or "Focal Plane" sync ("FP"). When selected, the flash starts generating pulses of before the first curtain opens and continues pulsing until the second curtain is closed. Because just a small part of the sensor is exposed at a certain time, this costs quite a lot of energy and the GN will not be met in FP mode. How much energy is lost and what GN is available in this mode is hardly ever specified - use it at your own risk.
Note: as with rear curtain sync, this feature can be set on both, the flash and in the menu on certain bodies. And as with rear-sync, the setting on the flash might override what you set on the body.
3.4 Stroboscopic flash
A feature that is available on some flashguns is "stroboscopic" flash. With this feature enabled, the flash fires several times during the time your is open. In combination with longer times, this gives you the possibility to create images in which you see how an object moves. It is a fun feature that is very nice with sports like motocross and ski board-jumping. However, as with most of these things, the effect soon wears of its novelty. To me, it is more a gadget than a serious feature (except maybe for scientific or sport analysis purposes...).
Example of stroboscopic flash (Click for larger image)
- flash with speeds < X-sync will generate a partly exposed image only
- rear curtain sync makes motion move forward"
- caveat: rear curtain sync might not work on speeds < 1/40" ( !)
- FP flash costs a lot of energy; you won't be able to use the full GN
- Settings on the flash often override settings on the body ( !)
4. Main versus fill
Note: this chapter probably is quite specific. Would appreciate though if some kind soul adds similar information for other brands!
A flash can be used for several reasons. You could use it simply because there is not enough (use as main !), but you could also use it to control shadows (fill ). Other create applications include contrast control and motion stopping. tries to help its users to "guess" how the flash should behave. Thus, the behaviour of the flash and the camera depend on the mode the camera is set to as well as the amount of ambient available. An explanation...
4.1. Fully automatic (P mode)
In 'P' mode, the camera will choose a somewhere between X-sync and 1/60" - it will try to choose such a speed that you could shoot without the use of a . If there is enough (> 13 Ev*), the will match the ambient and the flash will be used as fill- . If it's quite dark (< 10 Ev), the is set wide open and the flash will function as main source. In between, the flash will balance in ½ between main and fill .
So, what this means in reality:
- outside, when conditions are quite good, a is selected that matches the scene. The flash will make sure the subject (that is close by) is lit well.
- inside, when conditions are much worse, the is fixed to 1/60". The result of this choice is that the background can become quite dark, but the subject should be well lit.
*): Ev = Value. This is the number of required to get a "good" measured from an f/1, 1 second at 100 . 10 Ev is ca. 1/60" at f/4, 13 Ev is ca. 1/125 second at f/8.
4.2. Half automatic with priority (Av)
In Av mode you choose the (duh..!). The body will choose a that somewhat* matches the ambient as if no flash is used and the flash will work as fill only.
*): If there is very little (< 8 Ev), the camera will choose about half the it should use without flash. If there is more ( > 9 Ev) the is not changed.
4.3. Half automatic with priority (Tv)
In Tv mode you choose the and the camera chooses the correct to get as good an of the background as possible. The flash will function as fill , until the is not enough to get good of the foreground. In that case, the flash will add as much as needed to get good on the subject.
4.4. Manual (M)
In manual mode, you are in control. If you set the very closely to match the ambient , the flash will function as a fill . If there is a large discrepancy between what the camera thinks is correct and what you dialed in, the flash will try to compensate for the missing .
More on main and fill will follow in another tutorial.
A. Frequently Asked Questions
Last but not least, an answer to the most frequently asked questions:
Why does my flash under expose?
Usually, the following things cause underexposure:
- The flash is not capable of lighting the complete distance. Check the settings of, and focal length against the guide numbers mentioned in your manual. Increase or choose a larger .
- The preflash is bounced against something highly reflective (windows!)
- There is a lot of white orin the scene
- Head is not aimed correctly (especially when bouncing is used)
- Camera in Av or Tv mode (flash works as fillonly)
- Camera in P mode whilstconditions are reasonable (flash works as fill !)
- Flash has no power (are the batteries okay?)
Why does the flash overexpose?
Over usually is caused by:
- A lot of black in the scene
- Your subject is too close
- Diffusedcauses indirect lighting through your omnibounce
Why does rear-curtain sync not work?
A couple of possibilities:
- Rear sync set on camera, not on the flash
- < X-sync
- Focal Plane (a.k.a. "HSS") mode set
Can I use my flash to trigger my studio strobes with?
Yes, you can. But (yes, there always is a 'but' )... modern flashes generate a pre-flash to find the correct settings. Your studio strobes may trigger on thus preflash and are not ready when making the real photo. Thus, they won't flash at all or flash without nay power. If you cover the flash and press '*' (FEL) you can make the photo without preflash. If you're using an external (system) flash, you should switch it to manual which will the flash from generating a preflash.
How do I prevent the background from turning all black?
Consider a flash photo as a double ; once from the flashlight and once from the ambient . The flash is not (or hardly) affected by the , the ambient however does depend on the . If you increase the , the ambient that probably lights the background becomes more effective. This technique is often called "slow sync" or "dragging the ".
Hoe do I get a black background?
decreases quadratic with distance. If the subject at 2 distance is nicely lit by the flash, it is underexposed by two at 4
How do I prevent "red eyes"?
"Red eyes" originate from the flashlight that goes at a straight angle through a person's pupil and illuminate the blood vessels in the back of the eye. If you look at almost the same angle through the pupil, you'll see the reflection of these blood vessels. If you increase the angle between the coming in and the optical line of the , this effect decreases. Thus, the solution is to increase the distance between flashlight and (bounce!). Now, if you're using an internal flash, you can't change that angle. Most camera's provide a "red eye flash" feature that triggers the flash a couple of times before taking the picture. The eye's reflex is to close the pupil, thus effectively removing the from getting into the eye. A disadvantage is that your model will probably squeeze his/her eyes which is not a pretty sight. Better to remove red eyes in post processing IMHO.
The flash head does not zoom anymore, is it broken?
If the head of a flash does not zoom anymore with the focal length of the , the most likely causes are:
- the head is not aimed straight forward. If the head points up or down or is turned left or right, it automatically zooms to 50mm. Note that "down" can be very subtle -'s SpeedLites for example can be pointed down just 7 degrees for close-up photography!
- the diffuser for wide angle is (partly) folded out (note: if you're using an omnibounce you can have a hell of a time looking for this!)
- some (usually old)do not communicate a focal length to the camera
- the head on most flashguns can't zoom more than 105mm. With modern flash/camera combinations, that can include the cropfactor from the sensor. Thus, if you're using a APS-C camera ('s xxxD en xxD series for example) and you have a 70-200 mounted, the flash will always be in the 105mm setting (when pointing straight forward!).
- en last but not least: yes, it can be broken...
 NK Guy: Flash Photography with EOS Cameras , Version 1.7. 23 February, 2007, http://photonotes.org/articles/eos-flash
 Neil van Niekerk: flash photography techniques, http://planetneil.com/tangents/flash...phy-techniques
 Herbert Waldhecker & Stefan Gross: besser blitzen mit -DSLR, http://www.traumflieger.de/desktop/b...port_teil1.php (note: German language)
 J. Voorhaar: Licht, belichting en verlichting, Maart 2004, Photographic Memories (note: Dutch language)
 USA: Speedlite System Tips, http://www.usa.canon.com/dlc/control...288&fromTips=1
 USA: Fill-in flash use with EOS cameras and speedlites, http://www.usa.canon.com/dlc/control...&articleID=106
 Japan: http://web.canon.jp/imaging/flashwork/, http://web.canon.jp/imaging/flashwork/
 Kevin Björke: Strobe Trigger Voltages, Dated 2004/04/06 04:51:29, http://www.botzilla.com/photo/strobeVolts.html
 M. Buschman: Basisboek licht meten, Focus Media Groep, ISBN 9072216598
 M. Buschman: Basisboek flitstechniek, Focus Media Groep , ISBN 9072216822 (Dutch language)
 Steve Edgell: Licht en belichting, Cantecleer, ISBN 9021323443 (Dutch language)
 Hicks, R.: Licht!, Cantecleer, ISBN 9021328526 (Dutch language)
 Toomas Tamm: Electronic Flash Information, 28 August 1999, Internet http://www.chem.helsinki.fi/~toomas/...flash-faq.html
 Bob Atkins: EOS FAQ, Version 2.4, http://www.bobatkins.com/photography/eosfaq
A special thanks to Rick for his assistance in getting this tutorial cleaned up - thanks mate!