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Canon Flash Primer

by Gisle Hannemyr

This page is part of a series of articles about using flash on digital cameras. The complete set of segments in this series is:

Table of Contents

  1. Introduction
  2. Exposure Modes
  3. Off-camera Flash
  4. Choosing a Flash
  5. Flash Link farm

1. Introduction

This primer is part of a series of articles about using flash on a digital camera.

This segment deals with flash and digital Canon cameras (DSLR system cameras and the more advanced PowerShot compact cameras) and in particular Canon's dedicated system for controlling flash.

Another segment covers Nikon's dedicated system for controlling flash.

A third segment addresses using flash outside a dedicated framework, (i.e. non-TTL auto and manual flash, as well as non-dedicated off-camera flash).

Flash units can roughly be classified in four groups:

  1. Dedicated units made by the original manufacturer (i.e. Canon).
  2. Dedicated units made by various third party manufacturers.
  3. Generic flash units with Auto mode.
  4. Generic flash units with Manual mode only.

Dedicated units are compatible with the manufacturer's dedicated flash system. In Canon's case, this system is known as E-TTL (Evaluative Trough The Lens). Dedicated units are specially adapted to work with one particular manufacturer's system, and will not be compatible with other manufacturers' systems.

In addition to dedicated units made by the original manufacturer, various third party manufacturers such as Nissin, Sigma and Sunpak make units dedicated to work with Canon's E-TTL.

Generic units are not compatible with the advanced dedicated flash control system used by dedicated units. Instead, they provide a more basic functionality, but on many different systems.

Dedicated units only offer full functionality when used with the system they are designed for. Some dedicated units will not work at all when moved to a different system. Others, when moved to a foreign environment, will “dumb down” and operate as if they were generic units .

Both dedicated units and generic units remain popular choices.

Generic flashes are often preferred over dedicated flashes for studio use. Also, generic flashes are, as a rule, cheaper than dedicated flashes with the same power output. Another advantage with generic flashes is that they may be freely moved across systems. The downside of generic units is that they lack the advanced controls and features of dedicated units.

However, getting the exposure right with low intensity fill flash is much simpler when you use dedicated flash. And dedicated flash can give you automatic power control in complex setups with multiple flashes – where some of the units even may be sitting inside soft-boxes.

Dedicated Flash

image of hotshoe
Canon's E-TTL hot-shoe.
Photo: Jailbird. Used under: CC BY-SA 2.0.

In 1995, with the EOS Elan II camera, Canon introduced a new, sophisticated flash control system, known by the abbreviation E-TTL (Evaluative Trough The Lens). It replaced and obsoleted the earlier TTL and A-TTL systems.

E-TTL is now the foundation for Canon's dedicated flash control system.

For a list of models that can be used for dedicated flash, please consult:

Users familiar with Canon's TTL on their film cameras will notice a subtle difference when moving on to E-TTL. In the case of the E-TTL, the power of the flash is not controlled during the exposure by measurement off the film surface itself. Off-the-film (OTF) measurement is not possible with digital cameras as the sensor's surface is not appropriate for measuring off. This factor, combined with the decreased latitude of the digital sensor when compared to film means that the E-TTL user must expect slightly less accuracy when using E-TTL, compared to the traditional OTF TTL measurement used on a film camera.

Instead E-TTL relies on something called pre-flash for exposure control. It works like this: The camera fires a low power pre-flash milliseconds before the shutter opens. It then measures the light from this pre-flash as it is reflected from the subject through the lens (TTL). The camera uses this reading to compute the power ratio for the flash for correct exposure. The camera communicates the desired power-ratio to the flash and the flash adjust its power accordingly. Finally, the camera opens the shutter and fires the flash to make the exposure. The E-TTL system provides a fully automatic exposure control that seamlessly integrates camera and flash, but the pre-flash sequence also introduces a tiny shutter delay.

E-TTL is a dedicated flash system that is supported by the some of Canon's film bodies, and all their DSLR models. I am less sure of how well supported E-TTL is by Canon's compact digicams, but at least the more advanced compact cameras such as the Pro 1 and the Powershot G-series supports at least some E-TTL features. Point and shoot Canon compacts such as the Ixus-series do not support external E-TTL flashes and are outside the scope of this article. To make sure what features are supported, check the manual for the particular model you are interested in.

Newer Canon cameras and Speedlites use an improved version of the E-TTL system, called E-TTL II. E-TTL II is supported by all all Canon DSLRs except 1D, 1Ds, D30, D60, 10D and 300D).

Here is what I believe is the major changes from E-TTL to E-TTL II.

However, all the main features of E-TTL and E-TTL II are the same, and an E-TTL flash unit will work fine on a E-TTL II body, and vice versa. In the remainder of this note, for brevity I just write E-TTL instead of E-TTL and E-TTL II.

The major features of E-TTL are:

Not all features are available on all compatible models. See the manuals and specification sheet for the model you are interested in for details. Below is an (incomplete) list of limitations I am aware of.

E-TTL works through a very high level of integration between the lens, the camera body and one or more Canon Speedlites. To use E-TTL, the lens, the body, and the flash units need to be compatible with E-TTL.

Generic Flash

Generic flash units are are flash units that are not compatible with Canon E-TTL II. Instead of the advanced controls of E-TTL II, generic units are designed to fire when there is a (short) circuit between the flash's center pin and edge.

As there is no dedicated control system for flash exposure control, the power output of generic units must be controlled by other means. Most of the generic units offer at least manual (with adjustable power ratio) and non-TTL auto exposure modes.

2. Exposure Modes

In order to have the scene properly lit, with correct exposure and with a good balance between foreground and background light, we need to control the amount of light put out by the light, and adjust aperture, shutter speed and ISO to match that, as well as the ambient light. In this series, the following flash exposure control modes will be discussed:

The Canon TTL exposure mode is discussed in the next section. The non-TTL Auto exposure mode and Manual exposure mode are discussed in the segment about generic flash.


E-TTL is the name for Canon's dedicated metering system for high-end digital cameras. It replaces and obsoletes the earlier TTL and A-TTL systems. This note only discusses E-TTL, not the obsolete version of Canon's TTL.

Canon's E-TTL flash exposure system is a complex interplay between the camera and the flash. Because the system is highly automated, with its own built-in logic, it is sometimes behaves like it has a mind on its own. Without understanding this internal logic, it is difficult to predict how the flash will behave in different situations.

To make matters even more complex, the way Canon has set up E-TTL varies to some extent from camera to camera. These variations originate partly from physical constraints (such as the placement of focusing points and flash sensors) and partly from subtle design variations.

Below is my understanding of how Canon's E-TTL flash exposure system works. Canon's documentation does not go into much detail about E-TTL, so the findings below is based upon my limited experiences with the system on equipment I have used, and may therefore be inaccurate. Corrections and additions are welcome.

Some EOS bodies let you choose between two flash metering modes by use of custom functions. These modes are called “average” and “evaluative”. If the camera don't offer alternative modes, you should assume that it uses evaluative flash metering.

E-TTL is based upon measuring the flash light reflected from the scene through the camera's lens. The measurement is done by firing a low-power pre-flash. The delay between the pre-flash and actual flash is so short that the human eye is not able to distinguish between them. (However, the pre-flash will trigger plain optical slave strobes, so in order to use this type of slave flash, you need to disable the pre-flash.)

When the pre-flash fire, the light reflected by scene is picked up by one or more internal sensors. If the body has multiple focus points, there will be a separate metering at each focus point. Canon calls this AIM (Advanced Integrated Multipoint) metering.

These measurements are used to compute how much power to use for the actual flash. If you use auto focus and evaluative mode, the reading is biased towards the sensor area corresponding to the active focus point. In average mode, the measurement is averaged for the entire frame. If you use average mode, the flash works as main flash and the internal logic seems to be much less sophisticated than evaluative mode. The discussion below focuses on how the flash works in evaluative mode.

Note that the AIM system means that in evaluative mode, it is best to rely on selecting off-centre focus points for flash photography rather than using the centre point and then recomposing the image. (unless you use FEL, flash exposure lock).

In evaluative mode Canon's E-TTL flash exposure system is set up to work as either main flash or fill flash. As main flash, it will try to expose for the main foreground subject, and let the shadows fall wherever they fall. As a fill flash, it will adjust the camera's aperture and shutter speed to correctly expose the background, and adjust the flash power to fill in the foreground so that it matches the surroundings.

The first rule of E-TTL is to understand that the default settings that Canon has selected for flash photography are rather extreme, with a strong bias towards settings that work fairly well when the flash only being used to “fill in” the ambient lighting, but with a tendency to underexpose when the flash is used as the main light. The good news is that the settings can be adjusted, and Canon expect you to understand how and when to do so. Here is an excerpt from an answer from Canon on the subject of the tendency of the 580EX2 to underexpose when used as main flash:

“The 580EX Speedlite is equipped with functionality to either overexpose or underexpose, depending on how you manage it's controls. The EOS camera also has custom functions to manage flash exposures with '+' or '-' exposure compensation. If you take the time to properly understand how the custom functions of your Speedlite work in conjunction with the custom functions in your camera, you will be impressed with their capabilities.”

To cut a long story short, until you've gained enough experience with E-TTL to dial in the required flash exposure compensation (FEC) without even thinking about it, fire frequent test shots and use your camera's histogram as a flash exposure meter. Set FEC if necessary. About +1 stop FEC when using an E-TTL flash as main flash is a common setting.

The second rule of E-TTL is that (except in the special FP high speed sync mode) the system will never let you exceed the maximum x-sync speed (1/200 or 1/250 second on most Canon models). When optimizing for main flash, the minimum shutter speed will be limited to 1/60 second for best handheld performance. When optimizing for fill flash, it may stretch the exposure to as much as 30 seconds.

The drawback of using main flash is that photos taken in dimly lit areas usually end up with a black or very dark background. The drawback of using fill flash is that dark surroundings may lead to very slow shutter speeds (Av mode), making it necssary to use a tripod and for subjects to hold still to avoid blur, or a too wide aperture (Tv mode) with a depth of field that does not suit the scene..

Whether the system optimizes for main flash or fill may depend upon on the type of Canon camera, the setting of the camera's mode wheel, and the ambient light.

With the camera's mode wheel set to program mode (P), auto mode (Auto, and/or green rectangle) and most of the “scene” modes (i.e. the modes identified by small icons), something like the following algorithm is appearently used to decide whether to optimize for main flash or for fill flash: If the ambient light level is suitable for handheld shots (i.e. EV 11 or higher, typically open shade or heavy overcast daylight), the system optimizes for fill flash. If the scene is darker, the system optimizes for main flash. In both cases, the program will try to use the fastest shutter speed/widest aperture possible within the other constraints. The lowest shutter speed the camera will select in these modes is 1/60th of a second.

Some say that the third rule of E-TTL is that you should never use auto mode, program mode (P), or any of the “scene” modes. To many users, the camera's behaviour when using these modes in combination with E-TTL flash is just too counter-intuitive to be helpful. YMMV, but you should be aware that these modes may not be the simplest to master with E-TTL flash. Many users of Canon DSLRs (as opposed to a compacts), recommend putting the camera in manual mode when using E-TTL indoors, and aperture priority (Av) for fill flash outdoors in daylight.

When you use P, auto or one of the scene modes, you are essentially telling the camera to do pick the settings to use for you. If you want to pick the settings, you should use M, Av or Tv.

With the camera's mode wheel set to manual mode (M), aperture priority (Av), or shutter speed priority (Tv), behaviour depends on the type of camera.

Canon DSLRs is by default set up to use the Av and Tv modes for fill flash. You set the aperture (Av) or shutter speed (Tv), and the DSLR will adjust the shutter speed (up to two seconds) or aperture to expose the background for the ambient light. Flash power is adjusted to just fill in the foreground. However, most Canon DSLRs have a custom setting that let you change the shutter speed constraint in Av mode.

In Canon's compact models, such as the Powershot-series, the Av and Tv modes work similar to the P mode and the camera will never select a shutter speed slower than 1/60th second.

Some Canon camera's (i.e. compacts and consumer DSLRs such as the 350D) has a “scene” mode called Night Scene that will fire the flash to correctly expose the forground subject while extending the exposure for up to two seconds to also capture the surroundings.

In manual mode (M) you can set both the aperture and the shutter speed to whatever you want. In Canon DSLRs, the E-TTL-system in M mode will measure the light reflected by the foreground subject and adjust flash power to expose the foreground correctly. To get fill flash in M mode, set the aperture and shutter speed to correctly expose the background, and the E-TTL-system will take care of the foreground.

Many people find that the simplest way to use E-TTL flash with a Canon DSLR, is to put the flash on automatic E-TTL (ETTL) and the camera on manual (M). Then select a suitable combination of shutter speed and aperture (e.g. 1/100 second and f/8.0). With this setting, the flash will automatically be adjusted to expose the foreground adequately, while the background exposure is determined by the shutter/aperture combination. If your choice of shutter speed exceeds the x-sync speed of your camera (1/200 or 1/250 second on most Canon models), you also need to use the FP high speed sync mode on the flash.

In manual mode (M), Canon compacts such as the Powershot G5 switches off the pre-flash (and thereby E-TTL). This makes it feasible to use plain optical slaves, that otherwise are disturbed by the pre-flash. This has the unfortunate side effect that E-TTL can not be used to control the power of the flash in manual mode (see p. 101 in the Powershot G5 manual for details).

Because Canon's peculiar preference for fill-flash, you may find that the camera warns about severe underexposure when you use settings suitable for main flash. These may be confusing until you learn to ignore them.

The big advantage of E-TTL is that because E-TTL measures reflected light through the camera's lens, the position of the flash (or flashes) does not matter. The flash may be in or out of the hot-shoe, facing away from the camera or even put inside a softbox. The set-up may involve multiple flashes controlled by Canon's wireless flash control system. No matter what, E-TTL metering means that the camera meters the actual scene as seen through the lens. The sensor on an non-TTL Auto flash may “see” the wrong scene in many situations where the flash is off-camera.

3. Off-camera Flash

To move the flash off-camera, you can use wires or a wireless setup. For a wireless solution, you can either use Canon's dedicated wireless sytem, or you can use a generic solution using wires, plain optical slaves, radio control, or a combination of all these.

Dedicated Wired Flash

To move a single Speedlite off the camera, you can use the Canon Off Camera Shoe Cord 2 (OC-SC 2) or Off Camera Shoe Cord 3 (OC-E3). These are short (about 60 cm) coiled cords. The difference between them is that the OC-E3 has better seals against moisture than the OC-SC 2. These are just extension cords and preserves all flash functions including E‑TTL (i.e. the flash works like it has been mounted directly in the camera's hot-shoe). Their main use is for mounting a Speedlite flash on a flash bracket.

For multiple off-camera flashes, Canon used to offer a wired solution built around the Hot-Shoe Adaper 3 and the TTL distributor. This system, however, is not compatible with E-TTL.

For digital cameras, Canon instead provides a sophisticated wireless system for controlling multiple off-camera Speedlites. This system is described in the next section.

Dedicated Wireless (light based) Remote Flash

Canon's wireless flash system let you can fire two or more Speedlites together without any cables linking them. This dedicated wireless system uses visible or infrared light for signaling.

To use wireless slave flashes with Canon's dedicated flash system, you may use the built-in flash on a EOS 7D (currently the only model with this feature), or you may place an E-TTL-compatible commander in the camera's hot-shoe. This commander uses infrared (ST-E2) or visible (Speedlites and compatible third-party flashes) light to control one or more remote units. The system is quite sophisticated, and lets the photographer select one of four channels (to minimize the risk of interference from other photographer's equipment), and to control flashes in several groups with different power ratios. Wireless remote units may also be fired in manual or vario-power modes.

To use Canon's dedicated flashes as wireless remote inits you need to use a dedicated flash with the capability to act as wireless commander (as indicated by the letter “c” in the column “WL” in the models table), or you need to have Canon's dedicated wireless transmitter ST-E2 in the camera's hot-shoe. The camera's own pop-up flash can not be used to trigger Canon's dedicated flashes as wireless remote units.

Canon's wireless flash control system works well indoors. Outdoors, it requires a line of sight between the receiver and transmitter and is not reliable in bright sunlight. Note that the transmitter on the 550EX, 580EX and 580EX2 is part of the flash head, so this restricts positioning of the commander. However, setting the unit to “commander” will zoom out to give the signal an 80° coverage.

Dedicated Radio Flash

Canon's own system for dedicated wireless flash is based upon the commander using light to signal the remote units.

Some third party vendors, however, offer dedicated systems that use radio to signal remotes.

These vendor includes Pocketwizards who both makes a generic radio control system without TTL support, and a dedicated one with TTL support.

Dedicated flash units made by Quantum have their own radio-based TTL.system called FreeXWire.

Finally, a company known as radiopopper provides an oddball hybrid solution that lets you use optical TTL exposure control by means of radio. To make it work, you put your master dedicated flash in the hot-shoe, and attach a radiopopper radio transmitter to this with Velcro. Then you take a radiopopper receiver and Velcro it to a remote flash, and you then use a bendable fiber optic cable that goes into from the receiver and into the remote flash's optical sensor.

Generic Off-camera Flash

For working with multiple off-camera flashes, Canon's wireless flash control system works fine in many situations. However, there are situations where you will not want to use it for off-camera flash. For instance, if you want greater range, when you are working with studio strobes or in some other environment where Canon's wireless system is not an option, or when you are using a manual lens. In these situations, you will use generic wired, plain optical or radio slave flash instead.

For more about using generic off-camera flash, see the segments discussing third party options.

4. Choosing a Flash

What type of flash should you buy? Below is some points to help you decide, but only you know your requirements.

As we've seen, there are four types of flash to choose from:

  1. Dedicated Canon models.
  2. Dedicated third party models.
  3. Generic flash models with Auto mode.
  4. Generic flash models with Manual mode only.

Dedicated units made by Canon are designed to work with your Canon camera.

Dedicated units that are designed by third parties are also supposed to be tailor made to work with your Canon camera, but at a lower price point. Canon, however, seems to make more changes to the interface between devices over time, than other manufacturers. I will not speculate about why Canon do this, but it means that while a third party device like a flash may work fine with all Canon DSLRs at the time it is put on the market, it may lose sertain functions and even stop working completely with future models. In some cases, the flash's manufacturer may offer a firmware upgrade to resolve such issues, but not always.

Both Canon's dedicated units, and dedicated units made by third parties, are designed to communicate with your Canon body, and should be able to pick up ISO from the body and aperture from a compatible lens. They should also monitor the shutter speed and make sure you don't exceed the x-sync speed unless you are in HSS mode. Some third party dedicated units do these thing less than perfect.

The TTL exposure control work well in many situations, so you can just leave control of exposure and power to the flash, even in diffucult fill-light situations and when working with off-camera flash, soft-boxes, snoots, etc.. This means that you can consentrate on composition, framing and shooting, and feely change aperture and ISO, without worrying about the flash.

Generic flash units with Auto mode will also control flash power and therefore exposure for you. However, a non-dedicated flash will have no idea about the ISO and aperture in use. This means you need to transfer those “by hand”. Also, they do not measure the ambient light and can not provide automatic fill flash in auto mode (but most of these also offer Manual mode, which can be used for fill). Since exposure control is done with a sensor on the flash itself, they may not provide accurate exposure control when used out of the hot-shoe, i.e. when the sensor is not aligned with the lens.

Generic flash units that only offer Manual mode requires the use of a separate flash meter or cumbersome guide-number calculations to nail exposure. Because power must be explicitly set on the flash, manual flash works best in a studio environment were you set the power-ratio on one or more manual flashes placed on light stands. Then the distance between the scene and the flash or flashes remain constant, and you can keep using the same power ratio as long as you also keep using the same aperture and ISO. If you want to have your flash in the hot-shoe and move around, so that the distance between flash and subject constantly changes, manual flash may be quite cumbersome to work with.

For fill flash, dedicated TTL-flash is at its best, and non-TTL Auto flash useless. With Manual flash you can at least set a power ratio suitable for fill flash if you want to.

If you buy a non-dedicated flash and intend to use it in your camera's hot-shoe, you also need to consider trigger voltage safety.

I think it is safe to say that you can not go wrong with a Canon dedicated Speedlite. All the current units have good reputations.

The downside of Canon's dedicated flashes is cost. They usually cost more than third party dedicated with similar specifications, and they may cost more than three times as much as generic flash unit with Auto mode with equal power output. If you want a bright flash to be your main light, then you can save some money by choosing a generic flash. For instance, the dedicated Canon Speedlite 430EX2 (GN 32m) carry a sticker price of around $330. More powerful generic flash units such as the Vivitar 285HV (GN 31m) or Sunpak 383 Super (GN 35m) will cost only about $70-100 brand new, and used models can be had for a lot less than that.

The E-TTL system provides a fully automatic exposure control that seamlessly integrates camera and flash, but the pre-flash sequence also introduces a tiny shutter delay. For instant response (e.g. skateboard photography), you may be better off using a dedicated flash that also gives the option of using a non-TTL mode such a manual or non-TTL auto, or just use non-dedicated flash units.

There are also third party dedicated flashes from Metz, Quantum, Sigma, and others. Currently, I know little about the compatibility and quality of these units, so if you consider one of these, make sure you check it out is the store before committing to a purchase.

Power matters. Whether you choose a dedicated or generic flash, if you intend to use bounce flash, I would not recommend a unit with less power than the Canon 430EX2 (GN 32m) or a Vivitar 285HV (GN 37m). Be warned that the Canon 430EX2 can only be bounced in small rooms with a low, white ceiling. Depending upon imager sensitivity, room size, distance to ceiling, ceiling whiteness, etc. you may need even more power than the Canon 430EX2 affords to get good results with bounce flash.

Manual only flashes are going out of fashion, and while stock remains, they can be picked up from bargain bins for next to nothing. A number of perfectly working manual flash units can be had for small change at eBay and garage sales. Recently, Chinese manufacturers has started supplying brand new manual only flashes such as the Yong Nuo YN460 at quite low prices.

If you learn how to use a manual flash, you may save a lot of money by being able a reuse any old flash unit you may have left over from your film days, a cheap manual flash you may buy at a sale, or a new Chinese unit. If you buy an inexpensive handheld flash meter, you'll have no trouble getting the right exposure, even in complex situations involving fill light or multiple flashes. If you don't want to buy a flash meter, you should be able to pick the correct aperture for a manual flash from tables of guide numbers and subject distance. This may sound awkward, but it is not difficult after you've gotten used to it.

However, if the manual flash have no variable power setting, your options for controlling the light will be limited. Also, metering a test flash, or using guide-number tables may slow down your action. If you don't want to go through these steps, make sure you buy an E-TTL capable dedicated flash or an auto flash.

Canon E/EG/EZ/ML/TL-series vs. EX

Canon's older series of Speedlites have used various suffixes (E, EG, EZ, ML, TL) after the model designation. While the names of some of these are very similar to modern Speedlites (i.e. “430EZ” vs. “430EX”), the older series flashes are not compatible with modern Canon digital cameras.

Canon offers the following advisory on the use of Canon Speedlites other than the EX-series in the User's Manual for the EOS 400D/Rebel XTi:

“The flash cannot be fired with an EZ/E/EG/ML/TL-series Speedlite set in the TTL or A-TTL autoflash mode. Use the Speedlite's manual flash mode instead if provided.”

However, this is often not suffiscient. Some non-EX-series Speedlites will not fire if placed in the hot-shoe of a Canon EOS digital camera, even when set to manual flash mode. They can, however, be pressed into service with a pc-connector/adaptor, or a slave receiver. To use it directly in the camera's hot-shoe,you can put insulating tape over the “extra” pins, exposing only the center pin and edge connector. (However, there are user reports that Canon is quietly improving support for use of older flashes. In particular, firmware ver. 1.0.5 for the EOS 400D/Digital Rebel XTi, released in April 2007, is reported to make a number of older flashes work in the hot-shoe again.).

If you can get it to fire, a non-EX-series flash will operate in manual mode only on a modern camera.

If you already own an old Speedlite, it may be worth a try, but I do not recommend buying non-EX-series Speedlites for use with Canon digital cameras.

TTL-support and older cameras

Most older Canon film-based EOS bodies does not support E-TTL (there are some exceptions, such as the Elan II/EOS 50, so check the manual for the particular model you are interested in). Instead they control the flash by having an internal sensor that measures flash light reflected off the film during exposure, and uses this data to switch off the flash when just enough light has reached the film. This mode of measurement is sometimes called OTF TTL (Off The Film Through The Lens).

All modern EX-series Speedlites, as well as the Sigma 500/530 DG Super, supports TTL mode. This means that you can buy these flash units for use with older cameras as well as new.

Don't be confused if your camera's manual mention something called A-TTL. A-TTL was a small improvement that Canon introduced at one point. The improvement was to emit a series of pre-flashes when the shutter was half-pressed to compute optimal aperture in P-mode. However, in A-TTL actual flash output is measured by the OTF TTL sensor, just as it is with “plain” TTL, and “plain” TTL works fine with all cameras capable of A-TTL.

Final remarks

If you intend to use several flashes in a wired or wireless setup, you need to think careful about your options. For a wired setup you're better off with flashes with a pc-connector (otherwise, you need to buy adapters as well). For a wireless setup, you need to decide whether you want to use Canon's dedicated wireless system, or to use third party devices built around optical or radio receivers. Not all flashes are compatible with all types of receiver, so if you build your wireless system from components from several sources, you need to make sure that the units are compatible before you buy.

When buying second hand, make sure: 1) That the flash you buy is compatible with your camera with respect to trigger voltage, electrical connections, and operational modes; 2) that the battery compartment is clean and the contacts free of corrosion; 3) that the body, including the foot, is mechanical sound and free of cracks; 4) that the recycle time is reasonable with fresh batteries; and, 5) that the colour temperature has not shifted (photograph a WhiBal-card or a neutral grey surface, locking the camera's white balance on “flash” and make sure that the RGB-values are reasonable neutral.

5. Flash Link farm

EOS Speedlite Tips (Audio commentary by Stephen Wilkes on general flash use, while George Lepp discusses macro flash photography.)
Flash Exposure Lock and Compensation (Short turorial on using FEL, FEC and FEB)
Chuck Gardner:
The Canon EX Flash System (Introduction to use of wireless power ratios and more.)
David Hobby:
Strobist (Great blog about flash use and lightning in general by Balitimore based photojournalist David Hobby.)
N.K. Guy:
Flash Photography with Canon EOS Cameras (More than you ever wanted to know about EOS flash.)
David J. Herzstein:
Canon EOS Speedlites Comparison Table (Huge table covering most Speedlite features)
Vincent Laforet:
Show Me the Light: Lighting with the Canon 550EX flashes (Photojournalist on wireless E-TTL on location.)
Edwin Leong:
Flash, Flash technical (Basic tutorial on flash photography.)
Neil van Niekerk:
Flash Techniques, (Tutorial on flash photography for weddings and portraits.)
Vinicius Matangrano:
How to turn the 380EX into a Manual-mode or a TTL-only flash unit (Details on E-TTL flash contact layout.)
Ralph Paonessa:
Quantum Turbo batteries: Supercharge your flash (Using Quantum battery packs on a canon 550EX Speedlite)
Ralph Paonessa:
High Speed Sync for flash at any shutter speed (Introduction to FP flash use for Canon and Nikon)
Daniel Rocha:
Flash Work (18 part tutorial on EOS flash)

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