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Articoli tecnici

Questo articolo non disponibile in Italiano
September 2010

By Syl Arena

In the first of this four part CPN series on 'Getting the most from Speedlites' we will survey the current Canon Speedlite flashgun family, examine their various modes of control, and take a look at the modifiers that are built into the flashguns. In the subsequent parts of this series, we will look at options for moving Speedlites off-camera (including implementing Canon's built-in wireless system), ways to modify and shape the light created by Speedlites, and advanced topics for various professional applications.

Current Canon Speedlites

The Speedlite 580EX II (introduced in February 2007) is the flagship of the Canon Speedlite flashgun range and is used by many professional photographers around the world. In addition to being the most powerful Speedlite, the 580EX II is also the most versatile. It offers four modes of flash power control: Evaluative Through-The-Lens (E-TTL), Manual, Multi/Stroboscopic, and External Flash Metering.

When using several Speedlites on a shoot the 580EX II can be used as either a master or a slave. The 580EX II can be controlled via the Speedlite's LCD panel or via the LCD menu on Canon DSLRs (LCD camera menu control of flashguns was introduced by Canon in mid-2007). For high-demand situations, the 580EX II can be connected to the CP-E4 Compact Battery Pack for faster flash recycling.

Canon's mid-powered Speedlite, the 430EX II (introduced in June 2008), has 2/3rds of the power of the 580EX II. The power level on the 430EX II can be adjusted in Manual mode, from full power to 1/64 in 1/3-stop increments. It will operate as an off-camera slave, but it cannot be used as a master to control other Speedlites. The 430EX II is well suited as a starter Speedlite for enthusiasts and as a backup or slave Speedlite for professionals. It can be controlled via the Speedlite's LCD panel or via the camera LCD menu on Canon DSLRs.

The Canon DSLRs that offer in-camera LCD menu control over flash settings are the EOS 40D, EOS 50D, EOS 60D, EOS 5D Mark II, EOS-1D Mark III, EOS-1Ds Mark III, EOS-1D Mark IV, EOS 7D, EOS 500D, EOS 1000D and the EOS 550D.

© Syl Arena

An EOS 7D DSLR LCD panel showing flash control options via the camera's menu. The External Flash function setting is highlighted.

The Speedlite 270EX (introduced in May 2009) is a compact Speedlite that's well suited for less experienced DSLR photographers or as an accompanying flash for the PowerShot G-series cameras. With around twice the power as the pop-up flash found on consumer-oriented DSLRs, the 270EX offers a two-step zoom (28mm to 50mm) and a three-step bounce angle - both of which are controlled by hand. The 270EX doesn't feature an LCD panel so its advanced features (such as changing the power or sync mode) must be controlled via the camera's LCD menu.

Basic types of flashgun operation

There are three main factors to consider when operating a flashgun:

  • Setting the power output of the flashgun (flash exposure modes).
  • When the flashgun fires (the sync mode).
  • What the flashgun covers (zoom, bounce, and rotate).

Many of these features can be controlled automatically by the camera or manually by the photographer. Deciding between automatic or manual control is best determined by the circumstances of the shoot.

© Syl Arena

Evaluative Through-The-Lens (ETTL) mode shown on a Speedlite LCD panel.

Speedlite Exposure Modes - controlling the power of the flashgun

Canon's Evaluative Through-The-Lens (E-TTL) flash technology sets the power level for the Speedlite automatically. In E-TTL, the camera takes an ambient meter reading and then instructs the Speedlite to fire a low power pre-flash. The camera meters the flash coming back from the scene and compares it to the ambient reading. Metering zones that measure significantly brighter under flash than ambient are assumed to be reflective objects and, therefore, aren't included in the exposure calculation.

For many lenses, the camera will also take the camera-to-subject distance information from the lens, but note that this data is not used if the head is rotated or bounced or if the on-camera Speedlite is being used as a master to control off-camera Speedlites. After evaluating the difference between the ambient and flash meter readings, the camera instructs the Speedlite to fire at a specific power level and then fires the Speedlite at the correct moment (as determined by the sync setting - the Speedlite flash sync modes are explained later in this article).

© Syl Arena

An example of ETTL pre-flash blinks. If blinking happens repeatedly you can switch the Speedlite to Manual to eliminate the pre-flash or use Flash Exposure Lock (FEL), which fires the pre-flash, and then immediately press the camera's shutter button.

The power and convenience of E-TTL is that the pre-flash and exposure calculations happen in, literally, the blink of an eye. E-TTL is especially well suited for situations where the distance between the Speedlite and the subject is dynamic. Remember: a subject that is very close to the flashgun will require less power from the Speedlite than a subject that is further away. So, a subject that is moving back and forth, such as a child on a playground swing, is a perfect situation for E-TTL. Another dynamic scenario for E-TTL is event photography where a photographer is likely to be capturing candid portraits as he moves quickly through a crowd.

There are two small shortcomings of E-TTL. The first is that some individuals are hyper-fast blinkers. They respond to the pre-flash with a blink that shows up as droopy eyelids during the actual exposure. If this happens once, consider it to be coincidence. If it happens repeatedly, you can either switch the Speedlite into Manual mode (which eliminates the pre-flash entirely) or you can press the camera button for Flash Exposure Lock (which fires the pre-flash) and then immediately follow this with a press of the shutter button.

The other small downside to E-TTL is that you will never know the power level at which the Speedlite fired. It is neither displayed on the Speedlite, nor is it recorded in the metadata. This is only a small inconvenience that will manifest itself when you are trying to recall what you did during the shoot so that you can learn from your experience. For this reason, when you are shooting to learn the mechanics of flash photography, it is recommended that you switch the Speedlite to Manual mode so that you can see the effect of specific power levels in specific situations.

© Syl Arena

Flash Exposure Compensation (FEC) mode shown on a Speedlite LCD panel. The exposure values can be dialled in via the Speedlite's dial on the back of the flashgun or via the camera's viewfinder or LCD panel. If FEC is set on the Speedlite and in-camera the Speedlite setting always overrides the camera setting.

As sophisticated as E-TTL technology is, it is critical to remember that the camera has no concept of the photographer's vision or intent. The objective of the E-TTL programming is to provide a perfectly lit frame, fine-tuning the amount of flash emitted by a Speedlite is the responsibility of the photographer.

Flash Exposure Compensation

Flash Exposure Compensation (FEC) enables the photographer to increase or decrease the amount of E-TTL flash by a specified amount. When dialled in through the flashgun's LCD panel on a 580EX II or 430EX II, the FEC can be adjusted by up to +/- 3 stops in 1/3 stop increments. FEC can also be dialled in via the camera's viewfinder or the camera's LCD panel. Depending on the exact camera used, the on-camera FEC range is either +/- 2 stops or +/- 3 stops. When FEC is set on both the Speedlite's LCD panel and in the camera, the setting on the Speedlite always overrides the camera's setting: they do not combine to increase the amount of FEC.

In Manual mode, the photographer sets the power level of the flashgun; either directly via the Speedlite's controls or via the camera's LCD menu. There are three main advantages to setting the power manually: the amount of flash is consistent from shot to shot, the absence of a pre-flash enables the Speedlites to work with the optical slaves typically found on studio packs, and the photographer knows the power level at which the Speedlite is firing. The latter is very helpful when one is shooting, primarily to learn the mechanics of flash photography.

© Syl Arena

Manual (M) mode shown on a Speedlite LCD panel.

In Manual mode, full power is indicated as 1/1. Just as the change of aperture from f/8 to f/11, or the change of shutter speed from 1/125sec to 1/250sec, reduces the amount of light passing through the lens by half (one stop), the fractions of power on a Speedlite should initially be worked in whole stop increments: 1/1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, and, (on the 580EX-series only) 1/128. Then, as one needs to fine-tune the amount of flash, the power can be adjusted in 1/3 stop increments (expressed in decimals with 1/3 stop = 0.3 and 2/3 stop = 0.7). When dialling the power down, the LCD displays the last whole stop minus 0.3 or 0.7. When dialling the power up, the LCD shows the last whole stop plus 0.3 or 0.7. So, 1/2 -0.3 is actually the same power level as 1/4 +0.7.

Flash Exposure Compensation does not exist in Manual mode as there is no automatic calculation to override. Instead the photographer needs to increase or decrease the flash power by hand to suit his vision.

Sync Modes - first and second curtain sync

The shutter mechanism in Canon's DSLR cameras is a focal plane design, comprised of several metal blades, which are divided into two groups and are positioned immediately in front of the digital sensor. These two groups are referred to simply as the 'first curtain' and the 'second curtain'. The co-ordination of the movement of the two curtains with the firing of the Speedlite is known as 'flash synchronisation' or, more simply, 'flash sync'.

To understand the various types of flash sync, it is helpful to first understand the mechanics of the camera's shutter. Before you take a picture the second curtain is stored away and the first curtain covers the image sensor. When the shutter button is depressed fully the first curtain moves across the sensor to allow the passage of light. At the right instant, the camera closes the second curtain to end the exposure. The shutter then 're-cocks', drawing the first curtain back over the image sensor again and storing the second curtain ready for the next exposure.

© Syl Arena

Second curtain sync setting shown on a Speedlite LCD panel.

At relatively slow shutter speeds, the first curtain opens completely, exposing the whole sensor, before the second curtain begins to close. At faster shutter speeds, the second curtain begins to close before the first curtain is completely open, thus exposing only part of the sensor at a particular moment in time. At very fast shutter speeds, the second curtain follows the first curtain so closely that the opening appears as a narrow slit traveling across the sensor. The faster the shutter speed, the narrower this slit becomes.

The fastest shutter speed at which the first curtain completely clears the sensor before the second curtain begins to move is the camera's 'maximum sync speed'. At this shutter speed or slower, the full sensor will be exposed when the Speedlite fires. At a faster shutter speed a portion of the sensor will be covered by the second curtain during the flash - leaving a dark border along the bottom (if the camera is held horizontally) or one side, depending on which way the camera is held vertically.

For most Canon DSLRs, the maximum sync speed is typically 1/200sec or 1/250sec. For the EOS-1D series, it is 1/320sec. When a Canon Speedlite is attached to a Canon DSLR, the camera will not fire the shutter at a speed faster than the sync speed - even if the camera is set to do so. Instead, the camera will fire the shutter at the sync speed; resulting in a shot that may be overexposed or underexposed.

© Syl Arena

First curtain sync image shot on the EOS 5D Mark II with the EF24-70mm f/2.8L USM lens at the 24mm focal length. Exposure was manual at 0.5sec at f/5.6, ISO 200. In first curtain sync the flash fires immediately after the first curtain has opened completely, so you get the ambient-lit motion blur that can cause the image to look as if a subject is going backwards.

© Syl Arena

Second curtain sync image shot on the EOS 5D Mark II with the EF24-70mm f/2.8L USM lens at the 24mm focal length. Exposure was manual at 0.5sec at f/5.6, ISO 200. In second curtain sync flash the flash is fired an instant before the second curtain begins to close - at this slow 0.5sec shutter speed the image appears more natural than the first curtain sync shot of the same subject.

The default flash sync, known as 'first curtain sync', fires the Speedlite immediately after the first curtain opens completely. In 'second curtain sync', the camera fires the Speedlite an instant before the second curtain begins to close. At slower shutter speeds, when the subject is in motion, second curtain sync creates a more natural looking image - one in which the ambient-lit motion blur trails behind the subject. In first curtain sync, the flash fires and then the ambient-lit motion blur is created - which can make subject appear to be going backwards.

At shutter speeds faster than 1/50sec, the camera will fire in first curtain sync even if it is set to second curtain sync. As a practical guideline, it is difficult to see the effect of second curtain sync at shutter speeds faster than 1/30sec.

Sync Modes - High-Speed Sync

One of the great advantages of using Canon Speedlites and Canon cameras together is the availability of a third sync mode - High-Speed Sync (HSS). This unique sync mode virtually turns the Speedlite into a continuous light source for a brief instant so that any shutter speed - up to 1/8000sec - can be used. While HSS is easy to implement when Canon Speedlites are controlled by Canon cameras it should be noted that HSS can't be replicated with monolights and studio packs. It is a Speedlite-only function.

© Syl Arena

High Speed Sync setting shown on a Speedlite LCD panel.

There are two primary reasons to use HSS. The first is when the photographer desires to use a wide aperture to limit depth-of-field in a scene where the ambient light is very bright. If the subject is lit from the side or back, and requires a bit of fill flash to reduce the contrast of the shadows, then activating HSS will enable the camera to fire at the fast shutter speed required to offset the use of the wide aperture. HSS also provides great opportunities for the use of flash when an extremely fast shutter speed is desired - either to freeze high-speed action or to significantly dim the ambient light for creative effect.

In HSS, the camera changes the way the Speedlite fires. Rather that emitting one large burst of light, the flashgun turns itself on and off up to 30,000 times per second. To facilitate this nearly continuous output of light, the Speedlite loses 2.5 stops of power. For fill flash applications in bright sun, this is generally not an issue. On the other hand, if the objective is either to freeze high-speed motion from some distance or to make a scene lit by noon sun look like a moonlit night, then the use of several Speedlites may be required. Fortunately, Canon's built-in wireless control system makes simple work of controlling multiple Speedlites.

© Syl Arena

High-speed Sync (HSS) enables the use of Speedlites at virtually any shutter speed. The left hand image was shot at 1/1600sec with ambient sunlight - it only lacks punch because the sun is at camera left. In the right hand image the subject was rotated 90º so that he was backlit (which makes the water drops glow) and two Speedlites were placed to the right and left of the camera on stands about two metres away and angled steeply down to provide the balanced fill light.

Sync Modes - Slow-Speed Sync

A fourth type of sync, 'Slow-Speed Sync' is actually a camera function; not a Speedlite function. Slow-speed sync does not actually change when or how the flashgun fires. Rather, it changes the length of the ambient exposure.

In a dimly lit scene, if the subject is some distance from the background, then the flashgun will only have enough power to illuminate the subject. In this case, the background will disappear to black unless a longer shutter speed is used to collect more ambient light. This is especially true when the camera is in Program (P) mode as it prioritises using a faster shutter speed, to eliminate camera shake, over a slower shutter speed that will collect ambient light from the background.

To tell the camera that it should use a shutter speed that will collect enough ambient light from the background, check your camera's instruction manual for details of how to activate Slow-Speed Sync. Often it will be discussed as a setting under the camera's Custom Functions for 'Flash sync speed in Av mode'.

Zooming a Speedlite

Given that many photographers shoot with zoom lenses rather than prime lenses, it is a great benefit that the 580EX II and the 430EX II have the ability to automatically zoom the flash tube to coincide with changes in focal length - from 24mm to 105mm. The idea is that if you are shooting with a 50mm lens it doesn't make sense to throw flash across the area seen by a 24mm lens. Matching the coverage to the Speedlite to the view of the lens not only saves power (thus enabling a faster recycle), but it also concentrates the light so that it can cover the longer distances of a mid-telephoto lens. An added benefit of the automatic zoom is that Canon's technology compensates for the crop factor of cameras with APS-C or APS-H sensors.

Zooming a Speedlite manually is a creative tool used by many photographers. By zooming the Speedlite to a focal length longer than that of the lens, the flash can be concentrated on a specific area, such as the subject's face, with the perimeter of the frame falling off to a darker vignette. In manual zoom, the flash head can be positioned at 24mm, 28mm, 35mm, 50mm, 70mm, 80mm, and 105mm. For manual zoom, it should be noted that there is little difference between the near-pairs of 24/28, 35/50, and 70/80. An easy way to see the difference in coverage of the various manual zoom settings is to lock your camera down on a tripod after sunset and fire the Speedlite at a large, blank wall.

Whereas zoom is a motorised adjustment on the 580EX II and 430EX II flashguns that happens inside the flash head, it's also possible to tilt and rotate the flash head by hand - this is facilitated by pushing the large button on the right hand side of the flash head.

The Speedlite 580EX II, shown above, rotates 180º to the left and right for full 360º coverage, whilst the Speedlite 430EX II rotates 90º to the right and 180º to the left. The 270EX flashgun can't be rotated.

Bounce flash

The heads of the 580EX II, 430EX II, and 270EX can be tilted upwards from 0º to 90º. The 580EX II can also be tilted downwards by 7º - this is helpful when shooting macro shots with subjects close to the lens. The main reason to tilt the Speedlite's head upwards is to bounce the light off a ceiling as a way to soften the shadows on the subject. By spreading the flash across a larger surface, the light approaches the subject from multiple angles. So, shadows created by light coming from the left are filled by light coming from the right, and vice versa.

When using a ceiling for bounce, be aware that the colour of the ceiling will tint the colour of the flash. So, it's best to avoid bouncing the flash if the ceiling is a deeply saturated color. Also, be mindful that if the light comes at your subject's face from too steep an angle, then the eyes may appear too dark. A quick fix is to hold your left hand directly behind the angled head of the Speedlite to throw a bit of light forward. The 580EX II has a small plastic panel above the wideangle diffuser panel for this purpose; but a hand has greater coverage and is faster to deploy for a quick shot.

Rotating the flash heads

Several of Canon's Speedlites feature the ability to rotate the head of the flashgun horizontally. The Speedlite 580EX II rotates 180º left and right whilst the Speedlite 430EX II rotates 90º to the right and 180º to the left. The 270EX flashgun cannot be rotated.

There are three main reasons to rotate the head of a Speedlite. The first is to soften the shadows by firing the flashgun off of a nearby wall or disk reflector. Similar to bouncing the flash off of a ceiling, firing the Speedlite into a wall or other reflective surface increases the apparent size of the light source and softens the shadows by sending the light at the subject from multiple angles.

The second reason to rotate a Speedlite is to 'feather' the light on your subject. This means that rather than hitting your subject with the centre of the flash, you use the edge of the Speedlite for a more dramatic quality of light - letting the centre of the flash 'fly past' your subject. When you test fire your Speedlite into a wall (as suggested above) to see the various zoom patterns, you will also notice how the edge of the flash falls off to darkness at various zoom settings. You will discover that manual zoom, when combined with a rotation of the flash head to feather the light, can create dramatic lighting for a quick portrait.

A third reason to rotate the head arises when shooting with Speedlites wirelessly. As Canon's built-in system requires a line-of-sight path between the master and slave(s), it is recommended that the body of the slaves be positioned so that the wireless sensor (located on the front, just above the large red panel) faces the master Speedlite. If the body of the Speedlite is rotated backwards to face the master, then you will want to rotate the head so that it points at your subject.

If you are shooting outdoors in very bright sun and the slaves are relatively close together, you can pan the head of the master so that it concentrates its signal in the direction of the slaves. This technique assumes that you have disabled the master - meaning that it sends instructions to the slaves and then remains dark during the actual exposure (as will be discussed in Part 2 of this series).

Biografia: Syl Arena

Photographer Syl Arena became fascinated with photography at the age of eight when an aunt gave him a Box Brownie camera. He later studied at the Brooks Institute of Photography, before earning a BFA in photography at the University of Arizona. Today Syl shoots the people, lifestyles and products of central California for advertising, editorial and corporate clients. He runs a blog, PixSylated.com, and in 2009 founded the Paso Robles Workshops. Flash expert Syl's latest book, 'Speedliter's Handbook: Learning to Craft Light with Canon Speedlites', will be published in October 2010.