Friday, November 26, 2010

Flash: The Speedlite range


Over the years, there have been five different types of Speedlite, each operating in a slightly different way.

M
The Speedlite 200M (discontinued) does not support any type of TTL metering. Instead, it has its own built-in sensor to control the flash output. It was designed for use with the Canon EF-M camera. If used with an EOS camera, both shutter speed and aperture must be set manually.

E
The Speedlites 160E and 200E (both discontinued) are low power units designed as an alternative to built-in flash for those EOS models without built-in flash. They operate with TTL autoflash metering. E-series Speedlites are compatible with all EOS film cameras, but not with EOS digital cameras.

EG
There is only one EG model − the Speedlite 480EG (discontinued). This is a hammerhead style unit that dates back to pre-EOS days. It is compatible with all EOS models, including digital, because in addition to TTL metering, it features an external sensor. This independent sensor means that flash metering can be done without using any of the flash sensors inside the EOS body.

EZ
EZ-series Speedlites operate with A-TTL metering on all EOS film cameras. In addition, they can be operated in TTL autoflash mode with the camera shutter speed and aperture set manually. This is useful when you need to shoot at a particular aperture − for increased depth of field, for example. They are not compatible with EOS digital cameras.

EX
EX-series Speedlites operate with E-TTL metering on EOS Type A cameras. They switch to TTL metering when used with EOS Type B cameras. This means that EX-series Speedlites can be used with EOS digital and film cameras.

Only EX-series Speedlites are now current.


Speedlite 580EX




In August 2004 Canon introduced a new flash gun to its range, the Speedlite 580EX. It replaced the previous top-of-the-range Speedlite, the 550EX, but uses many of its features. The result is an easy-to-use, powerful, versatile flash unit for lighting on the go. In addition to making the unit even more feature-packed, Canon has also managed to make the entire unit smaller, lighter and far more aesthetically appealing.

Increased power
The most obvious change between the 550EX and the 580EX is hinted at in the name. The flash power has been increased from 55 at 105mm (ISO 100, metres) to 58 at 105mm (ISO 100, metres). This may not sound much, but extra flash power is always useful. And this increased flash power has another benefit, something which is very important in a flash gun − a faster recycle time. Because the flash is more powerful, you are rarely using it at full capacity, so it recycles to full charge more quickly. This means you don’t have to wait around for the flash to be ready to fire again in circumstances where speed and time are of the essence. Canon has also re-engineered the electronics so that even on a full power it will be ready to fire again more quickly than the 550EX. In fact, from a full power flash (with fresh batteries) the 580EX will recycle in six seconds or less, two seconds faster than the 550EX − and that’s with a more powerful flash.

The digital design
The biggest difference between the 580EX and the 550EX is that the new model has been specifically designed with digital cameras in mind. This means it has been endowed with two features not found on any previous Canon flash:

Sensor size detecting autozoom
Colour temperature transmission from flash to camera.
The Canon digital camera range incorporates models with three different sensor sizes: full frame (as found on the EOS-1Ds and 5D models), APS-H (EOS-1D models), and the most common size, APS-C (all EOS consumer DSLR cameras).

Previously, a flash gun would assume that the sensor was full frame, as most cameras were film and therefore used the standard 36mm x 24mm film size. Now, however, with the three different sensor sizes, there is more of a problem with flash coverage. To overcome this, Canon has developed a system to allow the camera to communicate its sensor size to the flash. This allows the flash head to zoom appropriately to suit the angle-of-view of the lens and sensor combination.

The biggest advantage of sensor-size detection is that it does not ‘waste’ power and light by spreading the flash over a wider area than is needed. You obtain more flashes per charge and a faster recycle time, as well as effectively extending the flash range.

The other digital-only feature is the colour temperature transmission from flash to camera. As the charge levels fluctuate in the flash power source, the colour temperature of the emitted flash varies. With this new feature, each time the flash fires, the colour temperature is passed to the camera so that an appropriate Kelvin value can be set to ensure the colours are more consistently correct between exposures. This will operate when the camera is set to either Auto White Balance (AWB) or the flash white balance setting.

The result is that you will obtain more accurate colours for each image, which will save time in post-processing on the computer.

Getting wide
In conjunction with the digital sensor autozoom, the built-in wide panel has been changed to give an even wider angle of coverage. You can use lenses as wide as 14mm with the Speedlite 580EX.

The top end of the flash zoom range remains the same, giving coverage for lenses with a focal length of 105mm. However, this is not the maximum focal length you can use with the Speedlite. It simply means that with longer lenses the flash will provide coverage greater than the field-of-view and some of the flash illumination will be wasted.

Bright eyes
Also new for a Speedlite is a catchlight reflector. This is found in the same slot as the wide-angle diffuser panel. It provides a much more flattering result when shooting portraits, allowing you to fire the majority of the flash up to the ceiling or off a wall, while bouncing enough light for some fill-in illumination on the face and a catchlight in the eyes to give them some sparkle. It will certainly be a welcome addition for anyone who shoots a lot of portraits, where direct, harsh light can be unflattering to your subject.

Fully focused
A big advantage of using a Speedlite on-camera is the help it can provide with focusing in low light, and the 580EX is no exception. Three ultra-bright LED lights are arranged on the flash to provide horizontal and vertical line patterns, resulting in an autofocus assist beam that is compatible with all EOS autofocus systems. This is an improvement over the 550EX, which could not provide complete autofocus coverage for all EOS cameras. As long as the subject is in range of the focus light beam, it should make difficulties with autofocusing in low light a thing of the past.


Bouncing around
In many situations where flash is used, direct light from a flash gun is often too harsh, giving unnatural and unflattering shadows. The 420EX and 550EX helped overcome this by adding a bounce flash capability, enabling angling of the flash head so that it can fire onto a reflective surface, such as a white wall or ceiling.

This has been further developed in the Speedlite 580EX, where a single button releases both the vertical and horizontal bounce flash movements. This makes the feature quicker and easier to use than before. The head is also now able to rotate 180° both left and right, compared to the 550EX, which could only be rotated 90° to the right. There is also an extra vertical click stop on the 580EX at 45°, giving more options when bouncing the flash from different surfaces.

In keeping with the improved ease of use and improved ergonomics of the new Speedlite, gone are the +/− push buttons on the rear of the unit. These have been replaced by a single control dial with a central button for scrolling between settings. This dial is used in the same way that the +/− buttons are used on the Speedlite 550EX. It makes choosing settings on the 580EX much quicker and easier.

Going manual
Despite the accuracy and simplicity of the E-TTL/E-TTL II algorithms, sometimes you need to set the flash manually to get the exact result you want. The 580EX gives you more control than its predecessors, with manual power selection in 1/3 stops from full power down to 1/128 power. This hands control back to the photographer in situations where the metering system could be fooled.

Custom functions
The number of Custom Functions has been increased from six on the Speedlite 550EX to 14 on the Speedlite 580EX. CF-1 to CF-6 are the same on both Speedlites − it’s from CF-7 onwards where changes have been made.

CF-7 and CF-8 are designed for shooting environments where speed is important. They allow you to recycle from internal and external power simultaneously, or fire when the lamp is yellow-green (i.e. not fully charged) respectively.

CF-9 and CF-10 give you control of test flashes, either doing a test fire or using the test button to fire a modelling flash.

CF-11 allows you to turn off the sensor size autozoom if, for example, you only use a full frame camera.

CF-12 turns the focus assist beam on or off − useful in circumstances where you don’t want to project a red beam onto your subject.

CF-13 controls the use of the command dial on the flash. For speed, you can set it so you only need turn the dial to set flash exposure compensation, instead of pushing the central button and then rotating the dial.

CF-14 allows you to disable the auto power off feature.


Speedlite 580EX II

Updating the Speedlite 580EX, the 580EX II offers faster, silent recycle times and a more durable build quality.

The Speedlite 580EX II improves on many of the specifications of its predecessor. The silent recycling, for example, is up to 20% faster.

Weather seals ensure that when attached to the EOS-1D Mark III, the Speedlite 580EX II achieves the same level of dust and moisture resistance as the camera itself.

A redesigned metal flash foot plate and connector pins allow more stable communication between the camera and flash, while a quick release mechanism minimises wear and tear on both of the units.

The flash head zoom covers the range 24mm to 105mm and an integrated diffusion panel allows extended wide-angle coverage to 14mm.

The Off Camera Shoe Cord OC-E3, Compact Battery Pack CP-E4 and Speedlite Bracket SB-E2 also allow sealing against dust and moisture, giving photographers a complete system to achieve off-camera lighting effects in difficult weather conditions.


Speedlite 430EX
The Speedlite 430EX flash unit replaced the 420EX. It improves on many of the specifications of its predecessor and includes new features to maximise digital image quality when using a flash. These include automatic selection of camera white balance settings and auto-adjustment of the zoom flash position to match the sensor size of the camera to which the unit is attached.

The Speedlite 430EX has an increased guide number of 43 (m/ISO 100 at 105mm) and has approximately 40% faster recycling time than the Speedlite 420EX. An ultra-bright 2-LED configuration focus assist-beam has been designed to be compatible with all focus points within the frame of EOS AF systems, up to 9-point AF.

Optimum flash coverage
The flash head zoom covers the range 24mm to 105mm and an integrated diffusion panel allows extended wide-angle coverage to 14mm. When attached to digital EOS cameras with smaller than full frame sensors the Speedlite 430EX gives a more accurate flash coverage by detecting the model to which it is attached and automatically narrowing the angle of coverage. This has the effect of eliminating light loss in peripheral areas and extending the effective flash range.

Ideal white balance
The Speedlite 430EX automatically transfers colour temperature information to recent models of digital SLR cameras. The camera then sets the colour balance optimally for the flash shot. This feature works when the camera’s white balance mode is set to auto white balance (AWB) or flash white balance mode, compensating for any changes to the Speedlite output caused by age or battery condition.

Other features
The Speedlite 430EX is fully compatible with the distance linked E-TTL II system found on recent EOS cameras, and supports other EOS cameras that do not have E-TTL II.

It also serves as a wireless slave when either the Speedlite 580EX, 580EX II, 550EX, Macro Ring Lite MR-14EX, Macro Twin Lite MT-24EX or Speedlite Transmitter ST-E2 is used as a master.

An intuitive and ergonomic interface includes an LCD panel for clear indication of modes and settings. A single bounce lock release button provides immediate control over the bounce head angle for flexible positioning of the flash head. The flash head can be moved up from 0 to 90° (five settings), left from 0 to 180° (seven settings) and right from 0 to 90° (four settings).

Six custom functions allow customisation of the flash operations. Despite high power and short recycling times, the unit is small and lightweight.

Other features include first and second curtain flash synchronisation, modelling flash, high-speed synchronisation (FP flash) and manual adjustment of flash output from full to 1/64 power (7 levels).

Speedlite 220EX

The Speedlite 220EX is a low-power flash gun for EOS cameras that do not have a built-in flash unit. It offers twice the power of built-in units, but only half that of the Speedlite 430EX. It is mostly useful for fill-in flash photography. The fixed head means that you need the Off Camera Shoe Cord for bounce flash photography.

Flash: Speedlite compatibility


When the first camera with evaluative autoflash metering was launched, EX-series Speedlites were introduced to make use of the E-TTL metering. These EX-series Speedlites are also compatible with TTL flash metering, so will operate with all EOS models.

All the new film cameras offering E-TTL metering retain the flash sensors for A-TTL metering, so are also compatible with EZ-series Speedlites.

When Canon introduced digital EOS models, they omitted the flash sensors in the base of the camera (the sensor reflects light differently to film). This means that EZ-series Speedlites can only be used in manual mode with EOS digital cameras.

Canon updated E-TTL flash metering in 2005. E-TTL II is a camera feature, not a Speedlite feature, though it only operates with EX-series Speedlites.

Here is a short guide to compatibility:

Type A cameras: E-TTL autoflash metering is only supported by EOS cameras introduced at the same time or later than the EX-series Speedlites. These models allow the viewfinder sensors to be used for both ambient and flash readings. These cameras, called Type A, include the EOS 1V, 3, 30, 30V. 33, 33V, 300, 300V, 300X, 3000N, 3000V, 50E, 50, 500N, IX, IX7 and all EOS digital cameras. Type A film cameras also include sensors that can read flash illumination off the film during an exposure, so EZ-series Speedlites can be used with A-TTL autoexposure.

Type A-II cameras: There is a sub-group of Type A cameras which enables E-TTL II flash metering with EX-series Speedlites. These include the EOS 30V, 33V, 300X, 1D Mark II, 1D Mark II N, 1D Mark III, 1Ds Mark III, 5D, 5D Mark II, 20D, 20Da, 30D, 40D, 50D, 350D, 400D, 450D and 1000D.

Type B cameras: Other EOS film models are known as Type B cameras and can be used with EZ-series Speedlites in A-TTL (or TTL) mode or EX-series Speedlites in TTL mode.

This may seem complicated, but if you are using an EOS digital camera all you really need to know is that it is only compatible with EX-series Speedlites.



Left: Type B cameras have flash sensors in the bottom of the camera body. Light is reflected down to the sensors by a secondary mirror hinged behind the main reflex mirror. The centre of the reflex mirror is semi-silvered, allowing light through to the secondary mirror. This allows A-TTL metering with EZ-series Speedlites and TTL metering with EX-series Speedlites.
Centre: Type A cameras have sensors in the viewfinder area that read both ambient and flash illumination. These sensors operate with EX-series Speedlites. The cameras also have flash sensors in the bottom of the camera body for A-TTL metering with EZ-series Speedlites.
Right: EOS digital models are a sub-section of Type A cameras. They only have sensors in the viewfinder area, so can only be used with EX-series Speedlites.



Power control
Autoflash means that a flash gun gives just the right amount of light for correct exposure. It could do this by altering the power of the flash, increasing or decreasing the brightness as you change the distance of the camera from the subject. But this does not happen. Instead, Speedlites increase or decrease the duration of the flash as the subject distance changes. The brightness of the flash remains constant. However, even a long Speedlite flash is very brief and you are unlikely to notice much difference between short and long electronic flash exposures either as you shoot, or in the results.



Saturday, November 6, 2010

White balance (WB)




What is WB?
Our eyes and brain make a wonderful partnership. Together, they automatically adjust the exposure of whatever it is we are looking at to achieve a balanced image. More importantly, they correct any colour cast so that anything white actually looks white, regardless of the ambient light.

Unfortunately, digital cameras are not so clever. They record the scene as they see it − within their limitations. This is why, in tricky lighting conditions, we have to set the white balance to ensure the result we want. It is also why, to get results of the optimum colour, we usually have to tell the camera the colour temperature of the light falling on to the scene.

In simple terms, light is made up of the three primary colours − red, green and blue. These colours are present in different proportions in all light sources. For example, tungsten lights have more red in them than fluorescent lights, which are greener. This proportion of colours is measured as the colour temperature.

If you are shooting your images in any mode other than RAW, the camera will post-process the image to make the colours in the scene as accurate as possible. However, this is not always as easy as it seems − the colour temperature of the light falling onto the scene affects the way the camera sees the colours and, unlike our brains, it does not automatically correct it. For example, with no correction, a white wall photographed under tungsten lighting will appear very yellow, and under a fluorescent light will look very green. This is why all digital EOS cameras have the ability to set the white balance to suit the ambient light, no matter how complex the lighting conditions are.

What do the settings mean?
There are seven standard white balance settings, your choice of which will depend on the type of light you are shooting in.

Auto White Balance
You can use this setting as a default in most straightforward lighting conditions. Auto White Balance works by evaluating the scene and deciding the most appropriate white point in it. The setting works reasonably well if the colour temperature of the ambient light is between 3,000-7,000K. However, if there is an abundance of one colour in the image, or if there is no actual white for the meter to use as a reference, the system can be fooled, resulting in an image with a colour cast.

Daylight setting
Use this setting if you are shooting in bright sunshine. It will balance for a colour temperature of around 5,200K, which is actually very slightly cooler than noon sunlight. However, it is very rare that you will actually be shooting at noon and so this setting will work best for the greatest part of the day.

Shaded places
Although we perceive shaded areas to be colder, the colour temperature is actually higher (bluer), usually around 7,000K. This setting is most suited to areas of light shade rather than very heavy shadow.

Cloudy or hazy
This sets a colour temperature of around 6,000K. It is best used on days when the sun is behind the clouds, creating a very even and diffuse light.

Tungsten setting
The first of the artificial lighting settings, this assumes a colour temperature of around 3,200K and is suitable for most tungsten lamps that normally emit a yellow light. It is the equivalent of an 82-series blue filter used with a film camera to correct for the same colour cast.

Fluorescent setting
The second artificial light setting is set for around 4000K, the approximate colour temperature of fluorescent lights. The problem with fluorescent lights is that there are six types, each with a different colour temperature. They also emit an interrupted spectrum with peaks over quite a wide range. To complicate things further, they also change over time, gradually altering the colour temperature of light they emit. This setting has the same effect as fitting an FL-D filter to a film camera.

Flash setting
For use with either a built-in flash or an external Speedlite. Flash is a very white light with a colour temperature around 6,000K.

All these settings still rely on the camera doing some calculations to obtain the correct colour balance. However, there are two further settings which give you total control.

Custom white balance
This allows you to tell the camera which area in the scene is supposed to be white. The camera can calculate the colour shift required to make that surface white. It then applies that shift to all colours in the scene to provide a correct colour balance to the image, whatever the lighting.

Kelvin
This enables you to set the colour temperature in degrees Kelvin in 100K increments from 2,500 to 10,000K depending on model. If you have a separate colour temperature meter then this may be the best setting to use as you can set the exact colour temperature shift needed. But, remember, if you do this you will need to take a few test shots to calibrate your colour temperature meter with the camera’s meter.

PC-1, PC-2, PC-3
In addition, on professional EOS digital cameras there are three custom white balance settings − PC-1, PC-2 and PC-3. These allow you to save the three white balance settings that you regularly use. This is useful if you do a lot of studio photography, for example, and always use the same lights. It enables you to save the colour temperature of those lights so you do not have to colour balance each time. However, initially the settings need to be made on the camera via a computer using supplied software.


White balance bracketing
If you find that you still cannot get the perfect colour balance, then EOS digital cameras from the 10D onwards have a white balance auto bracketing function. This allows you to bracket the white balance setting in the same way that you can bracket exposures. You can select the level of change between the images up to ±3 steps in full-step increments. The images are then recorded in the sequence: 1 - set colour temperature, 2 - bluer colour, 3 - redder colour.

With all these options, it is possible to obtain a completely neutral tone in most shooting situations. However, is this always best? Consider a fairground where there is a diverse mix of light sources − tungsten giving a yellow glow, fluorescent adding some green, not to mention all the neon lights. If you were to balance all the light sources present, the result could end up looking very clinical and fail to convey the fun, warmth and atmosphere of the show.

So do not always assume neutral is best − be a little creative and see what happens.

Working in RAW
If you shoot in RAW, white balance will not affect you at the time the exposure is made. White balance corrections are normally applied by the camera in post-processing of the image, before it is saved to the card as a JPEG file.

By shooting RAW, you avoid this processing as the image saved on the card is exactly as captured by the CMOS sensor. It is then up to you to adjust the white balance in your RAW file editing program.

One of the advantages of shooting RAW files is that you can apply different white balance settings to the image to see which give the most natural, or most attractive, results. The original RAW file remains unchanged. All the work is done on copies of the RAW file, which means that you can return to the RAW file and try again if the initial results are not what you want.

Setting the white balance
It is possible to set auto white balance for all your shots and let the camera sort out the light, or to select the white balance symbol appropriate to the lighting conditions. However, no matter how good these settings are, they will never produce the perfect white balance in all situations.

Instead, use the following procedure and you will end up with images that are properly white balance. Unless you are working indoors light changes constantly, so you will need to repeat the procedure for each new scene.

You need a sheet of white paper. With your scene set and the lighting arranged, place the card in the scene. Making sure that the white card covers the centre circle marked in the viewfinder, take a shot. The autofocus may have trouble focusing on the flat card, so focus on the edge of the card and then recompose.

Find the menu item ‘Custom WB’ and select it so that the custom white balance screen appears. Now turn to the image shot in the previous step and select this. The white balance data from the image will be imported.

After exiting the menu, select custom white balance from the white balance settings. The pictures you shoot will now be balanced to your test image.

Colour temperature
It is useful to know where the term ‘colour temperature’ comes from and what it means.

Colour temperature is measured in degrees Kelvin (K). The Scottish mathematician and physicist William Kelvin proposed the absolute, or Kelvin, scale in 1848. This scale uses −273.15°C as its zero point or ‘absolute zero’. The colour temperature is simply the colour a standard black body (a piece of metal which is perfectly black and reflects no light) glows at a certain heat. Surprisingly, the cool colours are red and orange, around 2,000-3,000K, while the warm colours are the blues at the 20,000K end of the spectrum. Neutral white light is 6,504K.

Comparison shots
The following pictures of a stamen against the white petals of a lily flower were all taken in daylight in the middle of the day. Each was taken at different white balance settings. The colour changes to the images show, in effect, the ‘filtration’ added by the camera to balance with the different light sources.


Auto − this close-up of a lily stamen was taken in midday window light so the Auto setting has actually done quite a good job of making the lily’s white petals white although there is a hint or red.
Daylight − this setting has done slightly better, with no red and the white being a cleaner white.
Shade − this setting has also achieved a reasonable colour balance, however, you can see it has added yellow to compensate for blue that would normally exist in a shady scene.
Cloudy − as with the shade setting, the cloudy setting has achieved a satisfactory result, but again there is still a hint of yellow in the whites.
Tungsten − here the camera has added blue to compensate for the yellow that would be present under tungsten lighting giving the whites a very blue appearance.
Fluorescent − this has had a similar effect to the tungsten setting, but the camera has added the equivalent of a magenta filter to compensate for the green emitted by fluorescent lights.
Flash − this setting has produced a result very similar to the shade setting as they set a very similar Kelvin temperature. If anything, the flash setting has done slightly better by adding less yellow to the image.
Custom − here we set the colour balance manually by using a grey card. This has produced a result with clean, natural whites.