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Home >> Learning >> e-Book on Photography Table of Contents Photography e-Book Chapter 9 Subsection - Flash Technical Manual Flash
The tiny Cullman flash seen here is a Manual only flash with a built in slave sensor, allowing it to be used a "kicker" secondary fill in flash. Manual flash in its basics is not that difficult as it comes down to a few things only, distance, aperture, film speed, and flash power otherwise known as the Guide Number or GN. Your shutter speed does NOT play a role in flash exposure except in terms of the flash-sync speed available on your camera but more on that later. Take a flash, any flash, and it will have a Manual setting no matter how high tech it is or how basic, in fact the most basic flashes are only Manual flashes. Using the venerable Vivitar 283 as an example of an affordable flash with a decent amount of power, this flash unit has a Guide number of 120 feet at ISO 100. Caveat here, the GN is just a guide number to use to calculate your aperture and it does not mean that the flash can actually output enough power to reach to 120 feet, especially if using relatively slow ISO 100 film. Most if not all flash manufacturers pad their power ratings and experience from use is the real determinant of what your flash can do. From your known guide number, you then divide the GN by the distance to your subject. Therefore, if your subject is 10 feet away, you divide 120 by 10 and receive 12. This is your working aperture but as you may well know, 12 is not exactly a common aperture setting and only if you have a camera capable of 1/3 stop settings could you actually come close to this desired number. Another way to do the calculation is to divide the GN by your desired aperture and receive the working distance you have to be at to properly illuminate the subject. If your desired aperture is a moderate one of f5.6, you divide the GN of 120 by 5.6 and receive a working distance of 21 feet (rounded down to nearest whole number).
Doing fill flash with Manual flash is not that hard once you have your working distance and aperture figured out. If you desire a minus one-stop fill, you would merely stop the aperture down by one, so using the example of f5.6 above, your aperture setting for minus one would be f8 and if you wished for a minus two-stop fill, then you would set f11 on your lens. Using flash to overexpose the subject is just the opposite with f5.6 being opened up to f4 for a one-stop overexposure or f2.8 for a two-stop overexposure, not that you would really want to overexpose anything by two-stops. Manual flash is really not that hard to figure out but a pain to setup on occasion, as I have heard stories of photographers from the old days before automated flash, pulling out the tape measure to make absolutely sure that the distance was correct and religiously using the recommended aperture for a given ISO no matter what the lighting conditions were, indoors or out - like my father with his old Canon FTB and small manual flash unit, f5.6 and 1/60 and be there for him. Where manual flash becomes a true pain in the ass to work with is with macro photography or when trying to do bounce lighting. God help you if you were to try to calculate the working distance and aperture under those circumstances. The fastidious photographer would probably take a number of test slides in various bounce lighting situations to understand what sort of compensation is required. Macro photography is where the major brain hurt occurs especially if you are using extension tubes and teleconvertors to get closer to the subject. John Shaw wrote the book on macro photography in the field but today he does not bother advising anyone to learn the old manual flash calculations as he himself uses TTL flash for macro shots via his Nikon kit. A lot of manual flash brain hurt can be alleviated with the purchase of a flash meter. Fire off your flash with the meter held in front of the subject and the meter will calculate a working exposure for you based upon the parameters you set. When working with my Multiblitz flash units and umbrellas, I manually meter the flash exposure with a Sekonic 508 based upon the aperture I wish to work with. I simply adjust the flash output until I receive the correct amount of light for the aperture. Auto Flash
An Auto flash is capable of Manual operation in which it dumps out its full rated load at the subject but we want a bit more flexibility from our flash and we do not always want to do a full dump or be stuck with a given distance for our film being used. We need a bit more control and finesse. The Auto flash answered this need by installing a sensor on the front of the flash. This sensor reads the amount of flash-light reflected back from the subject and cuts off the flash once it receives a reading that the subject has been properly lit for the parameters the flash has been set to. The better Auto flashes have a number of aperture setting choices for the photographer to choose from, the Vivitar 283 has four while other flashes may have more (such as my Metz 45 CL-4). Film speed is still an important consideration with Auto flash but now the photographer can choose more than one aperture to work with. Distance is still a factor but with Auto flash, the photographer just has to be aware of the maximum working distance for his choice of aperture instead of one rigid working distance. The main caveat to Auto flash is that changing the aperture setting on the lens means changing the setting on the Auto flash otherwise the subject will no longer receive proper illumination. Unless, of course, you wish to do some fill flash work in which case the photographer must alter the aperture to achieve the desired flash compensation. Bounce lighting is bit easier with Auto flash but still not, what we would desire from an automated flash system. Off-center subjects can also present problems because the flash sensor will always read from the middle that it sees. Direct mounted Auto flash requires the subject to be centered and if the subject or the flash itself is off centered, inaccurate flash exposures may result, depending on the exact circumstances of the flash to subject relationship. Update - Metz users can purchase an Auto flash adatper that has a sensor mounted on the camera's hotshoe with a cable extending out to the flash allowing bounce lighting techniques or off camera flash while still having the Auto sensor seeing very similarly to what the lens sees. Although Auto flash is now dated, it remains a favorite among wedding photographers using manual medium format kits. I currently use a TTL adapter with my own medium format kit and find it highly convenient to do fill flash outdoors.
TTL Flash
Instead of relying on a sensor built into the flash, camera companies installed flash sensors into the camera body and allowed the sensor to see through the lens instead of being placed many inches away from the lens. Whatever the lens sees the flash sensor sees and can make quick adjustments as required of the subject. In a very simplified explanation of the TTL flash sensor, the sensor resides behind and under the mirror and when the mirror rises to allow light onto the film, the sensor reads the amount of light being reflected back by the subject. Due to the sensor being at an angle, it cannot read the reflected light directly so it reads the flash-light being bounced off the back of the mirror, which is traditionally painted 13% gray (or perhaps 18% depending on the company and how secretive they are about it). Once the correct amount of light has been read for the parameters in which the flash has been set to, the sensor cuts off the flash from dumping anymore light. TTL flash results compared to a good Auto flash to that of a properly exposed Manual flash setting should be minimal. What sets TTL flash apart from Auto and Manual is its ability to adjust the shutter speed automatically on some systems. You must experiment with your brand's TTL flash and what it provides you in various lighting situations. The more you know how your TTL flash works the better and more consistent your results will be. TTL flash has evolved so that camera companies can now tie the flash sensor into the Matrix or evaluative metering patterns developed since the early 1980s. Since I am less familiar with what other companies offer by way of their latest flash technology, I will provide some examples of Nikon flash capabilities but I suspect most if not all features are also available with other brands and perhaps even more than what Nikon offers today.
TTL flash allows you complete control of the aperture with the flash adjusting its power output and distance scale as required. Modern day flash units will have a bar graph display of the working distance for the aperture set and film loaded into the camera. This graph will show a minimum and maximum distance scale and the photographer need only pay attention to ensure he/she is within that distance scale. After that, everything is automated. Unless something wrong is with your flash unit or flash sensor in the camera, flash provides a known quantity that can be reviewed and compensated for. Experience is the key to understanding how your flash will work under various conditions and the effect that you desire. There are some other factors to keep in mind with flash work. When using Matrix or evaluative flash metering, you have to have a little bit of technical knowledge, of the parameters set by the camera company for its flash and camera units. Generally, Nikon's 3-D Matrix flash metering will underexpose the background by one-stop vis a vis the flash exposure in low ambient light conditions. The result will be a correctly exposed subject in a wash of black if taking shots with a low ISO film. Higher ISO films will register more of the background in the scene but many people are not satisfied with this default flash exposure from Nikon. The alternative is to take the shutter speed into your control and adjust according to your choice of lens and desired result on film. When using Nikon flash in Aperture Priority or Program Auto mode, the camera defaults to 1/60 of a second in very low light on the basis that you are using a standard lens and you would desire minimal handshake. However, the shutter speed does not change no matter what lens you mount so, if you are using a 24mm lens and would assume safe hand-holding speed of 1/30 of a second or conversely if you were using a 180mm lens and required a 1/200 shutter speed, you would need to be in Shutter Priority or Manual control of the exposure in order to change the shutter speed. In lighting conditions that require flash but are not wholly dark, such as an indoor-daylight scene, the Nikon 3-D flash will provide acceptable results, as the shutter speed will increase to match the light. However, the more discerning photographer will be fully aware of the ambient light conditions and adjust accordingly. What some photographers like is a more equal ambient and flash exposure, meaning often having to use slow shutter speeds or higher ISO films to bring the background closer to matching the flash exposure. Other photographers do not bother with the complex Matrix or evaluative flash metering capabilities with their expensive brand flashes. It seems silly to spend so much money on a basic TTL flash but it always seems the case that a camera company will pack every high tech feature it has into its most powerful and most expensive flash units, despite the small number of photographers who would actually make use of every last feature offered. Many outdoor photographers work in Standard TTL mode to get away from the nuances of Matrix flash metering and manually adjust the flash compensation for their desired results. Galen Rowell's much ballyhooed minus 1.7 compensation is a result of using the Nikon flash in Standard TTL and Moose Peterson is another who chooses to leave his flash on Standard TTL with a minus 1 setting. Manual compensation of Standard TTL provides the photographer with a known quantity and quality to work with. In other words Matrix flash metering is not trusted. In conclusion, flash is determined by a few basic factors,
All flash exposure is based upon these parameters and the difference between Auto and TTL flash is merely about the convenience of measuring flash lighting reflected off of the subject and providing you with more choices for aperture desired. From there on, how you use flash and adjust for its known weaknesses is up to you according to your desired results.
Flash Lighting Flash lighting can be divided into three different types, key, balanced, and fill (there is also bounced lighting but that can be a combination of the three types of lighting). Key flash is when the external or built in flash unit is your primary source of light and the ambient light is either fill or background light. Key flash will usually be used in situations of low ambient light, such as indoor and nighttime settings. One of the more commonly seen byproducts of key flash lighting is the spotlight look of your subjects being flashed but the area around and behind them being a mass of darkness. This is often the result with flash and camera set to a Program Auto mode with slow films. Nikon (perhaps others) sets the flash to a default 1/60 of a second when using flash in low ambient light in Program Auto and Aperture Priority modes. This is to provide photographers with a fail-safe for handshake using normal range lenses. This feature along with slow films can mislead a photographer into believing that the camera and flash are underexposing the background in flash exposures. This spotlight look is not one that many would find endearing yet some camera companies believe this what the consumer wishes. To avoid the spotlight look and bring about a better balance to the scene there are a couple of things you can do,
Key flash lighting can also occur in outdoor sessions too, it is all a matter of shutter speed if your flash lighting is set for a balanced 1:1 ratio. By setting a faster shutter speed than dictated by the ambient light metering, you will underexpose the background but because your subjects are flashed, they will be properly lit.
Balanced Lighting is when your flash exposure is equal to your ambient light exposure, known as 1:1 ratio. Simply put, if your ambient light exposure is 1/60 for an aperture of f8 then your flash is set for f8 light too. Adjusting the shutter speed to a faster speed of 1/125 would result in a one-stop underexposure of the background only while your subject will continue to receive proper f8 lighting. You would not normally overexpose the background when doing flash photography by setting a slower shutter speed.
Fill flash is when your flash exposure is below that of the ambient light exposure. Fill flash is most often used for outdoor photography and as such, benefits mostly from cameras that are capable of high speed flash sync speeds in the 1/250 to 1/500 range (some Schneider lenses can sync at 1/1000!) If your camera is not capable of high speed sync then you will be forced to use small apertures and/or neutral density filters to drop the ambient exposure down to the range of the camera's shutter sync speed. The medium format Pentax 67 is not known as a flash photographer's camera (but a great field camera) due to its very slow 1/30 sync speed whereas Hasselblad and Bronica medium format cameras are favored by many wedding and portrait photographers for their 1/500 sync speed. Oh yes, sync speed means that is the fastest shutter speed the camera is capable of synchronizing the shutter blade movements with a single flash burst. The best 35mm cameras sync at 1/250 and some can even do 1/300 but going beyond these speeds and the shutter is no longer fast enough to keep up with the flash output. The result of shooting faster than the sync speed will result in the shutter being captured on film as it moves across or down the film plane, obscuring portions of your scene on the film. Yes, cameras today can fire off a shutter at 1/8000 of a second or faster but flash bursts are much faster being in the multiple 1/10,000 speeds. Some companies, such as Canon, have devised a method of mimicking extremely high-speed sync without the problems of actually syncing the shutter and flash output. The flash units will not output one continuous burst of flash as would normally happen with regular flash sync exposure but instead will emit a series of flash bursts that will seem like one flash pop to the human eye. Nikon flash can do this too but Canon has automated the feature to make it much easier to use for those times that you actually do want to fire off a flash while shooting at 1/4000 with the camera. The downside is that your flash power output is severely curtailed, meaning your subject needs to be very close to the camera location for best effect. Now, while cameras are limited by the fastest sync speed they are not limited by the slower shutter speeds. In fact, slow speed sync is the best way to balance a flash exposure with low background light. I digress, back to fill flash. Fill flash is normally in the range from minus one-stop of flash to ambient to minus two-stops to ambient light. The following below assumes the use of manual flash settings (the exposure values are just arbitary examples)
Remember, your camera settings remain the same because 1/125 and f8 at ISO 100 is for the ambient background light. Change these settings and you will alter the whole look of the scene as far as the background is concerned. Only the flash settings are modified to adjust for the desired fill on the subject - remember, fill flash is about balancing flash output on a subject with a camera exposure set to expose the background properly. These instructions assume that you are using an Auto flash or a TTL flash on standard mode. Use of a TTL flash in the more advanced Matrix or Evaluative modes can bring about a mix bag of results depending on how the Matrix meter reads the background and attempts to compensate the flash and exposure. This is one of the major reasons why many pros and serious amateurs eschew the more advanced fill flash features of their top of the line flash units for the more constant and known values that standard TTL provides. My own results with Matrix TTL fill flash usually results in a bit too much flash output and that compensating the flash in Standard TTL mode with a minus 1 to minus 1.7 results in more natural looking flash fill. This really depends on what you consider the right amount of fill so experiment and dial in what pleases you or if you are happy with what the camera and flash calculate for you, more power to you.
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Correspondence & About this website Copyright © 1998-2008 Edwin Leong |
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Manual
flash has often been the bane of a photographer's existence and until
the arrival of Auto flash and then TTL flash, learning the intricacies
of Manual flash meant some mental gymnastics in calculating proper flash
exposure. Some diehards who learned how to work with Manual flash effectively,
still swear by it and will trust no other method of flash exposure.
Years of experience has provided them all that they need to do things
right. Steve Sint of Popular Photography Magazine is such a professional
who eschews automated flash work.
That
is really all that manual flash requires and all manual flashes have
a calculator dial or table to indicate what the proper aperture setting
should be for a given ISO based upon the power output of the flash.
Since flashes come in so many sizes, you have to be aware of the particular
requirements for the flashes you use and be very ware of your film speed
in the camera because an ISO 400 film will alter your flash calculations
by two-stops from the base ISO 100. You would actually benefit from
using faster film as your flash power can be extended farther due to
the sensitivity of the film. However, using a slower film means losing
working distance as the flash has to compensate for the slower film
- actually the flash does not compensate anything in Manual mode, it
is your working distance and apertures that would be modified for the
slower film.
Manual
flash obviously has its limitations so thank goodness for the arrival
of the Auto flash. I am not certain when Auto flash arrived in the history
of photography but I am aware that the Vivitar 283 auto flash has been
a favorite of photographers since its arrival in the early 1980s. The
283 still goes on strong and remains a popular option for photographers
on a budget or for those seeking a no-nonsense backup flash. 
The
Calculator Dial on a Vivitar 283
The
Calculator and Mode Dial on a Metz 45 CL-4 - the green aperture settings
are for the Auto flash mode
I
do not care for the dial on the Vivitar 283 flash so I taped my own guide
to the top of the flash, which allows me to glance what settings I need
while shooting quickly. The #1 signifies one of two Vivitar 283 flashes
I own.
The venerable Auto sensor on the Vivitar 283, still going strong after
two decades.
Auto
flash provided a very nice workaround to Manual flash limitations but
there are still weaknesses to Auto flash and the next advancement in
flash technology is TTL flash or Through The Lens flash readings.
The
Vivitar 283 hotshoe compared to the TTL Nikon SB28 hotshoe - one hot
pin versus four hot pins on the Nikon
A cheap way to add slave capabilities to your flash but of course you
would need to set the flash to Auto mode to keep the flash exposure relatively
painless. Manual mode would mean having to use a flash meter to obtain
the correct flash exposure. Optical slave devices can be set off by other
flashes too so beware.
One
feature that a flash purchaser should look for is a tilt/swivel flash
head that allow for flexible bounce flash. All the top flash heads from
camera companies have this feature. Note that bounce flash may cancel
out some features of the flash. In the case of the Nikon SB28 above,
bounce mode cancels out the monitor pre flash impulses sent out by the
flash before the actual flash burst occurs. Monitor pre flashes help
to obtain more accurate flash exposures due to the flash meter in the
camera body taking those pre flash readings into account and then calculating
the overall flash exposure, all milliseconds before the actual picture
taking process. Not everyone is sold on this feature and quite frankly
I am not so sure I would ever be able to tell any difference between
a pre flash exposure and one without.
Another feature to look out for is a wide-angle diffuser, outlined in
red above on the Nikon SB28. In normal mode without the wide-angle diffuser,
the SB28 can cover down to a 24mm wide-angle lens. The diffuser allows
the flash to cover a very wide 18mm, which means that the overall distance
reach is shortened but the lateral spread of the flash is much wider.
Many photographers choose to leave this diffuser down all the time to
achieve the wide spread for all their flash shots. I do this too most
times because my subjects are usually within the distance scale for the
flash power reach. When doing bounce lighting, I may put the diffuser
back in if I decide I need the extra reach of the regular flash head -
depending on the lens I am using at the moment.
When
in low ambient light, Nikon cameras default to a shutter speed that
tries to minimize handshaking. On the CP950 digital camera, that speed
is 1/30 and in this spotmeter (off of the central flower) shot above,
caused severe underexposure of the background for a spotlight look.
This
shot was handheld for about two-seconds, hence the blurred image, without
flash. However, it reveals what the scene on the left actually looked
like in the late summer evening light.
Ambient light exposure - chandelier behind the bear is the only source
of key light, f3 @ 1/4
f3 @ 1/4 with flash for Balanced Lighting - since the CP950 digital camera
offers no flash compensation, it is essentially 1:1 all the time
f3
@ 1/2 second for one-stop ambient overexposure with flash - ambient
is key light as it is stronger than the flash lighting
f3 @ 1/8 for one-stop ambient underexposure with flash becoming key light 
f3 @ 1/30 for three-stop ambient underexposure - flash is now very much
key light in the scene
