A FLASH PHOTOGRAPHY PRIMER <ul><li>Why Use Flash? </li></ul><ul><li>Stop action. </li></ul><ul><li>Can freeze motions that are too fast for the eye to see. </li></ul><ul><li>Lots of light to give good depth of field and fill in shadows caused by sunlight or other bright light sources. </li></ul><ul><li>More comfortable than working with hot lights. </li></ul><ul><li>Same color as daylight. </li></ul><ul><li>Lots of power/light can be obtained from a small package. </li></ul><ul><li>Portable. </li></ul><ul><li>Controllable with light modifiers. </li></ul>
A FLASH PHOTOGRAPHY PRIMER <ul><li>Working with Flash </li></ul><ul><ul><li>Guide Numbers are a way to determine correct exposure. They incorporate the sensitivity (ISO or EI) of the film or sensor, the distance from the flash to the subject, the power output of the flash and the desired f/stop. Typically, guide numbers are used to calculate the exposure for flashes with manual power level settings. </li></ul></ul><ul><ul><li>UV (ultra violet) correction is usually in the form of a coating or filter placed on or in front of the flash tube. This correction minimizes or eliminates the effects of ultraviolet light that the flash tube may produce when it flashes. </li></ul></ul><ul><ul><li>Recycle Times refers to how long the flash will take to charge up and be ready for the next flash. This can range from instantaneous to several seconds depending on a number of factors. </li></ul></ul><ul><ul><li>Color Temperature . Most electronic flash units are rated between 5,000º and 5,800° Kelvin. This is basically the same color temperature as the sun on a cloudless day between 10:00AM and 3:00PM. </li></ul></ul>
A FLASH PHOTOGRAPHY PRIMER <ul><li>Working with Flash </li></ul><ul><ul><li>Flash Duration . Rather than changing the amount of power dispensed into the flash tube, usually the duration of the flash is adjusted while the output level of the flash remains constant. Flash durations can range from several hundredths of a second to several hundred thousandths of a second. Reciprocity Law failure should be considered in these cases. When using an automatic or TTL flash close to a subject with a large aperture and a relatively fast ISO/EI, flash durations can be extremely short. This can be very helpful in stopping very rapidly moving subjects. If the light from the flash is the only source illuminating the subject some spectacular results can be obtained. Harold Edgerton did a great deal of pioneering work in this area and is often considered the father of electronic flash. </li></ul></ul>Photos on this page are provided courtesy of the estate of Harold Edgerton
A FLASH PHOTOGRAPHY PRIMER The Inverse Square Law “ Light intensity falls off with the square of the distance ” Example 1: A single light in a dark room will cast 4 times the amount of light on a subject when it is 2 feet from the subject as it will when it is 4 feet from the subject. Example 2: A single light in a dark room will cast 4 times the amount of light on a subject when it is 5.6 feet from the subject as it will when it is 11 feet from the subject. Example 3: A single light in a dark room will cast 4 times the amount of light on a subject when it is 16 feet from the subject as it will when it is 32 feet from the subject. ( Do you see a pattern emerging??? Hint: Think in terms of f/stops.)
A FLASH PHOTOGRAPHY PRIMER Watt/Seconds vs. BCPS Watt/Seconds is a measurement of stored electrical power. BCPS (Beam Candle Power Seconds) is a measurement of actual light output. The reflector and its finish (polished, stippled or matte), shape, and size have a direct effect on the amount of light that is output from a flash head. Hence, you can achieve different BCPS output by changing the reflectors and/or light modifiers with the same amount of watt/seconds.
A FLASH PHOTOGRAPHY PRIMER How to Use Guide Numbers The key to using flashbulbs (or any manual flash system) is the concept of guide number . The guide number expresses the amount of energy contained in the flash in a way directly useful to the photographer, and relates distance covered to lens f-stop, as follows: F = G / D where F is the lens f-stop, G is the guide number, and D is the distance. Whereas for electronic flash (strobe lite), the guide number depends only on the film speed, for flashbulbs a guide number is stated for a certain film speed, shutter speed, and film sensitivity (B&W or color). The reason that shutter speed enters the equation is that a flashbulb flashes over a relatively long period of time, and shutter speeds of faster than 1/30s cut off some of the light from the bulb.
A FLASH PHOTOGRAPHY PRIMER How to Use Guide Numbers On just about any hot-shoe flash capable of manual, there's a guide number calculator built in.
A FLASH PHOTOGRAPHY PRIMER How to Use Guide Numbers The four flash exposure variables are: F/stop, distance, power and ISO. You plug in any three, and the calculator spits out the fourth. Play around with your buttons a bit and you will see how yours works. What I like to do is to already know my ISO, my desired shooting aperture and an estimated flash-to-subject distance. Now, by setting up my GN calculator, I just dial in the different manual power settings until my desired f/stop lines up with my flash-to-subject distance.
A FLASH PHOTOGRAPHY PRIMER This GN calculator is set for full power manual at ISO 200. It is telling you that, at 30-40 feet, you would get about f/4 out of this flash. And if you set the flash to 1/2 power, you'd get f/2.8 out of it at that distance. Here's the cool thing: If you zoom the head -- even on this old-design flash -- it will move the dial and adjust the result. Full power 200 ISO
A FLASH PHOTOGRAPHY PRIMER <ul><li>When the flash is triggered, a burst of light leaves the flash head and travels to the subject. </li></ul><ul><li>Some of the light is absorbed but some will reflect off the subject and return to the sensor window on the flash’s automatic sensor. </li></ul><ul><li>When the circuitry in the flash senses enough light at the sensor to yield the desired exposure it will instantly cut off the light being output by the flash head. </li></ul><ul><li>With a thyristor flash (like the one pictured below) any unused stored electrical energy will be conserved thereby keeping recycling times as short as possible. </li></ul>How does an automatic flash work?? S
A FLASH PHOTOGRAPHY PRIMER <ul><li>There are three types of flash meters: </li></ul><ul><ul><li>Incident </li></ul></ul><ul><ul><li>Reflected </li></ul></ul><ul><ul><li>Spot (a reflected light meter that measures very small areas (spots) of the scene before it) </li></ul></ul><ul><li>Flash meters can be triggered by the actual flash of light emitted by the flash unit(s). Additionally, you can trigger the flash unit(s) with the meter by connecting them to the flash meter with a sync cord. </li></ul>How to use a flash meter <ul><li>To use a flash meter, follow the steps below: </li></ul><ul><li>Select the triggering mode you wish to use. </li></ul><ul><li>Set the ISO or EI into the meter. </li></ul><ul><li>If using an incident meter, hold the meter at the subject with the receptor (a white dome) pointed at the light source(s). </li></ul><ul><li>If using a reflected or spot meter, aim the meter’s receptor (light sensing area) at the subject from the camera position or at an 18% gray card that is illuminated by the same light that is falling on the subject. </li></ul><ul><li>Take a reading and transfer the settings to your camera and lens. </li></ul><ul><li>Expose. </li></ul>
A FLASH PHOTOGRAPHY PRIMER How to use an Automatic flash Most automatic flashes have multiple auto setting options. The one pictured to the right has four. They are color coded yellow, red, blue and purple. In the example to the right, a yellow setting on the flash sensor will give correct exposures with the lens set to f 2.8 between 50ft and 4.5ft. A red setting will give correct exposures at f5.6 between 25ft and 3ft from the subject. Blue would be good @f11 from 12ft to 1ft and purple – f16 between 8ft and 1ft.
A FLASH PHOTOGRAPHY PRIMER <ul><li>Syncro-sun or flash fill </li></ul><ul><li>When flash is the only light source it is the duration of the flash that serves as a shutter speed. The actual camera shutter speed is not a factor with electronic flash under these conditions. </li></ul><ul><li>As the ambient light level increases to the point where it can affect the exposure, the camera shutter speeds DO become significant. It is in these conditions where it is helpful to understand how to utilize flash fill or synchro-sun techniques. </li></ul><ul><li>Procedure </li></ul><ul><li>If you are outdoors or in a brightly lit environment and want to use flash to lighten up (put detail into) the shadows, here is how to do it with an electronic flash: </li></ul><ul><li>Determine the exposure for the existing (no flash) light. You will get a shutter speed and an f-stop based on the amount of ambient light and your working film speed (EI/ISO). The shutter speed won’t have an effect on the flash exposure (as long as it’s longer than or equal to the maximum sync speed of your camera/lens). The number you’re interested in here is the f-stop. </li></ul><ul><li>Use guide numbers, a flash meter, automatic or TTL settings to adjust the flash output to give you the same f-stop you achieved in step 1. This will result in a one to one flash to ambient ratio. </li></ul><ul><li>By varying the flash f-stop relative to the ambient exposure f-stop you will be able to control the ratio of how much effect the flash has on the shadow areas. </li></ul>
A FLASH PHOTOGRAPHY PRIMER Focal Plane Shutters vs. Leaf Shutters Focal Plane Shutter Leaf Shutters Focal plane shutters have a maximum flash sync speed which is slower than their maximum mechanical speed. This is due to the fact that there are two blades in a focal plane shutter and how these two blades move at different shutter speeds. Leaf shutters will sync to flash at all shutter speeds. This is because the flash is not triggered until the shutter blades (right) are all fully open. (FLASH IS TRIGGERED)
A FLASH PHOTOGRAPHY PRIMER Focal Plane Shutters and Flash Synchronization <ul><li>In standard. flash sync. mode the flash fires as soon as the entire film frame is fully exposed to the incoming light (see picture above). This time period is obviously limited towards higher shutter speeds dependent on the speed of the shutter/curtain mechanism. This max. flash sync. speed is given in the specifications of a camera. Consumer grade SLRs can normally sync. up to 1/180sec. By using repetitive flashes (high speed “FP” synchronization) some advanced camera/flash combinations can achieve higher flash sync speeds. </li></ul><ul><li> </li></ul><ul><li>Despite the short flash duration, the chosen flash sync. speed has certain effects on the final image. The main (flash) subject itself is quite independent from the chosen flash sync. speed because it is exposed with the speed of the flash duration. However, this is not true for the surrounding scene. So, the faster the flash sync. speed is... </li></ul><ul><ul><li>With a moving scene (or a static scene with moving objects) The objects which are not (significantly) exposed by the flash’s light are less blurred due to the faster shutter speed. </li></ul></ul><ul><ul><li>The scene around your main subject will get darker as the shutter speed increases because the ambient light has less influence on the exposure. The effect is obviously dependent on the level of the ambient light. </li></ul></ul>
A FLASH PHOTOGRAPHY PRIMER First and Second Curtain (Front & Rear) Sync. First (front) curtain sync Second (rear) curtain sync Many cameras offer the possibility to synchronize either on the 1st or 2nd curtain. With 1st curtain sync. the flash is fired as soon as the 1st curtain is in upward position while with 2nd curtain sync. the flash is fired just before the 2nd curtain moves upwards. Obviously this means that the natural (ambient) light of a scene exposes the film/sensor either after or before the flash burst. If you shoot a fast moving object with 2nd curtain sync. you'll get a blurred moving effect which will end in the (flash-) exposed object. With 1st curtain sync. it'll be the other way round.
A FLASH PHOTOGRAPHY PRIMER Hi-speed (FP) Flash Synchronization Focal plane (FP) flash seems to be a quite new technology but surprisingly the concept is already known for some decades. It allows faster sync. speeds than just e.g. 1/200s. With very fast shutter speeds the opening between 1st and 2nd curtain is never as large as the whole film/sensor area so a single flash burst would lead to a partially exposed film. As a solution you have to have a constant flash light for the whole exposure time. Unfortunately modern flash units have a peak emission characteristic so a single flash is not usable for this purpose. Today most manufacturers use a series of high frequency flash bursts (say 50 kHz) with reduced single light emission to simulate a (theoretically) long single constant flash burst.
A FLASH PHOTOGRAPHY PRIMER Flash Sync and Shutter Speeds Starting in the early and middle 1950's a number of cameras were made with a flash sync position called "FP" which means the same then as it does now. It is a high-speed flash sync for use with focal plane shutters at speeds of 1/100th second and faster, and flash bulbs. As today, this feature was found generally only on the higher end cameras during the flash bulb era, mostly professional grade models. An examples of these cameras is the Zeiss Ikon Contax IIa and IIIa Color Dial. These were introduced to the market in 1954 and had " M " sync for shutter speeds of 1/30th second and slower, " X " sync for 1/50th second (for electronic strobe flash!), and " FP " sync for 1/100th second and faster. Standard flashbulbs (designed for "M" [20ms to peak output] and "F" [5ms to peak output] synchronization) did not have a long enough peak light output for the "FP" sync even though the duration of their light output is very long compared to an electronic strobe's. A special long-duration or "FP" bulb had to be used with this sync. FP sync X (flash) sync M sync
A FLASH PHOTOGRAPHY PRIMER Red Eye Reduction What is “Red Eye”? What causes it? and what can I do to prevent or fix it? “ Red Eye” is the appearance of eyes which are red in color photographs. “ Red Eye” is caused by light which enters the eye and bounces off the blood vessels in the back of the eye. Since the pupil is actually a clear lens the effect is to give a glowing appearance to the red color of the blood. The reason that this red color can be seen in photographs is that the angle that the light from the flash enters the eye is too similar to the angle that the light leaving the eye is from the lens axis. To prevent “Red Eye”, simply move the flash source away from the lens. The thing to keep in mind here is that the angle of incidence is equal to the angle of reflection. Some flash units have a red eye reduction feature which causes a pre-flash that causes the pupil to close down thereby reducing the appearance of “red eye” when the actual photograph is taken. This causes a delay in the time that the desired expression is captured and, as a result, these expressions may be missed. If you have photographs that already have “Red Eye” this can be corrected in most photo editing programs like PhotoShop, Lightroom, iPhoto and many others.