Flash in Stereo

Home , Fill flash, Flash (photography), Flash synchronization

FLASH IN STEREO

“Golf Legend Bobby Jones Taking a Swing", photo taken by Dr. Harold Edgerton , the inventor of electronic flash in 1938, using stroboscopic flash photography. A Presentation by George Themelis NSA / ISU 2017

Flash Workshop at NSA 2010 What has changed in 7 years?

• Not much… . Stereo Photographers continue to avoid flash….

• Inexpensive Chinese flash units and photographic accessories in general...

• LED lights developed as an alternative to flash...

• New developments: High Speed Flash, wireless flash control...

Outline

• Why Flash? • Short History of Flash Photography • Flash Bulbs vs. Electronic Flash • Flash Synchronization • Flash Exposure • Issues with Flash & Alternatives • Flash w/ Slide Bar (Single camera) Stereo • Flash w/ Vintage Stereo Cameras • Flash in macro with the Panasonic 3D Lens • Flash with digital stereo cameras (Fuji) • Flash with twin cameras • Favorite Flash units • Useful Flash techniques

Workshop notes will be made available at the Stereogram CD Convention web site: http://www.3d-con.com/

DrT’s Blog: http://drt3d.blogspot.com/

Lots of information on the internet. Look for flash Tutorials and youtube videos.

Why Flash?

When the existing light is dim, there is a need for artificial light in order to get good exposures .

Example: In a well-lit interior space a typical exposure using 100 ISO is f8 at 1 second. Compare this to a “sunny day” f16 1/100, 2+7 = 9 f-stops less light. Hand holding the camera or taking pictures of people at these long exposures is impossible. Hence flash is a necessity for taking pictures indoors.

Without extra light, the photographer has three options: 1) Open up the aperture (f-stop), 2) Increase the time of the exposure . 3) Increase sensitivity (ISO) . These methods have disadvantages & limitations: • Opening up the lens aperture reduces the depth of field (can be a problem in stereo) increases lens aberrations, plus there is a limit (lens maximum aperture) • Theoretically, there is no limit in increasing exposure time, but in practice 1) film reciprocity, 2) digital noise, 3) blurry pictures without solid support, 4) subject movement. • Increased sensitivity leads to film grain or digital noise.

In addition to exposure considerations one might want to use flash light , to freeze motion , darken the background (macro/close up) for special effects, etc. One of the most important reasons for using flash (usually in a studio setting with multiple flash units) is to control the light (its direction, distribution, etc)

Flash Powder (1880-1930)

• In the early days of photography the only source of light was the sun . First artificial light photography dates as far back as 1839 . Studio arc-lamps helped reduce exposure to 2-3 seconds for a carte-de-visite, in 1880s. First portrait taken using magnesium powder in 1864 .

• Flash powder : Mixture of magnesium powder and an oxidizing agent (potassium chlorate) put on a plate and ignited by a spark from a flint wheel. Used from 1880s to 1930s

• Early flash photography was not synchronized, which means that the photographer had to put the camera on a tripod, open the shutter, trigger the flash, close the shutter. This technique is known as “ open flash ”. 2009 photo by Race Gentry in flickr. 1909 Victor flash lamp and a 1903 View camera .

Flash Bulbs (1930-1970)

• Flashbulbs were first produced in the 1930s as a replacement for flash powder. The glass envelope makes them safer to use and gets rid of the smoke problem. Originally expensive, they increased in popularity because of their convenience and safety, until they were eclipsed by the electronic flash. • Flashbulbs have a piece of tungsten or zirconium filament between their terminals. This wire is covered with an explosive primer paste. When current is applied, the wire heats up, igniting the paste, which then ignites the tin, aluminum or (in later years) aluminum wire (or wool). An oxygen atmosphere increases the brilliance of the flash. Blue coating is used for color correction with daylight films. • Still used because: 1) they are more powerful than compact electronic flash, 2) burn slower and do not freeze motion. Today, flashbulbs are in high demand by cave photographers. Many large cave passages and chambers could never Top: variety of flash bulbs (wikipedia) be adequately or effectively illuminated without Bottom: from www.darklightimagery.net the use of photoflash bulbs.

Electronic Flash (1970-Today)

• Result of the pioneering work of Harold “Doc” Edgerton in MIT in the 1930s. • Electric energy from batteries is converted to high voltage (300 volts or more) and is used to charge a large capacitor. The converter often makes a high-pitch sound, which you can hear when the unit is charging. The capacitor is permanently connected to two electrodes in a glass tube filled with xenon gas . When the flash is fired, a second small transformer generates a pulse of very high voltage, which causes the xenon gas in the glass tube to ionize. Ionization makes the gas conductive, and the big capacitor starts to discharge through the xenon gas. • Bright light is emitted by the xenon gas during this process . The discharge is rapid. About 1/1000 - 1/200 seconds later the capacitor is essentially empty, and the voltage has dropped so low that the xenon stops to conduct electricity. At this point, the process can be started from the beginning.

From Wikipedia, article on “flashtube”

Flash Synchronization I Physical Connection

• Issue : Fire the flash when the shutter is open or sensor ready to accept the light.

• Mechanical Cameras : Electrical contact made when the shutter is open. Electrical connection between flash and camera is made by a PC (Prontor/Compur) plug or a flash mount (hot shoe). • Digital cameras : Programmable electronic timing circuit.

Flash Synchronization II Timing

• Cameras with leaf shutters (Stereo Realist, etc) or electronic shutters (compact digital cameras like the Fuji W3) allow flash synch across all shutter speeds (up to 1/1000 in some cameras). • Cameras with Focal Plane shutters must use shutter speeds slow enough for the entire shutter to be open at once. The maximum shutter speed for flash to be possible is the Flash Sync speed (typically 1/60 in older film cameras, faster in digital cameras). 3A3A3A 3B3B3B

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Flash Exposure

Flash

Flash Light

Ambient 1. Aperture Light (f-stop) Camera 2. Sensitivity (ISO) Shutter speed has no effect on flash 3. Shutter exposure (it only affects ambient Speed light). Only the aperture (f-stop) and ISO affects flash exposure.

Flash Exposure Modes

Guide Number (GN) : A measure of the strength of a given flash. GN = f-stop x distance (usually in meters) at given ISO.

• Manual Flash (M) : Flash fires entire the charge GN = 20m (amount of light). The photographer controls exposure by changing f-stop, depending on subject distance. For example here, subject at 5m (16ft) the table (or GN) says to set f4 (4x5 = 20) • Variable Manual : Flash can fire a fixed fraction of the full charge: 1/1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64… (not available with this flash) • Automatic Flash (A) : User sets a given (specified from flash unit) f-stop. Sensor (on flash) measures reflected light and stops discharge when exposure is satisfied. This flash offers two automatic modes at f2.8 and f5.6. If set at f2.8 at ISO 100 the light is good for up to 23ft (7m) • Through The Lens (TTL) : Flash communicates with the camera. During exposure the amount of reflected light is measured by the camera. When exposure is satisfied, the camera signals the flash to stop the exposure. Not available for this flash. Also not of Trend in modern flashes : interest for stereo photography in general. • Offer variable manual mode • Omit Automatic Mode

My Recommendations

Pro-mode (Photographer has full control) • Set the camera in manual mode (M) • Set the flash in manual mode • Fix the ISO (100 or 400) • Set the shutter speed at some value at or below the camera’s flash sync speed • Control the flash exposure using the f-stop and/ or the flash output • Control the ambient light (if any) using the shutter speed • Use trial and error (take one picture, judge the exposure, make adjustments, take another

Alternative #1 : Alternative #2 : • If the flash has Auto mode , set it in an • To balance ambient light set the Auto mode (given f-stop for ISO) and camera in some automatic mode ( P, A , then set the same f-stop in camera S) but keep an eye on shutter speed. (lens). Set 1-2 f-stops under-exposure and then use the flash to fill in.

Issues with Using Flash • Low intensity (for compact commercial units) • Quick Light drop off (~ 1/d 2) for point light sources causes near objects overexposed & far objects underexposed. • Harsh Shadows : This happens when the relative size of the light source (as seen by the subject) is very small.

• Red Eye : Flash highlights the blood vessels on the back of the eyes. • On-camera flash is unflattering (objects look flat) • Built-in flash in stereo cameras (Fuji, Panasonic 3D1) has been badly implemented . Located between the lenses, it leads to unnatural shadows and other problems. • External flash with stereo cameras is complicated (if not impossible).

Result : Many (stereo) photographers avoid flash completely

Alternative to Flash LED Lights

• LED lights originally developed for video , can and are being used for still photography.

• Advantages : What you see is what you get (no surprises). Also, lower heat/power consumption (compared to Halogen, etc.), inexpensive.

• Advantages of Flash over LED : Higher intensity, can freeze motion, better color balance, more subject- friendly.

Outline

Flash in Slide Bar Stereo

Flash must stay stationary! Do not move with camera. If moved with camera, then shadows will appear pseudoscopic!

Flash with Vintage 3D Cameras

1) Flash Connection 2) Flash Synchronization

Many vintage stereo cameras (Realist, Revere, TDC) have a hot shoe with a “bump”. Solutions: 1) Put a groove in flash. 2) Modify a flash adapter.

Some stereo cameras do not have a hot shoe, instead unusual flash connections (Kodak ASA, TDC Vivid, VM Personal.) For Realist : Bending a metal contact will Use an adapter. Some technicians install a PC Plug convert the M (flash bulb) synchronization to X (flash) where the flash fires when the shutter is fully opened.

Flash bulbs can still be used with slower shutter speeds.

Flash in Macro (3D Lens)

• On-Camera Flash : Because of the very short Metz 15 MS-1 Macro distances to the subject, this flash is relatively high and large, compared to the subject, so it is not too bad.

• Macro Flash : Metz 15 MS-1 Macro flash with two flash heads independently controlled.

These solutions give front lighting .

KX800 Twin Flexible Macro Flash

Front / Side / Back Lighting

1) The position of the light can affect the character of the picture. 2) Front even lighting is the least exciting but it shows the most details, without distractions. 3) Side-lighting can create shadows, adding drama to the picture. 4) Back-lighting can bring up interesting details that are missed with front lighting. 5) Experiment with the position of the flash. Different subjects work better with different directions of light. It is not a one size fits all. 6) Having a flash with flexible arms like the KX800 or using two (or more) flash units that can be positioned independently , is the best way to experiment with different flash/light placement.

Flash w/ Digital 3d Cameras (FUJI)

Distracting shadows: Because the flash is centered between the lenses, it casts shadows where the left eye sees the left shadow, and the right eye sees right shadow. In real life light never comes between the eyes. It comes from above, forming shadows in the same side.

Dust Halos & Red Eye: Because the flash is very close to the line of sight of the lenses, small particles in the air will be recorded as out of focus distracting areas, known as “dust halos”. Also, red eye more of a problem.

Direct Light is Unflattering: Lack of shadows.

Solution for Fuji

Use External Flash: Without any provision for external connections, the only solution is slave flash. Use an optical slave or a flash with built-in slave mode and trigger it using Fuji’s flash.

Fuji flash uses “preflash”, so instead of one flash burst, you get two. The first one is used to determine exposure and adjust “white balance”. Only the second flash is used to illuminate the scene. There is no way to turn the preflash off. The first flash will trigger the slave flash. Solutions: 1) Use a digital slave with preflash/ Metz 34 CS delay, 2) Use regular flash in “weak” auto mode

Tip : To eliminate Fuji’s flash completely, but still fire the slave, cover the flash with a piece of exposed film . This stops the visible light but lets IR go through, and this can still trigger slave flash. For best results (consistent exposure) use the Fuji in Manual Mode .

Cyclopital Auxiliary Lens Adapter

Has a hot flash shoe based on an optical slave.

This is the easiest way to use an external flash with the Fuji.

Flash with the Panasonic 3D1

With no way to control the flash manually (force it on for one thing) I cannot see any way to use external flash with this camera.

Flash with Twin Cameras

Challenge : Synchronize the flash exposure .

Possible courses of action : • Use two flashes, one on each camera

• Use one flash attached/connected to one camera. The camera firing the flash will see the entire flash burst. What will the other camera see?

Success : Other camera sees the entire flash burst. Failure : Other camera sees partial or no flash.

Model for Flash Use - Cameras with Focal Plane Shutter

3A3A3A 3B3B3B Camera #1 (Flash) 000 111 222 444 555

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0 Signal to Fire Shutter 0-1 Shutter Lag 1 First curtain starts to move (shutter starts to open) 1-2 Shutter is partially open 2 First curtain (shutter) fully open 2-4 Shutter is fully open to complete exposure 3 Flash fires (A at start of exposure, B at end of exposure) 4 Second curtain starts to move (shutter starts to close) 4-5 Shutter is partially open 5 Shutter is fully closed—end of exposure Camera #2 AAA BBB CCC A: Camera #2 is “faster” (shorter lag - opens shutter first). Sees the entire flash. B: “slower” camera (longer lag). Flash fires while shutter (1st curtain) is partially open. Partial exposure. C: “much slower” camera. The shutter has not even started to open when flash fires. No exposure. D (not shown), camera #2 “much faster camera” (or #1 is very slow). Imagine camera #1 with very long lag. It is possible for camera #2 to fire and complete the exposure while camera #1 has not fired the flash yet, so flash missed. It also possible to get partial exposure from 2nd curtain.

Flash-induced delay (Panasonic GX1 and GX7)

Observations : Shutter Travel - Flash often works for 1/30 (~1/200 = 5 ms for GX1, faster for GX7 ~1-2ms) - Flash almost never works for 1/60 Exposure Time: 1/60 = 17 ms - Partial exposures are rare 1/30 = 33 ms

Normal Flash-induced Flash Shutter Lag shutter lag #1, 1/60 Time

#1, 1/30

#2, 1/60

#2, 1/30

Conclusions / Suggestions :

− Shutter speed of camera #1 is irrelevant if the flash fires at the start of exposure (first curtain) − The presence of flash delays camera #1. The delay is in the order of 1/60-1/30 (closer to 30ms or longer) − Partial exposures are rare because the curtain travel speeds are fast (compared to the exposure time) − To improve odds, delay camera #2 by using a slower shutter speed − Use flash in both cameras (this will eliminate the flash delay factor). Firing the flash at the end of the exposure (rear curtain) improves success. − Use the Magic Flash. You then get 100% success at 1/60

Magic Flash

Left : Basic idea.

Right : “Magic Flash” twin camera adapter by Rob Crockett. From Rob Crockett (www.ledametrix.com )

How it works : Attaches to each camera and the flash attaches to it. The Magic Flash monitors the cameras and fires the flash after the second camera (slower) is ready.

Why it works (improves the chances of “flash success”) : 1. Eliminates any flash-induced delay because both cameras experience the same delay. The flash is fired by the “Magic Flash”, not a specific camera. 2. Essentially, the slower camera fires the flash . The flash can still fail if the first (faster) camera has started to close when the flash fires. But if you slow the shutter speed sufficiently, you will get to a point of 100% success.

Data from a pair of Samsung NX500 cameras: • @ 1/200 (flash sync speed): 40% success w/MF, vs. 30% w/out • @ 1/100: 70% (MF) vs. 40% • @ 1/50: 100% (MF) vs. 70%

Summary Flash with Twin Cameras • When one camera fires the flash, “ Shutter Lag ” tends to make flash with twin cameras (also, synchronization) problematic. The camera firing the flash always see the entire flash burst. What does the other see? Success : Other camera also sees the flash. Failure : Other camera sees partial or no exposure. • If the cameras are consistent (Samsung NX1000), then have the “slower” camera (the one with longer shutter lag) fire the flash , to get 100% success. • When the cameras are not consistent (show random shutter lag, example: all Samsung NX cameras except for NX1000) then use Magic Flash or delay the flash firing. Using a slower shutter speed will achieve 100% success. • If the camera shows “flash-induced delay” (example: Panasonic), using a sufficient slow shutter speed will work. If you cannot live with the slow shutter speed, then use the Magic Flash (there are other tricks too).

Flash Unit Classification Based on size/weight

Class of Unit Power Guide Number Weight Comments (m @ 100 ISO) Professional use Large / Studio Lithium, external 70 or higher Heavy (weddings, etc.) home / studio use 1 lb (500g) typically Most common, 4x AA 25-50 Medium (w/batteries) lots of choices

2x AA or AAA or As light as 100g 10-20 Best for travel for me Compact small lithium (3.5 oz)

Large Flash Units

Quantum QFlash T5D-R Bolt VB-22

Example of Simple Medium Size Flash

Bolt VD-410

New Chinese Unit or Vintage Classic? Today the market is flooded with Chinese-made units which go with a variety of names (Godox, Neewer, Yongnuo, Bold, Altura, Powerextra, Apeman, Photoolex, Bower, Holga, Interfit, Cheetah...). Often the same unit is marketed under different names. And German / Japanese flashes are made in China. Should you buy a new Chinese flash or an older unit by Nikon, Metz, etc.? It is up to you.

Metz 54 MZ-3

Introduced in 2001, original MSRP : $496.00 - Today one can find a gently used fully functional unit for ~$50 “The flagship of the Metz compact flash series presents itself as simple to operate and loaded with special functions.”

In Search of the Perfect Flash

For me, the ideal flash should have the following characteristics : 1. Be compact and lightweight 2. Powerful with fast recycling time 3. Tilt & swivel head for bounce flash 4. Manual mode with variable intensity 5. Auto mode with at several settings 6. Zoom head (optional) 7. Slave mode (optical)

Construction & Power : Clearly, #1 and #2 do not go well together. Especially older flash units with lots of options tend to be heavier. Some newer units, aimed for smaller mirrorless digital cameras, are compact and lightweight, but also expensive. One might need two units, a compact for every day travel and a more powerful one for home or special uses.

Exposure Control : #4 is important if you use off camera flash or bounce flash or fill flash. In general, manual camera and flash settings will give you the most consistent results. #5 is handy.

I am still looking for the perfect flash.—Some favorite flashes are shown next

A few favorite Compact Flash Units

Nikon SB-30 Sunpak PF20XD

Metz 20 C-2 FlashQ Q20

Nikon SB-30—A fine little flash

Auto modes Wide Angle Panel Infrared Filter

Variable Manual

Slave at Full Power GN 16m @ 100 ISO

Useful for macro Runs on one CR123A Lithium Battery

Instructions at: https://cdn-10.nikon-cdn.com/pdf/manuals/Speedlights/SB-30.pdf

Sunpak PF20XD Manual Mode with 3 Auto Modes variable output

3 Triggering Modes: − X (on camera) − Slave (w/ or w/out preflash)

Metz 20 C-2

− Decent power − Full power manual − Two Auto settings − Bounce head

FlashQ Q20

− Variable manual − Variable Video light − Slave modes − Bounce head − Wireless mode with re- movable bottom contact

Flash Techniques

• Flash Ghosting : Use of slow shutter speed and flash to illuminate a moving subject. Use flash with zooming and panning.

• Fill Flash Outdoors : Soften harsh shadows from sun. Results in more pleasing portraits. Add a catchlight: Even at long distances flash can add a hint of light to a person’s or animal’s eyes .

• Fill Flash Indoors : Balancing ambient & flash exposures.

• Colored reflectors/gels : Use with flash for creative effects.

• Tunnel Flash : Use telephoto setting to focus flash light for creative effects.

• Freeze rapid motion : Duration of flash burst can be as short as 1/10,000 (using consumer flash with a fraction of full power, 1/16, 1/32) which will freeze motion better than fastest shutter speeds of most cameras.

• Multiple Exposures/Stroboscopic : Fire flash several times in the dark with the shutter open and without advancing the film. Also, flash light painting. Stroboscopic photography: flash fires at constant rate to record motion in one frame. • Bounce Flash, Off camera Flash, Multiple Flash

On-camera flash Problems & Solutions

With a few exceptions on-camera flash is the worst way to use flash, because of a number of reasons: 1. Harsh Shadows 2. Quick light drop off 3. Artifacts, like red eye and dust halos 4. Flat (unflattering) pictures (especially portraits)

To overcome the issues with on-camera flash, there are several techniques that I would like to discuss here: 1. Fill Flash 2. Bounce Flash 3. External / Slave / Multiple Flash 4. Flash modifiers

Fill Flash

• Fill flash is the one exception where on-camera direct flash can be useful. Here the flash is used not as the main source of light but to fill-in the shadows (usually from the sun, outside) and to throw some extra light to our subject (often a person). • You can see great images using this technique by googling “fill flash” and selecting “Images.” My personal favorites are pictures at sunset, by the beach, with a person or persons in the foreground. Without fill flash the photographer can either expose for the background, in which case the people will appear as silhouettes (dark, underexposed), or expose for the foreground, in which case the background will appears washed out (overexposed). With fill flash it is possible

to balance the exposure and have a rich http://www.lighting-essentials.com/january-28-a-quick-look-at- saturated background and a well-lit balancing-flash-at-sunset/ foreground. • How does one go about balancing the exposure when using fill flash ? I would start by first selecting the exposure for the background, even underexpose it a bit for more rich colors. Then I would use the flash in manual mode and vary the (fixed) flash output for best results. It is very important not to overexpose the foreground. Some trial and error might be required for best results, which is not a problem with today’s digital cameras.

Bounce Flash

• With “bounce flash” you can still use an on-camera flash but instead of pointing it directly at your subject, you point it elsewhere (typically up at the ceiling, or sideways at a wall). As a result, the light is reflected from a larger area (softer shadows) and comes at the subject from a different direction (top or side), both of which result in more pleasing light. • Ideally, the flash head should be able to move not only up and down but also sideways, to be able to bounce it in all different directions. This is called “ bounce and swivel .” Some units have a secondary flash or a “ catch eye card ” or you can add one yourself. This is used to send some direct light to the subject to create nice catch eye reflections. • When done properly, bounce flash can eliminate all the problems associated with on-camera flash: 1) No harsh shadows since a much larger surface is used to illuminate the subject, 2) No light drop off because the light path is increased by bouncing so the distance of the light to a person in the front (in a case of group picture) is not very different than a person in the back, 3) No red eye or halos because the direction of the light is not from the front, 4) More pleasing shadows. Catch eye card

Direct vs. Bounced Flash “The Long Dining Table”

Ceiling Bounced Flash : − Not a point source − Even distances = even illumination − Better angle Flash

Direct Flash : Dinner Table − Point source (inverse square law) − Front object ~ 4x exposure of back object

Bounce Flash II

Here are a couple of things to have in mind when doing bounce flash :

1. A lot of light is lost in bouncing so you need a strong flash, or use high ISO/ wide aperture. If a room has very high ceilings, bouncing off ceilings will be of no use. You can bounce your light off anything, even a person’s white shirt standing close to you.

2. Be careful about the color of the bouncing surfaces . If they are not white, the main subject color balance can be off.

3. Do not come too close to your subject (for portraits) or the light might come directly from the top, which creates a situation known as “raccoon eyes” (dark circles under the eyes). Stay back and zoom in.

4. Balancing bounce flash and existing (ambient) light is a trial and error situation. Experiment with different bounce directions and camera/flash settings to get the best results. Bounce flash can work well with portraits, group pictures, and pictures of interior spaces.

External / Slave / Multiple Flash

Taking the flash off the camera is a bit of a hassle but often gives better results. How do you fire the flash once it is off the camera?

1. Use a cord . One choice is a used 5ft coiled Nikon SC-17 cord, which can Emitter be found used for about $10. Receivers 2. Optical Slave Flash : The flash is fired by another flash, usually the camera’s flash (as in the case of the Fuji camera) or a small on- camera flash. You can minimize (or even eliminate) the on-camera flash by reducing its intensity or covering it with a material that blocks visible light but lets infrared light go through and it is the IR light that triggers the slave. Some flash units have a built-in slave mode or one can buy an external slave to attach to the flash. One potential problem with optical slave flash is that the flash can be fired by another photographer taking flash pictures in the same room. So this will not work well in a place where other people are taking flash pictures.

3. Radio Slave flash : This is the method of choice for most Newer , very inexpensive system ($16) professionals. The emitter attaches to the camera and receivers attach to various flashes, which fire when the camera is fired. Usually there is a choice of several channels to avoid interference by other photographers . Once the flash is off the camera, it is possible to fire more than one flash unit at the same time, either wired (a bit awkward) or, most likely, as slave flashes. This opens the way to many different situations / effects. I recommend reading some books or websites on this topic and FlashQ , extremely compact wireless system then experimenting for best results.

Slave Flash

− Two types , 2xAAA (100g), 2xAA (150g) under different names − “Bare Head ” type − Full Power (no output control) − Can be easily modified (remove top, install filters, etc)

Flash Modifiers

A flash modifier is anything that attaches to the flash and alters the light (direction, distribution, color, etc.) The goal is more pleasing flash pictures, especially with on-camera flash.

The flash housing itself is a modifier . The heart of the flash is the flash tube. Some flash heads (known as “bare flash” heads) give you just that, the flash tube that will distribute light uniformly over a large area around it (not only in front but also behind and up). In a standard flash unit, the flash tube is housed and this housing directs the light in a certain direction. Some flashes have zoom heads that can spread the light at different angles. Some flashes also have built-in wide angle panels or diffusers that further modify the light.

Past the unit itself, there is a great variety of commercial units that one can buy and attach to the flash. Also one can make their own flash modifiers. There is a plethora of information, websites, videos, etc., that discuss and compare the various modifiers. Needless to say, there is no one single modifier that will magically transform your flash light to wonderful light for portraits, group shots, etc. If this is something that interests you, my advice is do some research, and experimentation to find what works for you.

One thing to remember : Flash modifiers reduce the amount of light that you get out of the flash. You trade quantity for quality.

Summary

• Many indoors pictures are impossible without flash & many outdoors pictures can be improved with flash. • Advantage of flash in stereo include 1) allowing use of smaller f-stops (increased depth of field), 2) freezing motion (sharper pictures), 3) illuminating the foreground which carries most of the stereo information, 4) macro stereo photography (impossible w/out flash). • Flash exposure depends only on the aperture (and ISO), not the shutter speed. Manual (with variable intensity) or Automatic modes are common in stereo. Trial and error is often used with digital cameras and flash. • In addition to providing needing light many special/unusual effects are possible by using a flash. • In slide bar stereo , the flash must stay stationary and not move with the camera. • Vintage stereo cameras can fire an electronic flash, once the details of the physical and electrical connections are worked out. • For close-up macro , consider side and back lighting. • Slave external flash can be used with modern compact 3d digital cameras to improve flash exposures. • Some techniques to try: Fill Flash, Bounce flash, multiple flash (possible with slave or wireless flash).

Try flash with your stereo camera system today!