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Paul C. Buff unveils 640ws Einstein 640 monolight  
Wednesday, October 14, 2009 | by Rob Galbraith
Paul C. Buff has released full details about the company's next studio strobe. Called the Einstein 640, it amalgamates the features of the AlienBees AB MAX series, which the Nashville-based strobe maker had intended to release earlier this year, into a new 640ws monolight designed to provide superb action-freezing capabilities - perhaps the best available in a monolight when set to about 320ws and below - as well as colour temperature consistency on par with a premium-priced power pack.

Illuminating: Views of the Paul C. Buff Einstein 640. Click to enlarge (Graphics courtesy Paul C. Buff)

Colour temperature consistency and crisp freezing of motion are the signature features promised for the Einstein 640, Paul C. Buff's most ambitious studio flash to date. In other respects it's very much like what AB MAX was intended to be. Beyond obvious internal design differences resulting from the fact the Einstein 640 employs insulated gate bipolar transistor (IGBT) circuits to cut the flash tube's output below full power, something the AB MAX series did not do, the Einstein is very similar in overall implementation to the never-released Paul. C Buff monolight.

In other words, the Einstein 640 is meant to be an AB MAX 640, only better.

The Einstein 640 is roughly the same size as was planned for the AB MAX 640, which means it's also about the same size as the existing AlienBees B1600. It's somewhat heavier than the B1600, says Buff, because the Einstein 640 has a sturdier stainless steel accessory/reflector mount and incorporates a dome over the flash tube and modeling light.

Feature summary

Einstein 640 features include:
  • Worldwide power compatibility (95-265VAC, 50Hz or 60Hz, autoswitching)

  • Full power recycle time of 1.7 seconds at 120VAC (60Hz) or at 240VAC (50Hz)

  • 2.5-640ws range, settable in 1/10-stop increments

  • CONSTANT COLOR and ACTION modes; one is optimized for colour temperature consistency and the other for stopping motion

  • 5600K (+/-50K) colour temperature throughout the power range in CONSTANT COLOR mode

  • Approx. 1/666 (t.1) flash duration at 640ws; flash durations become dramatically shorter at settings below full power, particularly in ACTION mode

  • Can be powered by lower-cost pure sine wave inverter/battery units such as the Vagabond II

  • Worldwide 250W quartz modeling light (bayonet socket)

  • Removable Pyrex flash dome over the flash tube and modeling light

  • Precision modeling light tracking of flash output power

  • Thermostat-controlled cooling fan

  • Umbrella mount accepts up to 9mm shafts and is designed to handle beefier umbrellas than the AlienBees B-series

  • einstein_640_03.jpg
    Ready for Launch: A rendering of the LCD display on the Einstein 640 (Graphic courtesy Paul C. Buff)
    Illuminated LCD display (shown at right) and push button controls for setting and reviewing of flash functions

  • Compatible with the Cyber Commander wireless control system (optional CSXCV Transceiver module is required), including turning the Einstein off/on and changing power settings remotely

  • Easy Set button returns the flash to a default state

  • Ready light and beeper

  • Built-in optical slave

  • User-replaceacle flash tube (with UV coating)

  • User-upgradeable flash firmware (via microSD slot)


Unlike almost all monolights, which rely exclusively on reducing flash capacitor voltage to decrease output brightness, the Einstein 640 instead uses multiple IGBT circuits to cut the flash tube's output below the full power setting. This is similar to all shoe-mount flashes, but is comparatively rare in flashes designed for the studio (we know of only one other comparably-powerful monolight, the Photogenic Solair, with this capability).

The flash output curves below shows how IGBT works. On the left is full power, and so the flash's IGBT circuit is not invoked: the flash tube quickly reaches peak brightness, and then is allowed to naturally trail off from there. The result is the flash's maximum output brightness, but also a long tail of light that can lead to blur when photographing moving subjects.

On the right the flash has been set to quarter power. The flash quickly reaches the same peak brightness, but then shortly after that the IGBT unit kicks in to rapidly quench flash output. This greatly improves the flash's ability to stop motion. IGBT is often referred to as tail cut circuitry, because of the rapid falloff of the light that results from the IGBT's truncating of the flash tube's otherwise slow progression back to darkness.

Curvy: Oscilloscope traces of a Nikon Speedlight SB-900 set to full power, left, and quarter power, right

We captured the curves above using a Nikon Speedlight SB-900 and not an Einstein 640, but the purpose and behaviour of the IGBT circuitry is the same: to trim the tail of the light when a setting lower than full power is selected. The photo below is of a wheel spinning rapidly and at a constant rate, lit by an SB-900 at full power. You can see the effect of the light's long fade on the left side of each moving 0 and 1. Roll your cursor over the photo to see what happens when IGBT tail-cutting is invoked, at quarter power in this example. As you'll notice, the long fade has been snipped away and the white numbers are very nearly stopped in their tracks.

Mr. Freeze: The photo above is of a wheel spinning rapidly and at a constant rate, lit by an SB-900 at full power. You can see the effect of the light's long fade on the left side of each moving 0 and 1. Roll your cursor over the photo to see what happens when IGBT tail-cutting is invoked, at quarter power in this example. As you'll notice, the long fade has been snipped away (Photos by Rob Galbraith/Little Guy Media)

When set to ACTION mode, the Einstein 640 relies almost entirely on IGBT magic to quench the flash's output. This results, says company founder and lead Einstein designer Paul Buff, in a flash duration of approximately 1/2200 (t.1) at the 320ws power setting.

Flash duration shortens progressively as power is lowered from there; at the lowest power settings, flash duration is approximately 1/10,000 (t.1), says Buff. Monolights that rely on voltage reduction to lower the flash's output behave the opposite way: turning down the power lengthens flash duration. Employing IGBTs to do this instead is a big deal, if your goal is to avoid strobe blur in your pictures.

Note: Our experience with IGBT-equipped flashes like the SB-900 is that from about half power and below, typical notions regarding flash duration specifications and how they should be interpreted don't apply. Instead, things become much simpler: flash behaviour and the flash duration numbers equate almost exactly to the motion-stopping capabilities of the equivalent shutter speed when shooting pictures under continuous light.

This is definitely true of t.1 (the time during which flash output is above 10% of peak brightness) and nearly so of t.5 (
the time during which flash output is above 50% of peak brightness ), because of the steep falloff of the flash's output.

Assuming the IGBT circuitry in the Einstein 640 performs as it does in shoe-mount flashes, and the 1/2200 (t.1) flash duration specification for the new Paul C. Buff monolight at 320ws proves to be correct for production units, then the new flash will almost certainly have the motion-stopping ability of a shutter speed of 1/2200 at this power level (and better still as power is lowered further).

All of this is subject to verification with actual testing of the Einstein 640 of course.

ACTION mode, as the name suggests, is intended for use by those who need the Einstein's best action-stopping capabilities. In this mode, the flash's colour temperature will drift upwards as power is lowered. For example, the Einstein's 5600K colour temperature specification at 640ws rises to about 5800K at 320ws.

Internal flash capacitor voltage is attenuated slightly to reduce the colour temperature drift at lower power settings, says Buff. But only slightly, as lowering the charge voltage significantly would have the effect of lengthening flash duration. Since the purpose of ACTION mode is to keep flash duration as short as possible, when the Einstein 640 is set this way you can expect to see the colour temperature shift upwards fairly noticeably as output brightness is decreased.

Buff notes that in a strobed sports scenario, where all lights are operating at or near the same power level, a custom white balance will readily correct for the higher colour temperature of all the Einstein 640s on duty.

When the goal is to have all strobes operating at a similar colour temperature, even if they're set to varying power levels, the Einstein 640 offers CONSTANT COLOR mode. To achieve a colour temperature specification of 5600K (+/-50K) throughout the unit's 2.5ws-640ws power range, the unit employs a mix of capacitor voltage reduction and IGBT tail trimming.

This degree of colour temperature consistency is absolutely unheard of in a monolight, where it's typical for colour temperature to warm by several hundred Kelvin or more as power is lowered.

In CONSTANT COLOR mode, flash durations below full power are longer than ACTION mode. Because the Einstein 640 doesn't have to rely only on reducing internal charge voltage to lower flash brightness, however, flash duration remains comparatively short. In CONSTANT COLOR mode, at 320ws, flash duration is specified to be a still-impressive 1/1800 (t.1), says Buff.

Similar, but different

If you had your heart set on an AB MAX earlier this year, it's probably apparent that the Einstein 640 is shaping up to be both similar and superior. Most differences between the products stem from the IGBT-based design of the Einstein 640. Most, but not all. Other differences include:
  • The Einstein 640 is not an AlienBees-branded light. Nor is it to be sold as a White Lightning, or a Zeus. Instead, it will simply be the Paul C. Buff Einstein 640.

  • The AB MAX's umbrella mount was planned to run along the bottom of the flash. The Einstein's umbrella mount is along the top. The reason for the change is straightforward: Buff discovered that the slight downward bend of a mounted umbrella would put the flash tube closer to the ideal position within that umbrella if the mount was on the top rather than the bottom.

  • For use on location, away from wall AC power, the AB MAX series was intended to be compatible with both pure sine wave and modified sine wave inverters, the latter being generally less expensive and more broadly available. The Einstein 640's power supply requires that a pure sine wave inverter be used. It is, however, designed to work with entry-level pure sine wave inverter/battery combo units, even ones whose output voltage drops significantly during the flash's recycle period.

  • The Einstein 640 will not be available in the rainbow of shell colours typical of AlienBees strobes. It will be black only, and a 640ws version only. Buff says that, in time, he may consider developing a more powerful version of the Einstein for those who need more than 640ws of light. At launch, though, there will be a single Einstein model to choose from.
Price and availability

The Einstein 640 is tentatively scheduled for release in December 2009 direct from Paul C. Buff at a projected price of US$439.95. The optional CSXCV transceiver is priced at US$29.95. The Cyber Commander control unit is beginning to ship now, for US$179.95.

More information about the Einstein 640 is in the text below, prepared by Paul Buff. A page on the Paul C. Buff website gives an interesting description of flash duration, IGBT circuitry and more.

POWERING: Auto switches to operate from 95VAC to 265VAC, 50 or 60Hz with no user attention or adjustment required.

RECYCLE TIME: 1.7 seconds to full 640WS at 120VAC 60HZ or at 240VAC 50Hz. Cycle time proportionally decreases as power setting is reduced.

CONTROL CIRCUIT POWER: EINSTEIN 640 can tolerate power line voltages as low as 35VAC from Vagabond or similar pure sine inverters without crashing. Many competitive digital flash units crash if input voltage falls below about 80 to 90VAC.

INITIAL SURGE AC CURRENT AT 120VAC: In spite of the fast 1.7 Second recycle time at 640 true WS, the initial recycle surge current is 16A and tapers down to 5A during the recycle period. This is slightly lower than previous Buff monoflash units and most competitive lights of similar power. When operated at 240VAC 50Hz the surge and operating currents are approximately half the 120VAC values.

MODELING LAMP: EINSTEIN 640 uses a standard, relatively inexpensive 120 Volt 250W bayonet style quartz modeling lamp. It is precisely voltage controlled to maintain consistent luminosity and to track flash power within plus or minus 1/10 f stop at any AC input voltage and any power setting within it's specification. Thus, no user intervention or lamp changing is required to operate at different AC line voltages. The design of the modeling lamp regulator is proprietary to Paul C. Buff and yields dramatically less interference transmitted back to the power line in comparison to the unregulated and inaccurate household style "phase control" dimmers used in most flash units.

The frosted Pyrex dome protects the lamps from damage and serves to reduce UV emission from the flash tube, and to equalize the effective size and shape of the modeling lamp and flash tube. The modeling lamp filament is in exactly the same focal point as the UV coated flash tube. This combination of factors results in an extremely close relationship between flash and modeling light and vastly diminishes the effect of any design or manufacturing anomalies in reflectors.

POWER CONTROL RANGE: EINSTEIN 640 uses multiple IGBT devices to allow a 9 f stop (2.5WS to 640WS) flash power range, adjustable in precise 1/10f steps from the rear panel or Via Cyber Commander when optional CSXCVR Transceiver is plugged in. Voltage regulation consistency is typically accurate to better than 1/50f at 640WS and 1/10f at 2.5WS. Setting accuracy is typically within plus or minus 1/10f over the entire operating range.

FLASH DURATION AND COLOR TEMPERATURE: The proprietary IGBT control employed in EINSTEIN 640 allows the flash duration to dramatically decrease as power settings are lowered. This is opposite to conventional studio flash designs where the duration lengthens and the color temperature falls when power is reduced. Two distinct operation modes are available from the rear panel:

In CONSTANT COLOR mode, the emitted color temperature is held constant at 5600K plus or minus 50K at any power setting or input voltage. At Full Power, the t.5 flash duration is 1/2000 second and the t.1 time is 1/675 Second. As power is reduced to 1/2 power the color remains constant, while the flash duration decreases to approximately 1/1800 Second t.1. (Note that with IGBT control, the t.5 spec is no longer meaningful, so the only t.1 flash duration appears on the rear LCD display.) As power is further decreased, the Color Temperature remains constant and the t.1 flash duration falls ultimately to 1/10,000 Second at the lower power settings.

In ACTION mode, the color temperature rises as power as reduced but the t.1 flash duration is minimized even further for maximum action stopping capability where absolute color consistency is secondary to motion freezing. At 1/2 power in ACTION MODE the t.1 flash duration is approximately 1/2200 Second and the color temperature is approximately 5800K. Absolute values of flash duration and color temperature are indicated on the rear LCD display and are yet to be fully specified.

READY INDICATOR AND FIRING FREQUENCY: An advantage of the IGBT flash control is that, at reduced power settings, the flash capacitors are not completely drained when the unit is fired. Therefore it is possible to perform a rapid sequence of shots. The READY state indication is selectable from the rear panel and READY state can be indicated by the audible beeper, by the modeling lamp dimming when fired and returning on when recycled, by both, or by none. The rear panel READY indicator always turns green when the unit is fully ready to fire.

As an aid to sports shooters, EINSTEIN can be fired before the READY state is reached. Depending on the power setting and number of frames per second being shot, this can however produce successively increasing reductions of exposure value and color temperature in a rapid series of shots at relatively high power. In typical fast action sports shooting, setting the power to around 1/10 power (64WS) will allow frame rates or bursts on the order of 5 to10 frames per second with excellent frame to frame consistency and extremely sharp action freezing.

REAR PANEL CONTROLS AND DISPLAY: In normal operation, the illuminated LCD display reverts to "FLASH MODE", as indicated by the blue icon box. Assuming the model lamp is set to TRACK FLASH mode, operating the ADJUST UP/DOWN buttons will raise or lower flash power in 1/10f increments per click. Holding one of the ADJUST buttons in will cause scrolling. The modeling lamp will follow the flash power for what-you-see-is-what-you-get (WYSIWYG) modeling previews. At each of the 90 possible power settings, the power reduction relative to full power, current t.1 color temperature, current t.1 flash duration, current flash WS, current Modeling watts and current EU reference number are all displayed. All functions of EINSTEIN 640 are accessible from Cyber Commander and the above mentioned parameter is also shown on the Cyber Commander LCD.


Pressing the function button cycles through the other LCD sub screens to allow the user to set the desired function of each parameter, turning the selection function sub screen blue for identification.

MODEL SUB SCREEN: Notice the second sub screen (MODEL LAMP) is currently -0.2f below Full brightness, as is the flash. Assuming the Model Lamp is set to track flash, operating the ADJUST buttons while in the MODEL sub screen will introduce an offset between the model intensity and flash power. The Model will still track the flash, but with a different relationship of Model Watts to Flash WS. This allows the user to set this ratio match that of a different light(s) that might be in use so as to enable WYSIWYG modeling between dissimilar flash units. In past systems accomplishing this required physically changing the wattage of the modeling lamps.. If the Modeling lamp is set to be separately adjustable from the flash, operating the ADJUST button will independently raise or lower the modeling lamp intensity.

After selecting any of the sub screens, the LCD will automatically return to the flash sub screen in ten seconds as this is the primary screen used for using the EINSTEIN 640 once the parameter are set to the user's needs.

POWER SWITCH: EINSTEIN 640 functions like a modern TV. That is, when turned OFF the Transceiver module remains powered. Because of this, the EINSTEIN can be remotely powered off or on from Cyber Commander. All current settings are remembered when the unit is powered off or unplugged. Thus, in a studio using multiple EINSTEIN lights and Cyber Commander, the user can shut down all the lights from the Cyber Commander when a session is finished, and turn them all back on the next day, also from the Cyber Commander.

REMAINING SUB SCREENS: The remaining sub screens allow the user to set the parameters of each function shown, including the Frequency and Channel used to communicate with Cyber Commander.

EASY SET: This is a recessed button used for instant setup to the most commonly used function parameters. When the Easy Set button is pushed, EINSTEIN 640 is set as follows:

Model lamp tracks flashpower with no offset.
Ready State is indicated by both modeling lamp dimming and by the beeper.
The slave sensor is turned On,
The unit is set to Constant Color mode,
The Transceiver Channel and Frequency are both set to "1"

Thus, EINSTEIN is ready to use in plug and play fashion for most users. After pushing the EASY SET button the user can then use the function button to change any of the settings mentioned.

MICRO SD CARD SLOT: EINSTEIN 640 features a plug in slot for inserting a standard 2GB Micro SD card. This is used to upgrade the firmware via download or email should added features be added in the future,

NOT SHOWN: EINSTEIN 640 also contains additional menu screens that allow the user to upgrade firmware, to set the LCD brightness, to set the delay time before reverting to the flash sub screen and to perform other advanced setup information as yet to be defined.

COLORS AND MODELS: Initially, EINSTEIN will be offered in only one model (640WS) and only in black. This is because of the exceedingly low 2.5WS minimum power and the relatively small cost advantage gained by offering a lower power version. Another factor is that, unlike in AlienBees, Zeus or White Lightning and most competitive models, shorter flash durations are obtained from a 640WS Einstein than could be obtained from a lower powered EINSTEIN.

SIZE AND WEIGHT: EINSTEIN 640 is approximately the same size as AlienBees B1600 and very slightly heavier due to the all-stainless-steel improved accessory mount and the Pyrex frosted dome. The dome and lamps are removable and user replaceable. A thermostatically controlled high velocity fan and improved air flow, coupled with multiple internal heat sensors and circuit fault detection assure reliable performance under the most demanding commercial shooting.

The information presented here is preliminary and deemed accurate, but is subject to possible change.

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