Photography & technology ” Buying which flash system ?”


Which flash system should I buy ?

A question that I hear at least once a week, and I cannot answer the question.

Its like asking “ Which car do I buy?”.   It is impossible to answer without knowing the photography requirements, besides the available budget.

There are “high end” and “low end” products and so is he price. Obviously there is a difference in quality.  If the difference in quality warrants the higher cost is another question.

I will not try to convince you to buy one or another brand.  Instead, this article addresses the parameters that define the quality of a flash unit. It is up to the reader to figure out what is best suited for his or her needs.  Some might need short flash charge times, other will be focused on the stability of the light temperature.

Recap 

Before we dig into the technical specifications , lets have  a look at the functional diagram and the associated functions.

flash.001

The flash unit is an electronic device consisting of six major functional area’s;

Flash Bulb:  Responsible for creating the flash light

Capacitor: A storage reservoir for a controlled and measured electrical charge.

Charge Controller: Electronic circuitry that controls the load of the capacitor

Power Supply: Feeds the entire flash unit (capacitor and all circuitry)

Trigger system: Controls the discharge of the capacitor  and triggers the flash

Controls: Human interface to set the values

When power is applied either through a battery or mains supply, the unit starts up and the internal power supply feeds the electronic circuitry.  The operator dials in the desired flash strength through pushbuttons, dial wheel ,keyboard or whatever method is available. The Charge controller translates the desired flash strength in Joule (measure of power) and starts to load the capacitor with a specific charge (electrical load).  The capacitor is  a big reservoir and stores the energy.  Once the charge cycle is complete the unit is ready to be triggered.  Triggering can be through a wireless or cabled system and is driven by the sync pulse of the camera (flash contacts).  The trigger system activates the discharge switch,  the capacitor discharges across the flash bulb. The intensity  of the light is determent by the load of the capacitor. The discharge pulse is controlled by the discharge control circuitry and for matters of simplicity that is part of the trigger system in this example.  The unit has now produced a flash, after the completion the cycle starts all over .  The Charge controller reloads the capacitor, when completed it, the trigger logic is signaled and the next shot can be taken.

Characteristics of a Flash unit

The flash characteristics determine the quality and stability of the light and  not to forget the cost.

Flash stability: The capacitor is an electronic component that can be loaded with an electrical charge  (electrons) and be quickly discharged across the flashbulb. The charge must be measurable and accurate, based on the operator input. Hence the capacitor is the most important element.

Low-end flash units will use less quality capacitors, they will be slower to load and discharge.

Capacitors have what is called a “leak current”, that is a drain of electrons (charge) that leaks through the dielectrium .Just like a glass of water that has a leak.  The leak current determines how long a charge can be retained.  Low-end flash units suffer from higher leak currents and are therefore far less stable in terms of light intensity and  consistency.  That means that the initial loaded charge will be reduced over time and when sufficient time has elapsed  an offset on the exposure can be noticed. Low-end devices will have a limited range of charges that can be applied, especially in the low power range.  The reason is that the discharge time of a capacitor is much longer at low charges then at high charges. Low end flash units use fewer  and lower grade capacitors for cost reasons; high-end flash units have multiple capacitors that can be cascaded, allowing for granular and very low Loads.

All electronic components have a “tolerance”.  This is a defined variation that can occur under certain circumstances.  For instance a resistor can change it value based on the ambient temperature.  Those who have been shooting with flash units will know that they can become very hot.  Low-end flash units will exhibit a much bigger drift due to the heath and the lack of sufficient compensation circuitry, poor design and lower quality components.

So what does this mean?  If you require fine power adjustments, high stability and minimum drift under high operating temperatures. Then do not buy a low-end device.

Flash temperature and shift; Flash bulbs are nothing more then a thin wire made out of special material.  When an electrical charge is applied to the wire, current flows through the wire and results in heath and light.  We all know that the light temperature is a very important factor in Photography as it determines the white balance.  Flash units should be near to daylight .  Hence most flash bulbs will produce a flash with a light temperature of about 5300 degree’s Kelvin. Low-end devices tend to suffer from 8 to 10% variation, hence light temperature coherence is very often a problem and varies with the power setting and operating temperature.  They also tend to create red and magenta colors, while the flash is dimming (see pulse shape).

What does this mean? If light temperature consistency is important go for a high-end flash unit, unless you want to shoot a shot of a gray card for each following picture.  Check that the light temperature is stated, and across the power range.

The light temperature and tolerances are typical announced in the technical specifications.  If they are not, be aware.

Charge time; The capacitor is key and defines the time it takes to load the charge. In between each flash the capacitor(s) needs to load a new charge.  The time it takes will depend on the selected charge (power level) and the quality of the capacitors and the charge control circuitry.  Low-end devices often require more then a second and will show a big difference in “load time” for high and low power settings.  If you require to shoot at a high frame rate, it can be very annoying having to wait for the units to be ready.  Typically you can set a “Ready” warning signal such as a “beep”.

Be aware for products that are cheap and still pretend to have short charging times, often they take a shortcut by charging quickly but with an inaccurate  charge volume. High end products have charge times as low as 0,2 seconds. When checking load times make sure that the specification refers to a 100% load.

If time is not a concern, why not buying units with a longer charge time.

Note that load accuracy and load times are hard to combine, just try  to poor water in a glass as fast as you can and stop at a set marker. Guaranteed that you will either overshoot or undershoot the marker.

 Flash pulse; the duration of the flash pulse is a very important element. When the trigger system discharges the capacitor is very quickly discharged across the flashbulb producing the flash.  There is an industrial specification for the pulse shape, those are commonly referred to as T.5 and T.1 .

t

The flash duration is defined with two numbers: T.5 is the length of time for which the flash impulse is above 0.5 (50%) of the peak intensity, while T.1 is the length of time for which the impulse is above 0.1 (10%) . On flash units with a capacitor discharge, the T.5 and T.1 numbers increase as the intensity decreases (i.e. takes longer for the capacitor to discharge to that point). These times become important if a person wants to freeze action with the flash (as in sports).

Remember that most DSLR have a typical Flash sync speed of 1/125 sec.  Some can go up a bit higher,  pro cameras such as the Hasselblad and the Phase One can reach flash sync speed s of 1/1800 sec.

That means that a normal DSLR will have an exposed sensor for 1/125sec, and during that period the flash unit has to go off.  It is the  T.5 pulse time that freezes the object/subject action/movement. I call that the “virtual shutter speed”.  That is why you can freeze a jumping person with a camera shutter setting of 1/125 second.

How fast the virtual shutter (T.5 pulse time) is depends on the flash unit. Low-end devices have long T.5 pulses  (Elfo 1/400 sec) , where as high end device have often adjustable lengths (Broncolor Move upto 1/20000sec).

If it is required to shoot with a high-speed sync shutter, then ” low end” devices will not swing it. Because the T.5 Pulse will only fall partial within the camera shutter speed.  If the camera is set to a flash sync of 1/1200 sec, then a flash unit with a T.5 of 1/400  will result in exposure loss.

If your camera can not be set to high speed sync values faster then 1/250 sec, then I would not worry to much about the low end  T.5  flash units. If your camera can shoot high sync speed rates (1/1800), then you should use a high-end flash unit with adjustable T.5 durations.

 Trigger control; Some units come with trigger cords only, others with infra red or radio. Today some can even be adjusted remotely over radio or  WIFI.

There are products on the market that provide wireless transceivers that can be attached to your camera and the flash units. Professional cameras have build-in radio triggers. Unfortunately there is no common standard and most vendors have a proprietary system.

Depending on your use, one or the other option might be better.  I do like the radio controlled duplex systems proving two communication and zoning.

Power –  watts second – Joule;  The amount of watts per second or joules are a determining  factor for the price.  Guess why?  Indeed the size of the capacitor.

How much power is needed and what should the range be?  Well that depends on your use.  If you shoot portraits mainly in the studio then a 400 to 600 Watts second unit will do.  If you shoot often outside and in bright ambient light conditions, then you might have to step up too 1200 Watts second blocks.

Typical the power is expressed  in Joules or Watts second. Often you will find a statement referring to a F stop at 1 meter distance from the unit.

Adjustments; As a photographer you might want to adjust the intensity (power-stops) of light that the flash produces.   The means to set it comes in many flavors, push buttons, dials, soft buttons etc….  The most important factor is the lowest setting, the highest setting and the ability to increase or decrease the settings  in steps.  Low-end units tend to be limited in to x amount of steps, and often increase/decrease in full stops. High-end products have typical a coarse and fine adjustment allowing precise adjustments.  Besides the power adjustments several other features and operating modes can be available, such as setting the radio channels and groups, storing settings etc…..  Again, one should select what is important .

Pilot light; A very nice feature that allows the photographer to judge the effect of the flash before the actual shot through the use of continues light (pilot light) .  They come as halogen, led, wolfram  lamps and are embedded in the flashunit near the flashbulb. It has the advantage that in the dark studio the subject is always lit , making it easy for the camera to focus .

The pilot light can be controlled by the photographer, some will allow for a step less power adjustment , others are  On/Off or step wise.  The better devices have a proportional pilot light.  Meaning that the pilot light will automatically adjust, proportional to the selected flash volume.  I do find this a very handy feature.  Again it depends on what is important in your workflow.

Light shapers; They come in all forms an shapes, the main issue is the physical connection  between the softbox (light shaper) and the flash unit.  Avoid proprietary mechanisms from small and unknown brands. Well known brands have their own fittings, however you will be able to find all kind of adaptor rings.

The low end products tend to have a limited choice of light shapers and the use of well know light shaper brands is virtual impossible due to the lack of adaptor rings.

 Power supply: Flash units come as mono blocks or packs and Lamps. Mono blocks  contain all elements such as the power source (mains or battery ), control circuitry  and so on , all within one enclosure.   Where as packs typically have all the elements in one enclosure except the flashbulb. Which type is best depends on your use.   Packs are very common with professional photographers and very handy for shooting on location. Especially packs with batteries.

There are for sure many more aspect that need to be considered when selecting a flash unit, often we tend to forget the support ,  high end products tend to provide very good support , where as the low-end products are more “as is” with little to no support.

I have owned many different types, and like most of us , I started with some cheap low-end units “Elfo”.  They were OK , but while your grow , you keep improving your work.  I then moved on to Elinchron , not bad at all . However at that time I missed the mobility and the battery based kit was not available.   So Prio-light seemed the obvious choice . Great Mono blocks with build in batteries.  No more worries about cables. However very poor support, a new product with to many children deceases, all four units failed within the first four months.  Finally I moved to Broncolor “Move” the best choice I ever made.  If I had known all the aspects from the beginning, I would have gone for a high-end solution from the start.

So, which flash pack should you buy ?  It is your call and all depends on what has priority in your workflow.

Thanks for reading,

Steve

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