This blog entry is extremely long, and it also has all the usual, boring data – but it’s this data that shows the strengths and weaknesses of the products, so please bear with me…
What we’re testing here, apart from the usual and very important technical aspects such as flash energy consistency and colour temperature consistency, is flash duration and recycling speed.
Flash duration is perhaps the most important feature here, the IGBT (Insulated-gate bipolar transistor) technology gives it the incredibly short flash durations that allow it to freeze action. These very short flash durations make it easy to produce shots like this.
And of course, with very fast flash durations it’s possible to freeze much faster action than this.
These shots are an example, they were taken using a Nikon D3, firing in continuous mode at 8 frames a second – but the SuperFast flash heads can recycle even faster than that, and you can easily end up with a sequence of shots where several of them work well, making the process of capturing fast action much easier and quicker than with a conventional flash head.
What I’m doing in this blog is to show you how we tested the flash heads, and what those tests actually show.
Let’s start off with flash duration. A lot of people are confused by the jargon used to describe just how long the flash lasts.
Flash durations are normally expressed as either t.1 or t.5. But what does this mean?
When the flash is fired the tube output quickly rises to its maximum brightness. This is followed by a decline in light as the capacitors are discharged to zero.
The standard engineering term for stating flash duration is “t.5”. This describes the time it takes for 50% of the total flashpower to be discharged. Whenever the simple designation “Flash Duration” is used it’s usually safe to assume that the figure is quote is t.5. The reason for this is that this is the usual way that manufacturers describe the duration of their flash heads, and the artificially high t.5 figure probably suits them too.
But the t.5 spec doesn’t actually predict the actual motion freezing capability of a flash. There is a much longer trailing edge that carries on discharging the remaining 50% of the light, and which affects the shot because the camera shutter is normally still open. This causes a lot more motion blur than the t.5 spec implies. In order to match the flash duration to an equivalent shutter speed, the term “t.1” was introduced by the photo industry. t.1 specifies the time it takes for 90% of the total flash to be discharged. But even following the t.1 time there is still a little light being discharged, and this can cause some blur, although generally it isn’t obvious or even visible. My suspicion is that many manufacturers, and most resellers, don’t test flash durations at all. They just quote figures that are very unlikely to be accurate. If they did test them, then surely they would explain how the tests were carried out and show the results instead of just quoting impossibly good figures that most of their customers can’t verify for themselves…
Basically there are two possible testing methods, the scientific one and the practical one:)
The scientific method involves using an oscilloscope to actually measure the duration of the flash. This is a meaningful method to anyone who is involved with either electronic engineering or physics but it isn’t perfect because
- Many people find it hard to understand oscilloscope trace readings.
- Many people find it hard to interpret the actual info and relate it to action-stopping potential
- Most people don’t have access to an oscilloscope, so they can’t check the accuracy for themselves – and their use requires training.
- Most oscilloscopes can’t measure any flash duration shorter than about 1/5000th second, so their use is pointless with the SuperFast.
So, here at Lencarta we have moved over to a method that we believe to be far more useful – we photograph a revolving disk, it’s a CD, fitted to the spindle of a fan. This method produces more meaningful results because people can see just how well the flash freezes the movement of the disk – and they can, if they wish, check it themselves – fans cost a lot less and are far easier to use as a testing tool than an oscilloscope.
The theoretical flash duration figures don’t really matter. What matters is how well a flash head can freeze action, so we demonstrate this by taking a photo of the stationary disk, just as a benchmark. Total lack of blur is obviously something that can’t be achieved, but it”s good to know what we’re aiming for.
And then by taking a series of photos at various shutter speeds, starting at 1/250th second and going up to the maximum available on the camera, in this case 1/8000th second. These pictures show just how much blur appears at each shutter speed, and this degree of blur can then be compared to the blur created by the flash head. Of course, we have to use continuous lighting for these shots, and although we use the most powerful continuous lighting available to us, the Lencarta LED studio head, we have to turn the ISO up very high – to 6400 ISO on the 1/8000th second shots.
Here’s a shot of the revolving disk, taken at 1/8000th second.
It’s then easy to compare the photo with flash to the photo that most closely matches it for subject blur, taken without flash at a given shutter speed. If, for example, a photo without flash at say 1/8000th second has about the same amount of blur as a photo with flash, then it’s safe to say that you’ll get a very similar result with that flash as you would get without flash outdoors at 1/8000th second, so the effective flash duration is about 1/8000th second even though the t.5 flash duration may be very different.
As the shutter speed increases, there is obvious lateral movement. This shows even at 1/8000th second, and we can see that there’s a bit more to it than that – even though the very fast shutter speed of 1/8000th second has almost frozen the movement, the numbers on the disk have travelled quite some distance while the tiny slit in the shutter was moving through its cycle, causing distortion. A lot of people probably don’t realise that this happens, and that ultra-fast shutter speeds inevitably distort the shape of the subject. It’s worth googling “focal plane shutter distortion examples” to see what can happen when relying on a focal plane shutter to freeze movement – copyright law doesn’t allow us to post these images, but here are a few I found
The horizontal distortion in the old racing car shots is obvious, and is exaggerated by the fact that the old large format cameras used back then had a very long shutter travel. Jaques-Henri Lartigue took the iconic distortion shot in 1912, but the recent shot of the helicopter blades proves that the problem hasn’t gone away. Fast flash completely overcomes this problem and, whenever we have a choice of using a very short flash duration at normal shutter speeds or a normal flash duration at very high shutter speeds, the short flash duration wins every time.
Most other testers use a similar testing method to our own. For example, the Advanced Photographer magazine uses a spinning disk, photographing the edge rather than the face, to achieve a similar real-world test result. This image, courtesy of Bright Publishing, shows the SuperFast tested on their spinning disk. Again, the shutter distortion is very obvious
Recycling time is important too. If we use the SuperFast at full power, or something close to full power, then the recycling time is roughly similar to that of a conventional flash head, because we don’t get the benefits of IGBT technology until we reduce the power setting. It’s when we reduce the power setting that the flash heads recycle quickly enough for even the fastest DSLR cameras to fire in burst mode, for bursts of up to 3 seconds at a time.
Recycling time is pretty hard to measure, but it’s very easy to calculate. Just bear in mind that the reason that the SuperFast (and our Atom flashgun) use IGBT technology that quenches the flash as soon as the required amount of power has been discharged, leaving the unused power sitting in the capacitors ready for the next shot. Therefore, at half power the SuperFast (or Atom) will recycle twice as quickly as at full power, at 1/32nd power it will recycle 32 times as quickly and so on. This is why our SuperFast and Atom models can be used in “machine gun” mode at low power – the SuperFast will be able to keep up with a camera shooting 20 frames a second if one ever becomes available, and the Atom, which reduces right down to 1/128th power, can do even better!
Of course, all other IGBT flashes, including other makes and hotshoe flashguns, also benefit from very fast recycling when the power is turned down. But if they start off with very long recycling times at full power, they never get to the point where they can recycle really quickly, even at their lowest power settings.
Power consistency, or flash energy consistency, is the consistency of output between one flash and the next, at any given power setting. On some makes, this can vary by up to 120%, which is hopeless.
The SuperFast flash heads have a remarkable range of adjustment. We test the output consistency at the same time as testing for the guide number.
Testing the two SuperFast models at full, half, quarter, one eighth, one sixteenth and one thirtysecond power produced results that varied by no more than 1/10th of a stop.
To put those figures into perspective, 1/10th of a stop is the smallest incremental measurement of our industry-standard Minolta flash meter, and for all we know, the actual variation may be 1/20th, 1/30th or 1/6th stop, the meter just can’t measure that precisely because it just doesn’t matter. In reality, even if you photograph something really unforgiving, like a plain white wall, you won’t notice an exposure error of less than 1/3rd of a stop.
In theory, both models of flash head have the 5 stops of adjustment mentioned above, but in reality they both have far more; the SuperFast 300 has 6.6 stops of adjustment and the SuperFast 600 has 7.4 stops – a truly massive range.
With each head, if it is turned down to the very lowest possible power setting then there will be some inconsistency in flash energy, caused by the extremely low operating voltage, but it’s still within acceptable limits and is still better than the normal performance of most of our competitors.
There are 3 important areas to test here, and all tests were carried out using a Minolta Colour temperature meter:
- Actual colour temperature – 5600K
- Consistency between shots – 20K
- Variation at different power settings – 100K maximum, between minimum and maximum power.
You may wonder how we have achieved our own figures, and it’s a fair question because although the great benefit of IGBT technology is that the tail of the flash is cut off, or quenched at low power settings, making very short flash durations possible, the downside is that the tail that’s cut off becomes increasingly red as the flash dies out, creating a balanced colour temperature. Therefore, with IGBT, the colour temperature tends to become progressively more blue as the power setting is reduced. On some flash heads, this produces a colour temperature variation as high as 1000 K, which is totally unacceptable.
On the Lencarta SuperFast flash heads though, colour temperature variation is controlled extremely well, and this is achieved by reducing the input voltage as the power setting is reduced.
In the real world, unless you’re a top end advertising photographer photographing white ice cream against a white background, and have the world’s most demanding clients, you won’t notice any colour temperature variation of less than about 300K!
Again, many re-sellers of flash equipment seem to make wild statements, such as +/- 100K. These figures are wonderful, but I’ve never managed to verify them when I’ve tested their products with a colour temperature meter.