I have a particular interest in camera flash, as there are times where it could get a shot which would otherwise be impossible even with slower shutter speeds and high ISO.
This is particularly so with UV-imaging because:
1) The wind can cause movement of the flower and hence introduce motion blur into the image
2) There may be insufficient available light e.g. flower in dark shade
3) Flowers partly in shade and partly lit by direct sunlight, resulting in uneven lighting; using a flash will allow more even lighting
Downside of using flash:
1) Where subjects have higher reflective surfaces, it can result in ‘hotspots’ in the image where the highlights are blown
2) The background will receive very little UV and hence be much darker than images lit by sunlight
3) The Flash needs to be sufficiently powerful (and hence more bulky), otherwise there will be a need for higher ISOs and larger apertures used.
Do note that you will need a custom whitebalance for flash-illuminated images, as the whitebalance will be different from sunlight.
These are some of the Xenon flash I have found to be useful for UV-imaging:
1) Olympus FL-36R (safe sync voltage, can be modded for UV – I have done it)
2) Olympus FL-300R (safe sync voltage, head can be angled down for macro, follow link to mod page here)
Need extra power? How about 4 of these triggered wirelessly?
3) Canon 177A (safe sync voltage, less powerful and fixed head position)
4) Canon 199A (safe sync voltage, follow link to mod page here)
Now this is UV power. 4 x Canon 199A (each of these has more UV output than the Vivitar 283/285)
5) Rollei 134 REB (has high sync voltage so can fry many modern camera circuitry – needs to be used with Wein safe sync, but more powerful UV output than the Canon 199A)
6) Quantum T5DR 150Ws uncoated Xenon flash (safe sync voltage but requires external battery pack to use)
7) Quantum X2D 400Ws uncoated Xenon flash (safe sync voltage, click here for separate thread on my Quantum X2D setup)
8) Cokin creative ring flash – not actually a ring flash as it comprises 3 separate heads which can be angled as required. It has a trigger voltage of 10.5V, which is safe to use on my Olympus cameras, but may be too high for other maker’s cameras. It has long been out of production, and many people are not aware of its presence, but occasionally it does pop up on eBay.
I have used the Vivitar 283/285, but did not mention them above as they are already well known in the UV community. I have also tried the smaller models from Rollei, which do output UV but are less powerful and have high sync voltages.