I used to base my choice of flash gun mostly on how much power it can push out. If I was interested in a flash gun of GN64 I would most likely walk past it in favor of one with GN66 in the spec. Now I see that as being irrelevant. I found that in actual use, I was using the flash gun at it’s lower power settings most of the time. So I didn’t really need to highest GN number.
Picture a car with a top speed of 120 mph. Yes, it can hit 120 but you have to really push it hard and it will be quite slow to get there.
Much better to run it at 60 mph or so – it will be very good in this area. If you want to go faster that 120 mph, get a car that can go to 180 mph and apply the same logic.
And so it is with flash. Let me explain by way of a brief refresher…
What Does The Flash Capacitor Do?
Your flashgun uses a flash tube for it’s high-intensity short duration flash. This tube needs a high voltage to trigger it. This high voltage is generated from the internal batteries. If you listen to the flashgun when you switch it on, the whine you hear is the high voltage generator working. But the high voltage generator is not powerful enough to drive the flash tube by itself, so it ‘fills’ a high voltage capacitor – which becomes a reservoir of power for the flash tube.
Once the reservoir is full, the red light on your flash will turn green. The whine will stop or become very much quieter. Your flashgun is ready to use.
When you trigger the flash, the capacitor dumps its energy into the flash tube. When the capacitor reservoir is empty, the tube will extinguish and the capacitor will start charging again – you will hear the whine kick-in again.
But it doesn’t stop there…
If you decide to use the flashgun at a lower setting, you don’t need to empty the capacitor’s reservoir. So there are some clever electronics in the flashgun that will stop the capacitor dumping any more energy from its reservoir when enough light has been produced.
So when the high voltage generator starts to charge the capacitor again, the whine will be quieter but more importantly it will take less time to fill the reservoir because it’s not filling from empty. At the lowest power settings, the recharge can appear to be almost instantaneous.
Run your flash at full power
If you run your flashgun at full power, as well as getting the mega-blast of light, the first thing you will notice is the recharge time begin to increase. Soon it could be 10 seconds between flashes, and when you’re waiting – and your model is waiting, 10 seconds is a long time. So for full-power shooting, be sure to have spare batteries and a patient model with you.
If you are running mostly at full power then you can examine a few options…
- You could add more flash guns. If you add another similar flash gun this will give you one more stop of light.
- You could upgrade to larger flash guns or even studio strobes. These are less powerful – and are normally mains-powered, but can give a lot more light output than portable flash guns.
- You could use an external battery pack, if your flash gun can run with them. This will allow you to use more powerful batteries to reduce the recycle time and allow you to use the flash gun longer between battery changes.
Reduce your flash power by 3 or 4 stops
Running your flashgun at a lower power output will increase the number of flashes you can get from a charge, but more importantly it will reduce the recharge time for the flashgun so it is ready for the next photo almost as soon as you are.
What has all this to do with Guide Numbers?
If you are already running your flashgun at reduced power, then the full-power capabilities are immaterial.
If you need the extra power, maybe you should re-think your flash placement. If you’re shooting one or two people then you should be ok. If you’re shooting a group of 20 people or more then it might be better if you use multiple flashes with each flash concentrating one one part of the group. If you’re shooting someone who is quite far from the camera, you could move the flashgun closer to the subject without moving the camera – just ensure you can’t see the flashgun in the viewfinder.
If none of these things are work and you still need more power, it sounds like you should be running multiple flash units or maybe a higher-power studio flash is what you need.
If you have placed the flashgun in a softbox or are shooting through an umbrella, you will lose a few stops of light. In fact, as soon as you start modifying the light from the flash gun, you will start to reduce its intensity.
If you’re thinking of adding extra flashguns, remember that running two flash units will give you one stop more light. If you want two stops more, then you’ll need four flashguns! It could be much easier to get the extra stops by increasing the ISO setting on your camera!