The best shutter speed for indoor flash

Normal shutter speed (1/125th second)

Normal shutter speed (1/125th second)

When you’re using flash in the studio, and if you haven’t got incredibly bright overhead lighting, and if you haven’t got sunlight streaming through the windows, just about any shutter speed that works will do fine, because the only real thing that the shutter has to do is to be open with the flash fires.

I’d better explain that…
When we use a camera that has a standard focal plane shutter, the shutter consists of two separate ‘curtains’ – the first curtain opens, leaving the way clear for the light from the lens to enter and expose the sensor (or film). If you have set a shutter speed of say 1 second, what happens is that 1 second after that first

1 second exposure, contaminated by ambient light

1 second exposure, contaminated by ambient light

curtain opens, the second curtain will close and will block the light – leaving you with an exposure of 1 second. Obviously if we actually used a 1 second exposure (which I did in the shot below) there would be more than enough ambient light to mess up the shot in normal indoor lighting, so we use a shutter speed that is slow enough for the flash to do its job but fast enough to make the normal indoor lighting level irrelevant – something like 1/125th second.

It will vary from camera model to camera model, but if you choose too fast a fast shutter speed, there will come a point where the second shutter curtain starts to close before the first curtain has completed its travel. When that happens, part of the sensor or film will

1/500th second, showing second shutter curtain in shot

1/500th second, showing second shutter curtain in shot

be covered when the flash fires, and that part won’t be exposed by the flash.  What you’ll see in that situation is a black area in the shot, which of course you want to avoid. This is shown in the shot below, with the shutter speed set at 1/500th second.

Cameras vary, some have powerful, fast shutters and some don’t. Some have large sensors, which require a faster shutter mechanism to operate than on a camera that has a small sensor, and some have small sensors. Because of these variations, I can’t tell you for certain which shutter speeds will be ‘safe’ for you and which will result in an area with no flash exposure (black line). See your camera manual for info on the theoretical maximum sync speed for your camera.

But, as a rough guide, most modern DSLR cameras are OK at 1/200th second, and some can go a bit faster than that.

So should you use the fastest possible shutter speed for your camera in the studio?
Well, you can if you like, but it’s pointless, and prone to error.
It’s pointless because, in a fairly dark area with a low level of ambient10 lighting, the lighting that is there won’t make a scrap of difference to your flash exposure, so there is no point in using a fast shutter speed that blocks out the effect of ambient light that is at such a low level that it doesn’t actually have any effect. You can test this very easily – just set up a shot that you’re going to take with flash, then switch off the flash and take it using just the room lighting. If the image is completely black, the ambient light isn’t affecting the shot in any way. This is what I did with the shot on the left, there is just enough contamination from the ambient light here to affect the shot – and if it had been a moving subject then there would have been enough ambient light to show motion blur too – but it took a shutter speed of just 1/10th second to introduce this much contamination. So, for most people, most of the time and in most studio situations, it won’t make a scrap of difference if the shutter speed is set somewhere between 1/30th and 1/125th second.

And, when used with flash, it isn’t the shutter speed that freezes movement anyway, it’s the flash duration that does that. The ONLY  real function of the shutter is to be fully open when the flash fires!

And it’s prone to error because if the shutter speed selector is at the maximum sync speed for your camera, and accidentally gets moved during the studio session (which happens all the time) you may think that you’ve been shooting at 1/200th but find out later that you’ve actually been shooting at 1/400th, the only thing that you’ll be able to do with those shots is to move them into the recycle bin…

So, I normally shoot at 1/125th, which is  a safe, reliable shutter speed for studio use. And, if the setting gets accidentally knocked a couple of notches higher, it won’t matter.

Radio trigger delays
Most of us use a radio trigger to fire our flashes, and with good reason. If you have a Lencarta radio trigger (or any other good quality make) then it should be OK even at the maximum flash sync speed for your camera (if you really want to use the maximum speed) – unless the radio trigger batteries are getting a bit tired – but the cheap and cheerful triggers sold on auction sites often don’t work at higher shutter speeds, because there is a built in delay due to bad circuitry, and the flash will only sync at a very slow shutter speed.

“High Speed” radio triggers
There are now lots of different brands of radio triggers that can be used at any shutter speed, right up to the camera’s maximum. These triggers are currently only available to suit either Canon or Nikon cameras, and basically they delay the firing of the flash until the shutter has started to open. They rely on the flash having a long duration, and use the long tail of the flash as it loses power. Because of this, although different manufacturers use different terminology to describe their products, they are generically known  as tail end sync triggers.
Do they work? Yes.
Do they work perfectly? No, because a lot of the flash power is used in the process, and because the illumination from the flash decays during the time that it takes for the camera shutter to complete its cycle, and because of this there can be a very substantial uneveness of exposure, from the top to the bottom of the frame – sometimes as much as 4 stops of light!
Are they worth having? Not normally in the studio, for all the reasons I’ve already given you, although if you really want to freeze action and if you haven’t got the right tool for the job for freezing action – a Lencarta SuperFast – they can be used with a very fast shutter speed with an ordinary flash, to freeze action by using a fast shutter speed instead of a fast flash. But tail end sync triggers are a very useful tool when using flash outdoors in bright light, and we’ll go into that in the next article.