When you use a flash, the shutter speed is not that important. Since the flash fires all its power in 1/1000th sec or less, it is not important whether your shutter speed is 1/200th second, or 1/100th, or 1/4 second. Only the ambient light will be affected; not the flash part.
Take this, from a Goldcorp goldmine I shot earlier this year in Timmins, Ontario:
3200 ISO, f/4, and 1/4 second. Handheld.
Why so long? Because I wanted the light at the end of the tunnel to look like, well, the light at the end of the tunnel. And I needed f/4 for depth of field, hence 3200 ISO and 1/4 second.
But Michael, things will be blurry!
Not if they are lit by the flash. 1/1000th sec is 1/1000th sec! And if they are also lit by a little ambient light, then a little ghosting will appear, mainly in the moving parts:
But that is still better than not having any background light. So I shot the goldmine at slow shutter speed, and you should feel free to try the same. Here I did it to capture the hard hat lights:
Use a wider lens, and go slow, even very slow, any time you are using flash and it’s mainly flash lighting the important bits!
Nikon calls it “slow flash” when you use a slow shutter speed while using flash. You engage this in semi-automatic and automatic camera modes (P and A) by pressing the flash button an turning the wheel until you see the word “slow” on the top LCD display in the flash area.
This is a misnomer. The flash is fast – in the order of 1/1000th second. It is the shutter that is allowed to be slow in this “mode” (really just a technique). That is why another, more correct, term for this technique is “dragging the shutter”.
And you want to do that why? As readers here now, you want that in order to allow enough ambient light in, to avoid those dark backgrounds.
But can you use a slow shutter speed when using flash? Surely a shot at, say, 1/30th second will be all blurry?
Not necessarily. While there may be a little ghosting, if your subject is mainly lit by the flash, it will be as though it was shot at 1/1000th second.
That is why “slow flash” is such an unfortunate misnomer: it is”fast flash in a slow shutter image”. Which is why the Willems 444 Rule for indoors flash (400 ISO, 1/40th sec, f/4) usually results in crisp images. Have you tried it yet?
A quick note for you today (and this is the kind of thing my students learn at length in my advanced courses, like the one tomorrow in Mono – there’s still some space).
Every had your camera react unpredictably when using flash? Yeah, I thought so. You flash and then the shutter stays open for a second and it’s all a blur. Or you flash and the background is dark black.
When you shoot indoors, say, and use your flash, your camera behaves differently in different modes – and this behaviour varies per camera.
Aperture mode (A/Av):
- Canon: the shutter will be as slow as needed to expose the background too (caution: this may lead to very long shutter speeds if ambient light is low).
- Nikon: the shutter is restricted to 1/60th of a second or faster (this can be set). But… if you also engage “SLOW” mode, the shutter will be as slow as needed to expose the background too (caution: this may lead to very long shutter speeds if ambient light is low).
Program mode (P):
- Canon: the shutter is restricted to 1/60th of a second or faster.
- Nikon: the shutter is restricted to 1/60th of a second or faster (this can be set). But… if you also engage “SLOW” mode, the shutter will be as slow as needed to expose the background too (caution: this may lead to very long shutter speeds if ambient light is low). .
- Canon is simple: Av = long shutter speeds, P = 1/60th or faster.
- On Nikon cameras, both modes are restricted to 1/60 or faster normally, but either mode can be freed from this by using the “SLOW” setting.
So what is the best mode when using flash indoors?
Ah, that would be Manual. That way the camera does exactly what you want. But we will get to this again another day.
TIP: if you want to try Manual indoors flash, start at 400 ISO, 1/30th second, f/4. And bounce your flash off the ceiling/wall behind you.
So you are surprised that your flash pictures always turn out differently and unpredictably, especially when using automatic (“TTL”) flash?
Then this may help:
A. First, worry about the background, ambient light:
- First, decide “should the background light do any work?”. If you are using an automatic or semi-automatic mode, like P, Av/A or Tv/S, the camera will try to light the background well. so it will not just be the flash doing the lighting.
- Realise that there are limits to the previous: on Canon always in P mode, and on Nikon in P and A when “Slow Flash” is disabled, the camera will limit shutter speed to avoid blur.
- So if you want total predictability of the background, use manual, and set your meter to the desired ambient lighting level (I recommend you start at -2 stops, i.e. the light meter points to “-2″). See a recipe below.
In a typical room, a starting point might be 1/30th second, f/2.8, 400 ISO, and the flash pointed behind you. Auto ISO is not recommended!
B. Then, concern yourself with the flash:
- The foreground is mainly lit by flash, not by your Av/Tv/ISO settings.
- Canon cameras in particular try to avoid overexposing part of the picture, so even a small reflective object in the flash picture can result in a dark, mainly underexposed photo.
- The flash exposure metering is, on most cameras, biased toward your focus points. So the camera looks mainly where you focus.
- If you take a picture of something bright (a bride in the snow) the camera will underexpose it to give you a grey bride. If you take a picture of a dark object (a groom in a coalmine) the camera will overexpose it to give you a grey groom.
- To fix this, you can turn the flash up and down using flash exposure compensation (“Flash Exp Comp”).
- Play with the light: aim your flash at walls or ceilings if you can. and create a “virtual umbrella”.
Try it and see if you get more consistent!
Here’s a typical recent flash picture, of a nice photographer I met recently:
A flash photo - yes really.
Doesn’t look like your usual “deer in the headlights” snap? That’s because I was following my own suggestions above. Note I also used a Honl Photo 1/2 CTO gel, to make the flash light look a bit more like the background Tungsten light. I like warm backgrounds, but I often make them a tiny bit less warm this way.