Flash – The Basics

I want to keep this really simple, as it’s a huge topic in it’s own right, and I’ve already gone on for a very long time! However, I can’t overlook flash, as so many cameras come equipped with one, and I use flash all the time. I’m planning an entire lighting course for the future, so this will only be a brief intro. If you’re interested in flash, I’d highly recommend you check out strobist in the meantime.

Anyway, back to flash. Flash is a great way of adding light to a scene, to reduce contrast, to create certain looks or effects, or to simply light a scene that’s too dark to shoot in. Built in flashes or Flashguns (or speedlites, if you insist) are very portable and powerful ways of adding light. They function by storing the power from the batteries in a capacitor, then releasing all of that power as light in a very short burst.

Flash Synchronisation

The burst of light from a flash is very brief, therefore it has to be synchronised to the shutter so that it’s in time with when the shutter blinds are open and exposing the image sensor. This means there’s a maximum sync speed, – a shutter speed you can’t shoot faster than – otherwise you get bands like this:

Banding caused by syncing with a flash at too fast a shutter speed.

This is caused by the shutter blinds (think back) starting to close before the flash has had a chance to light the whole image. Beyond a certain speed the sensor is never fully exposed during the exposure – the 2nd blind has started it’s journey before the first has finished. At speeds just past your max sync the effect is quite subtle, but once you start getting really fast, you’ll see almost no flash. This is because the gap between the 2 blinds gets smaller and smaller as the shutter speed increases.

Basically, synchronising the short pulse of the flash, with the narrow window between the shutter blinds is quite tricky, which is why it tends to top out at around 1/250. There is a way round it (called high speed sync) and your camera may be able to switch to this automatically. This works by letting out the power of the flash in a slow pulse, so it functions more like a torch than a flash, and stays lit during the passage of the shutter blinds. Of course, in doing so it loses power, as the same amount of flash spread over a second or so would be enough to create dozens of shorter flashes. You can’t have everything! If you’re using a mirrorless camera, then most of what I’ve just said doesn’t apply – your shutter functions differently, and doesn’t have any blades. You can generally sync at any speed, well done you!

Slow Sync” Flash

Depending on your camera, you may have a “night mode”, or it may be called “slow sync flash.” These both mean the same thing, and they’re ways of letting more of the ambient light into a shot when you’re using flash, so that you don’t end up with just your subject lit, and the rest of the scene pitch dark.

Generally speaking, if you’re somewhere without much light around, and you shoot with flash on any automatic mode, the camera will give you a nice fast shutter speed to reduce the risk of camera shake, and expose for the flash. This tends to mean that the rest of the scene is pretty dark – we’ve all seen this with pictures taken at gigs, or at weddings late at night.

Night/slow sync mode usually works by letting the camera choose a slower shutter speed, so that more of the light from the scene can be picked up on the exposure, and you’ll now be able to see the surroundings better. Of course, if you’re shooting in manual mode, you don’t need any of this, because you can choose the exposure combination you want anyway, but I think it’s still worth knowing what some of this automated tomfoolery does.

Red Eye reduction mode

Something else your flash or camera may come with is a “red eye reduction” mode. Let me save you a lot of time, and just say “never use this”. I don’t think I’ve ever intentionally used this in my life – only when I’ve slipped and it’s come on by accident. It exists because flashes tend to be located very close to the lens axis, and when taking pictures of people in low light situations, the light from the flash bounces directly back from the subject’s eyes, having illuminated certain pigmentation in the iris, and you get “red eye”.

Now, I’ll admit, it’s not a great look, but it takes about 10 seconds to remove it in photoshop, and nowadays even camera phones often have software that can locate and remove it. The problem with “red eye reduction” mode, is that it works by firing a pulse of flashes before the shot, or a beam of light, in an attempt to reduce the size of your subject’s pupil, and lessen the effect. Not only does it not work all that well, but more importantly, it creates a huge delay between when I press the shutter and the picture actually being taken. I’m not a fan of this – I like to be in charge of when the picture is taken thanks!

That’s really all you need to know to use the flash that’s built into your camera. Like I say, I don’t want to go into too much depth, as it will only confuse you, there’s only so much you can do with a flash that’s built in to your camera

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