Automatic flash

Auto flash was used in older generations of flashguns to automatically curtail the flash when the correct exposure was reached. The principle is the same as that of TTL flash, but auto flash uses a sensor on the camera body, rather than linking up with the camera’s through-the-lens metering. It’s still possible to buy auto flashguns, and they do provide good results under many circumstances. They’re also cheaper, partly because they don’t require the sophisticated electronic linkages and controls of TTL flashguns, and partly because they can be made in a generic form to fit many different camera models.

How it works

Auto flash uses a light sensor mounted on the front of the flashgun, rather than working with the camera to take a reading through the lens. This external sensor is simpler and cruder than TTL systems, and works independently of any in-camera metering system – the camera has no control over the flash output. Operation is pretty simple; you just choose a lens aperture that will put your subject within range of the flash. The flash duration is governed by the amount of light reflected back to the flashgun’s sensor. The angle of coverage of this sensor only approximately matches that of the camera at normal focal lengths, and doesn’t change to match different zoom settings. Auto flash lacks the sophistication of multi-pattern TTL systems, so exposures tend to be less accurate, and you may need to spend more time experimenting with the flash power.

Cheaper auto (non-TTL) flashguns still have their place. As long as you’re prepared to make more of an effort with exposure calculations, in order to balance the flash and ambient lighting, you can get great results.

When would you use it?

Auto flashguns don’t necessarily offer any photographic advantages, but they do have practical and economic benefits. They’re much easier to understand than the latest dedicated TTL flashguns (the manual for Canon’s 550 EX runs to 128 pages). They’re also dramatically cheaper; you can pick up a Jessops 280 Auto Bounce Zoom flashgun with a guide number of 28 for just £30 – that’s up to a tenth of the price of a top-flight dedicated flash from your camera’s manufacturer. In addition, a generic auto flashgun will work with most cameras, which makes it perfect if you have more than one model. Auto flashguns are ideal for occasional use, and occasions when you have time to re-try shots that don’t quite work the first time around. And, if you prefer manual flash control, they’re every bit as effective as a dedicated flash.