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Flash Photography

Strobist Style

Every camera, from a cheap compact to a £6,000+ professional DSLR camera, either has a built in flash or, in many cases, can accept a larger, more powerful flash unit. However, many photographers are still unsure when it comes to utilising the full possibilities of flash with their photography, mainly because they don’t know how to use it properly.

Flash photography is used heavily by many professionals especially those shooting fashion or portraits as it can give a much more aesthetically pleasing image. All photo manufacturers spend millions developing their cameras capabilities yet an inbuilt flash can still be brutal and result in harsh directional light.

This is no fault of the manufacturers but to make the built in camera flash as versatile as possible they need to be directional to throw light onto subjects that can be some distance away. The main downside with on camera flash is its position on the camera, this is particularly important when you are close to your subject as light naturally falls off and disperses the further the subject is from you.


Camera Flash Guide Number

Flash is measured by a unit of measurement called Guide Number (GN). This gives a universal standard to measure the power of the flash, undertaken by measuring the maximum flash to subject distance and the correct aperture required to expose it. When using flash, shutter speed has little effect and so the only other variable which is ISO is kept at 100.

GN= Distance x Aperture

In short the higher the Guide Number the more powerful the flash.

Manufacturers use this to easily identify the power of their flash units. For instance, the Canon Speedlite 580EX Mk II has a guide number of 58, the Metz 48 AF-1 a guide of 48. Don’t be fooled by this as some manufacturers misquote the guide number, Nissin in particular do this with their Speedlite Di622 - they quote 62! Though this is in GN 62 at 200 ISO, those of you who have read our articles about ISO and exposure will know this is twice the power and in reality the guide number is only 31!

To put the power into context most built in flashes have a guide number about GN10, the Canon EOS 550D has a guide number of GN13, much less than any additional on camera flash.

On the LCD on the back of the flash gun the power measured is displayed as a fraction of the flashes maximum power, i.e. 1/1 or 1/8. So a flash with a GN of 58 at 1/1 is more powerful than a flash with a GN 48 at 1/1.

Sync Speed

Although not as important with on camera flash as with studio lighting (where the camera cannot capture images if the shutter speed is beyond the cameras sync speed), it is still important to not exceed the cameras sync speed ability where possible (though please read the high speed flash sync section below.)

Sync speed refers to the maximum shutter speed the camera can sync up to, though in fact you could use almost any shutter speed up to this and you’ll still capture a clear crisp picture (see flash duration).

Camera Flash or Photography Studio Flash

With the built in on camera flash you are a little limited with what you can do as you cannot tilt or bounce them, the only option you have is to turn down the power of the units through the exposure value (EV). Turning this down obviously reduces the power of the flash but this means the flash doesn’t appear as harsh in your images. The downside, however, will mean that any subject that is more than six feet will not have any benefit from using the flash at all.

Many cameras have a control on the outside of the camera, unfortunately this varies between brands but it is typically one button press and/or rotating one of the rear dials.

If you intend to do any serious flash photography it is worth investing in some good equipment. We suggest looking at either an on camera flash like the Canon Speedlite 580EX Mk II, Canon Speedlite 430EX II or the other option is the looking at large studio flash systems like the Elinchrom Dlite 4.

All have their pro’s and con’s but this article focus is on smaller flashes and how to get the most from it.

Flash in Auto

One of the most common uses for flash is as a fill in flash to balance flash with ambient light (i.e. natural light). Flashes will give you a similar look to this naturally but, as mentioned above, tweaking the exposure value may be required to get an even exposure. This raises another point about the colour temperature of the flash which is quite likely to be different from the ambient light (look further down this article for more details on this).

The simplest way to start to get to grip with what you can do with flash is experimenting with flash in auto, forcing the flash to correct the exposure. Just remember the flash is only so powerful and has its limitations.

Another slightly more creative technique is to over expose the flash and under expose the camera. This can be done in either auto or manual giving a very edgy look to the image. This technique is extremely popular with fashion photographers and gives them a striking impression similar to shooting at night.

Flash with a long exposure can allow you do some very creative shots, in particular they allow you to capture light trails over the image making a rather bland background dramatic. This works well in particular for music photography, the flash freezes your subject and the long exposure allows some fill in from the ambient light, especially if the flash comes at the end of the shutters duration (see rear curtain).

This can also work for portraits at night though you need to use a tripod to keep the background steady, see our image for an example of this. This enables you to turn night into day (unlike the technique above which is quite the opposite).

Bounce Flash

A simple way to help vary the intensity of the flash without having to turn the EV down is to either tilt or bounce the flash head, and the good thing about this is that it works in auto!

Tilting the head works particularly well for straight on portraits, with a slight tilt this can either be bounced from the ceiling (see below) or just allows it to be softened to give a pleasing, slightly more natural look to your images.

Bouncing allows you to give a softer look to you images by pointing the flash at a nearby wall or reflective surface gives you a larger light source surface ares (e.g. the wall) which in turn is more flattering and appealing.