Green Tree Frog

The above image, in line with the title of this Blog, has been captured using electronic flash, together with a Nikon, D700 camera and 105mm Nikon Micro lens.

In general there are several ways to use electronic flash and we I will attempt to cover all aspects below.

Built-in Camera Flash Versus External Flash

In general the flash built in to most cameras is of limited power and will only be satisfactory to illuminate a subject quite close to the camera. Also an in-built flash will only give direct lighting and is mainly useful for fill in flash to supplement normal daylight.

An external flash can either be used on the camera or with a seperate cable can be used off the camera. Also external flashes can be used in a multiple flash configuration, with one flash on camera as the master and other flashes configured as slaves off camera.

Built-in Flash Settings

Most built-in flashes will have some of the options as shown below.

  • TTL Setting – This setting will enable automatic operation by the camera, measuring the reflected light back through the camera lens.
  • Manual Settings – Manual settings may be available, ranging from full power down to 1/128 of full power.
  • Commander Mode – In this case the flash can be set so that external slave flashes can be used, triggered by the camera flash.

Camera Settings for Flash

Flash Synch Speed – When using flash with cameras having a focal plane shutter (most digital SLR cameras) the flash may need to be synchronised to a certain range of shutter speeds. With most cameras the highest shutter speed may vary between 1/125 to 1/500 of a second.

Auto FP (focal plane) High Speed Synchronization – Also another option may be provided making it possible for the flash to be used at the highest shutter speed supported by the camera. This is a very important feature in some of the latest flash units whereby electronic flash can be used at all shutter speeds. There is some limitation in this feature however, as at higher shutter speeds the flash power available will be reduced, however it is still an important feature to utilise.

Flash Modes

Several flash modes as follows may generally be available.

Red Eye Reduction – This mode gives a flash slightly before the main flash causing the subject’s eyes to contract before the main flash, thus stopping red eye occuring in the image.

Front Curtain Synchronization – This mode is used in most situations with the camera in Programmed Mode and Aperture Priority Mode and the shutter will be set to the highest shutter speed allowable for the shutter, or even higher if the camera is set to “Auto FP High Speed Synchronization” as discussed above.

Slow Synchronization – The shutter light and flash light is combined  for shutter speeds down to 30 seconds. In this mode the flash operates just after the shutter opens. Used in Programmed and Aperture Priority modes. This mode is to capture the foreground and background at night and in dull lighting.

Rear curtain Synchronization – In  this mode the flash fires just before the shutter closes. Used as a creative effect to give a stream of light behind moving objects at night. Used in Shutter Priority and Manual modes.

Slow Rear Curtain Synchronization – Used to capture both foreground and background at night and in dull light. Used in Programmed and Aperture Priority modes.

Flash Settings

In general the following flash setting may be available on an external flash.

ISO Sensitivity – Sometimes this may be set from the camera information.

Zoom Head – Some flash units may have a capability to zoom the head to allow for telephoto or wide angle lenses.

Auto TTL Mode – This is to set the flash to operate automatically, with the camera measuring to light through the lens.

Auto Non TTL Mode – In this mode the flash measures the light reflected back to the flash unit and not the camera.

Balanced Mode – This mode will allow a balanced amount of flash, compared to the amount of daylight. This can be very effective to provide daylight fill in flash.

Manual Mode – In this mode the flash is set manually and not controlled by the amount of light reflected back. Further details are given below.

Manual  Operation of Flash

Every flash has a Guide Number specified for it, to enable the lens aperture to be calculated from the flash to subject distance.

The guide number is specified either in feet or metres at a particular ISO, generally ISO100.

The Guide Number is defined as:

G = f x D

Where G = Guide number,

f = the lens Aperture,

D = flash to subject distance.

A typical in-camera flash may have a Guide Number of 10 metres (33 feet) at ISO100.

A typical external flash will generally have a Guide Number of 20 metres (66 feet) to 60 metres (197 feet).

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