Monday, 24 August 2015

Flash Photography


“The most important part of the camera is the 12 inches behind the viewfinder”: Ansel Adams




FLASH PHOTOGRAPHY

by Peter Hardie




·       To understand flash photography you first need to understand how the mechanical shutter works.

·       The flash will only operate when the camera sensor is 100% exposed when the shutter is fully open. This only happens at the camera’s ‘flash (x) sync speed’ (or slower), normally around 1/160 to 1/250 shutter speed (see camera manual). Any faster and the shutter is partially covering the sensor.

·       To determine flash sync speed set camera to shutter priority (Tv or S) and set shutter speed to say 1/500 second. Now turn on the flash and take a shot. The camera will revert to the flash sync shutter speed (eg 1/200) automatically.

·       Flash exposure is only affected by the aperture and ISO and not by the shutter speed. The flash duration is usually around 1/1000 second or faster, which is faster than the camera’s flash sync speed of around 1/200 second.



·       Flash photography is a double exposure. Firstly, the camera’s exposure of the surrounding ‘background’ ambient light and secondly the exposure of the artificial light from the flash on the ‘foreground’ subject.

·       The camera only helps the flash to measure exposure by way of ETTL (Evaluative Through The Lens) metering.

·       Using flash outdoors :
·       Portraits, sun behind subject, macro, panning, increase/decrease contrast
·       Turn flash off and with camera set to Shutter Priority and the maximum flash sync speed (eg 1/200), expose camera for background (away from subject) or bright side of face.
·       Change to Manual (M) camera setting and enter shutter and aperture settings from the above background shot. This will fix the correct exposure for the background.
·       Turn on flash, focus on subject and re-compose to take shot.
·       Adjust ** Flash Exposure Compensation (FEC), if required, and re-shoot.

·       Using flash indoors:
·       Turn on flash
·       Set camera to fully automatic (green rectangle)
·       If possible, avoid direct flash and bounce flash off white ceiling or wall.
·       Alternatively use Manual camera setting of say ISO 400, Max aperture (eg f/3.5) and 1/60.

·       Preferable that light from flash is bigger than the subject. Bounce off wall or ceiling or white object.
·       ** Camera has a flash exposure compensation (FEC) button. Use FEC to lower or increase the severity of the flash’s light (eg -1 Stop for fill flash). Balance flash light on subject with background ambient light to look natural. Adjust camera’s exposure compensation (EC) to lighten or darken background. EC (camera) and FEC (flash) can both be changed to suit balance. FEC does not affect ambient light.

·       REMEMBER: Always reset your FEC setting to zero before turning off camera.

·       Try flash off camera (with cord or remote) and aim from different angle. Direct flash can look flat.

·       Shutter speed and flash. Shutter speed has no affect on flash, as flash duration is much shorter than the maximum shutter speed. Only affects ambient light.

·       Aperture and flash. Aperture effects ambient and flash light equally and depth of field.

·       ISO and flash. ISO setting affects the light sensitivity of the image sensor and, like aperture, affects flash and ambient light equally. Higher ISO increases flash range (ISO100 to ISO400 doubles range).

·       Effect of distance to subject. If shooting in manual flash mode then yes distance to subject is important. Shooting in ETTL will remove any issues here.

·       Ensure lens hood is not on when using pop-up flash. Hood can cast shadow.

·       Flash can be set to fire at start of exposure (front/first curtain sync) or at end of exposure (rear/second curtain sync). Rear/second curtain is more natural looking. Good for panning and sports shots.

·       High speed sync flash (Canon: HSS, Nikon: Auto FP). Allows flash operation at shutter speeds higher than the flash sync speed (eg 1/1000). Good for darkening the background when using flash. HSS is not available with a pop-up flash.

·       With dedicated flash and HSS always check flash for distance range limits. You will have to stand closer to the subject to light it with HSS. HSS has much lower light output than normal flash.

·       Flash accessories: Reflectors, diffusers, umbrellas, wireless triggers, off camera flash cord etc

·       Flash limitations:
·       On-camera pop-up flashes have limited short range and can cause “red eye”
·       Dedicated slide-on flash units have larger range and more versatile (eg bounce flash)
·       Harsh light when directed straight at subject

·       Flash alternatives:
·       Large circular reflectors/diffusers to control sunlight. Requires assistant to hold.
·       High ISO setting. May introduce unwanted background ‘noise’.

·       Flash photography references:
·       “Understanding Flash Photography” – Bryan Peterson (Amazon or Bookdepository.com)
·       www.neilvn.com/tangents/flash-photography-techniques
·       www.strobist.blogspot.com.au
·       Canon and Nikon books on flash – very extensive manuals
·       YouTube and Google
·       Inexpensive flash workshops - Ken Wilton at www.eeek.com.au

·       PRACTICE, PRACTICE, PRACTICE will improve your flash photography