Know your stuff

Us­ing ar­ti­fi­cial light (and how to bal­ance it with nat­u­ral light)

Getaway (South Africa) - - PHOTOGRAPHY MASTERCLASS -

The best un­der­wa­ter shots ap­pear nat­u­rally lit be­cause of the bal­ance of am­bi­ent (avail­able) light with strobe or flash. Get­ting this bal­ance right is key.

In the mid­dle im­age above, the colours are washed out and the back­ground too dark be­cause the am­bi­ent light read­ing has not been ac­counted for.

The cam­era’s aper­ture con­trols the amount of light hit­ting the sen­sor at any given mo­ment, while shut­ter speed con­trols the length of time the light hits the sen­sor. How­ever, flash is a very short burst of pow­er­ful light (1/2 000th to 1/15 000th of a sec­ond). Flash sync speed is the fastest shut­ter speed you can use with a flash. This speed dif­fers from cam­era to cam­era but is usu­ally in the 1/160 to 1/250 sec range. This is the short­est pe­riod of time the en­tire sen­sor will be vis­i­ble. At faster shut­ter speeds, parts of the sen­sor will be cov­ered by the shut­ter cur­tain as it moves across the sen­sor.

Be­cause it’s so quick, shut­ter speed will have no in­flu­ence on the amount of flash light hit­ting the sen­sor. So the only way to con­trol flash bright­ness is by us­ing your cam­era’s aper­ture and ISO set­tings.

The key to bal­anc­ing flash and am­bi­ent ex­po­sure is to first read your am­bi­ent ex­po­sure and then change the aper­ture set­tings to cor­rect for flash ex­po­sure. Fi­nally, bring back your am­bi­ent ex­po­sure by chang­ing the shut­ter speed.

Also re­mem­ber that dis­tance from the sub­ject plays a big role in the strength of your flash. As a rule of thumb: dou­ble the dis­tance away, half the flash power

– and the same in re­verse (half the dis­tance, dou­ble the power). Try chang­ing your po­si­tion, mov­ing back or for­wards, to get the best-lit shot.


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