Manual speedlight test

Location photography can be difficult in terms of lighting control, but a speedlight can make things simpler. To see how it works and how it can be used we tested our speedlights indoors.

  • We started from using speedlights as the main light source.But before actually using a speedlight you need to know its guide number (GN), so we started with metering it. Light meter reading for the full power flash in 10ft distance was f/9 (ISO-100, 1/125 sec). Formula for the futher calculations is GN = distance × f-number. That means the GN = 10*9 = 90 (for ISO-100, 1/125 sec).
f/9, ISO-100, 1/125 sec, full power, 10ft

f/9, ISO-100, 1/125 sec, full power, 10ft

  • For 5ft distance f-number = GN / 5ft = 90/5 = 18
f/18, ISO-100, 1/125 sec, full power, 5ft

f/18, ISO-100, 1/125 sec, full power, 5ft

  • Formula can be used to calculate a distance as well. For f/4 the distance = GN / 4 = 90/4 = 22.5ft
f/4, ISO-100, 1/125 sec, full power, 22.5ft

f/4, ISO-100, 1/125 sec, full power, 22.5ft

  • Speedlight can be used with various power settings. For half-power flash 1 full stop should be substracted. f/9 – 1full stop = f/6.3 for 10ft distance.
f/6.3, ISO-100, 1/125 sec, half power, 10ft

f/6.3, ISO-100, 1/125 sec, half power, 10ft

In the same way for 1/4 power you have to substract 2 full stops, 4 full stops for 1/16 power and so on.

  • Calculations for 1/16 power and 5ft distance is f/18 – 4 full stops = f/4.5
f/4.5, ISO-100, 1/125 sec, 1/16 power, 5ft

f/4.5, ISO-100, 1/125 sec, 1/16 power, 5ft

In overal the speedlight worked well providing nessasary lighting, however images look flat and the environment surronding the model looks unnaturaly lighted and has reflections on shiny surfaces such as glass, metal, ceramics and oil-painted window frames. 

Then we tested how speedlights work in combination with ambient light.

  • Light meter reading for ambient light was f/4. GN for ISO-400 is 160.
f/2.8, ISO-400, 1/125 sec, no flash

f/2.8, ISO-400, 1/125 sec

Exposure on the middle part of the face to avoid too dark shadows.

  • To create daylight balanced lighting I used my speedlight and set it up to produce the same f/4 (as ambient light reading).
f/4, ISO-400, 1/30 sec

f/4, ISO-400, 1/30 sec

  • Speedlights can be used as fill light by reducing its power or increasing a distance to get f-number lower than ambient light.
f/2.8, ISO-400, 1/125 sec

f/2.8, ISO-400, 1/125 sec

The technique works well because it fills in the shadows, but we can still see that the room is lighted by daylight.

We also tested bounce flash to get softer light. When I was making calculations I had to consider the distance that light travels from the speedlight to a ceiling/wall and from there to the model.

  • A flash bouncing off the ceiling creates natural look which can be compared to daylight outdoors.
f/14, ISO-400, 1/125 sec

f/14, ISO-400, 1/125 sec

  • A flash bouncing off the wall illuminates the model from the side.
f/16, ISO-400, 1/125 sec

f/16, ISO-400, 1/125 sec

At home I tested my speedlight once more to see how it works in combination with other light sources. 

f/4.5, ISO-400, 1/20 sec

f/4.5, ISO-400, 1/20 sec

I had a flashlight to highlight steam and the aroma lamp from behind and a tealight. Bounce flash off the ceiling and the lowest speedlight power thus avoiding the background to be illuminated.

Here are some nice articles about Guide Numbers, speedlight, using it in manual modeflash compensation and bouncing flash.

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