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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 02 May 2014 (Friday) 13:38
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Ratios with Speedlights

Cream of the Crop
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Joined Jun 2009
Location: Metro Chicago
May 02, 2014 22:24 |  #16

If you set two lights of equivalent output to half power, each 8 feet from the subject, with the same modifier, they will deliver essentially the same light. How you place them will determine whether there is overlapping or individual light sources on the subject.

Practice at home with one light. If its 8 feet from the subject with your chosen modifier at 1/4 power take a test shot, 1/200 or whatever your camera max sync speed is, F8 and ISO 400. If its over exposed stop down the lens two stops and try again. If its under exposed open up about what you think the under exposure is, say 2/3 stop. You end up at ISO 400, F10, with light 8 feet from subject at 1/4 power.

Now you have a basis for judging exposure. From there its just practice and experience.

Light meters are handy and over rated. I have one. I use it in the studio. On location I rely on experience, and the histogram on the camera.

David | Sharing my Insights, Knowledge & Experience (external link) | dmwfotos website (external link)

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Joined Feb 2013
May 03, 2014 02:52 as a reply to  @ dmward's post |  #17

I'll try and give you a brief rundown on Lighting Ratios as a lot of people are confused by them when it really isn't hard to understand.

Theres a difference between light intensities of two lights vs how the light falls onto the subject.

In light intensity terms, a 1 stop difference between main and fill = 2:1 ratio but how the light falls onto the subject is a 3:1 ratio. (as the fill is usually on or near camera axis, therefore there is another part of light hitting the side the main light is on)

Think of a lighting ratio as Main + Fill : Fill and not Main : Fill

Every stop is a factor of 2 (x2). The fill is +1 added on to the main light.

So a 1 stop (x2) difference between Main and Fill is 3:1 (x2 + 1 for fill : Fill), a 2 stop difference is 5:1 (x4 + 1 for fill : fill) and so on.

Too get Accurate results you need a light meter as just changing the power of two speed lights to have a 1 stop difference between the two doesn't necessarily mean its going to be a 3:1 ratio as the inverse square law comes in to play.

I hope that helped out a bit.

Canon 60D - 24-70mm 2.8 L II - 70-200mm 2.8 L IS II - Speedlight 600 ex-rt - Broncolor Move 1200L pack + A2L pack + MobiLED flash head

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Ratios with Speedlights
FORUMS General Gear Talk Flash and Studio Lighting 
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