Correct Answer for 3:1 Lighting Ratio

[Deb_Wat]

Hi Gang,

In preparing for our test next week, we have noticed that there are different answers in regards to a 3:1 light ratio.

The London book states that a 3:1 ratio is a difference of 1.5 stops.

But, I have found other sources (my lighting class at CPW and other lectures attended this year) that state a 3:1 ratio is a one stop difference.

Can someone clear this up for me. Why are there two answers and which is the correct one for the sake of the PPA Certification test?

Thanks

Deb

[mlphoto]

You are correct that there are multiple definitions of 3:1. I personally do not agree with the definition of the PPA but hey, it is a label...that's it. The key is to know the meaning behind the label.

The definition that PPA uses is that 3:1 has a 1 stop difference when dealing with strobes or hot-lights. 1 light unit hitting the entire face as fill and then twice as much light (1 stop more) hitting one side.

Now, when dealing with reflectors, PPA's definition of 3:1 includes a two stop difference. The "proper way" to measure that ratio is to meter off the reflector.

Personally, I feel this is just confusing.

[David_A._Lottes]

3:1 ratio example - fill on subject meters at F5.6 with main flash turned off and main meters at f8 with fill flash turned off for one stop difference. Been a long time since I took the exam so I can't guarentee this answer but if it's wrong my ratios have been off for twenty years. Which could very well be.

[Deb_Wat]

The definition that PPA uses is that 3:1 has a 1 stop difference when dealing with strobes or hot-lights. 1 light unit hitting the entire face as fill and then twice as much light (1 stop more) hitting one side.

Now, when dealing with reflectors, PPA's definition of 3:1 includes a two stop difference. The "proper way" to measure that ratio is to meter off the reflector.

Personally, I feel this is just confusing.

The sample question on the certification website states a 3:1 ratio is 1.5 stops difference. Should I just go with that answer for the test?

Anyone know why their are different answers.

[Mark_Turner]

I'm not sure there. I do know that if you have a unti of 5.6 hitting both sides of the face, and one unit of (2x5.6=8) hitting one side then that is 3:1, with 3 units on one side and only 1 on the other. However when you meter that with a meter (incident) pointed at the camera from subject you get 8.3 to 8.5 total exposure. Maybe that is where the extra 1/2 stop is coming from.

Now what to answer on the test....

[mlphoto]

If that is what the certification sample test says, then, yeah...I would go with it.

The different answers arise due to differing opinions on a variety of subjects:

1) Do you add up all the light units hitting the subject or do you only count the light units coming out of/off from the light source (light or reflector)
2) Is your fill light positioned near the camera?
3) yada, yada, yada.

Personally, I only count the light coming out of the light source. I also notate the amount as follows:

main:fill:separation:kicker:background

So, I can have a 4:1:1:0:3 ratio. It helps me remember how I set lights weeks or months later.

But, that is just how I do it.

[Derek_Alvarez]

Ratios



here is a way to look at it


1 ..2.. 4.. 8.. 16.. 32.. 64.......


each number doubles these number are your ratios

1:1 ... 1:2 ...1:4 ...1:8 etc

so let put this to an fstop

a 1:1 is f11/f11
1:2 is f11/f8
1:4 is f11/f5.6


now lets add 1/2 stops

go back to the ratio chart
1 ..2 ..4 ok
here is how it will look

1..2..3*..4..6*..8..12*..16........

the * number is the 1/2stop ratio

so a 1:3 ratio is 1 and 1 1/2
or F11/F 6.7

does that help

[David_A._Lottes]

The sample question on the certification website states a 3:1 ratio is 1.5 stops difference. Should I just go with that answer for the test?

Anyone know why their are different answers.

Well if I have my fill metering 5.6 and my main metering 8 then the highlight side probably will read 8.5. So the difference between the fill alone and both lights turned on is 1.5. But what a convoluded way to arrive at that conclusion

Seems like a very tricky question depending on the way it is worded. The answer of 1.5 would be missleading if it were phrased as (Where do you set your power) as opposed to (what does your meter read). Now if it is phrased as what is the difference between the meter reading of the brightest highlight and the meter reading of the shadows for a 3:1 ratio I guess 1.5 stops would make sense. This would be handy to remember in available light.

[Michael_Gan]

Deb!

The reason it becomes 1.5 stops is because you have to take into account the amount of light from the main light that "spills" onto the fill light area. Although your mainlight is 8 and your fill is 5.6, there is about 1/2 stop added to your fill source thus reducing the light differential to 1.5.

Michael

[David_A._Lottes]

Oh MAN am I getting mixed up. I thought it was the FILL light bumping my main up from 8 to 8.5 thus INCREASING the differential from 1 to 1.5 stops.
I'm going to leave this to smarter people. Sorry if I've confused you Deb. If you ever work for me and I ask you for a 3:1 ratio just remember to meter the lights seperately and put the main light at a 45 degree angle from and metering one stop brighter than the fill and I'll be happy.