Lighting Ratios

[Digital]

if you have two speedlights, one set at full power (key light), and the second speedlight (fill light) set at 1/2 power, is this a 2:1 ratio?


Bruce

[Martin A]

Much more info is needed to determine this. Are they identical speedlights? Are they both set at equal distance to the subject? If so, then yes, this would be a 2:1 ratio because 1/2 power is equal to one stop less output. If not so, then it becomes a bit more complicated.

[Manfred M]

No. Power levels don't work that way. On my main lights, half power is (assuming same distance from subject and same light modifier in use) a difference of around 4 stops, or a 4:1 lighting ratio.

If your incident light meter is also a flash meter; if you set up your key light and the meter says that the correct exposure is f/8 and you set up your fill light and the exposure reads f/5.6 you have a 2:1 lighting ratio. Each light is set up individually and only the light you are taking the reading with fires.

[Martin A]

... if you set up your key light and the meter says that the correct exposure is f/8 and you set up your fill light and the exposure reads f/5.6 you have a 2:1 lighting ratio.

We agree then that one stop difference yields a 2:1 lighting ratio. Bruce said he was working with two speedlights, which may be different from studio strobes. A speedlight set to 1/2 power will output one stop less light. With the other speedlight set to full power the ratio then would be 2:1. No??

[Manfred M]

We agree then that one stop difference yields a 2:1 lighting ratio. Bruce said he was working with two speedlights, which may be different from studio strobes. A speedlight set to 1/2 power will output one stop less light. With the other speedlight set to full power the ratio then would be 2:1. No??

Martin - Every light manufacturer has its own measurements and idiosyncrasies in the way they measure / show power settings

If you are saying turning down the power settings one full stop means the output will be half the power of the full power setting, I agree and that will produce a 2:1 lighting ratio. The term that Bruce has used "1/2 power" is not clear. Working in stops (or ev) is.

I have run into a second way of measuring lighting ratios, which I find rather non-intuitive and confusing. The key light value (always 1) is added to the fill light value (lets assume the same settings as we have been discussing; 2). The two lighting values are added together 1 +2 = 3, the under this system we are looking at a 3:1 lighting ratio for exactly the same setup.

[Digital]

If you are saying turning down the power settings one full stop means the output will be half the power of the full power setting, I agree and that will produce a 2:1 lighting ratio. The term that Bruce has used "1/2 power" is not clear. Working in stops (or ev) is.

Manfred, this is exactly what I meant. I am sorry that I did not make it any clearer.


Bruce

[Digital]

So, if the key light is set at full power, and the fill light is set at two stops less (1/4) power you will have produced a 4:1 lighting ratio. Am I correct?

Bruce

[Manfred M]

So, if the key light is set at full power, and the fill light is set at two stops less (1/4) power you will have produced a 4:1 lighting ratio. Am I correct?

Bruce

All things being equal, that is correct.

By all things being equal I mean that both flashes put out light as per the setting, both flashes are exactly the same distance from the subject and light modifiers are both the same and absorb the same amount of light.

[Martin A]

Martin - Every light manufacturer has its own measurements and idiosyncrasies in the way they measure / show power settings

If you are saying turning down the power settings one full stop means the output will be half the power of the full power setting, I agree and that will produce a 2:1 lighting ratio. The term that Bruce has used "1/2 power" is not clear. Working in stops (or ev) is.

Manfred - Okay. basically we do agree. I have never owned any strobes other than 'speedlights'. Nikon, Olympus, Canon, and good independent brands, and I do not remember any of them offering anything other than power ratio settings to adjust the output. And virtually all of them claimed each step was a full stop difference in output. I assumed because of the info he gave that he had no other means of determining actual output. That is why I said it wasn't that simple but based on the info he provided and the parameters of equal distance from the subject and identical strobes, it would result in 2:1 lighting ratio if one strobe was set at half power.

[Manfred M]

Manfred - Okay. basically we do agree. I have never owned any strobes other than 'speedlights'. Nikon, Olympus, Canon, and good independent brands, and I do not remember any of them offering anything other than power ratio settings to adjust the output. And virtually all of them claimed each step was a full stop difference in output. I assumed because of the info he gave that he had no other means of determining actual output. That is why I said it wasn't that simple but based on the info he provided and the parameters of equal distance from the subject and identical strobes, it would result in 2:1 lighting ratio if one strobe was set at half power.

I own three Speedlights (Nikon and Godox) and will probably add another this summer, two bare bulb flashes (Godox) and four Paul C Buff Einstein 640 lights. The studio I frequently use has 6 Photogenic studio lights. I've owned Metz, Rollei and Vivitar flashes in the past and have shot with ProPhoto, Elinchrom, Broncolor and Norman lights, both monoblock and powerpack types). I shoot more studio lights than speedlights. Power, modeling lights and especially light modifier options are the main reasons.

Modern speedlights tend to follow what you have written, but some of the older ones not at all. Studio lights are all over the map; some follow speedlight conventions and others have their own unique schemes that one has to get used to on my Paul C Buff lights I have both the 1 - 1/128th power values as well as a numeric scale that goes from 0 - 8.

The other main difference is that speedlights tend to based on output (that's what guide numbers really provide) and studio lights measure input power (so it is hard to compare the two different light designs directly). Studio lights are rated in W-s (watt seconds).

That is why on multi-light setups (I generally shoot with at least 2 lights), I use a flash meter. With speedlights, I tend to avoid direct flash and either use on-camera bounce or off camera with modifiers (generally umbrellas; shoot through and reflective).

[Digital]

Using f/stops as a guide, how do you achieve a 3:1 ratio of lighting.


Bruce

[Manfred M]

Using f/stops as a guide, how do you achieve a 3:1 ratio of lighting.


Bruce

For 3:1; your fill light needs to be 1.5 stops darker than your key light.

If your key light is set to properly expose at f/8, your meter on the fill light should meter at f/4.8.

[Digital]

For 3:1; your fill light needs to be 1.5 stops darker than your key light.

If your key light is set to properly expose at f/8, your meter on the fill light should meter at f/4.8.

Manfred, thank you for the information.

Bruce

[Manfred M]

Bruce - a good rule of thumb is that for women and children, a 2:1 ratio is quite effective. This gives you a gentle and not all that dramatic look, with enough interesting shadows to help sculpt their faces. Loop lighting and even butterfly / paramount lighting work well here. These are typical "beauty lighting".

A 3:1 or even a 4:1 works well for men as well as for female performance athletes. These lighting ratios are quite dramatic. While loop or butterfly can work here, you can push harder and use Rembrandt or even split lighting for a dramatic look.

[William W]

I understand this began as a simple technical question, once we begin discussing "gentle look", "dramatic look", "rule of thumb for women and children", etc... then it is worthwhile underscoring that the other components of the Lighting Set, (mainly, but not limited to: Position and Modification) are most important.

The "Lighting Ratio", (even with only two lights) is only one factor in the Lighting Set.

Manfred alluded to this fact, I wish to underscore the importance of understanding this fact.

WW

[Manfred M]

I understand this began as a simple technical question, once we begin discussing "gentle look", "dramatic look", "rule of thumb for women and children", etc... then it is worthwhile underscoring that the other components of the Lighting Set, (mainly, but not limited to: Position and Modification) are most important.

The "Lighting Ratio", (even with only two lights) is only one factor in the Lighting Set.

Manfred alluded to this fact, I wish to underscore the importance of understanding this fact.

WW

Bill - let me say I 100% agree. My main complaint about photographic lighting is that that when this subject is taught, the emphasis is on how to set up the lights but little to no attention is paid to why we would light using a specific technique. One of my biggest beefs, even when I see commercial productions is that the photographer often executes the wrong lighting approach very well.

A young very feminine model shot with Rembrandt lighting or split lighting just does not work out well. Loop or butterfly lighting on a hot and sweaty male athlete does not generally work well either.

I find that I learned much about approprate lighting by studying the works of people like Yousef Karsh, Annie Leibovitz, Richard Avedon, Irving Penn and many others