Light Ratios Unveiled... The Mystery is Disspelled.

I have seen light ratios described two different ways: one way is to measure the light output of each individual light by itself, and the other method is by the actual resulting difference between the highlight side and the shadow side of a subject.  This is an important thing to consider, because light is cumulative, so there can be quite a difference.  As I have been studying, it seems that the latter method is the more widely considered and used method for portraiture, so that is how I'm going to teach it in this workshop.  However, I'm also going to state the incident reading of each light by itself, so you will be able to make a determination of the effects for yourself if you so desire.

I am using a spool of white thread for this workshop.  Partly because it became available much easier than a model, and also because I felt like I could show the effects better.  The spool is a simple shape, and the thread has some intricate details, so it should work well to demonstrate the accuracy of metering properly to determine the contrast you desire in your photographs.

I used two SB-600's on light stands.  The flashes have no modifiers on them and they are being fired with a radio slave system so I can set everything manually.  I am using a handheld meter on an incident light flash setting.  The fill is always metered at f/5.6.  I am adjusting the power of the main light and the aperture value of my camera to create the proper exposures at the varying ratios depicted here.  My ISO is at 100, and the shutter speed is 1/125 on all these images.  They were all shot RAW and then converted to .jpg files.  I did do a levels and curves adjustment on them, but I applied the exact same setting to each and every image in a batch, so they have not been enhanced with individual settings to create any effects other than what truly exists in each light setup.

Any measurements specified per light were measured with the meter pointing at the light being determined and on a tangent plane relative to the closest point of the spool from the light (as near as I could eye-ball).

I hope you all enjoy and learn from this.  Feel free to discuss or ask questions as you like.

Let's try to move one of the lights directly behind the camera and the other further to the side so we get more of a side-lit pattern (in order to more fully show our point).  The main light is now at more like a 75-80 degree angle, as shown by the shadow it creates.

Now all of a sudden we have one light acting as a main, and the other as a fill.  But we are going to make them each meter the same.  I'll explain in just a moment.

First, I want to explain that for this particular lesson, I'm not going to get into which side of the camera the fill should be on.  Technically speaking, a fill light is a flat light with no direction.  Therefore it should be exactly on axis with the lens and used only to open up the shadows, not enhance or create any of its own.  Now that I said that, you are going to notice that I wasn't as precise as I should have been with my fill placement.  You will know this because there is a cross-lighting pattern visible on all the following images.  The sliver of shadow you see falling behind the spool is from the fill, had I placed it more perfectly, there would be no visible shadow because it would fall directly behind the subject.  OK, enough on that point except to say that you will find what you like best with time and experience.

The following image depicts a 2:1 ratio.     But Travis, you just said they meter the same?!  Yes, I did.  I also said that light is cumulative (are you getting this yet?).  This means that my fill, measured by itself is at f/5.6.  My main, by itself, measures f/5.6.  Let's consider f/5.6 as one unit of light.  The fill is creating the same amount of light on both sides of the subject, so there is one unit of light on the right side, and one unit of light on the left side.  If I set up my main light on the left side of the subject and make it meter f/5.6, now I have two f/5.6 units of light on the left side of the subject.  To test this out, turn on both lights and meter again, only this time measure with the meter always pointing at the camera and at about the middle of the spool.  You will get measurements of f/5.6 on the right side, and f/8 on the left side.  Why?  Because two units of f/5.6 are hitting the left side, and twice the light of f/5.6 is f/8.

If you were to take a reflected reading, you would also see that the results would be twice as much light (or one stop) on the left side as on the right side.  Test it out, I promise this works.

Set the camera at f/8 because with digital we expose for the highlights, and KA-POW!!!!



Did it again!  Man, that's fun!  OK, so maybe I'm a little corny, but that's OK.  You can take condolescences in the fact that you're not the only one laughing at me !

Hopefully you can notice the difference between a 2:1 and a 1:1 ratio.  The 2:1 is not very contrasty, but there is a definite shadow side to the image.

Well, hopefully by now we're on the same page, so I'm going to move through these last two common ratios relatively quickly.  The first one is a 4:1 ratio and a long-time favorite of many portrait photographers.  With both lights firing, there is a two stop difference in light from highlight to shadow.  Again, this is the resulting ratio on the subject.  The main will meter at f/9.5 by itself and the fill is still at f/5.6 in this instance.  When both are fired, the cumulative effect will be f/11 on the highlight side and f/5.6 on the shadow side.  Two stops is 4 times as much light as its relative counterpart, so a 4:1 ratio is achieved.

Set your aperture to f/11.0... CHA-CHING!!!  Money in the bank!



The 8:1 ratio becomes even more difficult to calculate because a f/5.6 unit becomes such a small percentage of the ratio.  Suffice it to say that the easiest way to accomplish this ratio is just to meter with both lights on.  Get your fill light where you want it independent of the main, then leave it on and firing while you set your main light.  If the fill is still at f/5.6... hold on, I'll check... @#$% DOH!  Crap, I just tripped over my light stand and broke my collarbone.  I'll be back in a minute, after I get a sling and a bunch of pain killers to make me normal again...

Sorry for the delay, everyone still here?  So, the fill is still at f/5.6, and the main needs to read 8 times that brightness for an 8:1 ratio.  Hmmm, let's see here, 2X2X2=8 right?  So we need to increase its EV by 3 stops.  f/5.6 to f/8.0 is one stop, f/8.0 to f/11.0 is two stops, and f/11.0 to f/16.0 is three stops.  When all is said and done, we want the highlight side to measure f/16 if the fill is f/5.6, with both lights firing.  Dial in the power of the main until this is so.  You will probably be about 1/3 stop less than f/16, or f/14.  This will actually be approximate, but you will be so close to an 8:1 ratio that it would be difficult to disprove.  Which is also the reason why some photographers are willing to spend so much money on equipment with absolutely precise control.

Camera set to f/16...  Hold on, my batteries just died....  let's see here... I know I left them right over....  Here we go!  HOT DANG!!!  And Bob's your uncle!!



Well, if you made it this far, congratulations, and please accept my deepest sympathies for having to tolerate me.  The next post has a photoshopped image with all these exposures together so you can easily see what has changed with each one.  Feel free to comment as you feel is appropriate, even if it's to tell me I'm wrong.  I'm always open to learning as well, and I certainly don't intend to give anyone false information.

Thanks for hanging out this long and the best of luck with your next lighting setup,

Travis

Outstanding job Travis. That's a great tutorial.

Now how about deciphering that for someone without a handheld meter using two speedlights.

Thanks for the compliments, John.  As for not having a handheld, I am of the firm belief that it just can't be replaced.  I am young and of the digital age, which seems to be of the thinking that it's an obsolete item for professional photographers, but I cannot tell you how much easier it is to get precise lighting control with one as opposed to without one.

That being said... I also understand that a lot of people are working without one and I also have done some lighting with only my SB-600 speedlights and no metering.  So it can be done.  If I understand correctly, and if your camera meter is not fooled by other elements in a scene: you should be able to use your exposure values and remote speedlight capabilities of your equipment to accomplish the same thing.  Obviously light positions would remain the same.  Power output can be controlled by putting the two lights on separate channels and adjusting the exposure values respectively.  The camera will be working with reflected metering to determine each light's final output level, so in theory it should adjust accordingly.  So for each ratio, just set the EV adjustment value for each channel.

For example, you have your main light on Channel A, and your fill on Channel B.  We are setting up this way because we want the primary exposure to be based off the main light (i.e. the highlight).  Set the EV on the Channel B light to -1.0 for a 2:1, -1.5 for a 3:1, -2.0 for a 4:1, and -3.0 for an 8:1.  Again, this is mostly speculation because I don't personally use my lights this way very often, but in theory it should.  Test it out and see what happens, then let us know how things turn out.

It shouldn't matter how far the lights are set for your camera to get the exposure correct, but the final effects on the quality of the light will of course change.  Same goes for modifiers, the exposure should still be accurate if the camera is metering everything effectively.

Travis

Someone has been busy!  That last image is incredible.  Travis!  You should write photography books!  I am serious, I cannot believe how amazing this tutorial is.
Thanks!

I agree. great Job Travis!!!

A light meter is on the list as budget allows. I just have to muddle through as best I can until then.