How to Get a Pure White Background Using the Inverse Square Law | Ask David Bergman

Today's question from Nathaniel B. is, “When shooting portraits, I have trouble getting a pure white background. I’ve heard a little about the inverse square law, but I’m not sure exactly how to use it. Can you help?”
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#whitebackground #learnphotography #adorama
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00:00 Intro
01:16 Set.A.Light 3D virtual studio software
03:10 What is the inverse square law for photography?
04:39 Using the inverse square law to control your background
08:03 Other ways to use the inverse square law
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THANKS SO MUCH FOR WATCHING!

[@eradicator187]

I'm still pushing buttons that I have no idea what they do, but I'm learning a lot by watching your videos.

[@gregblue8113]

Really good explanation of the inverse square law! I'm a bit old-school with backgrounds - if I want a white background, I am going to use an actual white background (like you), move my subject further away from it, and use a couple of background lights to light it (assuming I want it even). I'd have 3 problems with using one light and moving it further away to achieve white; 1) you won't get a white background (even if you stand your subject right against it), you'll just get a light grey background; 2) you would likely radically alter the quality of the light on your subject for the sake of your background, and 3) the further your light is from your subject, the less control you will have over it. So I like to keep my subject light as close to my subject as possible, as I get more control (inverse square law also creates light fall-off on your subject when the light is in close, which can look beautiful - I'm not a fan of flat, even light). I then use a hand-held light meter with ambient and reflective readings to quickly tell me exactly what tone my background will be in relation to the aperture I have set for my subject light - for example, if my ambient light meter tells me to put my camera at f11 to properly expose my subject, I will then put on the meter's reflective meter disk, point it at my background and adjust my background lights until I get a reflective reading f32 - that tells me I will get a pure photographic white background (at least for my Nikon D810 - the ratio can be a bit different for other cameras).

[@sindbadsailor7868]

Hmm… this is really open my eyes about my light… thank you very much

[@jdanishevsky1]

Great advice and at first seems complex, but it makes more and more sense as you think about it and now thinking about some of the shoots I have done and the results I did and didn't achieve, I can see how it all comes together. Thank you for sharing David. Great video in deed.

[@rumporridge1]

Kind of mess around till I get what I like. Works most of the time. No matter what though the lighting process is fun fun and more fun.

[@wendystumbaugh695]

David, you explain these things so well!

[@avpjon]

Excellent video and explanation! Thank you, David

[@davidromano2421]

Good explanation of the inverse square law. I never consider it when trying to get a white backdrop though. I always light the backdrop and the model separately.

[@pictureeyecandy]

Great way to teach how light works.

[@T-Slider]

Sounds great! Oh darn, I just ran out of 40’ studios! Or, use an incident light meter, one with the little white dome on it, and move or add light so the metered light gives you the same reading on your model/subject and on your background.

[@tarjei99]

I tend to use stops. Light falloff is proportional to the distance between stops. 1.4 times further away means that light is halved. 4 times the distance is 1/16 times the light. The result is much the same as the inverse square law.

[@jer3006]

Well, David, everything you said is true about the Inverse Square Law yet everything you said pretty much defies the Law of Common Sense. So make the bkgd white by moving your light farther away from it? Hmm. Hey I love seeing you use set-a-light-3D! I've been using it for about a month but I still didn't realize you can move the bkgd as you did! Your examples using that program for this video are spectacular. One way I use it is to model what I see you YT pros illustrate in your videos, then adjust the diagrams until the setup works in my home studio and with my equipment. It is a great program. Really appreciate this video-thanks!

[@triteksolutionllc5000]

Thank you for clearing it out

[@DavidVelezPhotography]

Thanks, David, for a great tutorial.

[@tanweercaa]

Nice job David, thanks a lot.

[@AndyZavodny]

I like the light it separate method…take extra lights but I get better results that way.

[@JamesBoyer-plus]

Thanks, David. Your use of Set.A.Light 3D really helps in visualizing the inverse square law. I like using the second technique you presented to light the background separately. And, recently I've been experimenting with using a large softbox as the actual background. When the model is close enough the modifier acts as both background and edge lighting creating a soft wraparound from behind that highlights the cheekbones and clavicle.

[@AquaticBaboon]

I learned something! Love these videos

[@garrettfitzgerald955]

Great explanation of the Law. And bonus I forgot the name of the software. Thanks

[@felixrodriguez4263]

So working out the numbers to the distance can workout how much light is expose to the subject. But as you explained there numbers of way to balance out the light on the subject. Good and handy way to solve the lighting on the subject and background. Another one to place and keep inder one belt of tricks. Nice one David

[@tedk2814]

Its always helpful for me to hear different explanations of the inverse square law, but it doesn't work in Gavin's small home studio.....same strength from one side to the other. Actually, I have a conference scheduled with you mid July about lighting a very large high school band in the gym. I'm sure you will be a able to help me get it right. What I have so far is two 7' umbrellas with 600 watt strobes and the band has 250 members ( will fill the bleachers back 12 rows.) Of course there is natural light option also. This is my first big job with the band, football team and cheerleaders, I scheduled it for two days. Can't wait to speak with you. Thanks, Ted

[@marcelowilson-barnett3768]

Thanks so much

[@kapilbhallafoto]

Very useful

[@chikezieJack]

Interesting I like it

[@longliveclassicmusic]

One thing I feel like no one talks about with moving the light source further away from the subject is that you also need to raise it up higher, unless you want the light flatter and flatter. Say you have a gorgeous loop lighting or Rembrandt lighting pattern on the subject. If you move the light further away, all of that sculpting will just fall flat. This is why it's important to understand that the further the light source from the subject, the higher it needs to be raised to achieve the same lighting pattern on the face and background. What this can mean in a small studio especially is possibly using an extension head on your light so you don't have a huge monolight sticking out the back of the modifier and limiting how high you can get it. This became a problem in this demo because the further the light was moved away, the higher the shadow cast by the model moves upward behind her to where it starts to get in the shot. If the light was also raised up, the shadow cast by it would hit closer to the floor. This may not be totally specific to the inverse square law itself, but it's crucial to keep in mind when moving lights closer or further away to try to work with the inverse square law.

[@pattymattes7124]

I was putting the subject close to the background but now I light the background. Even with that the floor is not going to be pure white. You have to use some editing "magic" to get it all pure white. Gavin Hoey did a video on that.

[@tonytoffolo9915]

am i correct in saying that one other thing to consider in the second scenario, where the light source is moved backwards by a considerable amount, is that the light will end up being harsher (less soft) unless you compensate by using a much larger modifier?

[@DavidBergmanPhoto]

Yes!

[@icestrength7098]

Could you then use a second flash aimed on the backdrop, set at an intensity that would lighten the backdrop to the same intensity as the model regardless of distance? Say a flash was set at 1/4 max power and based on the inverse square law and the positioning, the backdrop got 1/3 of that (so effectively as if the light was set at 1/12 max if it was the same distance from the main flash as the model),. Could a second flash be set to the backdrop at the same distance as between the first flash and the model with the power set to 1/6 and achieve an even amount of light to the backdrop and model? The model should be taking on 1/4 max power and the backdrop should also be at 1/12+1/6 = 1/4 max power if my thought adds up.

[@DavidBergmanPhoto]

You can always add another flash to light the backdrop and simply adjust to taste. :)

[@b991228]

If you use a second pair of lights up close to illuminate the background to pure white and get a meter reading at f/5.6 yet have the camera and main light way-way back on the other side of the room will the camera at f/5.6 show a pure white background?

[@longliveclassicmusic]

Yes, but you want to meter the background with ALL the strobes firing as well. Otherwise if all strobes individually meter at 5.6, combined they will be overexposed and will start to create some serious haze and lens flare in your shot. It's actually safer to be a tiny bit underexposed and then bring down the white point in your raw processor, possibly using Luma Range in Capture One to isolate that adjustment, than it is to get a perfectly white background in camera. The goal is to get CLOSE in camera and take it the full distance in post-production, with anything.

[@DavidBergmanPhoto]

Yes, but usually better to overexpose your background a bit if you want pure white. So meter reading of 5.6 but the shoot at f/8 or f/11. Of course then you have to put more light on your subject so they are also f/8 or f/11.

[@SwoleBeastTribe]

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[@loribott6119]

Why do you keep saying it's white now, it just looks like a lighter gray. I am confused.

[@asterisk606]

It's just to prove the concept. The software is just a simulation. In real life you would keep adjusting it to get what you're after using the techniques he covered in the video like moving the light or the backdrop.

[@Devdattab]

It will never be true "white" till the time another light is used to illuminate it to a brilliant white.

[@nelsonclub7722]

Well. 1 In practice it is a lot more complicated than this. 2. There are many, many easier solutions.

[@asterisk606]

Like what many, many easier solutions other than lighting the background itself like he covered at the end? I'm sure people will appreciate being able to read about easier ways of doing it and get ideas to work with