stepped lighting setup and inverse square law (with pics)

it took me a while to figure out the right way to set up my strobes, and although i knew about the inverse square law, im just getting the hang of it. maybe this can help some new photographers. zack arias' one light dvd really helped me.

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Call me crazy, but I like the available light shot. I don't understand the point of your post. One light isn't about studio lighting, it's about lighting on location. White backgrounds are irrelevant.

The point of his post is to visually show the inverse square law.

Actually zacks one light DVD did have some studio work in it. The point of this post was to yes, show the inverse square law, as well as maybe help someone understand what seems to be difficult for some people including myself until recently. If you don't like it, you didnt have to comment.

You are improperly applying the inverse square law.

Moving a point source light half the distance closer to the light changes the exposure at the square of the difference, or 4 times.

The best exercise is to place a point source light (Think speedlite with out modifier) on a light stand and place the light stand 11 feet from the subject. Adjust light power and camera ISO setting for proper exposure at F8. Now move the light to 8 feet from the subject, you will find that changing the aperture to F11 will get the exposure very close.

That's the inverse square law at work. It also demonstrates that once you know that 1/4 power on your speedlite at 8 feet gives proper exposure with camera set to ISO 200, F 8 at x-sync shutter speed (or whatever your tests determine) you now have a reference for working in the field.

Here is my favourite video on it. Cleared it up for me. I think if you are into flash photography it is just as important to understand the inverse square law as understanding the ISO, shutter speed and aperture relationship for regular shooing.

http://www.youtube.com​/watch?v=f5BIvSBjvLg

Why worry about all the math. That was fine in film days but is it really needed any more. Its easy you move the flash closer it gets brighter. move it further away it gets darker. In real world you are not going to be at an wedding and be like i moved it 3 feet so I need to change this. So then you can balance everything shutter speed, aperture, iso, flash to subject distance, flash power. Really to me it is almost second nature. David Hobby phrased it the best in his first siminar. "Don't get caught up on inverse square law. its basically you move the flash closer the brighter it gets , move it back the darker it gets. "

Dont get me wrong its good to learn. However on an shoot I am not going to be sitting there saying well its 6 feet to the subject let me measure and move the light. There is already an ton of stuff flying through your head like in an wedding there is no need for more math.

I don't ever worry about the math but it sure was interesting to learn. I think the math makes it easier to understand and then you just work with it. It helped me set up first photo booth because I knew people were going to be 2 or even 3 deep at times and I wanted to light them evenly. I hate going into anything unprepared.

bhursey wrote in post #15821193
Why worry about all the math. That was fine in film days but is it really needed any more.

If folks understood the Inverse Square law, they would never ask

• "Will my flash reach (this far)?"
  
• "Will my flash overpower the sun?"

• "I was thinking of using HSS outside as fill flash (and the subject is 15' away)..."

bhursey wrote in post #15821193
Why worry about all the math. That was fine in film days but is it really needed any more. Its easy you move the flash closer it gets brighter. move it further away it gets darker. In real world you are not going to be at an wedding and be like i moved it 3 feet so I need to change this. So then you can balance everything shutter speed, aperture, iso, flash to subject distance, flash power. Really to me it is almost second nature. David Hobby phrased it the best in his first siminar. "Don't get caught up on inverse square law. its basically you move the flash closer the brighter it gets , move it back the darker it gets. "

Dont get me wrong its good to learn. However on an shoot I am not going to be sitting there saying well its 6 feet to the subject let me measure and move the light. There is already an ton of stuff flying through your head like in an wedding there is no need for more math.

I know what I'm going to do at a wedding and don't have to think about things like the ISL because I did all the testing and practicing to learn how my equipment performs long before I took the job to shoot the wedding.

If one has to think about this stuff on the job, they probably shouldn't be charging a client and calling themselves professional because they lack the knowledge, insights and experience that a professional brings to the job.

David Hobby, Joe McNally or anyone else can say whatever they want. They are knowledgable professionals that know what lighting equipment needs to deliver.

If they are trying to make something seem less daunting that's OK as a teaching method. It doesn't make the basic rules of physics void, it just means learn them later when you realize that that knowledge will be useful.

Saying "Its easy you move the flash closer it gets brighter. move it further away it gets darker." is singularly unhelpful. It's at about the same level as "Look through the back of the camera and point the front at your subject or you'll get pictures of your earhole". Both are 100% TRUE but actually explain 0%.

Some folks can do the math(s) (some of us learned our flash technique when that was the only way to calculate exposure) and some can't. To denigrate the need to do so on occasion simply relegates the basic laws of Physics to the same category as "You Press the Button, We Do the Rest". Hopefully, understanding has moved on from the 1888 stage.

The methodology of the OP in illustrating the Inverse Square Law was so far off the mark that I feel it detracts from understanding rather than adding to it.

You're right Phil, I should have been clearer about bad teaching techniques.

Wilt wrote in post #15821954
If folks understood the Inverse Square law, they would never ask

• "Will my flash reach (this far)?"
  
• "Will my flash overpower the sun?"

...and combined with the simple understanding that HSS immediately loses you -2EV of flash power when your shutter speed is even 1/3EV faster than X-sync speed, they would also never ask

• "I was thinking of using HSS outside as fill flash (and the subject is 15' away)..."

And they would immediately understand that moving the light from 4' away to 8' away makes that light -2EV as bright at the object being illuminated...because double the distance is 1/4 the light, or -2EV. An even the mathematically inept can remember to use distances as f/stops...f/4 to f/8 is -2EV, the same result and NO computation!!!

That's why!

Very well put. Says it all

dmward wrote in post #15822337
I know what I'm going to do at a wedding and don't have to think about things like the ISL because I did all the testing and practicing to learn how my equipment performs long before I took the job to shoot the wedding.

If one has to think about this stuff on the job, they probably shouldn't be charging a client and calling themselves professional because they lack the knowledge, insights and experience that a professional brings to the job.

David Hobby, Joe McNally or anyone else can say whatever they want. They are knowledgable professionals that know what lighting equipment needs to deliver.

If they are trying to make something seem less daunting that's OK as a teaching method. It doesn't make the basic rules of physics void, it just means learn them later when you realize that that knowledge will be useful.

I agree I should of not just done an statement like that. I know that it has an purpose.. Like you said you learn your equipment.. I have gotten where most of the time in quick strobist setups at weddings and on location shoots i have my starting points and normally can judge situations enough and i can normally get the exposure within one stop. Then i can do an single tweak to get the exposure i want just once.

digital paradise wrote in post #15820093
Here is my favourite video on it. Cleared it up for me. I think if you are into flash photography it is just as important to understand the inverse square law as understanding the ISO, shutter speed and aperture relationship for regular shooing.

http://www.youtube.com​/watch?v=f5BIvSBjvLg

Thanks for the link.

I don't think he made the "math" less intuitive (it is sort of common sense when explained correctly), but it's a nice reminder on how critical it can be to distance from light to main target as well as background.

In tabletop, it can be a tradeoff. Bigger lightsource, further can be more even on target object (esp with shiny rounded objects) but light spillage can be harder to deal with.