stepped lighting setup and inverse square law (with pics)

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!

Additional reasons why...

• So that you understand when you shoot a photo with one subject at 11' and another equally important subject at 16', that the person at 16' will be underexposed by -1EV when using direct flash to illuminate both.
  
  
• So that when you have a white background behind your portrait subject and you do not separately illuminate the background with a light source, that if your subject is about 5' away and the backdrop is at 8' away, you will never see the background as white...it will be grayish...and you will not wonder 'why?!'
  

Like I said I don't use the math but was going by 2 x 2 = 4 and drop the 1 in which equals 1/4 and so on. Wilt really explained it well. Makes it easy to understand. Learning how to isolate the subject and light multiple subjects is the key to this all, math or no math.

I agree with dmward and his f-feet example was right on. Where things get interesting is when you go to a broad source. You can think of that as a 2 dimensional array of point sources. Then the distance varies from each to the subject as d = sqrt(a^2 + b^2) with a = distance of center of source to subject and b = distance of array element to center of source. Therefore you won't get quite the same decrease in exposure per distance with various size broad sources. Fun calculus problem.

J Michael wrote in post #15826343
I agree with dmward and his f-feet example was right on. Where things get interesting is when you go to a broad source. You can think of that as a 2 dimensional array of point sources. Then the distance varies from each to the subject as d = sqrt(a^2 + b^2) with a = distance of center of source to subject and b = distance of array element to center of source. Therefore you won't get quite the same decrease in exposure per distance with various size broad sources. Fun calculus problem.

"Oh vey...head hurts" (as a Jewish Charlie Brown might say!) with that math

Far easier to think Inverse Linear when the large source is within about 2-3x the largest dimension of the source. So to move large light from 5.6' to 8' means not -1EV (as in Inverse Square) but more like -1/2EV

Point source, speedlite without modifier. move from 11 feet to 8 feet one stop.
Speedlite in 28" Apollo move from 4 feet to 2.8 feet or 2 feet somewhere between 1/2 and 1 stop.

At that point who cares. I'm chimping and if its within a 1/2 stop I'm not going to waste time making an adjustment in camera that I can make in a second or two in Lightroom after I choose the keepers.

dmward wrote in post #15828498
Point source, speedlite without modifier. move from 11 feet to 8 feet one stop.
Speedlite in 28" Apollo move from 4 feet to 2.8 feet or 2 feet somewhere between 1/2 and 1 stop.

At that point who cares. I'm chimping and if its within a 1/2 stop I'm not going to waste time making an adjustment in camera that I can make in a second or two in Lightroom after I choose the keepers.

BLASPHEMY, you anti-get-it-right-in-the-camera person, you!!!!

Bracket, man, bracket!

LOL

PacAce wrote in post #15829258
BLASPHEMY, you anti-get-it-right-in-the-camera person, you!!!!

Bracket, man, bracket!

LOL

LoL,
I spent too many years, planning lighting, creating the lighting scheme, then shooting packs of Polaroid to get everything just right for an AD, then bracketing the ***L out of the shot with transparency, and negative film.

Leo, you know as well as I do, that digital is SO much better than film for image control from capture to presentation. I just snicker when I'm with a bunch of young photographers who talk nostalgically about shooting film. Then I realize, its probably what I learned shooting film and lighting for shots with transparency film that makes it so much easier for me to do digital.

dmward wrote in post #15829606
LoL,
I spent too many years, planning lighting, creating the lighting scheme, then shooting packs of Polaroid to get everything just right for an AD, then bracketing the ***L out of the shot with transparency, and negative film.

Leo, you know as well as I do, that digital is SO much better than film for image control from capture to presentation. I just snicker when I'm with a bunch of young photographers who talk nostalgically about shooting film. Then I realize, its probably what I learned shooting film and lighting for shots with transparency film that makes it so much easier for me to do digital.

You did have an little more latitude in film than with digital. However I have never done film in an studio just outside. I still use it for my architecture photos because of the dynamic range and the feel of it. I use an old Nikon fm2n.

dmward wrote in post #15829606
I spent too many years, planning lighting, creating the lighting scheme, then shooting packs of Polaroid to get everything just right for an AD, then bracketing the ***L out of the shot with transparency, and negative film.

My favourite was always the AD who wanted "simple little things" like totally reversing diminishing perspective or placing highlights where they couldn't possiby fall relative to their associated shadows. Oh, such Happy Days

bhursey wrote in post #15829895
You did have an little more latitude in film than with digital. However I have never done film in an studio just outside. I still use it for my architecture photos because of the dynamic range and the feel of it. I use an old Nikon fm2n.

Architecture photography is SO much easier with digital. My 5DIII has auto bracket up to 7 frames. Lightroom 4.3 has the ability to process 32 bit floating point TIFF files. These are generated via Photoshop merge function. It is so much better than what I had to go through to get the images I wanted on transparency 4x5 sheet film.

TSE lens are almost as good as the movements on a view camera. If I could justify it, I'd get a digital back from a Sinar or similar view camera frame.

Eric Chan, an Adobe engineer who is responsible for the design of much of the processing power in Camera Raw and Lightroom engine, designed the exposure process using floating point files with extreme dynamic range. Once it worked to his satisfaction he reduced the range to 10 EV. They added the extended range capabilities into 4.3. When working on a floating point file the range is extended to 20 EV.

That's way beyond anything film could do.

As an aside; While on the plane today, I was doing some clean up on Lightroom working files and came across a 3 frame bracket, one image was -2EV, 0EV, and +2EV. I noticed that none of the images showed blown highlights or clipped shadows. I adjusted the exposure slider for the two that were minus and plus. When exposure was adjusted three are almost indistinguishable.

This of course has nothing to do with the ISL.

Whortleberry wrote in post #15830921
My favourite was always the AD who wanted "simple little things" like totally reversing diminishing perspective or placing highlights where they couldn't possiby fall relative to their associated shadows. Oh, such Happy Days

Phil, I always wondered where that guy went.

dmward wrote in post #15830995
Architecture photography is SO much easier with digital. My 5DIII has auto bracket up to 7 frames. Lightroom 4.3 has the ability to process 32 bit floating point TIFF files. These are generated via Photoshop merge function. It is so much better than what I had to go through to get the images I wanted on transparency 4x5 sheet film.

TSE lens are almost as good as the movements on a view camera. If I could justify it, I'd get a digital back from a Sinar or similar view camera frame.

Eric Chan, an Adobe engineer who is responsible for the design of much of the processing power in Camera Raw and Lightroom engine, designed the exposure process using floating point files with extreme dynamic range. Once it worked to his satisfaction he reduced the range to 10 EV. They added the extended range capabilities into 4.3. When working on a floating point file the range is extended to 20 EV.

That's way beyond anything film could do.

As an aside; While on the plane today, I was doing some clean up on Lightroom working files and came across a 3 frame bracket, one image was -2EV, 0EV, and +2EV. I noticed that none of the images showed blown highlights or clipped shadows. I adjusted the exposure slider for the two that were minus and plus. When exposure was adjusted three are almost indistinguishable.

This of course has nothing to do with the ISL.

Yah but what I mean is an single frame. Sure HDR will work great. I use magic lantern it does 7 also exposure. Normally my wife is saying hurry up Brian. I also like the feel of film, maybe im just crazy.. Maybe because it makes me think. I dono I like that it is something tangible. I am sort of backwards. Really started my digital slr then I started using film.

bhursey wrote in post #15831078
Yah but what I mean is an single frame. Sure HDR will work great. I use magic lantern it does 7 also exposure. Normally my wife is saying hurry up Brian. I also like the feel of film, maybe im just crazy.. Maybe because it makes me think. I dono I like that it is something tangible. I am sort of backwards. Really started my digital slr then I started using film.

HDR and 32 floating point are different. (At least the kind of HDR I see coming out of Photomatrix. )

As for film, I shot film professionally starting in 1968 and that was a lot of developing, etc. ago.

If it helps you creatively that's great. I got so sick of the smell, mess etc. that I quite shooting for myself. (I'd already quit doing it professionally.) The a friend showed me his G-2 Canon and Photoshop 3 on his computer.

I've been hooked on digital since. And now do it professionally again.

I do admit that what I learned shooting film helps me continuously shooting digital.

dmward wrote in post #15831123
HDR and 32 floating point are different. (At least the kind of HDR I see coming out of Photomatrix. )

I don't use Photomatrix I use nik. I try to keep mine realistic. I hate tone mapping.... See I don't over do it BTW this is 9 exposures its great except for the ghost children running to the water.

That's nice. Seems your waves would be a little hard to deal with across multiple images in addition to the people.