Photography Tip: Inverse Square Law

Man I hate maths.

Excellent video and it made sense (later), but maths just confuses me. Chuck numbers in front of me and my brain shuts down.

Good on them for demonstrating it practically. It makes sense how it can affect photography. Basically the closer you get the more contrast you get. In certain situations of course.

HOWEVER it must be noted that the closer a light source gets the softer it is. The sun is HUGE but it's really harsh because it's just a little dot in the sky. Note how they were using a huge soft box and had some ambient light to soften the edges. This video excellently displayed the how light falloff works in general of course.



I'd say this.
The closer to the light = softer but more contrast (handy)
The further from the light = more hard shadows, but less contrast difference... if that makes sense.

Bouncing your light off the roof over the heads of a group of people will let the light fall pretty evenly over them (if they have a roof over their heads that is).

image-vision wrote:

As far as I can say from one time viewing (on a foreign language) there’s nothing wrong what you were saying but the video is in parts very much misleading!
Also, knowing the rule before viewing this video I expected more questions to answered – may be that is something you can cover on your next videos.

Misleading:
You say , the farther a group of people (or a face lid from the side) is away from a ligjt source, the less is the light fall-off within the group (or within the face).
This is absolutely true!
BUT the photos, you shot, in the studio (face) – you are using ambient light. That is, the Octobox is not the only light source. So the photos you show in the video are not correct, since you use other lightsource(s) too, not only the Octobox!
The photos (and your words) give the impression: If you don’t want to have hard shadows in the face of a person your shooting – improve the distance between the person and the lightsource. – Which is ( I hope you know this) absolutely wrong – especially is you use such a large Octobox as you in the video.
The hardness, (harshness) don’t know the correct english word, is determined by the size of the lightsource versus the size of the object and the distance to the object. The bigger the lightsource the smoother the light, but the greater the distance between lightsource and object the harder (harsher) is the light.

(The best example is the sun – it’s millions of km or miles away. If on the early morning after sunrise, or late evening befor sunset, the sun is coming form the side you, get a huge fall-off in light – even bigger than you showed on the first picture when the girl ist just 1 feet away from the octobox – but the sun is muuuuuuuuch further away. So the way you explained it there should be no light fall-off, since the sun is really far away. You’r proven wrong!)

So it’s basically the opposite of that (what you don’t exactly say, but what you can see at the face-photography at… 8(?) feet) – actually at the end of the video you even say it – if you want to shoo a group, bring a greater distance between the group and the flash – this is (I’m sorry BULLSHIT). Please tell me who the heck would place a flash (if it’s only one flash) on the left or on the right hand side of the group (only in that case you would be right) instead of in the front of a group?)

What did I expected more and did not see in the video:
You shot this video in a photo studio, that’s the best location, to explain the correlation between (intensity of) light, aperture, ISO and shutter speed.
Let’s say, I already have the correct settings for a shot, but I want the model to move closer to me or further away (and that could be for example double, or half the distance (away from /towards to) the flash ---- How do I adjust my camera settings to have the same correct exposure? This is what I expected to see in the video.
Aperture (F-stops), ISO, shutter speed, are directly related to the inverse Square Law. (And it’s not too difficult to explain, with respect to the amount of light) Unfortunately you didn’t loose any word about that.

Please don’t get me wrong. But I see so often that people see the number (5.6. 8, 11…) of f-stops but they have no clue what it means in terms of “amount of light” and how it relates to ISO, or shutter speed. And a lot of it is explainable with the inverse square law – or “what to to if the distance between light and object changes?” – And btw. why are the Aperture numbers so odd – all explainable with this law….

Unfortunately you didn’t explain it. Hopefully in the near future?

Yes yes, but this video was explaining ONE thing not everything. Note how it's episode 59.

MLKstudios wrote: An example of a Week 4 student, posted today (shot yesterday). There's a lot wrong with it, she's still learning. She's had her T2i camera but a few months.

Can anyone tell me, after watching the video above, how come the second girl isn't darker than the closer one? It's lit entirely by on camera flash she got yesterday. Not off camera flash.

Bounce flash. You can learn that from a youtube video too. Your point?

I asked you to explain it using what you learned from the video above. It too applies.

Towcestermark wrote: I think that we must remember here that Mark Wallace produces marketing videos, not instructional videos. And, I mean that in the nicest possible way, the videos are made to gain revenue, sign ups, advertising, selling products that their company makes on.

[..]

Don't be too harsh, he's gotta present this stuff...!

Tow seems to "get" what the video is really about. You watch it and want new lighting. The tools he's using are very expensive, especially for a beginner. The impression he gives us, is one can't achieve great lighting, without buying fancy gear and having a big studio to work in with lots of light modifiers (umbrellas, softboxes and whatnot).

That's simply not true.

______

The reason the kids get exposed evenly is, when you bounce the light off the ceiling, the distance the light travels is about the same for everyone. That evens out the exposure.

This is one of the reasons why bouncing is important, and is why you should own a flash that tilts (and swivels). It allows you to do so much more with the flash than one that only aims forwards.

______

That was my point, SN. How to apply the inverse square law in more practical terms, and understanding how it applies to everyday photography -- without needing $10K worth of lighting equipment.

Matthew

T.Mark, good perspective; it's just one presenter's effort to answer a question/explain a concept, not meant to be comprehensive.

Square root and 8th grade math?? - that leaves me out of it! LOL I glazed over before the video was done. Basically, if you double the distance from the flash you don't cut the light in half, you cut the light... the square root of the distance? - well more than half. Or something like that.

So basically when people at sporting events are all shooting off their flashes the light doesn't even get close to lighting the subject which is probably a ballplayer down on the field and they're up in the cheap seats.

Matthew that did help explain why bouncing a flash works. I might actually buy a flash one of these days...

It's easier to calculate the other way. If your light is ten feet from the subject and you want to cut the power in half (and have already lowered the actual power all the way), then you increase the distance to 14 feet (10x1.4), or ten feet times the square root of two. Or you could instead add a one stop scrim (green edged).

Twenty feet away woud be two stops, and twenty-eight = three stops, forty feet = four stops, and etc.

To double it, would be the same as moving it from 14 to 10 feet. Or from 2.0 feet to 1.4 feet. Matches the full stops on your lens.

That's the more complicated part of lighting expressed mathematically. It does help to know when shooting movies and doing studio work.

And yes, the little flashes on cameras are lighting up the back of the heads in the row in front of them. Not reaching the field. But, don't say anything 'cause it looks cool when they all go blink.

Maths is a load of crap, you don't need it for photography. All you need is to be able to think like light.

I used to use this simple equation when I first got into lighting. Take a shot with the lights on, if your picture is too dark, move back or turn it down.

You'll find that doesn't actually work in real life, but it sounds like it does. Then take two lights, again, take a shot. If it's too dark move closer and vice versa.

What you end up with is a load of rubbish shots. It's at that point you may realise that taking a decent shot with lighting is a little more complicated. If you do the learning, and the experiments (like taking 100 shots of an egg with different lights), you'll become good (this isn't guaranteed).

Then you may get the ultimate accollade from a non photographer.

"Wow, that's a great shot, you must have a really great camera"

I reply, "Yes, I do have a great camera. Thank you."

You have a bad understanding,The initial power would be so great 1ft from the sun so it would have to be many, many millions of miles away to have a lose of strength great enough to be decernable. As to a group , if light was head on and real close, the distance from the first person(one on the front row), and the people on the back row would have a drastic appearance due to quick fall off statisically. The further away would make the light falloff less and thus the front and back rows would appear as the same strength of light.

I probably don't know what I'm talking about, but if that strobe is fired at full power, won't it overpower the ambient light in the room? Doesn't shutter speed affect ambient light exposure vs aperture which affects strobe exposure? If I wanted that background to go dark, couldn't I just shoot at 1/250 and maybe go to 1/2 power on the strobe? Or am I way off?

Thank You

I was like uhuh.. uhuh... then towards the end I was like holy crap! It is so useful and makes so much sense especially with group photos. Great work Mark!

nice thanks for that information