East of Toronto

Good news for those of you east of Toronto: The Durham Region gets its own specials in Whitby.


They are:

  • April 11: Camera Skills for the Emerging Pro”, Half Day Special
  • April 12: The Efficient Photography Business (Intermediate)
  • April 18: ”Introduction To Flash” All Day Special
  • April 19: ”Flash In Practice”, All Day Special

These four courses are for committed amateurs or emerging pros. And they come with special prices for the books, also. See learning.photography/collections/training-misc for details and booking.

Book now: each course will go ahead if we get enough people, and there is strictly limited seating.

 

The inverse square law

As you all know, the inverse square law states that light gets weaker in proportion to the square of the distance.

So at twice the distance I get one fourth of the light. At three times the distance, one ninth of the light. And so on.

Good. So if I aim a flash at an object at one metre and get good exposure at f/5.6, then at two metres distance I expect two stops less light, i.e. f/2.8, two stops more open (i.e. 4x more light).

Let’s see. First, let’s use an LED flash light. At f/5.6:

Now when I move from 1m to 2m and make the aperture f/2.8, it should be equally bright:

What gives? It’s brighter! Only by reducing the exposure 0.5 stops do I get to the same brightness (as verified with the histogram, and looking only at the lit part):

So it seems that the inverse square law does not hold!

Here’s another example. I will shoot at 1m, 1.4m, and 2m. If the first shot is at f/8, the second one should be at f/5.6 (half the light, because 1.4 squared is 2), and the third f/4 (a quarter of the light, because 2 squared is 4). When I do that, I get:

Hard to see here, but they get brighter each time, while theory says they should stay the same.

Only by reducing the second picture by 0.25 stops, and the third picture by 0.5 stops, do I get the same exposure. So my flash apparently needs to be corrected by -0.25 stops per stop.

Wait. Is this crazy Mr Willems saying the Inverse Square Law is incorrect?

Yes. Yes, he is. I am. I am saying exactly that. The Inverse Square Law does not apply. Not to concentrated beams. The Inverse Square Law applies only to point sources of light that radiate that light evenly in all directions. When we move the light away from the subject, the angle loses us photons, but the moment we “catch” some of these lost photons and send them to the object we are lighting anyway—and that is exactly what we are doing with a concentrated beam—that moment, the law no longer holds. Yes, the light gets weaker, but by a smaller amount. That smaller amount, the “escaping photon recapture rate”, or “EPR rate” if you like silly acronyms, is +0.25 stop per stop lost, in the case of my Canon flash.

So what would affect the numbers?

Clearly, at the extreme end, with a laser beam, the correction is virtually +1 stop per stop lost (think about it: how else could we do moonbounce, where we bounce a laser off the surface of the moon). Meaning, the light does not go down at all with distance.  With a flash light, it is, as you see, a little less extreme: there is dropoff; just a little less than you would expect. With a large softbox that radiates in all directions, you will get something closer to the inverse Square Law. With an umbrella, you get closer to it still.

But this is not a theoretical discussion, of interest only to geeks. This is important in practice to us photographers. If I move a snooted hair light twice as far away from the subjects it is lighting I should get two stops less light (2 squared = 4). But the light reduces less than that. So instead of going, say, from f/8 to f/4, I might need to go from f/8 to, say, f/5.

My advice: Learn how the light sources you use (straight flash, bounced flash, umbrella, softbox, etc) behave when you double the distance. Do this in the dark, so ambient light plays no role. Easy enough, and then you have an idea that will be valuable in real-life practice.


Check out my e-books on http://learning.photography/collections/books and learn everything I know. Taught in a logical fashion, these extensive e-books (PDFs with 100-200 pages each) will help you get up to scratch quickly with all the latest techniques. And when combined with a few hours’ private coaching, in person or via Google Hangouts, you have no idea of the places you’ll go. You’ll be a pro!

Stop!

Today, a word about stops.

First of all, they are called “stops” because the rotating wheels, like the one for aperture, used to click at certain settings (in the case of aperture, settings like 2.8, 4.0, 5.6, 8, etc).

These “stops” are chosen so that in all quantities, a stop is half, or double, the light. Here’s the options:

  • ISO: 100, 200, 400, 800, 1600, 3200, 6400  –> brighter as you increase
  • Aperture: f/1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45   —> darker as you increase
  • Shutter speed: 1 sec, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000   –> darker as you go faster (to the right).

To keep a picture at the same brightness, you need to increase and decrease by equal amounts. The three are related, in other words, like this:

So these would all be the same brightness:

  • 400 ISO, f/4, 1/125
  • 800 ISO, f/5.6, 1/125
  • 200 ISO, f/8, 1/15
  • 100 ISO, f/1.4, 1/250
  • 1600 ISO, f/16, 1/30
  • 100 ISO, f/1.4, 1/250
  • 1600 ISO, f/5.6, 1/250
  • 100 ISO, f/5.6, 1/15

So as you see, there is not “one setting” that suits a situation.

Look at the last three. The first one is what I can do in the room I am sitting in right now, with my fast prime 85mm lens. Now if you have an f/5.6 consumer lens, you need to either go to 1600 ISO (grain!), or to 1/15 sec (motion blur!). Just saying.

If you want to be a pro, you need to get a feel for this and for the numbers. So today, set your camera to manual and go take pictures. get a feel for “normal settings”. You should know, without trying, that a dark room at night will not work at 100 ISO, 1/500 sec and f/11. Or that a sunny day will look all white at f/1.4, 400 ISO, 1/40 sec.

And it’s cool to know this stuff!

 

TWIP

NEWS: On March 2, I will co-host TWIP—This Week In Photo, the world’s best and most popular weekly photography podcast.

If you don’t follow TWIP yet, start now. http://thisweekinphoto.com/ – live that day, and online the week after. Don’t miss it.

And if you have not heard it, listen to my previous appearance on TWIP, a long 2012 interview with Frederick Van Johnson. This was taped while I was teaching my 5-day Flash course at Brock University for The Niagara School of Imaging. Frederick is a funny and engaging interviewer.

TWIP is a pleasure to listen to, and it will be a pleasure to co-host it.

 

Fringe.

Or rather, de-fringe.

Look at this photo of my garage during last Sunday’s garage art sale:

But look at original size and at the very edges, where there is back light (think: a tree against a sky), you will see some colour fringing (known as “chromatic aberration”). Look at the black picture frame, or perhaps even more clear, at the model’s head, and you will see purple/red on the left, blue/green on the right (it may help to look at the image full size):

Now, in the “Lens Corrections” panel, you see the option “Remove Chromatic Aberration”? Let’s click that on. Now we see:

Can you see how it is now gone? You can go into the “Color” tab within this panel and tune the settings, but you usually do not need to do that.

Now, back to the exhibit. Look at the full image at its original size. That was my Garage Wall Art Sale. Now “was”: it is my sale, since it is ongoing. I am selling framed prints and unframed prints, mainly at 13×19″ size, some larger, in categories including:

  • Colourful: images whose bright colour is the main feature
  • Travel and cities: images of iconic cities like New York, Hong Kong, Toronto, London, Jerusalem, and so on: I have worked in 40 countries.
  • Black and White: images that look great as artistic B/W prints on any wall.
  • Nudes: artistic nudes, of which I have hundreds, featuring my muses
  • Sailing: showing that even “Lake Onterrible” can look great.

These prints are handmade by me on permanent museum quality paper using permanent pigments (not dyes, which can fade after just a few decades). They are also autographed, and are made in limited editions or even as one-offs.

In other words: they can form the basis of your wall art collection. Collecting such wall art can be an amazing hobby. See www.michaelsmuse.com for more detail, and remember: if you buy out of the garage, Garage Sale prices apply, and these can be as low as one quarter of art gallery prices. So, come see what’s in the bins and display racks and decorate your home with originals today.