Perfect Exposure is Easy

You know how you can read about something a million times, and eventually you come across wording that finally makes it all click?

No, I didn't take it! But I love the aperture illustration.

One of my readers from Australia, who knows much more about photography than I do, submitted a comment which turned into an email conversation which turned into a detailed treatise on Getting the Exposure Right.  Thanks Mike!  You are from Australia, right?

Anyway, Mike made quite a few ideas click for me.  (I know there is a photography pun in there somewhere, but I’m too tired to find it right now!)

I’m going to break his tutorial up into several short tutorials on exposure, because it’s good stuff.

We all know that we need to get the exposure right, whether we shoot on automatic or not.

The exposure depends on the amount of light hitting the sensor in the camera when the shutter is pressed.  Too much and the photo will be too light, possibly with “burned out” white skies and skin details.  Too little and it will be dark with areas of black where there should be detail.

And this cracks me up.  He says:

Ah but!  I hear you say, I keep my camera on automatic mode all the time, why do I need to know about how the thing works?  The answer is that the camera doesn’t know what you can see in the subject and/or what you had in mind when you took the photo.

In other words, sometimes the camera just can’t tell which details you think are important, and which it can blow or black out. 

 He went on to talk about the aperture, which is one way of controlling how much light passes through the lens.  I think most of us know that apertures are measured in f-stops.  These measurements are numbers like 2, 2.8, 4, 5.6 etc. 

Each successive number, going from smallest to biggest, stops half the light passing through from the previous number.

Got it?

Each f-stop blocks half the light that the previous stop allowed to go through to the sensor.  The bigger the number, the more light is being stopped.  The smaller f-stops represent the biggest lens apertures (openings), where the most light is coming through.

The larger f-stop numbers stop (or block) more light.  I always did have trouble remembering that larger F-stops make for a smaller aperture, but this makes sense to me now.

And here is something else that had never clicked for me:

. . . although the (f-stop) numbers look almost random, there are actually two series of numbers involved here: 2, 4, 8 and 16 alternately with 2.8, 5.6 and 11.  In each case, the number to the right is double the number to the left.  Therefore, all one needs to do, to remember the series, is to remember 2 and 2.8.  The rest can easily be generated from those two.

Of course, many of our digital cameras have more stops now, like 6.1 and 7.4.  But the main stops are still 2, 2.8 etc., with the other numbers being increments in halves or thirds between them.

Ok, that’s enough heavy technical stuff for today.  Next stop on this tutorial train will be Mike’s take on shutter speed.  I also have a couple of new actions in the works, and a new contest to announce this week!

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