Tech Talk: Candles and Calculations

Greetings, volks. Welcome to Hohenfels Volks, THE place for our place!

Today we’re going to go a little bit into what makes up your exposure numbers and how metering works. It sounds familiar, but we’ll be dealing with more math and other advanced parts of your exposure settings.

Let’s start with your ISO. Back in the old days there were lots of ways to label film sensitivity. There was by DIN number, ASA, Weston, and EV, as well as various others fallen by the wayside. Today we use ISO, which is for the most part ASA. Some folks use DIN, that’s why film still carries the DIN number. Under today’s scheme, 3 degrees DIN are equal to 1 full stop. ISO 100/21 has half the sensitivity of ISO 200/24. The Weston number, another popular standard used to gauge a film’s sensitivity, referencing Weston’s meters, is usually .8 times the ISO. Since we’re shooting today, we’ll use ISO, but there may be times we reference others in our future.

Moving on we come to light and light levels. Without the fancy gadgets we have to meter our exposure built into cameras, folks used external meters. Ansel Adams broke it down in his book The Negative. Meters used to measure light in candles, or candela, per square foot. That was the basis for your shutter speed. This will become important in a couple paragraphs.

Next we have aperture, the size of the opening through which light enters the camera. Each ISO had its native f/stop. To find the native stop for any ISO take its square root. For ISO 100 the native f/stop is f/10, for ISO 125 it’s 11, for 200 it’s about 14, and for 400 the native f/stop is 20. Apertures are measured in f/stop, which is a ratio based on the square root of 2, as each step is doubling or halving the light.

The last part is shutter speed. For a native aperture, the shutter speed should be 1/ the light measured in candles per square foot, or c/ft². If you read 125 c/ft², your shutter speed for a native aperture should be 1/125 second. It sounds easy doesn’t it? Well, don’t give up hope. Things are about to get tricky.

Since most light meters today don’t measure in c/ft², finding that speed may be difficult. Automation has taken away many of the tools used by those who came before us in every arena. You can buy a cheap ambient light meter and use it for your photography. The readings are usually in LUX. LUX can be converted, however, by dividing by 10.764. Just round to 10, and there you have it. 1000 LUX is 100 c/ft². At your native aperture, shoot 1/100 for zone 5 placement of what you just read and you’re cooking with gas. Using you digital camera’s metering, set your aperture to the ISO’s native aperture in AV mode. Then seeing the required shutter speed tells you there are that many c/ft² or 10 times that much in LUX.

It seems like talking about this doesn’t do much for you shooting digital, but knowing it will help you improve your light reading skill without your camera’s meter and make getting your exposure correct a lot easier. Plus, if you decide to go old school and shoot with an old camera or use an old meter it will help you to figure that stuff out. It also comes in handy when working with the zone system. Reading 1/100 at your native aperture, you have the knowledge of how to combine your speeds and apertures to get the right exposure for 100 c/ft². You also have the knowledge that you can move your image up or down a zone without playing guessing games as much. It’s quicker and easier to figure out once you try it a few times. A good example is on a bright, sunny, semi-cloudless day. The sky reads about 300 c/ft² when read usually. So for ISO 125 at f/11 you should be set for 1/300 as a good starting point. Then adjusting your speed inverse to any desired aperture changes, and you should have a decent exposure with the sky at zone 5. You can adjust just your aperture or speed to move the sky and other subjects into different zones and create what you visualized that way.

Ansel Adams described it as the exposure formula. He taught that zone 5 was 1/c/ft² at a film’s key aperture. It still holds true. Some minor adjustments may need to be made, but you should be almost dead on. It helps to spot meter for your highlights and shadows to get the best range in your image, but for quick shooting, try it out! I think you’ll see something very cool!

The new theme for this week is “Flattery (Not everything complimentary is flattery!)” You may have already guessed that this has to do with colors, right? Your shots should be composed with complimentary colors as a major element of your composition. Another aspect of your image must consist of contrast in your subject, as well as the contrasting complimentary colors. Perhaps age and youth, or hot and cold. I hope that you get the creative juices flowing for this one and get working on it soon! I also hope that we will see everyone out there submitting this time!

Don’t forget to post any of your images you’d like to see here at the Hohenfels Volks Facebook page. Of course, commenting on both Facebook and here is always appreciated, too!

Reading List: The Negative

Greetings, Hohenfels, welcome to Hohenfels Volks, THE place for our place. Shorter days and lots of fog made our visibility very limited this Tuesday. Cold, foggy, and wet, together they combine to make for some serious winter like weather. It looks like Hohenfels can expect snow before too awfully long!

This post will introduce the book “The Negative.” This is a piece of advice for those who desire more knowledge about photographic techniques and methods. Ansel Adams wrote The Negative in the 1940s as part of his series on photography. It was part 2 of a 3 book series. In its final version, written by Adams in 1981 and still published today, it provides an incredible amount of guidance to the photographer and would be photographer. It also helps the photographer understand exposure in more detail, breaks down controlling exposure and contrast, and introduces concepts and theories that will advance even the beginner along the path toward better photos.

The chapters include Visualization, Exposure, The Zone System, as well as chapters on natural light, artificial light, and filters. I find the chapters on exposure and the zone system to be the best material on the subjects. One of the main reasons is that Ansel Adams explains exposure in extreme detail, while making it understandable to anyone remotely interested. The other reason is he co-created the zone system. No one else could have brought it within the grasp of so many people.

Even though he wrote this book for users of film, Adams himself envisioned a sort of digital photography. When you take into account that photography remains writing with light, and that the concepts are the same, you can see the use of studying this handy book. Some of the terms used may no longer be common, like candles/square foot, but the information remains within grasp. For example, in the previous example of foot candles or candles per square foot, a lux meter will give you a measurement in lux, which can be converted to c/f2 by dividing the lux reading by 10. Knowing this, you can use a reflected light lux meter, do the math, and use the exposure formula in chapter 3 of this wonderful book to get your exposure correct. A concept introduced is that every ISO has a native aperture. That native aperture is the square root of the ISO. For example, ISO 200 has a native aperture of approximately f/14. ISO 125 has one of f/11; ISO 400 is f/20, and so on. Keep that in mind, as in an upcoming post we talk about the exposure formula.

Another great feature of this book is the inclusion of some of Adams’s amazing photography to emphasize a point or introduce a concept. If you only get it for the pictures, it’s worth the price. You can get it for as little as $12.00 new!

On to something else. Are you visualizing your shot for this week’s theme? Are you thinking about how to get something great, just the right DOF, and how to get the angle? I’ve had a couple cool ideas. I can’t wait to see what you come up with!

Well, Volks, here’s hoping your week stays short and interesting.

Remember to share your pics and post your questions at the Hohenfels Volks Facebook page, and or by commenting here!

Some Good Reading

Here's some further information on exposure;

Cambridge in Colour A Learning community for photographers. Sean McHugh puts a lot into his site, check it out!

For a more in depth and technical explanation on exposure, I recommend reading "The Negative" by Ansel Adams. His work has inspired folks for nearly a century and will continue to do so for as long as we admire beauty! You can get this book new from Amazon for about $14.00.

A great source for general photography, is the "Digital Photography" series by Scott Kelby. There are 3 books in the series with a fourth one coming soon. You can also get this at Amazon.

Here's a link to Amazon, just search for those books and read on. Just so you know, I'm not getting anything from Amazon for this.

I hope to see your questions and comments!

Take care.