This edition of PHOTO TIPS is written mainly for new photographers that have not yet grasped the basics of aperture, shutter speed and the resulting exposure.
Aperture (F Stops) relates to the amount of light your lens will let in to the sensor of your digital camera or the plane of film on a film camera. It has other purposes (depth of field) but we are dealing with light. Your shutter is a little door that opens when you click the shutter. The length of time it stays open ( shutter speed ) also controls the amount of light that reaches your sensor or film. Like aperture, shutter speed also has other purposes but for now we will deal with exposure. The balance between these two things is what controls your exposure. The higher the aperture (again F stop ) number the less light that can reach your target. F22 lets in less light than F4 and so on. The higher your shutter speed number the less light that reaches your target. So with a shutter speed of 1/500th of a second you will have less light than a speed of 1/15th of a second. Again how you mate the F stop and shutter speed determines your exposure. Let us say that the proper exposure of a certain subject in a particular light is a 1/500 of a second shutter speed, and an aperture of F 8. You decide that you want to use an aperture of F 11. Again the reason for wanting to do that is for another column. You have just cut the light in half by switching to an aperture of F11 ( trust me on this F 8 to F 11 halves the light ). Now you need to cut your shutter speed down from 1/500th to 1/250th ( in half ) to balance it and receive the exact same exposure as before.
All light meters arrive at exposure the same way. Your 50 year old film camera, your new trick film camera or your new digital camera all read tone and light to arrive at exposure the same way. They are called reflected light meters and actually read the light bouncing back off your subject. There are also hand held incident light meters. They are not contained in cameras and read the light falling on your subject. They still are using the same system of calculating exposure. I actually find the incident meters a better way of gaining a proper exposure as long as you take the reading in the same light that your subject is in. Having said that I mainly use my camera meter like everyone else. The principal used by meters is the secret to proper exposure.
All meters want everything in the viewfinder of your camera to be a neutral or 18% gray. Not to worry about specifically what that means. Think of pure white, and pure black. Basically a meter is trying to make everything almost between those two tones. Notice I said tones rather than colors. Your meter does not care about colors only tones. If you take the lightest tones regardless of the color and you take the darkest tone regardless of the color, your meter wants everything to be right in between.
Why you ask?
Most pictures taken are made outside in the natural world. Even most of your images of Spike the dog and your visiting Aunt Emma are taken outdoors. Mid tones, or neutral gray is the dominating tone in the outdoors. You would be surprised that most grass, trees, rock and even blue sky are close ( not all exactly ) to that mid tone.
Okay you had a prairie fire near your home that blackened ( dark tone ) everything and you would like to document the fire. Or there was a beautiful snow fall that blanketed everything in a perfect white ( light tone ).
Now what? Cameras can't think so you have to.
If you point your camera meter at that almost all black field what will happen? It will want to make that field mid tone. It means the blackened field will be gray. Remember the camera meter wants to make everything mid tone. If you point that camera's meter at the all white field of snow, what will happen? It will turn that snow field gray instead of white. Again camera meters want to make everything mid tone. The next point will require some reverse thinking. If the meter will make the blackened field gray it is overexposing it. If it turns your snow field to gray it is underexposing it. That is right, too dark a subject means too light of an image. Too light of a subject means too dark of an image. Dark tones mean too light of an image. Light tones mean too dark of an image.
Most camera meters have at least two modes. One is spot metering. When this mode is used it means you can take a reading from just 1% of the total scene. This is a valuable tool. In other words one mid tone rock in that blackened field or one such rock in the snow field and you can take a micro reading of off that subject and use that reading ( as long as that rock is in the same light as the fields ) and use that exposure to obtain a proper image. Most camera meters have a multi segmented mode as well. This means the meter reads the entire potential image and averages the light and dark tones to come up with the proper exposure. Using this mode will give you good exposures most of the time. However using the scenario that I listed above, where there is little or no mid tones in the scene, it simply will be overwhelmed by the too dark or too light tones. That is why using a 1% or slightly larger metering mode and understanding exposure is necessary to compute exposures that are right most of the time.
I have been teaching photography workshops for 15 years. Over the years exposure questions have dominated. As a long time user of slide film, one of the reasons I would give for taking my workshop is I was capable of teaching you to get perfect exposures 95% of the time. Considering that slide film has a very narrow latitude
( it can only record a couple of stops of light ) that was a boast for sure. It really is not difficult once the principle is realized. Today with most participants using digital
media I can no longer make that boast. Why? I'll give this my best shot. Film, especially slide film is made up of a series of mutually dependant emulsion layers. Each layer of film observes and records colors, tones ( exposure ) and all other information separate from the other layers. They are however dependant on each other for the finished exposure and other valuable things in your picture. It is a literal physical thing. As long as your film was not old and the chemicals used to process it were fresh, the results were the same pretty much every time. Digital images contain no literal physical properties. Your camera sensor is taking in and processing the same information as your film camera. It will take the tones, colors and other things and write them into a digital data file. When you view your photo on the back of your camera or on your computer screen it is decoded, or translated back into language you can understand and recognize. It is brilliant but it is flawed. Somewhere, either in the coding or decoding there is a lack of consistency. I have taken both of my Nikons, which are different models and made 20 images on each, of the very same scene, with the same focus, light and exposure and found a full stop of difference in my images with no logical explanation. I have done the same this year with Canons, Pentax and small Kodaks with the same results. Frankly most photographers I work with try to reach a proper exposure but live with the fact you never are sure what you will get. They fix it on their computers when they get home. I do the same. With all of that said you will never make great digital images without understanding the principles of exposure. It will get you within one stop instead of four stops. The danger is many of today's photographers tend to get sloppy with exposure because they can fix it at home. Trust me you will have better images, with fewer software headaches if you have down the principals of exposure. My guess is that as time goes on the exposure problems inherent in digital will be fixed. Also remember every computer screen, depending on resolution, brand and other things gives a slightly different look as far as colors, sharpness and exposure, making it impossible for everyone to get true perfect exposures. Even if they are correct it will look different on different monitor screens.
Again, regardless of which kind of camera you use, all meters want to make everything mid tone. Point it at something mid tone in the same light as your subject and you are almost there. Also remember aperture ( F stops ) and shutter speed both control the light allowed in your finished image. Blending these two things to arrive at a proper exposure is the technique used to control the amount of light you give your image.
I would display some pictures below showing under, proper and overexposure to illustrate this article but of course all my exposures are perfect. That is an untrue statement but I am always very close and you can be too.
Thank you,
Wayne Nelson
