Today, Jacob and I were working on understanding aperture, and he was struggling with some of the ideas (and who blames him…some aspects of aperture are hard!). We started by hammering out the basic (and perhaps boring) details. The aperture is the hole through which light enters the camera body, through the lens. The size of this hole is controlled by the diaphragm, which is usually located in the lens. The first difficulty (especially when relating it to children) is the idea that a smaller aperture number (f-stop number) actually means a bigger hole. So, the smaller the aperture number, the more light is able to make it to the sensor. While many lenses have a wide range of apertures through which they can shoot, a maximum aperture will be printed on the lens (for Canon it is on the end of the lens). Most kit lenses have a variable maximum aperture, with mine being from f/3.5-5.6. A “faster” lens will have a smaller number–down to f/1.2.
By understanding the relationship between the aperture numbers, a photographer can know how much to adjust the aperture to affect the exposure (supposing that he wants to keep both shutter speed and ISO unchanged). In the lists of f values to the left, each increment, starting at 1, cuts the transmitted light in half. So, f/1.2 allows half the light that f/1 would allow. It should be noted that f/1 does not really exist, but is a theoretical aperture. f/1.2 Lenses are readily available, but the larger the maximum aperture, the more expensive a lens will be.
Another confusing idea tied to these aperture values is that it would seem logical that going from f/4 to f/2 would let in twice as much light. However, that is not the case. Going from f/4 to f/2.4 lets in twice as much light, and then going from f/2.4 to f/2 lets in twice that amount. So, in reality, going from f/4 to f/2 lets in four times the light!
While cameras and lenses can be set to various f/stop values that are not shown on our chart, these represent the change of one full stop. So, a value of 3.5 (as many kit lenses have for a maximum aperture value) is somewhere between f/2.4 and f/4. the distance from f /3.5 to f/4 is not a full stop. If, however, you realize that your meter is showing that you are 1 stop under exposed at f/8, you will know that moving the aperture to f/5.6 will set your camera for proper exposure. Using the chart above with the meter readings from your camera will help you to understand what is happening. I understand that most DSLRs today have the information readily available, usually just by looking through the view finder. Simply line the marker up with the “0” on your scale, and your exposure will be correct. However, if you are like me, it is not good enough to just know what is correct. I want to know why the settings are correct! By understanding the relationship between each of these numbers, one can know what aperture changes to make without simply running through the trial and error process. Knowing what to do makes the process of changing settings on the fly much easier!
To illustrate these principles, we set up a little experiment to visualize the different light transmission based on the aperture set. Each of these photos were made with my Canon EF 50mm f/1.8 II Camera Lens, set at 1/40 sec shutter speed, and ISO 400. We set the first aperture to f/2 and then progressed one full stop at a time through f/11. Published below are the results through f/8 (the last photo with any discernible detail).
f/2.0, ISO 400, 1/40
f/2.4, ISO 400, 1/40
f/4, ISO 400, 1/40
f/5.6, ISO 400, 1/40
f/8, ISO 400, 1/40
Jacob found this exercise to be quite helpful in understanding the concept of aperture. He could see the distinct difference as the light was cut into half for every full stop. Principles that he was struggling with suddenly became clear to him. While he will still have trouble remembering the list of f/stops, how the change of aperture impacts his exposure will stick with him going forward!
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Jacob and I have really started hitting the books, and taking our photography education seriously. Of course, spending so much time on that has made it nearly impossible to find the time (around other obligations) to sit down and share what we are working on! We will try to rectify that, and get the blog updated more frequently, especially now that we have made all of the necessary repairs to the blog and have (hopefully) blocked off all the hackers who have been causing us grief!
One of the more basic things that we have been working on has to do with basic composition of photographs. I’m sure if you’ve had a camera in your hands, you probably have thought of some (if not all) of these tips, but hey, you have to start somewhere!
We have started with the idea that a photographer must have a strong subject in mind when that shutter is clicked. This is, quite often, the difference between a forgettable snapshot and a treasured memory. I know that this is an area that has been difficult for me to work on personally, and it is a challenge to teach a kid the principle as well.
I’ll use the picture to the left as a first example of NOT having a clear subject (click the picture to see larger). Obviously, the picture was taken at a birthday party for my son, and he should have been the subject of the photo. However, it is also obvious that I did not do a very good job of composing the photo to emphasize the subject. There are three people in the photo, all the same size and in relative focus. The two boys certainly compete for attention in the photo, one with a gift and the other with a great expression of excitement on his face. Another problem is the very busy background that is also in sharp focus. All of this takes away from picture, and causes it to lose any impact it might have.
There are many things that can help to clean up a picture. Once the subject of the picture is determined, the photographer must make some compositional choices to make that subject clear and make it stand out within the photo. Here are some suggestions:
- Fill more of the frame with the subject. The larger the subject is in the frame, the easier it is to distinguish from other elements that may be in the photo.
Science Project: Flower
- Blur the background. Blurring the background helps the subject stand out, as that subject will be the only thing in the photo that is in relative focus. In any photo, the area that is in the greatest focus will draw the attention of the viewer. This is called selective focus. That is, only a portion of the picture is in focus–it is selectively focused.
- Use elements such as framing or leading lines to draw attention to the subject. Anything that works to separate the subject from the background helps to emphasize its importance. Leading lines can draw the viewers focus through the photograph to the main subject. Framing can accomplish the same thing, pulling the eye of the viewer to the main subject.
The picture to the right uses some of the elements above to try and bring out the subject of the photograph. This project that my son put together this week is a model of a flower, but he went the extra mile and made a small bumble bee out of pipe cleaners to spice up the project. We set the aperture to about 2.0 to have a shallow depth of field, and then cropped tightly to fill the frame with flower. The bee, the main focus of this picture, is in focus, while even the near and far petals of the flower are thrown out of focus. While this photo breaks the rule of thirds (a subject for another post), sometimes rules are made to be broken! Often, at least in my experience it is not uncommon for macro type shots to be more centered in the frame.
Getting a good composition is the start of getting good photographs. It starts before you ever click the shutter. Of course, there is far more to good composition, but we are just learning, right? Stay tuned for more to come…