DSLR & Photography 101
The digital single lens reflex ( dSLR ) and Photography 101 course is a great step upward for anyone who wants to expend their creative horizons, or simply just get better pictures. Whether you want to become a serious photo hobbyist, have a hankering to turn pro. This is the perfect opportunity to build a strong foundation and understanding of DSLR & Basic Photography.
This week's class is Aperture!
Lesson - Aperture
THE APERTURE is built inside each lens and it controls the light entering a camera. A lot like the shades on a window control the light. The more open the shade is (lower the aperture number is) the more light allows in. The closer to shut the shade is ( larger aperture number) the less light lets in. Aperture is measured in f stops. The larger the number under the f, the smaller the hole (aperture) and the less light that comes in.
You may have also heard that larger the aperture the more depth of field you will get. ( We will learn later on more about DOF). A wide open aperture results in a shallow depth of field whereas a smaller aperture results in a great depth of field.
We’ve already taught that the aperture is measured in f-stops and that the smaller the number, the bigger the opening. The reason for this is because each measurement is actually the fraction of f/(number) IE f/1.4, f/2, f/2.8, f/4, f/5.6, etc. The f simply stands for the lens’ focal length. That way no matter what the size of the lens, the f-number would be proportional or universally applied across all lenses. In other words, when using the aperture and shutter speed, using one lens will generate about the same exposure as using the same setting on a different lens.
As you can see in this illustration, the opening can have the same size of f/4, while having different physical measurements.
So the point of the f-number is just to convey the illuminance of the aperture opening. It’s done as a fraction of f because the physical measurement may change from lens to lens but the light it puts out will be the same, if the f-stop setting is the same.
Grab your camera and figure out how to set it to aperture priority mode. (on the canon rebel, you set it to AV, and you can raise or lower the aperture by turning the dial on the top left of your camera to the right or left.
Incidentally, in order to go to the lowest available aperture on your lens, you need to have it zoomed all the way out. I think most lenses that come with the canon rebel these days have a 3.5 lens, which means the lowest available aperture to you is 3.5, in order to dial it down that far, your lens must be zoomed all the way out.) It’s a good thing to keep in mind when buying a lens because you may want to be zooming in a lot, but the fact is you may have to be used to just getting closer to things rather than zooming if you need a wide aperture.
Find two objects, place one in the foreground, the other in the back and slightly to the side so it is visible. (make sure that wherever you are shooting has plenty of light!) Adjust your aperture so that it is at the lowest possible number. Focusing on the object in the foreground, take the picture. Now, raise up your aperture. If you started at 3.5, go up to 4.5. Again focusing on the object in the foreground, take a second picture. Raise your aperture up a third time, this time to maybe 5.6 and take a third picture. Now you can compare them to each other. The background object on the first photo should be the most blurry, and slowly become sharper in the subsequent photos.
With each adjustment to the aperture, the shutter opens less and less wide, letting less and less light in, which changes the depth of field, or how blurry the background is. In aperture priority mode the camera will choose a slower shutter speed to compensate for lack of light. If the camera allows you to see the information on each shot, make note of the shutter speeds and how they change in comparison with how the aperture changes.
(Aperture image samples)