Ohh, the humanity!
This will be the first entry into the Glass Lakes educational series. This section will cover the basics of aperture and why it is important. Hopefully the ranting will be kept into check and this section kept on track. I will try to start with the basics and then launch into the more complex.
So, the basics then…
We shall initiate this exploration into the function and use of aperture with the very basic, basic, basic description. It is a hole. That’s it, a hole, or an opening if you prefer to call it that. It is a basic limiting device to control the volume of light passing through it. If you want more light then you make it bigger, if you want less light then you make it smaller. If you care to experiment with this please do so. I would take an opaque black piece of cardboard and cut a measured hole in it. Now hold it up against a light source in a dark room and note how bright the area is, now re-cut the hole so that its area is doubled and look again at the brightness, repeat as much as you like, or until you run out of space to cut. When you double the area of the hole you are allowing double the light through, simple enough. So lets keep this area vs diameter distinction in mind because we need to maintain a plane-frame of mind, for now. When we are looking at the basic formula for an exposure it is best represented by E=IxT, Exposure=Intensity x Time. Aperture in conjunction with the lighting conditions, filters, etc control the Intensity of the light that is transmitted to the photosensitive media. Seeing that the expression is algebraic then it stands to reason that the same exposure can be made by adjusting the variables I or T while maintaining E as a constant. So by taking a look at a lens, if you have one that still has the fancy aperture rings on it, or into your exposure settings on your camera you will see a bunch of numbers. They may be like 2.8, 4, 5.6, 8, 11, 16, 22, 64 sometimes they may look like f/2.8, f/4, etc. These are your aperture stops, essentially a division equation. Literally F/X whereas F is the focal length of the lens and X is the fancy calculated number that you divide that by to create a “stop”. As you go up or down the scale you are increasing or decreasing the amount of light by a factor of 2. There is a whole world of geometric mathematics to get into on this subject, but there is not enough coffee on the planet for that at the moment. Just remember the higher the number, the less the light; if you wish to keep it simple.
So can you mix or match speeds and apertures and come up with the same result?
Mathematically speaking, yes. But you need to know that we are talking purely about the amount of light that is received by the photosensitive media. There is a total disregard for the appearance of the image at this point. I have always told people that light is cumulative. What I mean by that is when it comes to photography; you can only add light never subtract it. You can control the amount of certain wavelengths, or exposure to specific areas in your media. You can never, ever, ever make it “unexpose”. If you want to experiment with this you can either play with a darkroom and some photo paper, or you can find the sappiest pine tree in the forest and give it a big bear hug. The sap is now attached, much like light to a piece of film, paper, or digital sensor. Yes, you can wash it off eventually but lets just ignore that for now because that would be like scrubbing the ink off of a piece of paper. You can keep adding sap by touching the tree, over and over again and it will build up on you but you can not really make it go away. This is light, so do your best to control it when you don’t want massive amounts of it stuck all over your media. There will be more on this later to prevent the bubbling confusion that may be occurring in your mind presently.
Lets apply some art to this thought process…
We have two photos presented for this part of the discussion The only difference in exposure is the adjustment of the aperture and respective compensation of the shutter speed. The camera was not moved, nor the lens changed. The first photograph was taken at a f/4.5 with a 1/2500 second shutter. The second was taken at a f/20 with a 1/160 second shutter. The difference in exposure is fairly small, there is a near 4 stop adjustment on both aperture and shutter. But take a look at the aesthetic difference in the images.
This is called Depth Of Field (DOF), a very useful creative tool.
How deep do you want it? Your field that is…
This is a very powerful question with some very powerful answers, but ultimately it is between you and the the people who are judging your work. Yeah that happens, best not to dread on it currently. The DOF is best understood by what it accomplishes visually. In the first example the leaf thingy is in sharp focus and the background is just a wash. The second image revels that a whole tree is there, and another tree, and buildings. There was no adjustment to the focus what so ever, just a 4 stop change in the aperture and shutter speed to compensate. What this dose is it creates a zone where objects within it are in “reasonable focus”. This is a linear kinda range that extends slightly to the front of the sharp focus, and a ways behind it.
What is this trickery???
In essence, the lens is magical. The decrease in the size of the aperture causes a decrease in the size of the image in the lens. Therefore there is an increase in sharpness. This combined with Timelord technology creates a zone of reasonable focus. When it comes to sharpness, smaller is better. The smaller the point of the image is on the media the sharper it must render. Remember, I am trying to keep this to the basics if you like then just look up DOF on Wikipedia and your brain may hurt for a while.
As you manipulate camera settings and experiment with the different DOFs that are possible you will learn, there really is not all that much more to ramble on about with that subject. You have the power to highlight different subjects, draw attention to, even ignore annoyances in the background if your lucky enough. Color washes are cool as well, and can be created by keeping the DOF shallow. There really is a lot to talk about when it comes to DOF, but I would rather that you as a reader get out of the chair and actually play with it, we can have that discussion at a later time.
How about your sweet spots…
We all have them, so do our lenses. If you talk really loving to your glass it may tell you, or maybe not and I will have to. If you are out photographing and clarity and contrast are important to you then you will want to use at least an F/8 to f/11 and up. This is because there is a sweet spot in your lenses, that is usually in the middle of the glass. This is because of the curvature of the glass elements and what not. When your aperture is knocked down to those smaller diameters the light can only travel through the center of the lens on its way to your media. This creates a sharper image with a little more clarity and definition then the larger apertures. This is all because of how the optical elements are shaped. The light that enters the edge of the element is scattered about a bit and causes some distortion. The light that is restricted to the center of the lens dose not scatter as much and therefore creates a sharper image. Also the effect that creates DOF also take a major role in this as well.
Give and take…
So lets take a final paragraph and discuss some of the gives and takes of the aperture world. The larger the aperture the more light that comes through, which allows for faster shutter speeds. You can always adjust the ISO higher to get a faster picture but that can have some of its own issues. This is not a shutter speed discussion so I will keep that topic brief. The faster the shutter, the quicker the snapshot you can take, the more you can “freeze” time and motion. This is useful for quick moving subjects like bullets, sports, agitated animals who don’t like you in their territory, and for the other guy that is laughing and clicking away as you attempt to outrun that mountain lion; which moments before you thought was cute. As we freeze time we seldom care about that background because it is the subject that we care about, so a fast image is the priority. But there are times where a good DOF is useful so that you do not need to do a split second focus onto the mountain lion as it charges at you. Pr-planning and snapping the image as it enters your DOF can also be a useful tool. Also there are times where the DOF dose not matter at all, for example shooting a subject that is up against a wall. You can not see through the wall so should it matter?
You should be asking yourself what matters in your image, the range of focus or the capture of a frozen moment. If the moment dose not matter, then the aperture and its associated DOF should be the priority when making your exposure. Following composition of course.
So, get out, go shoot, experiment, and for the love of beer and everything holy use the manual settings and focusing.
Check out http://www.facebook.com/glasslakes for photos and stories. 😉