I often get asked for help on various matters photographic, and noticed a common denominator caused by confusion sewn when people try to teach less acquainted students about DOF – Depth of Field. Everything goes perfectly until the tutor tries to explain that a large aperture is represented by a low F-Stop, and then by closing the aperture that F-Stop number gets larger! At that stage confusion reigns supreme and the tutor loses the student.
Early in 2016, while on a trip in the Okavango Delta (Botswana), and sitting under the stars, around an open fire with the owners of the concession area we were visiting, the inevitable subject of wildlife photography was raised. The expertise of their rangers, and their ability to provide their guests, who has spent a lot of money, coming to Africa pursuing their passion of wildlife photography drew more than just a passing interest.
Knowing my photographic experience, my training as a game ranger, and having spent many years chasing around the sub-Saharan wilderness areas, toting a bunch of cameras, I was asked if I would consider spending some time mentoring their rangers, in an effort to up skill them to provide a more fruitful photographic experience for their guests. The wine which we imbibed that evening, had almost certainly lolled me into a false sense of security, and mentally visualizing how much fun it would be to drive around in the bush, while giving rangers photographic instruction, I immediately agreed with alacrity.
A few months later, I found myself at the first of five of their lodges where I would spend the next month mentoring game rangers in the art of handling a camera themselves, understanding how to capture an image, from the correct approach and angle, and taking full responsibility for seeing to it that the guests left, satisfied having captured a great set of images.
Thankful for small mercies that we all spoke English, I started out by asking them what they knew about photography, and that’s when the fun began. Only about twenty percent of them owned a camera, and all of which should have belonged in a museum. No problem. I had a few modern cameras and lenses ( On loan with kind thanks to one of SA’s largest photographic retailers) so problem solved.
My next question, “What settings do you usually use?”, drew blank stares which threw me a little. Undeterred, I continued “Do any of you understand about focus points and focus clusters?”, which also drew blank stares!
I was becoming visibly alarmed, and started visualizing ways of trying to escape, under cover of darkness, never to be seen in that Okavango Delta concession ever again. But being the Okavango Delta, it is only accessible by small aeroplane, so I was forced into finding some other ingenious way of getting through to the rangers.
Being a trained game ranger myself, I immediately identified their training to use fire arms, so asked them what weapon would they use to shoot a guinea fowl flying. Of course it would be a shot gun, because a rifle would be only one bullet as opposed to a cluster of birdshot…And that gave me my opportunity to start them off on understand that a photographer needs to aim at his subject and use either a single focus point or a cluster. Using the examples drawn from their professional training, I employed the same principals to explain photography.
Physically aiming the camera at the subject:
In order to “aim” a camera at a subject, most cameras have some kind of reference marks eg: A point, a square or a series of little tiles. The factory default setting will always place that point / cluster right in the centre of your view finder.
Most cameras also provide a choice of focussing points ranging from a single point (eg: Shooting a target with a rifle which shoots a single bullet at a time), or a cluster of focus points from small, medium, to cluster which covers about 40%, and then about 94% of the view finder. (eg: A shotgun shoots a group of pellets which spread in order to provide more chances of hitting the target)
These points can be seen as little tiles in your viewfinder, and most cameras have a setting which provides the option to illuminate the focus points. *I always enable that feature as it makes it very easy to see where your camera is actually aimed.
Most of the modern generation of cameras have the ability to shift the focus points, usually with a little toggle / joystick. This can be very handy for composing an image. (Image No1 – Focus point shifted to the upper left intersecting point of the Rule of 3rds. On the lion’s face)
Traditionally modern cameras have a main shutter release button which is operated by the photographer’s right index finger. By pressing this button half way down, the camera’s auto focus mechanism is activated, then pressing the button down fully, the shutter is released and the image captured.
Attached to this same button is also the camera’s metering system. The moment the button is pressed half way down, the metering function is activated.
However, most modern cameras also offer a mechanical focussing method known as Back Button Focus or BBF. By employing this method to activate the auto focus mechanism, it effectively removes the focussing function from the shutter button, and relocates it to a button at the rear, top of the camera body, on the right side of the viewfinder. This button is usually marked AF – ON.
Once the AF – ON button has been allocated as the means of focussing the camera, it means that in order to capture an image, the photographer depresses the AF – ON button with their right thumb, while simultaneously pressing the shutter button to activate the metring function, and trigger the shutter to capture the image https://www.colesclassroom.com/back-button-focus-explained/
Once you have mastered this method of physically activating the auto focus function, it also means that you are able to use it as a very quick, and accurate method of composing an image. You simply aim the camera (Using the chosen focus point / cluster at the subject of the image, then remove your thumb from the AF – ON button, move the camera to compose the subject of the image, and then press the shutter button down to capture the image.
Two planes of focus:
I believe that all images should have a central story (pin sharp), supported by a complimentary, slightly “soft” or blurred peripheral foreground or background.
In an effort to describe DOF (Depth of Field) to un-sophisticated game rangers, I first had to get them to understand what basic “focus” is all about.
NOTE: “F” also stands for “FOCUS”…. “Focus” is defined as “The point at which an object must be situated with respect to a lens or mirror for an image of it to be well defined”
DOF is an acronym for – Depth of Field, but I prefer to use the term – Depth of Focus, which is more descriptive.
What many people don’t understand, is that when the camera is aimed at one spot, a zone of focus is created between a “front plane”, and a parallel, “rear plane”, like two, imaginary, parallel sheets of glass. The zone in between the two parallel planes is sharply in focus.
Depending on the size of the aperture which is set, the sharply focussed zone in between the two planes will vary in terms of the Laws of Geometrical Optics.
(*NOTE: The focussing mechanisms of most modern cameras are pre-set in the factory, to achieve a “sweet spot” situated 1/3rd in from the front plane. The “sweet spot” being defined as the absolute sharpest plane of focus, in an area between both planes of focus)
Analogy: Take your left hand and bend your fingers over at 90 degrees to form the top horizontal bar of the letter “F”. Then take the fingers of your right hand and place them on the palm of your left hand, parallel with the fingers of your left hand, to form the top and bottom, horizontal bars of that letter “F”…….
In photographic terms, a “small” gap, also represents a small F-Stop number eg f2.8.
While keeping the two sets of fingers parallel, and still holding the shape of an “F”, lower the fingers to create a wider / larger gap between the two horizontal sets of fingers eg: a bigger F-Stop eg: f13.
By dropping the fingers, even lower down your left arm, the gap becomes wider / larger, and the F-Stop accordingly bigger eg: f22. (Image No3 – The entire zone is sharply in focus)
With this in mind, it now stands to reason that the narrower / smaller the gap between your two sets of fingers, is a narrower / smaller Depth / Field /Zone of Focus, represented by a correspondingly, smaller F-Stop.
It also stands to reason that a wider / larger gap represents a wider / larger Depth / Field/ Zone, which is in focus, and a correspondingly, larger F-Stop. * In my teaching experience, this particular association between the size of an aperture, and the size of the F-Stop is where most people get confused, and miss the point when trying to understand focus, depth of field / focus and associated apertures. Therefor it is far simpler, just thinking about the zone which you want to be in focus, when selecting the aperture.
NOTE: The closer a subject is to the camera, the narrower the two planes of focus (Depth of focus). As the subject which are being photographed move further away from the camera, so the proportion of the two planes of focus become proportionally wider. ie: When you photograph eg: A pair of birds, which are 100 meters away, f5.6 will achieve sharpness of both birds, but if you photographed those birds 20 meters way, the whole bird would not be sharp, so you would have to increase the aperture to f8 to get that entire bird sharply in focus. (Image No4 – Tawny Eagles at approximately 20 meters)