Photography has been a passion of mine, and still is. I’ve been shooting for around 3 decades. I own over $4000 worth of Nikon photographic equipment, and have shot for newspapers, magazines, and shot a few weddings in my time. I enjoy nature photography more than any other form. I’ve shot every type of subject, from car wrecks to honey bees. I must draw the line on underwater and microscopic, but it has been a wide and varied field of subjects that I have explored in all this time.
I was first introduced to professional cameras while working for a local advertising agency in my hometown. Back then the light meters consisted of a tiny little black rod that showed up in the viewfinder of SLRs, accompanied by a second ’red’ needle which moved as you changed those mysterious settings on the camera body, or simply pointed the camera in a different direction.
The black rod had a circle near the end of it and when the red needle was within the bounds of that circle, the picture would be correctly exposed. In fact, that was my first lesson in photography.
One day I asked my boss, the owner of the agency, just how to take a picture, and he said, ’’...focus the camera by turning the lens adjuster to the right or the left, and when the needle is inside the circle you can take the picture.’’ As I got more practice with this, I started wondering about the other settings on the camera. When I was ready to learn something else about the camera, Earl Blair, the owner, would add to my knowledge. But he let the curiosity grow first, not trying to drown me in so much information that I could not learn and apply it.
So working through the settings on a camera became the next natural step. What does shutter speed do, and why did they pick these numbers to represent them? From 8 seconds, 4 seconds, 2, 1, 15th (of a second), 30th, 60th, 125th, 250th, 500th, 1000th... what was the significance of those numbers? Earl was an excellent teacher. He explained that all they were trying to do was provide a way to halve or double the quantity of light that strikes the film plane.
Let’s say you are taking a picture at 1/60th of a second. But the camera says there is not enough light to properly expose the film. You can DOUBLE the quantity of light that strikes the film plane by switching it to 1/30th of a second. Or, if on the other hand your light meter is saying you have too much light, you can half the volume by switching the shutter speed to 1/125th. (They wanted to be able to move up a natural progression that was somewhat tidier than 1/60th, 1/120th, 1/240th, 1/480th... so they just moved up a little more from 1/120th to 1/125th... then the progression led to 250, 500, 1000, etc.)
In each change for any given shot and set of lighting conditions, to change the shutter speed one time either halves or doubles the amount of time a given volume of light strikes the film plane. Suppose, however, that when you look through the lense at your subject, you see that you don’t have enough light to shoot at 1/125th. Then, when you ’double the volume’ by switching to 1/60th, you find that it is too much light. What now?
That’s where ’f-stops’ come in. If the f-stop is at the smallest number, that is the largest volume of light that the lense can allow to strike the film plane. The largest number in the f-stop ring on a given lense is the smallest amount of light allowed to pass through the lense.
In between, the same principle is used, i.e., each change in either direction represents a halving or a doubling of the volume of light FOR THAT LENSE. F1.2, 1.4, 1.8, 2, 4, 8, 16, 32...
A quick analogy that worked for me was to look at the shutter speed control as equivalent to a dime, while the f-stop ring was like a penny.
So, if you don’t have enough light at F1.2 at 1/125th of a second for a shutter speed, and you switch to 1/60th of a second, you have effectively doubled the quantity of time that the shutter is actually pulled back. This results in allowing the film to be exposed to the light running through the lense for twice as long.
But, lets say that at your original F-Stop, F1.2, it is still too much! Your next step is to fine tune by halving the volume of light passing through the LENSE by using the f-stop setting... go to F1.4, and progress up the number scale until ’the needle is inside the circle’, or, your light meter tells you you have the correct settings to capture the picture before you.
Certainly, this is a great simplification, but the simplest explanations are often better at helping you grasp the dynamics of light striking a film plane... or light striking a light sensitive medium whether it is film or digital... because the concept here is that the tuning devices of f-stop and shutter speed are very mathematical, and designed to help you find the correct exposure for the medium to record the image as you see it through the lense.
No matter how well you compose a picture, if you don’t understand the relationship between light and the medium where it is to be recorded, the image you really want will be very difficult to capture with any consistency. But, you say, why not just stay in ’automatic mode’? To which I reply, sure, go ahead. But there are going to be days when the subject matter will fool the automatic settings, and you might be required to think through the mechanics of capturing an image. That is when this knowledge will give YOU the ability to capture a difficult image by switching to manual and adjusting things yourself.