F/1.0

As I frequently find myself in the position of advising friends/folks getting their first dslr, I am often trying to come up with good ways to explain the basics of photographic exposure.

Here’s a good analogy that I’ve come up with (yeah, I’m sure others have come up with the same idea- sue me.) I know this may be basic for some of you but here goes anyway.

First off: some basic concepts - aperture and shutter speed. Pretty much everything in photography comes down to these two things.

Most everyone understands shutter speed- it is simply the length of time the camera “opens up” to let light in to the sensor/film. It is represented in fractions of a second (1/10th of a second, 1/20th, 1/40th, 1/80th and so on).

Aperture is also fairly straightforward: it is simply the size of the “hole” in the lens that lets light through - the wider the whole, the more light gets through to the sensor, the smaller the hole, the less gets through. Aperture is also represented by a number, often called the “f-number” or “f-stop”. These don’t seem to be as logical as shutter speed, you will generally see apertures of 2.8, 3.5, 4, 5.6 etc… (there is a mathematical reason for these though, although it is beyond the scope of this article). Generally all you have to remember is that the smaller the number, the bigger the hole - i.e. an aperture of f/2.8 means the hole in the lens is wide open to let as much light as possible in, whereas an aperture of f/22 is practically a pinhole - a tiny dot of opening. I know it’s counter-intuitive, but just remember it

Ok, now concept #3 which is also slightly counter-intuitive: there is only one “amount” of light that will give a “correct” exposure. Just hold that thought.

On to the analogy:

Imagine the camera is one of those 5gal Rubbermaid buckets, and the light that exposes the sensor is water from a hose.

Now there are 2 ways you can fill the bucket - you can either do it with a small garden hose or with a fire hose.

The garden hose has a small opening (think: aperture) so less water come through, ergo it takes more time (shutter speed) to fill the bucket.

the fire hose is a huge diameter opening, (aperture) so a lot of water comes through very quickly (shutter speed) and it fills the bucket in no time at all.

In both cases though, you still get 5 gallons in the bucket - the only difference is that in one case you are using less water over a longer period of time and in the other, you are giving it a huge blast of water very quickly. However, it is still the same amount in both cases.

This is essentially the basics of exposure - you are “filling up” your camera’s sensor with light. There is a set amount that you camera needs, and you control that by determining how long you will let it “fill up” and how big the hole is that the light gets through. The smaller the hole, the longer needed to fill up the bucket, the larger the whole, the less time needed.

That’s it - that wasn’t so bad, huh?

Now if you think about the above relationship - it is an *inverse* relationship - i.e. as the diameter of the aperture increases the length of time needed (shutter speed) decreases, and vice versa.

Further, it is a linear inverse relationship - i.e. if you let twice as much light in (double the size of the aperture) you need half as much time (shutter speed) and vice versa.

In other words, if you adjust your shutter speed from 1/10th of a second to 1/20th of a second you are halving the exposure time, therefore you must double the aperture to get the same exposure.

Now of course, you are asking - so what? Why is this important? The answer is, plenty of time it’s not. A great deal of the time, you can simply leave the camera on “fully auto” mode and let it determine the correct shutter speed and aperture for you. However much of the creative control in making a photo comes from manipulating these two variables, and they both have effects on how the final picture will look. As one progresses in skill and *wants* to have more direct control over the end product, it becomes critical not only to understand the concepts of exposure, but also to understand how they affect the image.

fin.

P.S. Yes, I know some of my definitions/explanations are not *technically* precise, but this is simply trying to be a basic explanation. there is plenty of time for esoteric nuances down the road…

Tags: tips and tricks

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