Ask Jimmy: A Lesson in Perspective

Hi DH. I think I know the image you were talking about but before I go any further, I'd just like to say one thing - Chlorpromazine.

OK. Back to business. Perspicuity, in this instance, is often used to visually describe a 2D representation of a 3D world with a reasonable amount of realism and faithfulness. Having said that, like with many creative mediums, the same 3D scene can be transmogrofied on the 2D picture plane an infinte number of ways. Here we'll discus some methods relating to photography.

Camera

The camera that comes standard in many mobile devices these days such as the one shown on the left will give you one representation of a scene while the purpose built camera and lens system depicted on the right will give you another.

Which one is better? Well, neither. Each one, as well as all the different offerings in between, has its place. You can't pull a 600mm telephoto lens and camera body out of your pocket on a whim and snap that chance meeting with a long lost friend. Nor can you capture that endearing shot of an African lioness caring for it's young from your hidyhole with your iPhone. The end result, often, is king. Both images will stir the emotions or bring back memories.

 

Location, location, location

Where you take a picture from is determined by many factors. Many, many, many, many factors. In fact, far too many to cover in today's little outing. Some are controllable, some are not. Today, we're just going to look at the difference between wide and narrow angle lenses and their effects on preceived perspective.

Ultimately, it's all about ratios. You've got a fixed area with which to compose / capture your scene. In the case of a digital camera, it's the CCD. Given a particular camera, it is a constant. Given the right opporunites, you can fill that same CCD with something as small as a grain of sand, or something as large as the planet earth.

Now, for the sake of our discussion, we'll also set the rule that light travels in a straight line... and the world we live in is actually how we perceive it to be. Hey, since we're taking licence, we may as well go all out.

To get the subject to fill the frame, you need to be closer to it with a wide angle lens and further away with a narrow angle lens.

In the pic above, Subject A (the 92" Talon) is in the forground and Subject B (the upscale 92" Spitfire) is in the background. The distance between the camera and its primary subject is about the same as the distance between each of the two subjects. Looking at the picture plane (which can be anywhere along the path of light), you can see a definite size difference - about twice the difference in this case. The wider the lens, the closer you can get to your subject and the smaller / further away the background appears to get.

Using a narrow angle lens, the distance from the camera to the Talon is many times the distance between the Talon and the Spitfire.. Alternatively, you could say that relative to the distance to the camera, the subjects are closer together. Looking at the picture plane you can see the background Spitfire is now much larger proportionally to the foreground Talon using the narrow angle lens than before when using the wide angle.

This effect is sometimes referred to, incorrectly I might add, as perspective compression. It is an effect of position and not of the lens. The lens just helps you fill the frame with a subject.

Ignorance through Obscurity

Well DH, ostriches have been perfecting this method of denial for eons. The effects of position work the same whether the subject is horizontal, vertical, laying seductively across the bonnet of a car or streaking upwards at speeds in excess of mach 1. So essentially, just because you cannot see it, doesn't mean it's not there.

Given the top view shown above, we'll keep the same distance from the subject but we'll change the height from which the image is taken and compare the size of the green area which will remain on the ground.

As you can see, from the elevated position (above), you can see a larger portion of the area around the Talon than from the lower position (below). It does not mean that the actual area photographed has gotten smaller, just that the position of the camera shows you less of it.

Topography

Another influence to consider is topography. The above examples have all assumed a flat landscape. There's not many places around however that allow you to launch from the geographical equivalent of a pool table. Undulations in the landscape, both large and small, help to determine the amount of ground you end up seeing in the image.

Localised vegetation also plays its roll in obscuring the image. Grasses in front of a cleared area - especialy when viewed from a lower position, will appear closer to the subject than they actually are.

But...
- wave your hands around in a slow meandering motion -
it's all an illusion...

So DH...
who's got your widdle nose...
who's got your nose...
Yeeessss. Who's got your nosey wosey...