View Full Version : Perspective

2010-Feb-26, 08:53 AM
How do I calculate perspective. I mean we're told that the moon is about 1 angular degree (if I remember rightly) so if I point a hollow tube of say 2 inches internal diam at the sky, how do I calculate how many degrees ( or minutes) of arc that I will see?

2010-Feb-26, 09:07 AM
For one thing, it would depend on how long the tube is. You probably realize intuitively that if it is only a centimeter long, you will see a lot, but if it a mile long you will only see a tiny portion of the sky.

2010-Feb-26, 11:06 AM
First off, Welcome.

Second, the moon is about 0.5 degrees, or 30 arcmin across.

As for the area you can see through the tube, that's basically trigonometry.

Diameter of the opening/Distance of the opening from your eye= tangent of the angle you can see.

A tube 12 inches long and 2 inches across, held tight to your eye, like a scope would show you about:

2/12 = 0.167
Take the inverse tangent of that tan-1 on the calculator, and you get about 9.5 degrees.

2010-Mar-04, 05:18 AM
You don't have to move through time to change perspective. Imagine a cube surrounded by cameras, the cameras equidistant from the cube and a trigger. Trigger the cameras, get a person to go from the trigger to the camera and back retrieving the photo (one person for each camera).
From the point of view of the trigger position, the cameras fired at the same time, but the photos will all be different because of perspective.