Explanation please: Pictures look inverted while making long exposure photograph

Question

I have a 5 year old Point and Shoot (Nikon 4600). Though it has very limited capabilities , I have been learning lot of things related to photography from it.

I was trying to make some long exposure photos in the dark with a very faint light source. This is to make those fancy looking art images. I was just trying to draw English alphabets.

Since the camera has a maximum exposure setting of just +2 seconds, I move the camera instead of the light source to create art forms, or in this case, alphabets. I see that the images look inverted. So I eventually visualize a mirror image of the letter and move the camera accordingly so that the output comes as a normal image.

Why does this happen?

Answer 1

When you move the camera down, the light source moves up on the film/sensor plane - just as if you look at something, then look down, the object you were looking at will be above your field of view (i.e. you'll have to look up again to see it). So if you trace a V shape from top left to bottom to top right, the light source will move from bottom right to top middle to bottom left.

This is not a feature of your particular camera, just geometry!