Camera History and a Light Concept
Knowing a few things on how light works helps us understand why cameras are designed the way they are, and their limitations. I'll start with the history of how cameras came to be since this helps to understand some principles.
The first cameras were actually a large room with no doors or windows, with a hole in the floor to crawl up into the room. It was completely light proof except for a very small hole in one wall that let light in. All the light that went though that hole formed images of what was outside, and the images were reflected on the opposite wall. Due to the way light works, the image was upside down and flipped from left to right (backwards). There was no film, just a person tracing the image on the wall.
I tried the same thing when I was in my early teens when I had the time to do experiments like that. I completely shut out all the light in my bedroom with cardboard and duct tape. Then I cut a small hole in the middle of the cardboard that was over the window about 1/4" to 1/2" in diameter. After my eyes had adjusted to the dim light I could see my dog's image walking by my bedroom window outside. When my dog walked by his image was projected on the ceiling walking the opposite direction he was actually walking, and he was upside down.
The fact that images are upside down and backwards creates the need for that funny shaped lump on top of SLR cameras. There is a pentaprism in there, a five sided mirrored glass element that turns the light right side up and not backwards by reflecting the light with the camera mirror and the pentaprism. These 3 reflections turn the image so when we look through the viewfinder we see things as we normally do.
Our brain turns images upside down and backwards for us automatically. There was an experiment done about 60 years ago on a man to find out more about the image processing that our brain does. They attached special binoculars so this man could only see things upside down and backwards. He had to keep them on at all times when his eyes were open. It was very confusing to him at first, but after about 2 weeks his brain adjusted to this and flipped all the images, he saw everything as he normally did before the experiment! Then the special binoculars were taken off. He now saw everything upside down and backwards without the special binoculars! Fortunately, this was not a permanent condition. It took another two weeks for his brain to switch everything back so he could see normally again. The point is our brain does a lot of image processing we don't consciously think about. This is covered in more detail in the "Brain" section.
The sensors in digital cameras see the image upside down and backwards. The camera electronics or brain as it is called here, turns the image right side up and flips it frontward for us on the back screen. The pentaprism on top of the camera and the mirror turns the image for us so we can see it "correctly" through the viewfinder.
Old fashioned large format cameras have a ground glass on the back where the image can be seen. The photographer would focus by looking at the image. Of course the image was backwards and upside down since there was nothing to correct it. Some photographers liked that because it helped them compose the picture artistically! It helped them think about the composition abstractly. The logical left side of our brain gives up and the artistic right side of our brain takes over more when the image is turned upside down and backwards. Photographers draped a large black cloth over the camera and their head so they could see the image that was shown faintly on the ground glass on the back of the camera. Then when they were ready, they would slide the film into the back of the camera and release the shutter. Large format cameras are still being used today due to the large size of their negative. The mega pixel equivalent of a large format camera is about 100-200 mega pixels due to the large negative size! Even if you don't ever use one, consider how long these photographers took to just get set up and compose their photographs. It helps to take more time composing photographs! Don't rush it if you don't have to!