Photo Lesson 2: Seeing is believing

Ok, so this is the point where you want me to rattle off the pro’s and con’s of the aforementioned cameras, but I’m not – Well, not just yet.  You see, this was supposed to be a series of posts designed to help you get the best out of your holiday snaps.  And to do that, there’s some basics that you need to understand.

Cameras work, either by design or complete coincidence, in a very similar manner to the human eye.   They both have a set of lenses that allows the light in, and manipulates it in order to focus it onto something that can collect the light and turn it into an image.   In the camera, that’s the film or digital sensor, and in our eye its the rods and cones at the back of our eye on the retina.  And in another amazingly similarity, both have a means of controlling the amount of light allowed to get to the image collector – in the eye that’s the Iris, and in a camera that’s the Aperture.  Also called the Iris in the olden days.


Woah – this is a photographic lesson, not a biology class.

There’s a reason for me mentioning this though.  Because, what a camera doesn’t have is a brain.

Ok, ok, so the latest all singing all dancing DSLR’s do have quite sophisticated processing units.  They take the image that is displayed on their sensors, and adjust things depending on what settings you have input.  They can adjust colour, exposure range, camera shake, red eye and all sorts of weird and wonderful things that you probably haven’t even heard of.  But the brain does more.

For a start, any camera image is actually upside down.

When you get the print, you think you turn it the right way up to look at it.  But of course the image falling on your eye is also upside down, but the brain reprocesses this immediately and shows it to you the “right” way up.  Your camera with a screen does the same. It inverts the received image before displaying it on your screen.   And “newish” optical viewfinders have a secondary lens to right the image when you look through the viewfinder.   Very old cameras would have displayed their images upside down in the viewfinders.   This is the same for new multi-lens cameras and the first pinhole camera:


But hang on.  If the image on the photo is actually upside down, so you have physically turned the photo the right way up to look at it, but your brain has then turned it again, doesn’t that mean the print was the right way up in the first place, before you turned it upside down to make it the right way up for your eye? Confused?

Eyes take snapshots too
Cameras take a single still image of what they see, with no, a little or a lot of post-processing in the camera.   Video is actually not a continuous moving picture at all, but a series of images, all slightly different from the last, which change so fast your brain can’t keep up.   Anything beyond 24 images per second and you eye perceives them as moving.  On video the images are called frames, and most cameras work at 24 frames per second (fps) or 30 fps.  Older webcams worked at 16 fps and appeared jerky to the eye.

But do your eyes view motion continuously?

Try this.  Without moving your head, look as far to the left as you can, then slowly pan your eyes from left to as far right as they will go.  Scan the room, or wherever you happen to be sat.

Did it appear jerky, or was it a smooth transition from far left to far right?

Smooth of course.

You might be surprised to know that your eyes actually also take snap images, and then brain stitches them together to create continuous motion.

If you try to take a photo of something moving, you will normally end up with blurry lines in your image. e.g.
Motion Blur PhotographyBut your eyes never blur when watching something whiz past – the brain prevents this blur by stitching together multiple crystal clear blur free images into one continuous motion.  Clever eh?

You can see this effect by staring at the centre of the image below.  It appears to be moving, but that’s just the effect of your persistence of vision;  as your head moves slightly, the multiple snaps go out of line, and your brain sees after images of the black and white pattern, and when stitching these together it appears the picture is moving.   Perhaps you need to hold your head steady on a tripod!


We will look at types of blur in your camera shots later on.

Something else your brain can do is fill in the missing blanks.  Did you know that you actually have a small blind spot in each eye, which means you should see a blank portion when you look at something?  But because the brain knows its missing, it can get the information from the other eye (which has a slightly different blind spot position) and fill in the missing bit of the image.

This can lead to some odd effects;  the brain constantly looks for patterns – which is why we can see animals in the stars and clowns in clouds.  Throw some coffee beans on a tray or tea leaves in a cup, and your brain immediately starts drawing lines between groups, trying to find the pattern in them.  Take the picture below , know as the famous Kaniza illusion.   Four circles, each with a quadrant removed.  But line them up in the right way, and your brain sees a white square which isn’t there.    Try covering two of them up, and the square will disappear!   Isn’t the brain a wonderful thing?  Your camera isn’t going to do this! :



That’s all for now.  Next we will look at how your brain processes colour.

To be continued.




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