Thursday, May 6, 2010

Lesson 01 - The basic principles of taking a photograph.

Well, I've posted a few pictures and chat, so figured it's about time to start sharing some knowledge. I don't pretend to know everything about photography, nor can I take stunning photos (at least not intentionally - all my best photos were accidents :D ). However, I do have a knack of being able to talk technical in non-technical language, which is often helpful to absolute beginners. And so, armed with this skill, and a little knowledge, I hope to write a few articles from time to time, that will bring some enlightenment to somebody out there who has got a camera, takes snaps, but wants to do more.

I know this is a long-ish post, but it sets the groundwork, and hopefully isn't too demanding to read.
I'll try and keep future lessons shorter - I promise.

The basics
There are just 2 things you need to create a photograph - light, and something that is sensitive to light, that will record your image.  That sensitive something used to be film but in today's digital age, is now frequently a little bit of electronic wizardry called the 'sensor'.  I haven't used a film camera in years, and the chances are that any new photographer these days will have a digital camera of some type, so I won't be talking about film too much.

So, you have your sunshine all around you, and the sensor in your hand, and... ah ok, the sensor needs to be attached to some electronics and a screen or monitor so we can see the image... (short break while I get out my soldering iron) 

Hmm, it's very 'white'... there's far too much light around - we need a way of controlling the light that gets to the sensor. So we'll start by enclosing the sensor inside a box which is nice and dark (perhaps we could call this a... camera - that sounds good...) Next, we'll make a hole at the front to let the light in, and we'll just open that hole very quickly and shut it again. Now we're starting to see some light and dark patches on the sensor. If we open the hole for a longer time, or make the hole bigger, more light gets in, and the picture gets whiter again. Open the hole for a shorter time, or make the hole smaller, and less light gets in, and the picture gets darker.

So - this is the first valuable lesson - we have to find the right balance of the time we leave the hole open, and how big it is, in order to let just the right amount of light into the camera.
This is probably the single most important technical concept you need to grasp - and it's not really that complicated, is it?

Let's use some proper names for these things...
The hole that the light comes through is called the iris. It is a set of interlocking blades of metal that can be adjusted to make the hole bigger or smaller. The actual size of the hole is called the aperture. Aperture is measured in f-numbers, which confusingly get bigger as the hole gets smaller - so f/1.4 is a big hole letting in loads of light and f/22 is really teeny tiny.

Covering the sensor (and keeping it nice and dark) is the shutter. Think of it as a set of curtains that can be opened and closed very quickly (as quickly as 1/4000th of a second!). The time that the shutter remains open is called the shutter speed.  Light is constantly coming into the camera though the iris, so the shutter controls how long the light actually gets all the way through to the sensor.

NB - Some cheaper digital cameras achieve the same thing electronically, rather than there being a physical shutter mechanism across the front of the sensor.  While this might seem like a simpler solution, there is a problem in that the sensor is always active, and that a camera that has no shutter must first clear and reset the sensor before 'taking' the picture.  In a camera with a mechanical shutter, this can be done while the sensor is in darkness, prior to taking the photo.  So a camera with a mechanical shutter will actually react a bit quicker than one without.

So, by adjusting the aperture and shutter speed, we can find a nice balance to let the right amount of light in, but hang on, it's all blurred. That's what the lens is for... (by this, I mean the actual piece(s) of glass, as opposed to the black cylindrical thing you screw on the front of an SLR camera).  The lens focuses the light that passes through the iris, so that when it arrives at the sensor, it is all nicely ordered and forms a recognisable image. Without the lens, the light is bouncing around all over the place and makes no sense - the lens helps straighten things out and aim it in the right direction. 

There is one more variable in the aperture/shutter speed equasion, that helps control the amount of light used for your photo, and that is the sensitivity of the sensor. Imagine the sensitive tips of your fingers, compared with the thick skin on the heel of your foot. Your fingers will feel the tiniest needle prick, while your heel will take a lot more punishment. Wouldn't it be nice if you could change the sensitivity of your fingers, to make them more like your heel, next time you wanted to prune a thorny bush? Well, the same principle applies to the sensor in the camera. If you have your lens wide open to the largest aperture, and the shutter open for 30 seconds, and STILL there is not enough light (yes - it CAN happen), then you can make the sensor more sensitive so it will react to the available light quicker.

Be careful here though - as you make the sensor more sensitive, it is also prone to accidentally registering light, and creating grainy spotty images that don't look so nice. In the digital world, this is called 'noise' (in the world of film and negatives, it is called 'grain' - it's the same concept but having a chemical rather than electronic cause). The sensitivity of the sensor is measured using the ISO scale. ISO 100 or 200 are usual for normal photography, but the values keep doubling as you make the sensor more sensitive (and more susceptible to noise), e.g. 400, 800, 1600 (now you're into risky territory), and some cameras go even higher.  100 to 1600 are the most common range of ISO settings on everyday cameras, but film can be rated better than 100 (i.e. a lower number meaning higher quality) down to ISO 64, though I've not seen the equivalent on a digital camera (I'm happy to be shown otherwise though).

Well - that's probably more than enough for the moment. I don't want to scare you off. I'll take a break before giving you lesson 2 (while I think what it should be about).

Now - back to the photography.

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