Photography 2 - Optics (1)

You don't need to be a physicist specialised in optics to take a good photo, but it is necessaary to understand some basic concepts about light: what it is and how it behaves, the relationship between frequency and colour and how to understand light to make the most of it.

I won't go into all the technical details about these concepts, as there are loads of extensive academical texts you can refer to. I will, however, mention specially a book which is used as basic academic material in photography. It is called "Basic photography", by Michael Langford, now available in its ninth edition in [Amazon] at a more than reasonable price for the knowledge it will give you. I strongly encourage its read to anyone who is considering taking up photography half seriously.

[Light] is a wave that behaves as a particle (photon) or viceversa... the long standing scientific argument is still raging, according to some. I won't take sides. The fact of the matter is it has direction, orientation, frequency and intensity.

...All of those who have ever stood next to a flash when it fires off can even tell you it has mass, but, as I say, I won't go into debates about this point X-D.

Frequency and colour

We will begin with the more "complicated" part: The relationship between frequency and colour. Light, as an electro-magnetic wave such as radio or even like a sound wave, "vibrates" or rather, oscillates at a certain speed. That is, there is a distance relationship between a light-wave and the next one. This distance determines the colour of a light-beam. The narrower this distance is (more cycles per second), the higher the frequency, the bluer or "colder" the colour. The wider the gap (less cycles per second), the lower the frequency and the redder and "warmer" the colour. We can see this relationship, for example, when we see blue or red stars, depending on wether our distance from them shortens or lengthens (relatively, of course).

This frequency is known, in terms of optics, as light "temperature" and it is "measured" in Kelvin degrees (you can see the scale on the lower part of the graph below).

We have all, at some point, seen a [scale graph] such as the one below, which looks like a section from a rainbow (which is what it actually is, since, due to refraction, the light is split into all its spectrum, showing the different frequencies at different angles and thus all the colours are shown... but I digress...). Towards the right is the ultra-violet range (too high a frequency for the human eye to see), and towards the left is the infra-red (too low a frequency for the eye to see). The colour scale continues on either side towards space background noise, gamma and X rays on one side and microwaves, radio and TV signals on the other.

This will help you understand the concept of "white balance" which is the reason why some of your photos will come out blueish when shot in a shadowed area un a very sunlit day or under fluorescent light (when the light frequency is very high) or will come out red-tinted when shot at dusk (when the sun, having to push through so much more atmosphere is "slowed down" to lower frequencies).

As an experiment you can, for example, stand in a room lit by fluorescent light at dusk. Everything on the inside will look normal but everything outside will look redder than it is. If you then go outside and look in, everything inside will look blueish, whilst everything outside looks more normal. This very same effect happens when you shoot in the wrong white balance setting: shooting with "daylight" setting in a room light by lightbulbs or a picture taken with "fluorescent" setting on an outside dusk environment.

All cameras have (either automatic, manual or both) an option so it may take into account the ambient light temperature, so that the camera may correctly interpret it and show an image that is closer to what our eyes perceive. Our brains, being that much smarter, does this adjustment all the time automatically, pushing the balance (to a point) so that everything looks "as it should".

Colours and coloured filters

Also, the images we perceive of things are made up from the light reflected or absorbed on/by them. For example, take a red car. It will look so because under a white light (with all the colours in it) will absorve all the colours and bounce back the red, which our brain will interpret is the actual colour of the surface. In the same way, if we look at the colour wheel on the right, we han asume as a rule for filters, any coloured filter will allow the same colour it is made of to pass through and will darken the rest of the colours. The further away from the original colour, the darker the resulting colour will be (the more light is stopped).

This is an important concept to understand when using coloured filters (wether they be real optical filters or "simulated" in Photoshop). For example, the same red car from before, seen through a green or blue filter will appear darker. However, if we see it through a red filter, it will stay the same, whilst everything else around it is darkened since all other colours have a harder time getting through the filter, making the car look lighter in relation to everything else.

You can practice this when, for example, you use the black and white smart layer in photoshop and place a red gradient layer under it with a "multiply" mixer setting. As you can see, both the sky and the blue bike appear darker. This adds to the skies intensities, setting a darker mood, for example.

Orientation and polarization

Light, as the wave it is, as we have already mentioned, oscillates. Now then, this oscillation has a defined direction on the plane, depending on the light emitter or the surface it is reflected on. This is called [polarization]

This is the reason why "polarizing" filters work. They actually are no more than a very thin mesh of straight lines which only allow the light to pass through if the waves are in the right orientation. This is the same effect that protects our eyes on the snow with polarized sunglasses, since they avoid a large percentage of the light bounced off the snow, avoiding the retinas burning off.

Polarizing filters, however, unlike the sunglasses, may be spun or re-oriented so we can decide what light to allow through so we may, for example, eliminate a large percentage of light bounced of a liquid surface (so we may take a picture of a dawn near to a lake and we can see through to the bottom of the lake). These reflections cannot be eliminated later in Photoshop since we would still be missing the information of what was behind them.

To be continued...
Next entry: Photography 2 - Optics (2) - Focus, focal length, contrast and histograms