White balance

The white balance feature on digital cameras deals with the differences in colour temperature.  This adjusts the overall colour in a scene so that the very brightest parts are captured as pure white and without a colour tinge from the light. 

The settings on my camera are:

• Auto
• Incandescent
• Fluorescent
• Direct sunlight
• Flash
• Cloudy
• Shade
• K - where you can set your own white balance.  This can be done by using a grey card. 

Exercise: Judging colour temperature 1

For this exercise I have to take 3 pictures of a friend in different daylight situations.  One in full sunlight during the middle of the day, one in shade during the middle of the day and one when the sun  is close to the horizon. 

For the best results I needed a clear day.  However, this is November and England and getting a day with any sunshine is a rare treat. 

All images were taken with the White Balance set to Daylight.

Full sunlight during the day

This image is very bright.   

Shade during the day

There is a blue hue to this image reflected from the light blue in the sky.  If the sky was bluer then this could be more noticeable.

Sun low in the horizon

The sun was not very bright for this shot but you can see a faint yellow hue in the shot. 

The colour of light

Sunlight is our natural source of light.  During the middle of the say it appears colourless - we refer to this as white light.  This is what we regard as normal light. 


Light becomes colour when a part of the spectrum is missing.  Daylight normally has two colour directions. On a good clear day, when the sun is lower in the sky it becomes yellow, then orange and if you have a good sunset red by the time it reaches the horizon.


The reason this happens is because all the particles in the atmosphere scatter some of the light and there is more atmosphere between us and the sun at sunset.  The blue wavelengths have been scattered leaving the yellow/orange colours to come through. 


On a sunny day in the shade the orange/yellow is scattered making the light coming from the sky blue.


The colours of daylight can be seen on a scale that runs from red to orange to straw-coloured to white and then blue.  This is called the colour temperature scale. The temperature is measured in degrees Kelvin.
Generally the cooler the Kelvin temperature the warmer the colour and the warmer the temperature the cooler the light.

Exercise: Higher and lower sensitivity

This exercise required me to take shots at different ISO settings. 

Firstly I had to look for marginal situations and take one picture at normal ISO setting and then one at a higher ISO setting. 

I chose to take these pictures near sunset to make shooting conditions more challenging.

ISO 100

I was able to shoot at f9 with a shutter speed of 1/60s which is really the limit for handheld.

ISO 400

I was able to shoot at 1/250s at the same aperture by increasing the ISO which is apporx 4 times faster.

ISO 100

I shot this at a low aperture f5.6 with a shutter speed of 1/6s of a second which is too slow for handheld.  You can see the image is slighly blurred close up.

ISO 400

This allowed me to shoot at 1/20s at the same aperture without creating too much noise but making the pictures less blurred for handheld.

ISO 100

Again this was shot at f5.3 at 1/10s which blurred the motion of the car but also the blurred the buildings

ISO 400

I was able to shoot at 1/40s by increasing the ISO.

ISO 100

Shooting at a low aperture of f5.6 at 1/8s

ISO 400

I could shoot at 1/20s

ISO 100

shooting at f5.6 and 1/5s

ISO 400

Allowed me to increase the shutter speed to 1/20s

ISO 100

I was restricted to shooting at 1/15s which was too slow

ISO 400

I was able to shoot at 1/60s which is acceptable for handeld.

Shooting these marginal scenes in lower light proved troublesome handleld.  Increasing the ISO sensitivity allows you to increase the shutter speed which in some of the cases made for acceptable handheld shooting. 

In the other cases above I should have increased the ISO further still in order to get a less blurred image. 

When I looked at the images up close those shot at ISO 400 were a little noisier but not so much that it took away from the image.  Increasing the ISO above 400 to perhaps 800 might have made for a faster shutter speed to use but it may have compromised the image quality a little too much. 

My preference for shooting these kind of situations is to use a tripod to get the optimum.  However, I know that this is not always possible and this exercise shows the effect ISO sensitivity can have on difficult to achieve exposures.

Exercise: Measuring Exposure Part 2

For this second part I had to take 5 or 6 different photographs 5 times varying the exposure.  The first is one stop darker, the second half a stop darker, the third average, the fourth half a stop brighter and fifth one stop brighter.  

Here are the results. 

One stop darker - the best as it records the bolts more accurately

1/2 stop darker - still keeps the detail but a little brighter than reality

Average - the meter reading has made the image brighter.  Not acceptable to me as it is too bright.

1/2 stop brighter - again this is too bright and the blackness of the image is lost.

1 stop brighter - the darkness of this image is completely lost and the image looks over-exposed.

1 stop darker - gives mood to the image and brings out the red of the house.

1/2 stop brighter - the sky is beginning to look a little washed out

Average - makes the image look flat and the colour in the sky is lost.

1/2 stop brighter - this image looks over-exposed at the top

1 stop brighter - the image  is greatly over-exposed

1 stop darker - the bricks are deep and colourful and this works well.

1/stop darker - the bricks have lost a little colour but this image is still acceptable.

Average - the average reading has given a washed out effect to the colour in this scene. It is still acceptable though.

1/2 stop brighter - the bricks look much brighter and very different to the first image.  They are still acceptable but no longer look like real bricks.

1 stop brighter  and over-exposed.  Nearly all detail is lost.

1 stop darker - I feel this is too dark and some of the detail is lost in the shadows.

1/2 stop darker - still some detail lost in the shadows but it is better than the first image.

Average - this gives a good and fairly accurate recording of what the scene was actually like.  There's more detail that the darker images.

1/2 stop brighter - this is also good and the greens are vibrant.

1 stop brighter - the greens are a little too bright.  I think average works best for colours like green because it gives a more realistic reading for the colour.

This detail is from my garden fence and looks like 2 horses' faces. 

1 stop brighter and it has a dark mysterious air.  You can see the texture.

1/2 stop brighter - this still holds the texture of the wood.

Average - gives an average that is pretty acceptable.

1/2 stop brighter - takes on a different hue and the whites become brighter.  A very different scene but it still works.

1 stop brighter - this also is bright and works well.  A good example of how the light can change a subject into something very different.



 On the whole the average reading are nothing more than that - average.  They meet what we would call an acceptable exposure.  however, if you want to show and record the scene as it really is and capture the shadows, highlights and colour more realistically varying the amount of light hitting the sensor will allow you to do that. 

Exercise: Measuring Exposure Part 1

For the first part of this exercise I had to take about 4-6 photographs which are deliberately lighter or darker than average and explain why.

This lock on this white garage door is a brighter than average.  An average reading here would have made the white door grey so I over-exposed to make it whiter and more realistic of what i was seeing in fornt of me.

I used spot metering for this shot to make sure that the brightness of the white was not lost and remained white and not grey.  This works well as it doesn't have a noticeable affect on the brickwork.  Therefore I didn't have to compromise the scene.

This section of a black wooden door was under-exposed to ensure it maintained the darkness of the wood.  An average reading would have made it lighter in colour and lost some of the texture.

This shot was over-exposed to show how this scene can be made brighter and give a different effect than under-exposing as in the example below.  Both these shots are more interesting as they give different versions of the same thing but adjusting the amount of light that enter the camera.

Light

Light is the language of photography.  It determines how we take a picture. 

Sensors on cameras are designed to work best in normal daylight.  Lower light levels require the sensor settings to be more sensitive ie a higher ISO setting.  But it's not just as simple as that.  Higher ISO settings introduce more noise into the image and this may be a problem. 

The intensity of light
Brightness varies through the day from dawn till dusk.  The sun is brighter during the day than at sunset or sunrise. Cloudy and foggy days are also darker.  Understanding this is very important as our eyes can adjust for these changes but the cameras sensor can't.

The normal ISO setting for daylight shooting is 100-200.   Increasing this makes the sensor more sensitve to light together with the ability to shoot in lower light.

Measuring brightness
Sensors are less efficient that our eyes at recording the light that is in a scene as they cannot cope with the same dynamic range as our eyes.

Cameras measure brightness using their in-built metering systems. 

There are 3 types:

• Centre weighted
• Matrix
• Spot

Centre-weighted and matrix weight their readings in anticipation of how you would compose and take pictures. Average centre-weighted reading ignores any thin bright strip at the top due to the fact that that is where the sky usually is.

Matrix is far more advanced and takes readings from several points in the image and compares it to a database of similar known types of scene.

Spot is exactly what it says it is - a reading taken of a small area.  This is useful and accurate for certain types of scenes or compositions for exmaple where there is a bright object with a dark background.

The basis for all averaged readings results in a mid tone or 50% brightness or 128 on a scale from 0-255.  However, depending on your scene you which may be brighter or darker than 50% you may need to adjust exposure accordingly.  This can be done by using M mode or the Exposure Compensation control.