1. Bokeh

Bokeh is a term used to descibe a deliberate blurring of part of an image. Finding an exact description on the net of what makes a good Bokeh image is pretty difficult, and it seems to be used fairly loosely for pretty much any image which is entirely on partly out of focus. There seem to be 3 main categories - the completely abstract ones which are entirely out of focus completely abstract ones which are entirely out of focus these are the ones that got me interested in the first place - the two layer ones which use the Bokeh blurring at a background for an infocus image, or a smooth transition in and out-of-focus with depth.

As a technique it's probably most commonly used in portrait photography to make the subject stand out. To get a good Bokeh effect you need to use the lowest apearture value on the camera and the effect can change drastically with the type of lens diaphragm - ideally you want enough lens diaphragm blades to form a circular aperture opening, rather than a hexagonal shape. Although you can create other interesting shaped Bokehs like this one .

Bokeh on Flickr
Photo.net article on Bokeh
Wikipedia entry about Bokeh
Flickr Discussion Group about Bokeh
Kid Bokeh
Christmas Tree Bokeh
Flower Bokeh
Bamboo Bokeh

2. Stops

When you want to start taking photographs using the manual setting on the camera you need to start managing the film speed, aperture size and shutter speed to get a proper exposure. This is made easier using the idea of stops. The term 'stop' represents a relative change in the brightness of light, with each stop represents a doubling or halving of the light. Double the light is +1 stop. Four times the light is +2 stops. Half the light is -1 stop. Quarter of the light is -2 stops. An eighth of the light is -3 stops.

Even though they each use different scales, Stops are interchangeable across the shutter speed, aperture size, and film speeds. When you go from one value to the next of each scale you are changing by 1 stop. Therefore if you have the correct exposure and change the film speed up by 1 stop, you need to move the shutter speed or aperture size down by 1 stop to compensate.

Film speeds are measured in ISO values. This scale is pretty easy as you just double of halve each ISO value, like you double or halve the amount of light for each stop change:

ISO 1600
ISO 800
ISO 400
ISO 200
ISO 100
ISO 50

So to correctly expose an ISO 800 film you need twice as much light as you need to correctly expose on ISO 1600. This is why high ISO number film is good in poor light conditions. You need 32x the light to develop ISO 50 as ISO 1600 (ie. you'll need a wide apperture and long exposure time).

The shutter speeds steps are close to doubled or halved (but not quite... why?) as you'd expect. If you leave the shutter open twice as long, twice the light gets in.

1/4 sec
1/8 sec
1/15 sec
1/30 sec
1/60 sec
1/125 sec
1/250 sec
1/500 sec

So if you get the correct exposure with ISO 100 and 1/60 sec, you'll also get a correct exposure with ISO 200 and 1/30 sec.

Aperture sizes are a bit trickier as they're measured in F numbers. These double or half every second number (should probably work out the actual pattern):

Smaller F numbers repesent a bigger apperture. Therefore F1.4 lets in twice as much light as F2.

There's a good example of all this here.

3. DIY Lightbox

I've had a go at a homemade lightbox. Details can be found here on Flickr.