Today we play with depth of field and the focusing settings.
A loose definition of the depth of a photo is the amount of the photo that is in focus. If everything is in focus, the photo is said to have a ‘deep’ depth of field. If a particular subject is in focus and the rest is not, the photo has a ‘shallow’ depth of field.
Ever since I have started to get into photography proper I have adored depth of field – I love the way that it can be used to guide the viewer’s eye, or focus his or her attention. On my old point-and-shoot camera, I discovered that I could get a very shallow depth of field by using the macro setting. On my new EOS 400D SLR, however, it works a little differently.
Shallow depths of field are created by using large aperture settings, or small ‘f stops’. The aperture is how wide the shutter in the lens opens, and an ‘f stop’ is a unit of measurement for apertures. It is measured as a ratio – an aperture of f3.5 can also be written as 1:3.5. With each f stop on a camera, the light intensity (or the light allowed to enter the camera) halves.
Large apertures (small ‘f’ numbers) let in more light than small apertures, and therefore are often used in low light conditions where longer shutter speeds would result in unsightly camera-shake. However, large apertures also result in shallow depths of field – and this can be put to good creative use.
So, a large aperture isolates a subject from its background – simple, right? Well, not quite; I have discovered that the DoF is also linked to focal-length (the distance between the lens and the camera’s CCD or ‘sensor’ – think of large focal lengths as ‘zooms’). Larger focal-lengths create shallower depths of field! This means that on my camera’s zoom kit lens, a picture taken at f5.6 at 55mm actually creates a shallower image than f3.5 at 18mm. The image above is taken at f5.6 at 41mm.
This probably means nothing to 80% of viewers, is old news to 15%, and is an interesting thought for perhaps 5%. Frankly I don’t care, it has doubled my interest in my camera and I intend to milk this lens for all it’s worth before I can afford a proper macro lens.
Oh, and the subject today is my guitar which my grandma gave me the money for shortly before she passed away – a Ibanez RGT42 DX FM TLF (thru-neck, with floating bridge and flame-maple top in ‘transparent lavender matte’ – more of a greyish blue and absolutely gorgeous). My grandma bought the best presents 🙂