Any newcomer to photography, picking up a modern digital camera is immediately confronted with a mystery. On the lens he or she might see something like SMC Pentax DA 1:1.8 50 mm. Turning to the camera – on a dial on the top they might see some of the following – B, M, AV, TV, SV P, AUTO. On the sides and rear of the camera there are acronyms such as AF/MF, RAW Fx1, AF/AE-L, ISO, WB, LV. If they were to ask what these initials mean, they’ll hear words like Aperture, Focal Length, Shutter speed, ISO. Pressed further, their mentor might mutter terms such as Depth of Field or Exposure triangle. As Eliza Dolittle sang to Freddy in the musical ‘My Fair Lady’, ‘Oh, words, words, words, I’m so sick of words…is all that you blighters can do?’
In the next few blog posts, I’ll try to explain just a few of these terms to the best of my ability. But you can find more detail by ‘googling’ any of the terms. Anyway, I’ll start with aperture. Essentially the word ‘aperture’ in photography refers to the hole in the lens through which light reaches the sensor – the bit that actually records your image. The hole in the lens is at the centre of the shutter which opens when you press the button to take a photo and closes when the shot has been taken. The shutter is made of ‘leaves’ that move both to do the opening and closing, but can also be set to change the size of the hole to create different effects.
This is a photo that I took in my garden this morning of a heather plant. I set the opening to create a wide hole – as wide as this lens would allow. Notice how only part of the plant is in focus and everything behind the plant is blurred.
The aperture – or size of hole – that I set for the the photo was f/1.8. Let me simplify that. 1.8 is almost 2 so when you see that f/ it refers to a ratio of 1/2 or half. So if the aperture size were f/16 the ratio would be 1/16. You know from simple arithmetic that 1/16 is much smaller than 1/2 – a sixteenth is smaller than a half. Why did I choose such a big aperture? I wanted only the plant to be in focus – I wanted the background to be blurred. That’s an effect known as a shallow depth of field where sharpness is confined to a very narrow band of depth.
I shot this photo at f/8 – an eighth, so I only allowed in a quarter as much light as in the first image in one way, but the camera compensated by opening the aperture for a shorter time, 1/5 seconds, to provide the same level of exposure.
The image looks different. In a way I’ve let in about the same amount of light, but I’ve changed the recipe for doing so. I used a smaller aperture but the shutter was open for 1/5 seconds whereas in the first photo it was open for 1/100 seconds. Look at the difference between them. In the second photo, the whole of the plant is in focus and the back ground is less blurred. In other words there is a greater depth of field. The field of sharpness extends further forwards and further backwards as well.
In my final photo, the settings are an aperture of f/22 and a shutter speed of 8/5 or one and three fifths seconds. Now look at the depth of field – how sharply the back of the garden has come into focus.
I don’t want to stray much further into depth of field, diffraction, ISO, angle of view and so on. Today’s blog is just to provide a simple introduction to the idea of aperture and the kind of role it plays in photography. I’ll just provide two examples below of deliberately choosing one size of aperture over another to change the depth of field.
I don’t do portraits of people, but that’s a definite area for wide apertures. This is just a handheld photo of my daughter’s dog, Ted. It was taken indoors in low light conditions, so I had to boost the brightness of the photo in camera using the ISO setting – I don’t have flash either. I took the shot at f/3.5 – quite wide with a shutter speed of 1/320. If you were to enlarge this image you’d be able to see that only the dog’s left eye (the one on the right of the photo) is in focus. You can almost see my reflection in the eyeball.
This final example is of a lone tree at Lake Wanaka in the South island of New Zealand. I shot this at f/14 (quite narrow) and 1/80 of a second. See how the image, though handheld, is fairly sharp from the beach to the mountains.
Tomorrow I intend to post about exposure, or more specifically about what sort of shutter speeds you might use for different types of photograph.