Cusp By Photographer to Focus
1. Understand aperture
The most fundamental element any photographer should understand is aperture. The aperture is the physical opening within your lens that allows light through to the sensor (or film in an older camera). The wider the aperture opening, the more light can pass through, and vice versa.
2. Aperture measurements
Lenses almost always have their maximum aperture setting engraved or stamped on one end of the barrel. On a zoom lens you'll see two measurements, often stated as f/3.5-f/5.9 or similar.
Rather than being opposite ends of a single scale these describes the maximum aperture at the wide angle and telephoto (maximum zoom) lens positions respectively. Always buy a lens with the smallest number you can afford in each position.
3. Avoid using aperture to compensate for poor lighting
Changing the aperture has a dramatic effect on the amount of light coming into the camera, as we have already said. You'll notice this is the case when shooting landscapes with a narrower aperture (higher numbered f-stop) as your camera will often want to take a longer exposure -- so much so that you may have to use a tripod to avoid motion blur.
4. Use a wide aperture for portraits
Anyone with a cat knows that when they're hunting or playing their irises contract to enlarge the size of their pupils. This has the same effect as widening the aperture in a camera lens: it makes the subject they are focusing on very sharp while causing everything behind and in front of it to blur. We call this a shallow depth of field. This is perfect for portrait photography, as it draws forward your model within the scene, making them the central focus while the background falls away. Choose f/1.8 or similar wherever possible.
5. Use a narrow aperture for landscapes
For landscapes, on the other hand, you want to have everything from close-at-hand foliage to a distant mountain in focus. This is achieved by selecting a narrow aperture. If possible stray towards f/22, or whatever the tightest setting your camera allows.
6. What does the ø symbol on my lens mean?
After the focal and aperture ranges, the other measurement you'll see on most dSLR lenses is preceded by ø and describes the diameter of the screw mount on the front of lens barrel. Check this number each time you head out to buy a filter or hood as you can't guarantee that it will be the same for each lens in your collection, even if they are all designed to be used on the same camera.
7. If you only buy one filter...
...make it a circular polarizer. This is the perfect beginner's filter, and one that will have the biggest effect on your day to day photography, giving holiday skies a vibrant blue tone and accentuating the contrast between the sky and passing clouds to afford your images greater texture. Although you can add blue to your images in Photoshop or a similar post-production editing tool, the effect is never as believable when done that way as it is when shot using a lens.
8. Don't confine it to skies
Polarising filters also cut through glare and reflection. Use it to shoot through windows and water.
9. Look for lenses where the zoom control doesn't change the filter orientation
Rotating a circular polarising filter changes the strength of the polarising effect, making skies deeper or lighter, and changing the amount of reflection they cancel out. If you plan on using such a filter then wherever possible buy lenses where turning the zoom control doesn't simultaneously rotate the end of the lens, and with it the filter, as this will change the effect. If you have no choice, set your zoom first and adjust the effect afterwards, being careful not to throw the lens out of focus in the process.
10. Don't forget about white balance
When using a filter set your the white balance on your camera to the appropriate conditions, rather than auto, to stop the camera compensating for the filter in front of the lens.