Digital SLR Handbook. John Freeman
Читать онлайн книгу.
• ISO 3200 As for ISO 1600, but where high shutter speeds are required; noise will be evident in shots.
White balance
The human eye and brain automatically compensate for the different colour temperatures of various light sources, so that white always appears white to us. As DSLRs can’t do this, they have special settings to ensure that white is white, no matter what the lighting conditions. If the WB (white balance) is not set correctly, it can make a huge difference to your shots and the off-colour casts created can ruin a photograph.
Professional tips
• The higher the ISO, the greater the risk of ‘noise’.
• If your camera has one, use the noise reduction setting from the menu.
• Remember that light is ‘warmer’ at the beginning and end of the day.
• In indoor light, your shots will come out with an unwanted colour cast if you do not adjust your camera’s WB from the daylight setting.
With a DSLR, you can quickly set the camera to, say, sunlight, cloudy conditions, tungsten lighting or fluorescent light, but there is also a separate easy-to-use manual setting, which you can save in the camera’s memory to use again, allowing you to tailor the WB even more closely to the lighting conditions. Typically, you’ll need a piece of white paper illuminated by the lighting you want the camera to be set for. Filling the frame with a sheet of white paper and setting the WB to it (the exact process is usually straightforward but varies from camera to camera, so check your camera’s manual) will mean the camera can shoot ensuring the whites are balanced and without any odd colour casts.
Left: The fluorescent lighting has created an unnatural green colour cast across the entire image because an incorrect WB setting was used.
Right: In this shot, taken at the same location and seconds after the first image, the WB was set correctly and there is no colour cast.
Although the human eye perceives daylight as ‘white light’, it is actually made up of lots of colours of light mixed together – all the colours of a rainbow, in fact. During the course of a day, the quality of light changes. At sunrise and sunset, for example, when the sun is visible, the light is said to be ‘warm’, or red, in colour. At noon, when the sun is at its highest, the light appears ‘cool’, or blue.
Kelvin scale
Without being bogged down by science, this variation in the colour of light is measured in Kelvins (so named after Lord William Kelvin who invented the scale in the mid-1800s by heating a block of carbon until it glowed, producing a range of colours as the temperature increased). Broadly, the lower the Kelvin figure, the warmer, or redder, the colour; the higher the figure, the cooler, or bluer, the colour. DSLRs that allow you to adjust the WB take account of this colour shift and correct for it; some even have a Kelvin scale adjustment for fine-tuning your settings.
The guide overleaf to colour temperature and the corresponding light source shows how adjusting the WB setting, or the Kelvin scale if your DSLR has it, can radically affect how colours appear in your shots.
Light is measured in Kelvins, and the temperature of light can affect your images. The atmosphere in this shot is helped greatly by the warm glow of the setting sun, which has a relatively low Kelvin temperature of around 2000k to 3000k. The same shot taken at noon in direct daylight, which has a Kelvin temperature of around 5500k, would have a blue cast if the WB were not adjusted accordingly.
• 1700–1800k Match flame
• 2000–3000k Sun: sunrise and sunset
• 2500–2900k Household tungsten bulbs
• 3200–7500k Fluorescent lights
• 5000–5400k Sun: direct sun at noon
• 5500–6500k Daylight (bright sun in clear sky)
• 6000–7500k Overcast (cloudy) sky
• 7000–8000k Outdoor shade
File formats
DSLRs shoot images and save them on removable storage or memory cards. But the way the images are saved – the file format – has a significant bearing on image quality. DSLRs can typically shoot and save using the JPEG or TIFF compression file formats, although the latter is less popular, or the image data is left unprocessed as RAW files.
JPEGs are processed inside the camera and then squashed down into a (much) smaller file size, thereby saving space on the memory card. The downside is JPEG compression loses detail; for that reason, it’s known as a ‘lossy’ format. As the file is compressed, the camera’s computer removes self-similar pixels, such as large areas of blue in a landscape’s sky, thereby reducing the size of the final, saved file. When the image is then opened up on a computer, for example, it ‘guesses’ which pixels to replace, reducing image detail. JPEG files can be heavily compressed.
TIFF files are also compressed files, but they use a different compression method, allowing files to be reduced by up to around 50 per cent, but no more. This is a ‘lossless’ format, as no detail is lost.
RAW is not a format as such but the raw, unprocessed image data from the camera. Advantages include no compression and complete control of how the image looks – after the fact. With RAW files, the photographer carries out the processing – exposure, noise, white balance, even control of detail – later on a computer. Put simply, a RAW file is a digital negative and one of the photographer’s most powerful tools.
See also:
Interchangeable lenses
One of the key benefits of a DSLR is the versatility offered by interchangeable lenses, and no matter what make of DSLR you own, there is a set way to remove and replace your lenses.
Removing a lens
Typically, there is a button or lug alongside the lens that must be pressed to release the lens locking mechanism. Then you need to rotate the lens, either to the left or right (this depends on the make of camera) to release it from the lens mount and body.
Always make sure that you replace the lens cap (and the body cap if you’re not going to replace the lens with another lens) to protect the delicate electrodes and mechanics of the lens’s mounting system, prevent damage to the mount itself and stop dirt and dust reaching the sensor.
On this model of camera, the large lock/unlock lug, which must be pressed to release a mounted lens, is positioned to the right of the silver lens mount ring.
Attaching a lens
To attach a lens to the body, you must align indexes on the camera body and lens, bring the lens into contact with the mount and then rotate the lens (again, clockwise or anticlockwise, depending on your camera) to lock it home. It will click into place and won’t budge once it’s there. If it doesn’t click or moves, it’s not locked home.
Don’t force the lens onto the mount in the wrong position – you could damage the mount or lens – and don’t touch any gold-coloured electrical contacts. Finger grease and sweat are slightly acidic and, as these contacts are the means of communication between the lens and camera, you really don’t want them to corrode and stop working.