Kitabı oku: «Collins Complete Photography Manual», sayfa 4

ISO ratings

Films come in different sensitivities, or ‘ISO’ ratings. High ISO films have more ‘grain’ (random speckling) and are not as sharp as low ISO films. As a general rule, you should choose a high ISO film when you are shooting in low light and a low ISO film whenever picture quality is crucial.

Special films

There are some special-interest films which can produce effects that are difficult to achieve in any other way. One of the most interesting is ‘infra-red’ film, which captures the heat given off by objects as well as the light that they reflect. Kodak’s High-Speed Infra-red black and white film is a well-known example. It reproduces blue skies as near-black but vegetation and human faces have a strange, ethereal glow.

All About Scanners

A scanner is used to convert a photograph into a digital image file on your computer. The photograph may be a print, a negative or a slide, though in order to scan negatives and slides you need a scanner with a transparency adaptor or a special film scanner.

Flatbed scanners

Most scanners are of the ‘flatbed’ variety. You lay the item you want to scan face-down on a glass plate, close the lid and then operate the scanner from your computer. The glass plate, or ‘platen’, is usually a little larger than an A4 sheet or US letter size. Larger A3 scanners are available, but they are specialist items and considerably more expensive.

Flatbed scanners are designed for all kinds of printed material. They can be used to scan articles in magazines, letters and business documents as well as photographs. However, there is some quality loss during the scanning process, however good the scanner, and photo prints themselves are often imperfect, so it is better, where possible, to scan the original negative rather than a print.

Flatbed scanners with transparency adaptors can do this, but the quality will not be as high as you will get from a dedicated film scanner. These are more expensive than standard flatbed scanners and can only scan 35mm slides and negatives. You can also buy medium-format film scanners, but these are many times more expensive and are impractical for amateur photographers.

DPI (Dots Per Inch)

Manufacturers will quote the scanner resolution in dpi (dots per inch). Typically, even an inexpensive scanner will have a resolution of 2400dpi. This is way beyond the level of detail you are likely to find in any item you might want to scan. In practice, the optical and mechanical quality of the scannerwill be far more important than the resolution figure.

UNDERSTANDING DYNAMIC RANGE

Scanner makers may also quote ‘dynamic range’ or ‘DMAX’figures for scanners designed specifically for photographers. The dynamic range figure refers to the range of brightnesses that the scanner can record. Film can have a very high brightness range indeed, so a large dynamic range (‘DMAX’) is an advantage. Avery good flatbed scanner is unlikely to have a DMAX value higherthan 4.0 while afilm scanner might have a DMAX value of 4.2 or more. The small difference in figures makes a big difference to how successfully the scanner can capture detail in deep shadow and bright highlight areas of your slides and negatives.

High resolutions are useful only when scanning film directly. Here, you need a resolution of 2700dpi or more to capture all the detail in the photograph. However, even though many flatbed scanners offer higher resolutions than this, their optical and mechanical components prove the limiting factor, not the resolution. You can usually expect to get sharper pictures from afilm scanner than from a flatbed scanner with a transparency adaptor, whatever the quoted resolution figures.

Using a Scanner

Whether you are using a flatbed scanner or a film scanner, the scanning process is much the same. The first step is to place the photographic print on the scanning platen or, if you are scanning film, place the film in the holder provided.

Preview scans

Once your item is on the platen or in the film holder, you can then carry out a ‘preview’ scan or ‘prescan’. This scans the image quickly, but at a lower resolution than the final scan. Its purpose is to display the image on the computer screen so that you can make the necessary adjustments before the full scan is carried out.

Cropping

First of all, you will want to ‘crop’ the scan or, in other words, remove any borders or empty space around the photo. Some scanners can ‘auto-crop’ your photos, but to get exactly what you want, do it yourself.

Colour settings

Next, you should confirm the colour settings. Many flatbed scanners will attempt to detect the type of item you are scanning as a ‘document’, ‘text’ or ‘photo’. It is always a good idea to check that the scanner has identified the type correctly and is not about to save your photo in the wrong format.

CORRECTING DEFECTS IN SCANS

35mm slides and negatives are very small and have to be magnified considerably to produce prints. This also magnifies any dust or hairs on the negative and this can easily spoil the image. You can use a blower brush or compressed air to try to dislodge any debris from the film before you scan it, but while this can help, it seldom eliminates dust entirely.

However, scanner makers have found a solution. Some scanners can identify dust particles, which stand proud of the film surface, using a special infra-red scan. Once the scanner knows the location of these particles it can ‘fill in’ the defects during the main scan to produce ‘spotless’ images. ‘Digital ICE’ technology is the best-known example of this.

Image adjustment settings

Now check the image adjustment settings. Most scanners have an ‘auto-adjustment’ option which measures the light values during the preview scan and adjusts the image brightness, contrast and colours automatically. These automatic adjustments will often be correct, but you may sometimes need to make adjustments manually if your photo looks too dark, too light or the wrong colour.

Resolution and output size

The next step is to check the scanning resolution and output size options. This can often be the cause of much confusion. The simplest solution is generally to leave the output image size the same as the original’s (or set the ‘scaling’ to 100 per cent) and then choose a resolution figure appropriate to the item that you are scanning. Afigure of 300dpi or 600dpi is usually plenty for scanning prints, and 2700dpi or 4000dpi will suffice when scanning slides or negatives.

Image formats

Finally, you will need to choose the format of your scanned image file. The JPEG format produces the smallest files and is usually the most efficient option. If you set the ‘quality’ to ‘high’ there will be a negligible loss in quality compared to other formats.

The Future of Photography

Experience has shown that trying to predict the future is fraught with problems. It is all too easy to get things laughably wrong. There are two types of change: evolution and revolution. Evolution is easiest to anticipate. You start from where you are now and simply project forward. But progress is rarely linear and logical. Which of us at the turn of the century would have anticipated that within five years virtually every mobile phone would incorporate a digital camera?

Pixel count

One thing we can be reasonably sure of in the future of photography is that camera pixel count will continue to rise – though how much benefit that will be to anyone other than the professional photographer is another matter entirely. The resolution currently available on even inexpensive models of digital camera is more than sufficient to produce quality images that will satisfy most amateurs – whether they want to view them on screen or make prints. Not many photographers often enlarge their pictures beyond A4, and that is easily achievable at the resolutions available today. However, that factor alone will not stop the pixel count rising – even though bigger files mean longer processing times and require more storage capacity.

Increased capacity

Higher resolutions will inevitably lead to an increase in the capacity of removable memory cards. Already you can buy cards that are capable of storing hundreds of quality images – enough for a whole year of picture taking for some photographers. One day, though, it might be possible to store an entire lifetime’s pictures on just one card. Doing so, however, without downloading or archiving them, would be a huge risk. Prudent photographers sensibly prefer to use several lower capacity cards just in case a card gets corrupted – which, happily, does not happen very often.

Screen size

Large screens on cameras will become the norm in the future, and the larger the better. Screens allow you to compose images more effectively, review them more accurately, and share your images with others more easily just after you have taken them. The limiting factor will be the size of the camera itself-which will surely remain as diminutive as possible.

Live preview on SLRs

Being able to see the subject ‘live’ on the LCD monitor has been the norm for many years – but for a long time SLR cameras only showed the image electronically after it had been taken. Pictures were still taken using the tried-and-tested reflex viewing system. In time all cameras will have live viewing, including SLRs, and it will seem perverse to have anything else.

Convergence

It seems likely that the various electronic items we use will gradually converge. Who wants to carry around lots of different gadgets? We are seeing this happen already, with phones featuring not only cameras but also music, email, games, the internet, diary and the capacity to play live and recorded video. Even so, it is likely to be some time before the SLR, used by most photo enthusiasts, goes the way of the dinosaur.

chapter 2 Lenses and Accessories

It is the enormous range of lenses and accessories on the market that makes photography so creative and so enjoyable. Compact digital cameras now generally have a zoom lens with a decent angle from wide-angle to telephoto – making it possible to tackle most popular subjects successfully. Step up to SLR ownership and there are no limits to what can be achieved photographically. Lenses and accessories are available to meet every possible need – from capturing distant subjects such as wildlife and sport to revealing the splendour of vast interiors or panoramic vistas. If you can imagine it, you can take it.

Understanding Lenses

Single lens reflex cameras enable you to change lenses to achieve a variety of effects. The camera’s standard lens will give an angle of view roughly similar to that we perceive with the naked eye, a wide-angle lens enables you to get more into the frame, while a telephoto magnifies distant objects.

There are other lens properties to take into account, apart from their focal length, including the maximum aperture. The larger the maximum aperture, the more light the lens can gather. This is useful in poor light or whenever you want shallow depth-of-field in your photographs, perhaps for throwing backgrounds out of focus, or for creating a similar effect.

Zoom lenses

In modern cameras, zoom lenses have largely taken over from lenses with fixed focal lengths (‘prime’ lenses). The versatility of zooms means that you do not have to carry around a number of different prime lenses, or keep changing lenses for different subjects.

However, zoom lenses do have a couple of intrinsic disadvantages. One is that their maximum apertures are lower than those of prime lenses. Whereas a 50mm prime lens might have a maximum aperture of f/1.8, a typical ‘standard zoom’ might have a maximum aperture off/4 at this focal length.

Lens mounts

Each digital SLR brand uses a different lens mount. A Nikon lens, for example, will not fit a Canon camera. However, you do not have to buy lenses made by your camera’s maker. Independent companies such as Sigma, for example, make lenses which can be supplied in different mounts according to the brand of camera you are using. These lenses are just as serviceable as those supplied by leading camera firms.

EQUIVALENT FOCAL LENGTH

Photographers using 35mm cameras are used to judging the angle of view of a lens by its focal length. However, with a couple of exceptions, digital SLRs have physically smaller sensors, so that the angle of view of the lens is reduced and it appears to have a longer focal length. You need to multiply the actual focal length by a factor of 1.5 or 1.6 to get its ‘effective’ focal length. For example, on a digital SLR a 50mm lens effectively becomes an 80mm lens.

Independent lenses versus marque lenses

Lenses made by independent companies are generally much cheaper than those offered by the camera maker. The optical performance is often very good and it may be difficult to see the difference in image quality between photographs taken using a good-quality independent lens and those taken on a more expensive ‘marque’ lens.

Having said that, when you buy a lens you are not just paying for image quality. Marque lenses may be better made than those from independent companies and are consequently more likely to withstand years of hard use. Their design and finish will be consistent with other lenses in the same range, and with the camera bodies which they are designed to accompany, and the lens range may include more sophisticated and specialized lenses that you cannot get elsewhere.

Standard Lenses

Digital cameras may be sold in ‘body-only’ form, but this option will normally only appeal to buyers who already have compatible lenses. Most buyers will choose a camera kit that includes both the body and a standard lens.

Although most new cameras come with zoom lenses fitted these days, until fairly recently film cameras were supplied with only a fixed focal length lens. Atypical standard lens has a focal length of 50mm or thereabouts, and is designed for general-purpose photography. Its angle of view closely matches that of the human eye, although some photographers feel that a 45mm lens is closer to the ideal. With a lens like this, the framing and perspective of shots looks natural, and this type has a large maximum aperture of f/1.8 or f/1.4. This makes it especially useful for shooting in low light or where you want shallow depth-of-field.

50mm standard lenses are light and compact, but some makers have produced shorter ‘pancake’ lenses for photographers who want their camera and lens to be slimmer still. These have a focal length of around 40mm and a smaller maximum aperture off/2.8, but their optical quality is usually excellent. They are more expensive, but for many photographers they are also more useful as standard lenses.

Standard zoom lenses

The zoom lenses that are a standard feature of most cameras sold today offer greater flexibility than the fixed focal length lenses of the past, covering a range of focal lengths from wide-angle through to telephoto.

On a film camera, the usual standard zoom has a focal range of 28-90mm. On a digital SLR it is usually 18-55mm, which gives a comparable angle of view. You can use a 28-90mm film lens on a digital SLR, but the focal range is not ideal, because it does not provide proper wide-angle coverage on the smaller sensor.

Zoom ranges are sometimes quoted as a factor – for example, ‘3x’, ‘4x’ or ‘5x’. This figure indicates the change in magnification across the zoom range. A 28-gomm zoom offers a 3.2x zoom range, for example, while a 28-135mm is a 4.8x zoom.

Zoom lenses with a longer focal range are more desirable, but they are also more expensive and much heavier. A lighter, inexpensive lens may be more useful on a camera that is going to be carried around all day.