A fisheye lens gives everyday subjects a radically different perspective. This shot was taken with a circular fisheye Lensbaby lens which replaces the camera’s lens. ( ©Victoria Hederer Bell.)
Lens hoods help block stray light from entering the lens. They vary in size and shape and are usually short and rectangular or petal-shaped for wide angle lenses. Longer lenses normally use cylindrical hoods. Hoods for zoom lenses are often petal-shaped, with cut-out sections to cater for the wider field of view covered by shorter focal lengths.
To be effective, the internal surface of a lens hood should be non-reflective. Most hoods have matte surfaces, sometimes achieved by flocking. Hoods for zoom lenses must be correctly orientated in order to block stray light without interfering with shots.
Lens hoods are most effective when the sun is at an angle to the camera and out of view of the image frame. They can’t block stray light when a bright light source is inside the shot.
Aside from minimising the effects of stray light, a lens hood will act as a buffer between the lens and the environment, preventing fingertips from straying onto the delicate front element and leaving greasy marks that will degrade shots. Hoods on longer tele lenses will also provide some protection against rain, spray and dust (although lenses that aren’t weather-resistant shouldn’t be exposed to the former).
Rectangular lens hoods are often used on wide-angle lenses, such as this 12mm M4/3 lens from Olympus.
Even effective lens hoods can’t prevent flare when the bright light source is inside the frame. But they can maintain image contrast with the aid of effective lens coatings.
Digital sensors are much less affected by UV radiation than film, so the traditional reasons for using these filters no longer apply. Unless they’re made of high-quality glass and properly fitted, filters can actually degrade image quality. They may also produce ghosting due to reflections between the internal surface of the filter and the front element of the lens.
Fitting a protective filter (UV or skylight) is wise in places where there is salt spray, blowing sand or dust, all of which can etch the surface of the lens. It’s also advisable when photographing small children and pets, particularly if the subject might touch the lens.
The UV and haze filters required for shooting with film are no longer necessary with digital cameras. But they can provide a useful protective barrier against sticky fingers, salt spray and dust.
Some filters are used for exposure control, examples being polarisers, neutral density (ND) filters and graduated filters. Polarisers are mainly used for suppressing reflections and reducing atmospheric haze.
Polarisers: There are two types of polarising filters: linear and circular. Both types can achieve the same objectives but circular polarisers shouldn’t interfere with autofocusing and metering, whereas linear polarisers may.
A polarising filter will darken blue skies and make white clouds more prominent, as shown in this picture. But they require careful adjustment in alpine areas to prevent the skies from appearing unnaturally dark.
Correctly used, a polariser will increase dynamic range and make it easier to record scenes containing a bright sky with a relatively unreflective land by decreasing the glare from reflective surfaces while darkening the sky. It can also increase contrast in scenes containing clouds and skies, although if the subject is highly reflective, it can reduce contrast.
Being highly angle-dependent, polarisers are best used with normal and telephoto lenses. Wide angle lenses can produce uneven results because parts of the scene facing into the sun will be strongly polarised, while the rest will not.
Polarisers have a number of disadvantages:
1. They normally reduce the light reaching the image sensor by between two and three f-stops.
2. They can reduce image quality if they are made from inferior materials and are not kept perfectly clean.
3. They require greater care with camera positioning and it can take longer to compose shots as the filter has to be rotated to the appropriate position.
4. It’s almost impossible to use a polariser successfully with stitched panoramas due to variations in the intensity of the polarisation as the angle of the camera to the sun is changed.
5. It may be difficult to record the ends of rainbows because of uneven polarisation when using a wide angle lens.
6. When the reflection makes the picture, a polariser is undesirable.
ND filters reduce the amount of light reaching the sensor without affecting the colour of the image. Their main use is for exposure control by providing greater flexibility to select wide lens apertures and/or slow shutter speeds in bright ambient lighting. They’re available in a wide range of densities from one f-stop to 13 f-stops, the latter being rated as ‘extreme’.
A popular application for ND filters is enabling slow enough shutter speeds to be used to capture motion blur, particularly with water. A three-stop ND filter can be used for photographing waterfalls or cascades in normal daylight because a couple of seconds’ exposure is enough to create an attractive blur. For seascapes, longer exposures will be required, typically 20 seconds or more, and denser ND filters will be required.
ND filters can also be used to eliminate human subjects from streetscapes and architectural photographs. Exposures of two minutes or more can make people ‘vanish’ when they move through the scene.
Another use for ND filters is to enable wide lens apertures to be used to obtain a shallow depth of field on bright, sunny days. They are ideal for blurring distracting backgrounds in portrait shots.
A popular use for neutral density filters is to enable slow shutter speeds to be used to record blurred water. A three-second exposure at f/11 with a 30mm lens on a M4/3 camera.
Graduated filters have variable light transmission with roughly half being optically clear while the remainder is of neutral density or has a colour that changes the hue in the areas it covers. The transition between these zones can be abrupt (‘hard edge’) or gradual (‘soft edge’).
ND graduates are mainly used to bring an overly-bright part of a scene within the dynamic range of the image sensor and prevent highlight clipping. Hard edge filters are used when there is an abrupt change in brightness; for example, between a dark area of land or sea and a bright sky.
Soft edge filters are used when the light and dark portions are not distinctly separated and when horizons aren’t totally straight.
Like regular ND filters, ND graduates come in different densities, the most popular being ND2, ND4 and ND8. Most photographers tend to buy a set of graduates to handle different lighting conditions. Coloured graduates introduce colour, while also reducing the light level in the filtered part of the scene.
Graduated neutral density filters can bring out details in bright skies that would otherwise be difficult to see.
Coloured graduated filters are mainly used to add drama to shots by altering the colour and intensity of part of the image frame.
Adapters allow you to fit lenses from one manufacturer on a camera with a different brand or older lenses on new camera bodies. Before buying an adapter, it’s important to understand the following:
1. Adapters aren’t covered by the camera’s warranty so any damage they cause is your responsibility.
2. Most adapters require you to use your camera in manual mode, which means manual focusing and metering at the shooting aperture.
3. Using lenses designed for film cameras on cameras with smaller sensors will almost certainly reduce image quality.
4. Using lenses from different manufacturers on cameras with the same sized sensors should not compromise image quality.
5. Adapters usually reduce the amount of light entering the lens, sometimes by as much as one or two f-stops.
The exception is the Metabones Speed Booster, which increases the maximum aperture by one stop and makes the lens faster by a factor of 0.71x.
Special Effects Lenses
Although many modern cameras include special effects, some effects can only be achieved with specially-designed lenses. Two types are available: lenses that are added to existing lenses and those that replace the lens.
Popular add-on lenses include wide-angle and fish-eye converters that extend the angles of view of regular wide angle lenses. There are also telephoto converters that extend the range of telephoto lenses and macro converters that enable closer focusing to increase subject magnification.
This picture of a Lensbaby Spark special effects lens in use was taken by Craig Strong using the Spark lens. (Source: Lensbaby.)
Conversion lenses are usually labelled with the degree of magnification they produce. For example, a 0.50x wide angle converter expands the coverage of a 50mm lens to the equivalent of 24mm, while a 2x tele converter effectively doubles the reach of a 50mm lens to 100mm. Most types of converter lenses will reduce the amount of light that reaches the sensor by between one and two f-stops.
For DSLR and CSC cameras, Lensbaby produces a range of creative lenses that replace the normal lenses and allow photographers to select an area in the frame that will be sharp while the remainder of the frame is blurred. Most have a fixed focal length and relatively small, fixed aperture (typically f/5.6).
The range includes lenses that can produce fisheye, soft focus and pinhole effects. Details can be found at www.lensbaby.com
Excerpt from Lenses Guide.