Commercial Photography Technique - Lenses
The anatomy of a lens
It’s well worth taking a bit of time to find your way around your lenses and brushing up your knowledge of all the key features. Lenses enable us to isolate a subject from its surroundings and create a sense of order. Different lenses can be used to frame wide aspects of a scene (wide-angle lenses) or to isolate smaller sections within it (telephoto lens), thereby presenting the world in fresh or unexpected ways for commercial photography.
Filter Thread
Every lens has a thread of a given diameter at the end of the lens barrel that lets you attach screw-in-filters, such as a polariser or UV.
Lens Hood
Supplied with some lenses but an optional extra for others, the lens hood’s role is to prevent unwanted light striking the front of the lens, which can degrade image quality by causing flare.
Distance Scale
This is a scale on the lens barrel in metres (and feet) that indicates the distance between the subject and the camera as well as the depth of field at a given aperture.
Focus Ring
This enables you to manually focus the lens. Focusing is performed automatically on most lenses but a focusing ring allows you to override this when necessary.
AF/MF Switch
This switch enables you to select either Auto Focusing (AF) or Manual Focusing (AF) mode. Some lenses have the additional feature that allows manual focusing override while in AF mode.
Aperture Ring
This is usually positioned close to the lens mount and allows you to set the aperture manually on the lens. Not present on most modern lenses apart from Nikon’s.
Zoom Ring
This ring enables you to alter the focal length of the lens by rotating the ring on the lens barrel, which causes the optical elements (individual lenses) within the lens to move accordingly.
Lens mount
This allows the lens to be mounted to a compatible camera with fully automatic coupling. Independent brand lenses can be bought with an appropriate lens mount for your brand of camera.
Focal Length Explained
Focal length is the distance between the optical centre of a lens and the sensor when the lens is focused at infinity and is expressed in millimetres, as in 28mm, 50mm or 200mm lenses, for example.
Rather than being baffled by physics it’s easier to think in terms of how the focal length of a lens affects image size when compared with a standard lens. For a camera with a full frame sensor, typically used in commercial photography, a standard lens is 50mm. Lenses with focal lengths shorter than 50mm are known as wide angles – they have a wide angle of view, thereby taking in more of a scene. Lenses with focal lengths longer than 50mm are referred to as telephotos – they have a narrow angle of view and magnify the subject.
The Focal Length Multiplier Explained
Most digital SLRs use a sensor that’s smaller than the frame of a traditional 35mm camera. This ‘cropped’ on non-full frame sensor has a reduced angle of view, creating what’s often referred to as a multiplier factor. The multiplier factor for individual DSLRs is used to work out the effective focal length of a lens compared to a full frame camera. This is simply a matter of multiplying the focal length of a lens by the multiplier factor.
Angle of View
Fisheye
Fisheye lenses (8-16mm) differ from conventional lenses by producing hemispherical images covering up to 180 degrees that have a appearance.
Ultra wide
Ultra wide-angle lenses range from 10-21mm and have a very wiede angle of view, which allows you to work very close to the subject and include it all in the picture.
Wide
A typical wide-angle lens falls between 24-35mm and is often incorporated into a wied angle to short telephoto zoom or can be a fixed focal length prime lens.
Standard
A standard lens is 50mm for digital SLRs with a full frame sensor or the equivalent focal length for cameras with a cropped sensor.
Short Telephoto
Lenses in the 100-200mm range are known as short telephotos. They are generally used for isolating sections of the landscape, portraits and close-up work.
Long Telephoto
Long telephotos are 300-600mm with a narrow angle of view and high magnification, which makes them ideal for wildlife and sports photography.
Understanding Aperture
Aperture refers to the size of the lens opening through which light passes to reach the CCD sensor. Aperture is measure in f-stops and is used in a direct relationship with shutter speed to control exposure. Some lenses have the f-stops marked on the aperture ring but it’s more typical to set the aperture (f-stop) by using one of the camera’s modes such as Aperture Priority (AV). Each f-stop number indicates the size of the lens opening and the sequence is usually listed in one-stop increments.
Each f-stop number in the sequence lets in half as much light as the previous number. For example, f/8 lets in half as much light as f5.6. The aperture selected is important because it influences how a picture looks in terms of depth of field and also determines how motion is recorded by the corresponding shutter speed.
Apertures f/1 to f/4 are used when a fast shutter speed is required or in low light.
Apertures from f/5.6 to f/11 are used when limited depth of field is needed for close-up work, wildlife and portraiture.
Small apertures (f/16 to f/64) are used to maximise depth of field.
Fast Lenses
A lens with a maximum aperture in the range f/1 to f/4 is often referred to as a ‘fast’ lens. Fast lenses are available for most focal lengths from 24mm to 600mm. A fast lens is most typically used when a fast shutter speed is required or in low-light conditions. They’re often the so-called pro lenses and are optically superb but they’re bulky and expensive so should really only be bought for specific applications in commercial photography. For those who require a fast shutter speed but don’t want to splash out on a fast lens, one option is to boost the ISO setting. For example, the fastest shutter speed possible with an f/5.6 lens used at ISO 400 is the same as an f/2.8 lens at ISO 100.
Prime standard lenses are traditionally fast (with a maximum aperture of between f/1.2 and f/2.8), lightweight and optically very sharp. They’re ideal for shooting in low light and are capable of producing an attractive background blur.
A limited number of fast zooms are designed to be mounted directly to the tripod. These lenses usually fall into the mid-telephoto range (e.g. 70-200mm f/2.8) and are perfect for portraiture, landscape, nature and commercial photography.
Fast prime telephoto lenses are ideal for sports and wildlife photography when optical quality and a fast shutter speed are required. The corresponding large aperture produces a diffused background – great for isolating the subject.
Controlling Depth of Field
Whether you want front-to-back sharpness or diffused backgrounds, understanding Depth of Field (DOF) is crucial.
The term depth of field (DOF) refers to the zone of a picture in front of and behind a focused point that appears to be sharp.
There’s some serious physics involved with DOF, but it’s worth remembering that DOF extends to 1/3 in front of the focus point and 2/3 behind it. In other words there’s twice as much ‘depth of field’ behind the focused subject than there is in front of it.
The most commonly used technique to control DOF is to select an appropriate aperture for a creative effect. A large aperture will result in a shallow DOF or zone of focus while a small aperture will produce an image with an increased DOF. Similarly, changing from a short focal length lens to one with a longer focal length decreases DOF – that is, a 200mm will have proportionately narrower DOF than a 100mm. Also, with any lens DOF diminishes as you move the camera closer to the subject – the reverse is also true, DOF increases as you move further away from your subject.
DOF Preview – The Pros and Cons
A depth of field preview button allows you to pre-visualise how a given aperture will affect the DOF of a shot. This is a great feature for assessing the ‘look’ of a background. A downside is that the viewfinder becomes darker at smaller apertures.
How to minimise depth of field
- Select a large aperture – for example, f/2.8 or f/4
- Use the maximum aperture available for your lens
- Shoot with a fast lens
- Shoot with a longer focal length lens
- Add a tele-extender
- Move closer to your subject
- How to maximise depth of field
- Select a small aperture
- Use the minimum aperture available for your lens
- Shoot with a shorter focal length lens
- Move further away from your subject
- Make use of the optimum focus point (hyperfocal distance)
- Use a specialist tilt-and-shift lens
How to maximise depth of field
- Select a small aperture
- Use the minimum aperture available for your lens
- Shoot with a shorter focal length lens
- Move further away from your subject
- Make use of the optimum focus point (hyperfocal distance)
- Use a specialist tilt-and-shift lens
This article shows the quality and variety of techniques that customers benefit from as part of our commercial photography and architectural photography service. Call now to discuss your requirements and timescales on 079101 68536.
Copyright - Adam Coupe Commercial Photography 2008
