Buyer's guide - Lenses
Contributing highly to the final aesthetic look of your image, lenses are one of the most important factors to consider when taking your pictures. Controlling viewing angle, depth of field and the overall image quality, lenses should be your next choice if you wish to improve or expand your photographic arsenal.
- Zoom Lenses - Lenses are primarily differentiated by their focal length, a good scale to understand the distance that the lens will offer is to compare its focal length (e.g. 18-55mm) to 50mm (or 35mm for cropped sensor cameras). A focal length lower than this will offer a wider field of view then your eye, a focal length higher then this will magnify the scene.
- Fixed Focal Length (Prime) Lenses - Zoom lenses are highly practical for their flexible shooting options, a basic 18-55mm kit lens will cater to your needs with a wide angle for landscape and low power telephoto for portraits. However these lenses have a high volume of glass to shoot through and each piece of glass or “element” reduces image quality. The benefit of fixed focal length lenses they need on average half the elements thus are higher quality optics and are smaller lighter pieces of equipment.
- Aperture - The aperture is the width that the lens opens, put simply the wider the aperture the more light that enters the camera, more light equals faster shutter speeds. As a secondary benefit wide aperture lenses offer a shallow depth of focus, allowing you to isolate your subject from the background by focusing on a small fraction on the visible scene
- Variable Aperture Lenses - Due to the complexities in creating zoom lenses, some lenses start with one aperture at the base focal length then when zoomed this aperture changes, e.g 18-55mm f/3.5-5.6. At 18mm this lens offers f/3.5 however when you zoom to 55mm the widest aperture available is f/5.6. Higher standards of lenses often offer fixed apertures to maintain consistency when shooting.
- Filter Size - Lenses vary in size due to the various focal lengths and apertures on offer; this in turn affects the size of the front element and therefore the size of the filter needed. Filter threads start as small as 37mm for camcorders and go up to 105mm for large aperture telephoto lenses.
- Image Stabilisation - IS to Canon, VR to Nikon, OS to sigma and VC to Tamron, these acronyms state that the manufacturer has included a form of image stabilisation. Offering up to 5 EV steps compensation, the stabiliser will allow you to operate your camera with slower shutter speeds whilst avoiding camera shake. Some lenses include two different operational modes for the image stabiliser allowing you to capture moving subjects with ease.
- Internal Focusing - Lenses can have significant variations in the design of their build, often lenses will use rotation to assist with the barrels adjustment in focusing the lens. Mid to high range lenses will have no rotational movement to the front element, thus not rotating the screw thread on the front and allowing the use of graduated filters & circular polarisers without the need for re-adjustment after focusing.