Here are some key specifications to look out for when purchasing a used camera lens.
This category of camera lens effectively makes objects or scenes that you are capturing appear much closer than they are in reality. The conversion number of the lens tells you how much closer an object or scene will appear e.g. a 3x lens will make the scene appear three times closer.
Bear in mind that because telephoto lenses screw onto the front of the camera, they can affect light processing and make the image look darker than it really is. For very well-lit scenarios they perform exceptionally well and will not diminish picture quality.
Wide Angle Lenses
These widen the visual scope of the camera, enabling the photographer to capture, say, an entire concert or theatre stage even though the standard video camera lens could not include the entire scene. The drawback is that, because they stretch the camera’s viewing area, they can make the resulting image look somewhat distorted. It is advisable to test out wide angle lenses before purchasing them as some will be better than others in minimising this distortion.
As with telephoto lenses, the number preceding a multiplication sign on the lens shows how much wider the resulting image will be. A 0.65x conversion factor for a wide angle lens, for example, converts the lens’s focal length by a factor of 0.65, expanding the perspective accordingly.
Fish Eye Lenses
These widen the field of vision considerably more than the usual wide angle lens, although at extremes they can result in a kind of curved distortion in the final image.
This isn’t actually an additional lens and is usually built in to the camera’s integral lens. It’s an image magnifier and usually comes equipped with optical image stabilisers which reduce the jarring effects of slight hand tremors (these are always exaggerated whenever magnification increases).