Close-up Filters
Techniques
13 June 2008 09:00
Close-up filters (often referred to as lenses) are a way of accomplishing macro shots without the expense of a macro lens. These screw-in filters are available in a variety of strengths. Most common are +1, +2, +3, +4 and +10 dioptres. A dioptre is a unit of measurement referring to the optical power of a lens.
A +10 filter is the nearest to a macro lens, although achieving anything close to the 1:1 ratio of a macro lens will depend on the focal length of your lens. A 1:1 ratio means 1mm of the subject will occupy 1mm of the camera sensor. Attached in the same way as a filter (your filter thread size can be found in the space around the lens glass), these convex lenses allow you to take images of small subjects such as flowers and insects.
One really useful feature of close-up filters is that different strengths can be combined to create a stronger effect. For instance, a +1 and +4 combination will give you +5 dioptres, +4, +2 and +3 will give +9. One thing to bear in mind is that it’s better to place stronger filters closer to the lens. Fortunately for the less technically minded, exposures are not affected by stacking these filters.
On the downside, as with many lens attachments, the more you stack, the more image degradation can occur. The surface area for dust to settle and fingerprints also increases, so this is something to watch out for.
Another feature of these filters is that they shorten depth-of-field. The stronger the filter, or combination of filters, the shorter the resulting depth-of-field will be; ideal for close-up photography.
The lenses typically cost from around £15 - £30, although the +10 will set you back slightly more depending on the manufacturer. Hoya, B+W and Lens Babies produce these filters in sets and individually. Close-up lenses can be purchased from leading high street photography shops, online and direct from the manufacturer so shopping around shouldn’t be too difficult.
Close-up lenses are most commonly used in conjunction with lenses with longer focal lengths, although they can also be used with wide-angles. Looking for close-up inspiration? Check out Chris Rutter’s dramatic wide angle lens technique in the July edition of Practical Photography (P.33).