Close-up Lens

A photographer's job is a georgeous one, to get the right image at the right time is the basic principle of photography. Image magnification plays an important role in that. There are various methods to achieve image magnification. Some methods make use of macro lenses, stacked lenses, extension tubes, bellows, reversed lenses, teleconverters, or close-up lenses. Close-up lenses, also known as supplementary lenses, macro filters, or close-up filters, can be considered as ‘poor man’s macro’ lenses.

A simple close-up lens is a single glass element (a ‘positive meniscus’ lens), fatter at the center, and tapering down at the edges. If you have seen a magnifying glass, you know what we are talking about. The glass element is enclosed in a metal ring which has a thread that allows it to be attached to the front end of your taking lens. By doing so, you produce a lens combination of shorter focal length, which in turn, allow you to focus closer. Obviously, with the close-up filter attached, you cannot focus to infinity!

An added advantage of using close-up filters is that there is no loss of light, as would be the case when using extension tubes, bellows, or even macro lenses at close distances.

It is a known fact that adding any glass to a taking lens degrades the image quality, so would not the addition of the close-up filter pose a problem? The answer is ‘yes’, but if you use a good quality close-up filter, and stop down the taking lens to f/8 or narrower, you are not likely to see the degradation in the image quality.

But how does stopping down to f/8 or narrower help? When we stop down the taking lens, we are using the light rays closer to the central axis of the lens, and this reduces spherical aberrations and produces a much sharper image.

So, in theory at least, if we stop down the taking lens to its narrowest aperture, will we further gain in sharpness? The answer is ‘no’. Stopping down will definitely increase the depth of field, but at very small openings, we get ‘diffraction’ of light that can degrade the image quality. We need to choose a balance between depth of field and the onset of diffraction. Depending on the film/sensor size, this limit could vary between f/8 and f/16.

Note: The shape of the lens diaphragm affects the diffraction pattern. For critical close-up work, try to use a taking lens that has a diaphragm as close to circular as possible as the lens is closed down. (Generally, the more the number of aperture blades, the more circular the opening).
Another important consideration to improve the image quality when using a close-up filter is to use what is known as ‘achromatic doublet’. This is a two-element close-up filter which reduces chromatic aberration, and thus improves the final image quality. To the best of our knowledge, currently, only Canon makes such achromatic doublets (250D and 500D). Nikon, which used to make several achromatic doublets (3T, 4T, 5T, and 6T), have stopped doing so a couple of years ago.
Note: You can attach a close-up filter manufactured by any company on to any taking lens. The manufacturer need not be the same. The only thing to consider is the filter thread diameter – which must be the same as that of the lens to which you attach the close-up filter.

But can we attach a close-up filter on to a zoom lens? Yes you can, though it is generally not advisable due to the complex nature of zoom lenses. Doing so could reduce the image quality.

Now that we have covered the general description, let’s get a bit technical. As mentioned earlier, a supplementary lens changes the focal length of any lens with which it is used. The power of a close-up lens is given in terms of ‘diopters’ and is mentioned as +1D, +2D, +3D etc. A diopter is defined as 1000/f, where ‘f’ is the focal length of the lens in millimeters. Thus a +1diopter has a focal length of 1000/1=1000mm; +2diopter is 1000/2=500mm; +4 diopter for example has a focal length of 1000/4 or 250mm. Note however that Canon does not label its close-up lenses as diopters. With Canon, 250D and 500D represent the focal lengths of the individual close-up filters. Hence 250D would be +4 while 500D would be +2. With Nikon, 3T, and 5T, are +1.5 diopters while 4T and 6T are +2.9 diopters.

Magnification (M) = Focal length of the primary lens in mm (set to infinity) divided by the focal length of the supplementary lens in mm.
Hence, if you attach a +2D on a 50mm primary lens set to infinity, you get 50/500 or a magnification of 1/10. If you attach a +4D to the 50mm lens, the magnification will be 50/250 or 1/5. If you attach a +4D to a 300mm lens, the magnification would be 300/250 or >1 (a little over life-size). From this we can see that when the same close-up filter is attached to a lens with longer focal length, the magnification is greater. This is one of the reasons why we generally do not attach a close-up lens to a wide-angle lens.

Another important point to note is that when you attach a close-up filter, the lens-to-subject distance will depend on the power of the close-up filter, irrespective of the focal length of the original lens (assuming that the primary lens is set to infinity focus).

What the above means is that if you attach say, a +4D to a 50mm lens as well as a 200mm lens (both set to infinity focus), the lens-to-subject distance will be the same (250mm or approximately 10-inches) for both the lenses. Obviously, the 200mm lens will offer greater magnification.


Can we use more than one close-up filter at the same time?
Yes, we can. But always remember to attach the more powerful filter first. So, if we wish to use a +2 as well as +1 (to make a +3), attach the +2 first, then the +1.

Would the image quality with a close-up filter be as good as from a true macro lens? The answer would depend on the quality of the primary lens, the quality of the close-up filter, and of course, your shooting technique. If you use a good primary lens, a good close-up filter, and if your shooting technique is good, and if your image enlargement is modest, we doubt if anyone could know the difference. That is why a close-up filter is known as a ‘poor man’s macro’.
tom@photographyforall.ie