Using Supplementary Lenses

 

 

The advent of digital cameras, many which have dedicated modes that allow close-range focusing, has served to generate tremendous interest in photographing small objects such as flowers, small reptiles and insects amongst novice photographers.

In fact, this ability to get right up-close to a subject, which in the past was a field limited almost exclusively to experienced photographers having specialised and usually very expensive equipment at their disposal, opens up a whole new world of photography for the beginning enthusiast. It is not an easy field to master as one is presented with many unique problems such as, very limited depth of field, exaggerated subject movement and camera shake as well as difficulties in properly illuminating small subjects. Yet it is these very challenges that make close-range photography such an exciting field.

Macro Mode

Digital macro modes, which are often designated by an icon of a tulip on the camera's mode setting dial or button, allow much closer focusing than would normally be the case, however, it must be appreciated that digital macro modes never really approach true macro photography which refers to taking photographs at life size or what is known as a 1:1 magnification ratio or greater. Although macro modes may allow quite sufficient magnification for most botanical subjects it can be limiting when one wishes to photograph smaller subjects such as some insects. Most digital macro modes restrict the photographer to photographing the larger insects such as grasshoppers, butterflies or beetles. Single Lens Reflex (SLR) cameras have many way of getting around this limitation as extension tubes or bellows can easily be added between the camera and lens allowing for extreme close-ups. Fixed lens cameras, on the other hand, limit one to adding optics to the front of the lens only. However, as digital cameras allow unlimited experimentation without having to waste expensive film various optical combinations to decrease camera to subject distance can easily be tested. Things one can try are magnifying glasses, loupes, binocular or telescope front lenses and even spectacle lenses. These can be taped to the front of the camera lens and should all serve to facilitate closer focusing and greater subject/image magnification, in fact I often use the found the front end of a pair of binoculars as a supplementary lens and get excellent results.

Commercially available supplementary lenses as described below can also be fitted. Any camera that that has threads on the front of the lens barrel to accept filters will also accept supplementary lenses of the appropriate size.

Supplementary lenses

Supplementary or close-up lenses as they are sometimes called, are by far the cheapest and simplest way of decreasing your camera to subject distance. Similar in many ways to the optics used in spectacles to counteract far-sightedness, supplementary lenses allow the camera to focus on close objects. Like filters they screw into the front of the camera lens and do not require the lens to be removed from the camera. They are thus suitable for use on consumer and other fixed lens digital cameras providing the camera has filter threads on the front of the lens. If your camera has a macro mode setting the use of supplementary lenses combined with the camera's macro setting will permit focusing of close to 1:1.

Supplementary lenses are measured in diopters, the higher the diopter number the stronger the lens and consequently the closer it will allow the camera to focus. Normally sold in sets of three lenses of +1, +2 and +4 diopters they can be used individually or stacked to decrease the focus distance still further. A +1 and a +4 diopter lens together will give +5 diopters and so on. When stacking it is important to always place the highest diopter number lens on the camera lens and then follow up with the next highest number, with the weakest being placed last. They do not effect exposure, that is no light is lost through their use, while all the camera’s normal functions such as TTL light metering, auto flash and auto focus will also remain functional.

 

 

 

 

 

 

 

The photograph on the left was taken at 150mm from the subject, using the closest focusing distance allowed by the camera's macro mode. For the photo on the right a combination of +1, +2 and + 4 supplementary lenses were added giving a total of +7 diopters. This reduced the focusing distance to 70mm allowing for increased magnification of the subject.

 

Although supplementary lenses offer many advantages as regards cost and simplicity of use and would appear to be the perfect answer to getting closer, they also have their downside. Most simple single-element supplementary lenses display colour fringing. This is caused by their inability to focus light waves of different lengths at the same point and results in the image showing a number of spectrum-like colours fringing around the edges. This can usually be corrected by the use of multiple-element supplementary lenses which are made by some camera manufactures. These are, as to be expected, in a considerably higher price range than single-element supplementary lenses but are well worth the additional expense. The number of glass-to-air surfaces that is caused by stacking supplementary lenses can also have a detrimental effect on the sharpness of the image as light reacts differently in the different mediums. Experimentation is the keyword.

 

 

This photograph taken with a combination of inferior supplementary lenses clearly shows colour fringing around the edges.

 

 

 

 

To sum up, however, supplementary lenses offer an easy and inexpensive way to get closer. Despite what has been said above, the loss of image quality and sharpness is generally minimal and will go unnoticed with most subjects except the most critical. Colour fringing usually only becomes apparent with subjects which have large mono-chromatic areas or backgrounds, and sharpness can always be slightly enhanced with the use of most image processing software applications.

 

 

Text and photographs copyright Lambert Smith.

 

© COPYRIGHT Lambert Smith, 2010