The longer macro lenses (150, 180 or 200mm) are usually described as specialist lenses. Big, relatively heavy, limited to a single focal length, hardly suitable for hand held use at close up range, let alone 1:1 macro distances, they lend themselves to slow, unhurried work with a tripod, remote release and, where necessary, mirror lock up. Exactly what I needed for my primary interest of plant and garden photography and a useful addition to my nature and insect photography equipment. There are two main advantages over my shorter macro lenses. Firstly they narrow the field of view, and secondly they provide a greater working distance.
What the narrower field of view means in practice is that the background in a shot is selected from a far narrower angle and is also more blurred. It is far easier to get an image with the subject beautifully framed against an almost smooth background. In this comparison I've shot a single, small head of a perennial wallflower with my three macro lenses. (Click the images to embiggen.)
All three shots were taken at ISO 200 and f8. The background is the rest of the bush and a large variegated Yucca (Yucca gloriosa 'Variegata') with prominent yellow edges. With the 50mm macro you can just see the spiky leaves of this. The 90mm macro is better, but the 180mm is rendering the background into a far smoother blur.
Obviously I've had to adjust the position of the camera and lens for each shot so the framing and subject size isn't absolutely identical. Even so, the differences in background blur are obvious. Of course, with careful selection of subject (smaller is better!) and background (far, far away is best) smooth backgrounds are achievable with any of these lenses. It's just a lot easier with the longer macro lenses. For example:
|Apple blossom, Cotehele, Sigma 180mm macro, grass bank behind|
|Gaura lindheimeri, lawn behind. The fly will give an idea of scale.|
|Tricyrtis hirta. Gravel path in the background.|
The second important advantage is working distance. It's easy enough to find tables of working distance at 1:1 for any of these lenses. The longer, the further. But what does it mean in practice at less than 1:1 close focusing distances? Well, here's the working distances for the wallflower shots. Bear in mind that the macro ratio is about 1:3 or 1:4 (1/3 to 1/4 life size on the sensor). I've topped and tailed the actual wallflower head with blue highlighting.
|Working distances for the wallflower shots|
For my interests, in many situations, distance lends enchantment. I hate trampling in my own borders to take close up shots of plants at a distance from the path - and I wouldn't dream of doing it in anyone else's garden. The extra reach of the 180mm macro is very useful in such cases.
There is another useful feature of a longer telephoto lens that combines the effects of extra working distance and the narrow field of view. This involves compression of the image. Because the background occupies a smaller angle of view it appears larger in the shot. Which means I can more easily position the camera and lens to provide a pleasing background in those situations where the heavily blurred background isn't possible, or in some cases, desirable. In the two shots below I've shot from a distance (no trampling to get a close up), at a low angle, and into a carpet of flowers. Unlike with a wide angle lens the background is confined within the carpet.
|Snake's head fritillaries, Fritillaria meleagris, in a meadow setting|
|Bluebells, Hyacinthoides non-scriptus in local woodland|
|Gunnera manicata in the valley garden at Cotehele|
|Eristalis pertinax on a Rudbeckia flower. Uncropped image.|
|Garden spider on her web|
|Brimstone butterfly feeding on dandelion|
Two final points. Even though the lens is an older version it works well with my more recent Canon 600D body. I use manual focus most of the time but the HSM autofocus is accurate and fast in normal use (slow when cycling from macro to infinity distances but this is hardly unexpected and can be countered by using the range limiter switch). Secondly - and oddly - the EXIF data records the Sigma as the Canon 180mm f3.5L macro lens. Sigma reverse engineer the lens - camera communication protocols and have had problems with older lenses and newer Canon bodies in the past. I wonder if they simply copied the Canon protocols and applied them to their identical focal length and aperture lens? If so the lens is future proofed and I can look forward to many years of service.