In the early days of my photographic career my weapon of choice for macro work was a close-up filter. Nowadays it the Extension Tube. Here’s why…
Extension Tubes – What are they…?
Extension tubes are very simple devices. They’re short tubes, usually in the region of 5mm to 25mm in length, with a lens mount at either end. One end of the extension tube fits on the camera body where the lens would attach. The other end replicates the camera interface and is where the lens mounts. The tube fits between the camera body and the lens, moving the lens further away from the film/sensor plane, effectively magnifying the image from the lens. The longer the tube, the greater the magnification.
The disadvantage of using an extension tube is that, when fitted, it reduces the maximum focusing distance of the lens from infinity to less than a metre or so. In extreme cases it can bring infinity so close the lens won’t focus beyond it’s front element.
Extension tubes can be bought individually or as a set, usually of three such as these Kenko tubes (12mm, 20mm and 36mm). Make sure you buy the ones with the correct mount for your camera and that they have the electrical contacts to pass data between the lens and camera. Metal extension tubes are more robust and also cost more too.
Extension Tubes vs. Close-up Filters for Macro Photography
A close-up filter is basically a magnifying glass that’s been adapted to attach to the front of the lens, either by screwing directly into the filter thread or via a holder system.. In the early days of my photographic career I always used a close-up filter for my macro photography. I made some great images too but there is one major drawback with them: they introduce another optical element and that will degrade image quality, no matter how good it is.
With the lenses I use now, the diameter of the front element is 77mm. Considerably larger than in my film days. I’ve also invested in pro glass so I’m very reluctant to add anything that will degrade the image. I did purchase a close-up filter that will fit a 77mm lens but every time I’ve used it I’m not, happy with the results. I know what my lens can deliver and with a close-up filter I just don’t get the results I want.
Extension tubes work by increasing the separation between the camera body and the lens thereby magnifying the subject. (Click to Tweet)
An extension tube on the other hand is just a cylinder filled with fresh air. They don’t contain any optical elements so introduce significantly less image degradation. Extension tubes work by increasing the separation between the camera body and the lens thereby magnifying the image.
As the lens is moved further away from the plane of the sensor, the image it projects inside the camera is enlarged.
(BTW, don’t confuse an extension tube with an extender – they’re very different lens accessories)
Extension Tubes vs. Macro Lenses
If you don’t have a macro lens in your kit bag, the extension tube offers a cheaper alternative to buying a new lens.
Macro lenses are designed to focus closer than a regular lens. They will also focus all the way out to infinity so are a much more flexible option than extension tubes, if you have the budget. You’ll also save time by not having to worry about attaching and removing them (e.g. if you’re a wedding photographer trying to get the ring shot you could miss a crucial moment by having to fiddle around with your lenses).
Image Comparison – 100mm Macro Lens vs. 70-200mm Lens + Extension Tube
All four of these images were taken under the same conditions. Same lighting and exposure (1/200th @ f/16, ISO200), same subject, same Canon EOS 20D body. The difference between them being the lens as indicated in the image captions. Two were made using the Canon EF 100mm f/2.8 USM Macro lens and two with the Canon EF 70-200mm f/2.8L IS USM lens with a 20mm extension tube.
Image results from both pairs of images are comparable. With the 100mm macro lens I managed to get slightly closer and focusing was definitely easier. Nevertheless, the extension tubes did a good job, making some great images.
Pros and Cons with Extension Tubes
Extension tubes work well and deliver good images but they are a compromise solution. As I’ve mentioned above, when attached to a lens the lens won’t focus all the way to infinity. If you need to do that, you’ll need to remove it and that takes time.
Not all extension tubes work with all lenses. e.g. I’ve never had much success using them with my 100-400 zoom whereas when used with my 70-200 zoom, the image quality is superb. Some configurations of extension tube length and lens focal length can reduce the maximum focusing distance of the lens so much it’s actually inside the lens itself.
Focusing can be tricky. Auto-focus will work but I have mixed feelings as to it’s accuracy. If you’re using an extension tube with a zoom lens I find it easier to use the zoom ring to adjust focus rather than the focus ring.
Image quality with an extension tube will depend on the quality of the lens you’re using it with. It will be better than using the same lens with a close-up filter (for the equivalent magnification factor).
How to use an Extension Tube for Macro Photography…
Using an extension tube is very straightforward. I tend to use them with zoom lenses as it makes getting a sharp focus easier and you will need to use a tripod for best results. They simply attach to the camera between the body and lens (in exactly the same way as an extender does). Follow the instructions provided with the tubes if you’re in any doubt. Whatever you do, don’t force them or you could do some serious damage to the tube, your camera or your lens.
When attached, mount your camera on your tripod for best results and frame the subject. You’ll find the camera to subject distance is critical, much more so than when using a macro lens. Extension tubes severely limit the focus range of the lens. You’ll need to play with the camera to subject distance and the focal length of the zoom lens to frame the shot as you want it in sharp focus. I usually just preset the focus ring and use the zoom ring to bring the subject into sharp focus.
Top tip – when using an extension tube for macro photography, always use a lens hood to protect the lens (Click to Tweet)
When using an extension tube for macro photography, always use a lens hood to protect the front element of the lens. Very often you’ll be working extremely close to the subject and when lining up for the shot it’s very easy to bump the front element of the lens. Having a lens hood in place can help to protect your lens.
This brings up another issue. The camera can and often does block light from the scene. You’ll need to use a long exposure to compensate. You may also need to light the scene for best results.
Depth of Field will be very narrow. Small apertures (larger f numbers) are the way to go. If possible I try to avoid using the smallest aperture supported by my lenses to help reduce chromatic aberrations and fringe effects on high contrast edges. Most lenses will be sharpest around f/8 or f/11 because of the way they’re designed giving a nice, crisp image right off the bat. Smaller apertures will give a greater depth of field but may not be as crisp. As the photographer you need to make a decision as to how much of the subject is sharp and how crisp that sharpness is. You do this through your choice of aperture.
All other good macro photography practices still apply. Use mirror lock-up and a cable release/self timer to help prevent camera shake, especially with a long lens. Use a tripod and don’t forget to turn off your image stabiliser.
Conclusion
Extension tubes are cheap, light and not susceptible to scratches. You will definitely need a tripod for good image results to reduce camera shake and make focusing easier but that’s good practice with macro photography anyway. They can also be stacked to further increase the magnification but I’ve found that a short tube on a short lens can give just as much magnification as a long tube on a long lens. (Magnification is a factor of tube length and focal length. There are equations out there if you really need to calculate it but I prefer to take pictures ;-))
They offer a cheap solution for macro photography without compromising image quality.
If you’re thinking of investing in an extension tube, make sure you buy one with the correct lens mount for your system!
Over to you…
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