Tele-extenders, also known as teleconverters or multipliers, are small optical accessories that mount between your lens and camera to extend your focal length. Tele-extenders come in several different multipliers, with the most common being 1.4x and 2x. The 1.4x will increase your focal length by 40%, making your 200mm lens act as a 280mm, while the 2x will increase focal length by 100%, turning the 200mm lens into a full 400mm.
This can have exciting implications for wildlife photographers. For one, having extended focal length that fits in a small camera bag gives you the tools to capture make-it-or-break-it moments while letting you be flexible and mobile. Not only do side-by-side comparisons of tele-extenders versus postprocessing crops show extenders to have a quality advantage in sharpness and precision, but tele-extenders are more budget-friendly than super-telephoto lenses, making experimenting and perfecting new types of birding or quick-action wildlife photography more accessible for exploratory photographers.
But while a tele-extender may sound like the perfect quick fix for any focal-length woes, it's important to know how to pair your extender with your lens to get the highest-quality images possible.
When light enters a tele-extender from the lens, the optics in the extender spread the light over a larger surface area. This magnifies the image, casting the central section over the camera sensor. At the same time, this dissipates some of the light from the edges of the image, decreasing the overall amount of light reaching the sensor.
Because of this, tele-extenders will decrease the maximum aperture ability of the lens. A 1.4x extender will always make the lens one stop slower. A 2x extender, in turn, will always make the lens two stops slower. For 1.4x extenders, it's best to pair them with at least ƒ/4 lenses, while 2x extenders are best paired with ƒ/2.8 lenses. This way, you're starting with workable combinations given variable lighting conditions.
This slower speed will affect the autofocus ability of the camera. For a camera to autofocus, it opens to its widest aperture, compares the angles of two paths to set the focus, then closes back to the set exposure. Prosumer-type cameras can generally autofocus up to ƒ/6.3, while pro DSLRs autofocus up to ƒ/8. Depending on the lens and lighting conditions you're working with, when you lose stops with the extender, you may lose the ability to autofocus.
Tele-extenders add an extra step between the lens and the camera, and in so doing also add an additional bend to the light. This may negatively impact the image sharpness and contrast, but the degree of impact often is dependent on the type of lens you're using with the extender. Images taken with wide-angle lenses are more adversely impacted than telephoto lenses—zoom lenses more than primes. The 2x extenders often have more noticeable effects than 1.4x extenders.
When you're using an extender, it's important to remember that as you're multiplying focal length, you're also multiplying the effect of camera shake. Some extenders have stabilizers built in, but using a tripod or monopod support will help you obtain sharp images.
| This Article Features Photo Zoom |
 Nikon AF-S TC-17E II 1.7X |
Nikon offers the standard 1.4x and 2x extenders, as well as a 1.7x length that increases the focal length of the lens by 70%. All of Nikon's extenders use a Nikon Integrated Coating, which enhances the light transmission and reduces flare while improving color consistency. The 2x extender uses an aspherical lens element that works to eliminate the aberrations that occur at wide apertures. All three extenders attach to F-bayonet mounts, but it's important to check with the Nikon compatibility chart for lens listings. One additional Nikon extender is the AF-S Teleconverter TC800-1.25E ED. This converter is specifically designed to be used with the AF-S Nikkor 800mm ƒ/5.6E FL ED VR lens, extending the focal length to 1000mm, or 1500mm on a DX-format DSLR. This extender is sold with the lens, and isn't sold separately. Estimated Street Price: $549 (AF-S Teleconverter TC-17E II); $519 (AF-S Teleconverter TC-14E II); $499 (AF-S Teleconverter TC-20E II). www.nikonusa.com.
 Canon Extender EF 1.4x III |
Three extenders are in the Canon arsenal—the Extender EF 1.4x III, the Extender EF 2x III and the Life-Size Converter EF. The Extender EF 1.4x III and 2x III both have a microcomputer built into the extender to aid in communication flow between the lens, extender and body. The placement of the lens in addition to the lens coating has been designed to reduce ghosting and flare. An additional Flourine coating has been added to reduce smearing and fingerprints that may find their way onto the glass. The body maintains Canon standards for rugged water-resistant construction. These converters pair exclusively with L-series 135mm and over fixed-focal-length lenses, as well as the EF 70-200mm ƒ/2.8L, EF 70-200mm ƒ/2.8L IS, EF 70-200mm ƒ/4L and EF 100-400mm ƒ/4.5-5.6L zooms. The Life-Size Converter EF pairs exclusively with the 50mm ƒ/2.5 Compact Macro lens and is specifically used for high magnification in the 0.26x-1.0x range, or approximately 1⁄4 life-size up to true life-size. Estimated Street Price: $499 (Extender EF 1.4X III); $499 (Extender EF 2X III). www.usa.canon.com
 Sigma 2.0X EX APO DG |
While many of the manufacturers insist that you stay brand loyal with each accessory for optimum results, Sigma carries 1.4x and 2x converters with mounts for several companies, including Sigma, Canon, Nikon, Sony/Minolta and Pentax. The converters have a multilayer coating to reduce flare and ghosting, and come with a carrying case. Check the website for a full list of compatible lenses. Estimated Street Price: $224 (1.4X Teleconverter EX APO DG); $249 (2.0X Teleconverter EX APO DG). www.sigmaphoto.com
 Kenko Teleplus Pro 300 AF DGX 2.0X |
Kenko has a myriad of extenders to choose from. The MC4 AF 1.4 DGX and MC7 AF 2.0 DGX come standard with Gate Array IC (Integrated Circuitry), which integrates the autofocus system with the camera. The extender's electronic system also communicates the full EXIF data from lens to extender to camera body. High-quality Hoya glass has a multi-coating to protect from aberrations. These extenders are available for Canon EF lenses (not for EF-S), Nikon AF and Sony Alpha. Kenko has also added a Pro 300 line of extenders designed specifically to match the optical quality of prime lenses and to avoid edge aberrations and vignetting. They're best used with prime telephoto lenses at 100mm or above (200-500mm is the sweet spot) and may be used with zooms. The Pro line includes the typical 1.4x and 2.0x extenders, but also the more rare 3.0x. The 3.0x multiplies focal length by three, turning a 300mm length into 900mm. Consequently, this reduces the light by three stops and means the lens must be manually focused. The Pro 300 line is compatible with Nikon AF and Canon EOS (but not Canon Digital Rebel XT/EOS 350D camera bodies). Estimated Street Price: $189 (MC7 AF 2.0 DGX); $149 (MC4 AF 1.4 DGX); $259 (Pro 300 AF DGX 1.4X); $269 (Pro 300 AF DGX 2.0X); $278 (Pro 300 AF DG 3.0X). www.kenkotokinausa.com
 Pro-Optic 2X for Nikon |
Pro-Optic makes standard converters that are compatible with Canon and Nikon cameras—a 1.4X and 2X for Canon and a 2X for Nikon. Pro-Optic characterizes their teleconverters as being specifically designed to be used with prime lenses of 100mm and longer, and they allow your camera's electronics to communicate with the lenses (contact Adorama to confirm that your camera and lens combination will work properly). The 2X model for Canon cameras won't work with EF-S lenses. Estimated Street Price: $79 (Pro-Optic Multi-Coated 1.4x Tele-Converter); $99 (Pro-Optic Multi-Coated 2.0X Tele-Converter). www.adorama.com
 Olympus EC-20 2.0X |
Olympus offers the EC-20 2.0X Teleconverter and EC-14 1.4X Teleconverter. Both are compatible with all ZUIKO digital lenses. Estimated Street Price: $479 (EC-20 2.0X Teleconverter); $439 (EC-14 1.4X Teleconverter). www.getolympus.com
Tamron also makes inexpensive extender options. Their 1.4x and 2x teleconverters are compatible with most autofocus and auto-exposure cameras. www.tamron-usa.com
Extending my “quality” reach? I would like some opinion on using a Canon 2x extender, on the 70-200 f/2.8 IS II vs. just using a Tamron 200-500 Di LD. Would the 2x degrade the quality of the 70-200 enough to justify using the less expensive Tamron 200-500? I shoot with the 7D so I realize I get more reach with the 200-500 but if I didn’t need the 800mm (equivalent) would I be better off using the Canon glass combo in the 2x and 70-200?