Gadget Bag: Teleconverters

A teleconverter offers photographers the means to shoot at increased telephoto focal lengths without buying a completely new lens. With 400mm and higher lenses costing thousands of dollars, an optical accessory that delivers an increased focal length at a fraction of the cost has its obvious appeal.

With magnification factors typically ranging from 1.4x to 2x, teleconverters increase the effective focal length of a lens. Modern teleconverters include high-quality optics and coatings that ensure sharpness, less flare and reduced optical aberrations when combined with a telephoto. Attach a 2x teleconverter to a 300mm lens and you have the equivalent of a 600mm lens.

A teleconverter (also called a tele-extender, converter or extender) is an optical device that fits between your camera and the lens. It optically magnifies a lens’ focal length. Most of today's teleconverters include electronic contacts that maintain numerous camera/lens functions, including autofocus, metering and special functions such as vibration control. The lack of such contacts results in the loss of autofocus and limits the use of exposure modes, leaving you with the option of manual mode.

Teleconverters are typically designed to work with specific lenses, primarily those with fixed focal lengths. Teleconverters are also optimized for lenses of a certain range, such as 200mm and below or 300mm and higher. Performance suffers otherwise. In some cases, there are physical obstructions incorporated in the converter and lens design that prevent the converter from being used with an incompatible lens. Check lens compatibility when considering any teleconverter.

The cost to be paid for the magnification a teleconverter provides is light loss. A 1.4x teleconverter results in a light loss of one stop, and a 2x teleconverter reduces the light reaching the sensor by two stops. So a 300mm ƒ/2.8 lens is transformed into a 420mm ƒ/4 with a 1.4x teleconverter and 600mm ƒ/5.6 with a 2x.

Although the light loss might seem a disadvantage, the benefits of having the increased focal length in the field can mean the difference between getting and not getting the shot. With today's digital cameras, it's an easy matter to increase the ISO sensitivity of the camera to compensate for the effective light loss.

Light loss is a problem for many variable-aperture zoom lenses. Attach a 1.4x teleconverter to a lens with a variable maximum aperture of ƒ/4-5.6, and your effective aperture becomes ƒ/5.6-8. This typically results in the loss of autofocus function, as most AF systems require a minimum light level of ƒ/5.6 to be consistently effective. Though there are fast zoom lenses that can be used with teleconverters, you generally can achieve better quality when using a converter with a fixed-focal-length lens. Read more.

Here’s a selection of the many teleconverters on the market today that will give you an idea of what’s available.

Some manufacturers, such as Nikon, offer both manual-focus and autofocus teleconverters. The Nikon TC-14E II is the autofocus version of the TC-14B, both of which work with a wide variety of telephoto and fast telephoto zoom lenses. The TC-14E II, however, maintains autofocus, even with lenses

incorporating Silent Wave Motors and metering functions with Nikon autofocus film and digital SLRs. The five-element teleconverter includes Nikon Integrated Coating to maintain good contrast and color accuracy. Estimated Street Price: $399.

The Canon Extender EF 2x II doubles the focal length of compatible Canon EF-series lenses, including those lenses with built-in AF motors, with a loss of two stops. The seven-element converter includes anti-reflective coatings and a water-resistant design. In addition to maintaining AF functions, the extender is compatible with the Image Stabilizer feature provided with some lenses. Estimated Street Price: $285.

The Konica Minolta 1.4x Teleconverter APO (D) is apochromatic, which results in improved color accuracy, especially toward the edges of the frame. This teleconverter, along with its 2x sibling, supports Supersonic Wave lenses, which provide smooth and quiet autofocus. Estimated Street Price: $289.

The Olympus EC-14 1.4x teleconverter is designed for the E series of digital SLRs, such as the E-1 and EVOLT E-500. The converter works with super-telephoto lenses and several fast zooms. Estimated Street Price: $439.

The Kenko Pro 300 AF 3X teleconverter offers an exceptional 3x magnification. Though its use results in a three-stop light loss, the in-creased magnification may be ideal for photographers who desire an extra-long focal length with little additional size, at an affordable cost. This accessory is designed with multicoated optics, and its Gate Array Integrated Circuitry, which maintains communication between the lens and camera, allows the converter to be used with cameras from various manufacturers. Estimated Street Price: $210.

The Tamron SP AF 1.4x teleconverter is made of four elements whose surfaces include multilayer coatings for quality contrast and color. It’s only 0.7 inches in length and supports the auto-focus function of cameras from Nikon and Canon. Estimated Street Price: $189.

The latest teleconverters from Sigma feature new coatings that reduce ghosting and flaring. The optics of the Sigma EX APO 1.4x reduce chromatic aberrations, which can be a problem with digital SLRs. The coatings also ensure a consistent color balance when the teleconverter is used with zoom lenses. Estimated Street Price: $169.

Available in a variety of camera mounts, the Phoenix AF C/D 7 2X Converter doubles the focal length of numerous compatible lenses. It maintains autofocus function with lenses of a maximum aperture of ƒ/4 or faster. With slower lenses, however, you may still be able to use the AF confirmation light in the viewfinder when manually focusing. Estimated Street Price: $149.

Digital Magnification
Photographers using digital SLRs are quite familiar with the magnification of a lens’ focal length. With magnification factors commonly ranging between 1.3x and 1.6x, today’s digital SLRs are already increasing the effective focal length of lenses that were originally designed for 35mm cameras. This has been beneficial to sports and nature photographers, who commonly use telephoto lenses. A photographer who, for years, has been using a 300mm lens suddenly enjoys the equivalent of a 450mm lens with a digital SLR with a 1.5x magnification factor.

Teleconverters, when combined with a digital SLR, can extend the focal length of the lenses even further, allowing that same 300mm lens to perform as a 630mm lens using a 1.4x teleconverter, or a 900mm lens using a 2x teleconverter.

Because there’s no light loss as a result of the digital SLR’s lens magnification factor, the only loss of light will come from the use of the teleconverter. So a photographer shooting with a digital SLR with a magnification factor of 1.5x using a 300mm ƒ/4 with a 1.4x teleconverter is shooting with the equivalent of a 630mm ƒ/5.6 lens. Considering that a 600mm ƒ/4 lens can cost a minimum of $4,000, the use of a teleconverter becomes both cost-effective and practical.