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What Is A Teleconverter?
Tele-converter (English trans. TTS) is an additional optical system that is fixed between the camera body and the main lens. The purpose of the teleconverter is to increase the effective focal length of the primary lens. TSs are characterized by a magnification factor that varies from 1.2x to 3.0x (the most common are 1.4x and 2.0x). For example, for a telephoto lens with a focal length of 300 mm f / 2.8, a 2.0x tele-converter will double the focal length and reduce the maximum aperture by two full stops, resulting in a focal length of 600 mm f / 5.6. Teleconverters have the same effect on the zoom lens – the entire zoom range will be increased, and the maximum aperture will be reduced. For example, a 1.4x TC turns a lens with a focal length of 70-200 mm / 2.8 into a lens with 98-280 mm / 4.0.
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Teleconverter consists of several optical elements. Typically, the larger the magnification, the larger the physical size of the vehicle. Its optical design usually includes standard lenses without optical corrections, which leads to an increase in optical aberrations. Manufacturers are trying to minimize their influence by including more complex lens elements, such as aspherical lenses, in the design of vehicles.
Teleconverters limit the use of extra-low dispersion lenses, in part because of potential compatibility issues with primary lenses. But sometimes manufacturers make vehicles specifically for one lens , and in such cases they can include any suitable elements of optical lenses. One of such well-known cases is the NIKKOR AF-S TC800-1.25E ED teleconverter, which was specially developed for the exotic Nikon 800mm f / 5.6E FL ED VR lens, and because of this, the TC800-1.25E ED teleconverter cannot be purchased separately, as other conventional teleconverters.
NIKON D700 + 300 mm f / 4D AF-S @ 420 mm (1.4x TC), ISO 250, 1/2000, f / 5.6
Each lens manufacturer also produces teleconverters; the most common models are 1.4x and 2.0x. Some manufacturers produce teleconverters with different multiples, but their use and effectiveness can vary greatly depending on the lens. For example, Nikon and Hasselblad produce 1.7x teleconverters, Kinko create TS with much greater multiplicity of 3.0x.
Unfortunately, teleconverters have a rather strong influence on the lens performance both in terms of overall sharpness and in terms of autofocus speed, so you need to be very careful when choosing a device with a magnification of more than 1.4x. To get closer to the subject, it is sometimes better to crop the image in post-processing than to do the same with the tele-converter.
Teleconverter and lens compatibility
Although teleconverters are usually designed to work with multiple lenses, there are no teleconverters on the market that work with any lens. Both Nikon and Canon have fairly small lists of lenses that are compatible with their tele-converters. Most lenses are not designed to be connected to teleconverters. Some have physical limitations, such as a rear element that extends too close to the camera mount, while others have optical limitations. Since most teleconverters are specially designed for professional super telephoto lenses, most wide-angle, standard, and telephoto lenses are not compatible with them.
However, there are exceptions: some macro lenses, such as the Nikon 105mm f / 2.8G VR, work pretty well with Nikon tele-converters. It is important to note that, with very few exceptions, vehicles manufactured by one manufacturer are designed to work only with lenses of the same manufacturer.
Using a vehicle with zoom lenses
Teleconverters generally work much better with super telephoto lenses than with zoom lenses.
There are several reasons for this:
- Zoom lenses are slower than normal lenses, i.e. they get less light for the camera’s autofocus system. As a result, this affects both the overall autofocus speed and its accuracy. Teleconverters can significantly reduce the maximum aperture of the lens, and even completely disable the autofocus capabilities of the camera.
- It is very difficult to optimize the zoom lens for uniform operation at all focal lengths, which when adding a tele-converter makes the sharpness uneven and unstable throughout the entire zoom range.
- With the increase in the number of lenses moving in groups during scaling, lens decentration and other optical problems become even more obvious.
- However, there are times when teleconverters work well with zoom lenses. For example, it is known that the Nikon 70-200mm f / 2.8G VR II works well with the TC-14E II / III, very well with the TC-17E II, and if someone is ready to stop on the f / 8 band, then even TC 20E III can be a very useful combination.
NIKON D700 + 300 mm f / 4D AF-S @ 420 mm (1.4x TC), ISO 500, 1/2000, f / 5.6
Pros and cons of using teleconverters
An obvious advantage of using a vehicle is an increase in the multiplicity of optics at a relatively low financial cost. For example, the Nikon 300mm f / 2.8G VR II is an excellent lens that works well with all three modern Nikon tele-converters: TC-14E III (1.4x), TC-17E II (1.7x) and TC-20E III (2.0x ) With these teleconverters, 300 mm f / 2.8G lenses can be transformed into 420 mm f / 4, 510 mm f / 4.8 and 600 mm f / 5.6 lenses, which is suitable for photography in sports and wildlife.
NIKON D700 + 300 mm f / 4D AF-S @ 420 mm (1.4x TC), ISO 800, 1/2000, f / 5.6
Teleconverters 1.4x and 1.7x have little effect on the performance and clarity of autofocus . The 2.0x teleconverter degrades autofocus performance and especially sharpness, but without autofocus, a 300 mm lens can cover three additional focal lengths from 420 mm to 600 mm!
Teleconverters actually only increase the central part of the frame. This means that a telephoto lens with a short minimum focal length could also be used for extreme close-ups or macro shots. For example, the Nikon 300mm f / 4E PF ED has a minimum focusing distance of 1.4 meters. The 1.7x teleconverter will significantly expand the range to 510 mm.
NIKON D700 + 300 mm f / 4D AF-S @ 420 mm (1.4x TC), ISO 800, 1/1000, f / 5.6
The effect of TS on the sharpness and contrast of lenses
Teleconverters significantly affect the overall sharpness of the resulting combination. In the case of the Nikon 70-200 mm f / 2.8G VR II lens, the teleconverter reduces sharpness by 26%.
Nikon TC-14E II (1.4x) – 5% Sharpness
Nikon TC-17E II (1.7x) – 17% Sharpness
Nikon TC-20E III (2.0x) – 26% loss of sharpness
And this is on a fast lens that is designed to work well with teleconverters. When using the same tele-converters on slower or older lenses, the sharpness loss will be even greater.
NIKON D3S + 300 mm f / 4D AF-S @ 420 mm (1.4x TC), ISO 450, 1/1250, f / 5.6
In addition to loss of sharpness, the overall contrast of the lens is reduced, which is especially noticeable when using 2.0x teleconverters.
The influence of the vehicle on autofocus performance
Teleconverters can have a significant effect on both autofocus speed and the accuracy of the main lens and camera, since less light is delivered to the camera’s autofocus system.
NIKON D700 + 300 mm f / 4D AF-S @ 420 mm (1.4x TC), ISO 800, 1/1250, f / 6.3
1.4x TC: Minimum effect on speed and autofocus accuracy for most lenses.
1.7x TC: The effect on autofocus speed and accuracy depends on the primary lens. Slower f / 4 lenses may not work well with a 1.7x tele-converter.
2.0x TS: Serious effect on the speed and accuracy of autofocus in most lenses. Only some f / 2.0 and f / 2.8 lenses work well with 2.0x teleconverters and only in bright light.
3.0x vehicles and multi-vehicle connection: autofocus disabled.
NIKON D700 + 70-200 mm f / 2.8G VR II @ 340 mm (1.7 x TC), ISO 800, 1/640, f / 5.0
TS against extension cords
Do not confuse extension rings with teleconverters. TSs always consist of optical lens elements, extension rings or tubes are physical mounts without any optics, the sole purpose of which is to reduce the minimum focusing distance. Therefore, extension cords are used for macro photography, while teleconverters are used for optical zoom.
NIKON D3S + 70-200 mm f / 2.8G VR II @ 400 mm (2.0x TC), ISO 800, 1/1250, f / 10.0
TS and framing in post-processing
Sometimes when using lenses with slow zoom with a vehicle or when connecting multiple vehicles, the deterioration in image quality is such that it is better to crop the images during post-processing. If autofocus functions are severely limited by the tele-converter, it is better to use vehicles with lower magnification or completely abandon it.
Solar Eclipse ILCE-9 + FE 100-400 mm F4.5-5.6 GM OSS + 2X Teleconverter @ 794 mm, ISO 100, 1/60, f / 13.0
NIKON D810 + 300 mm f / 4E FL VR @ 600 mm (2.0x TC), ISO 100, 1/100, f / 11.0
Often photographers avoid using 2.0x teleconverters, but regularly use 1.4x, and sometimes 1.7x TS. Sharpness and contrast can be increased during post-processing, but problems with focusing will remain.
However, some lenses work fine with 2.0x teleconverters. For example, the Sony FE 100-400mm f / 4.5-5.6 GM OSS, which works surprisingly well with the Sony 2.0 Teleconverter.
NIKON D750 + 300 mm f / 4E FL VR @ 600 mm (2.0x TC), ISO 3600, 1/1250, f / 9.0
NIKON D300 + 70-200 mm f / 2.8G VR II @ 280 mm (1.4x TC), ISO 800, 1/250, f / 6.3
TS and camera crop
Many modern cameras offer shooting in framing modes (for example, most Nikon FX full-frame cameras allow you to shoot in framing mode 1.5x DX).
Does it make sense to use crop mode instead of teleconverter?
NIKON D700 + 300 mm f / 4D AF-S @ 420 mm (1.4x TC), ISO 320, 1/1600, f / 5.6
Cropping in the camera is no different from cropping in subsequent processing, so it does not provide any additional benefits, except for a slightly increased frame rate and smaller files.
NIKON D3S + 300 mm f / 2.8G VR II @ 500 mm (1.7 x TC), ISO 1600, 1/800, f / 8.0
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