Teleconverter - This is a special device that helps to increase the focal length of the lens.
In fact, the focal length of the lens is a physical quantity and it simply cannot be increased. But due to the fact that the lens with the converter behaves in a completely different way, it is convenient to say that the tele-converter changes the focal length of the lens.
What is a teleconverter for?
The answer is very simple - to increase the focal length of the lens. For example, you have a 55-200mm telephoto lens, and desperately need a stronger zoom. There are two ways out: either buy a new lens or buy a converter. With a teleconverter with a magnification of 2x, you can achieve a focal length of 400mm with the same lens. It is very comfortable. Teleconverter can be used with any lens. If you have several lenses, then you can increase the focal length of any of them.
How does the teleconverter work?
The teleconverter actually enlarges the image from the center of the picture (from the center of the lens). This results in a visible increase in focal length. Teleconverter mounted between camera and lens. Usually, I install the tele-converter on the lens, and then install the resulting bundle on the camera. On the one hand, the teleconverter has exactly the same bayonet connector as the camera. On the other hand, it has exactly the same mounting connector as the lens.
Teleconverters are mainly characterized by a magnification factor. For example, the most common teleconverters have a multiplicity of 1.4X, 2X, 3X. This means that when using a lens with a converter, the focal length of such a bundle will increase 1.4 or 2 or 3 times, depending on the tele-converter.
Example of use
If I use a tele-converter with a magnification of 1.4x and with a 50-200mm lens, the result is a lens with a focal length of 70-280mm. And if you use a 2X converter with a 70-300mm lens, you get a 140-600mm lens. And 600mm is already really impressive.
Attention, keep in mind that by increasing the focal length, you thereby decrease the value of the relative aperture. If the teleconverter has a magnification of 2x, then in addition to doubling the focal length of the lens, the aperture value will increase by 2 times. And attention, the catch is that the difference in power will not change 2 times, but 2 stops - that is, 4 times.
Therefore, a teleconverter with a magnification of 1.4x reduces aperture 2 times (Exposition ceteris paribus falls by 1 stop). A teleconverter with a magnification of 2X reduces aperture 4 times (Exposition ceteris paribus falls by 2 stops). A teleconverter in 3X reduces aperture 9 times (Exposition decreases by more than 3 feet). It turns out that with a teleconverter with a power of 3x, the focal length increases by 3 times, but aperture falls 9 times. The aperture drop is equal to the square of the teleconverter multiplicity, for example, with a multiplicity of 1.7X aperture decrease by 1.7 * 1.7 = 2,89 times (actually 3 times, because 1.7 approximately corresponds to the square root of 3). Such subtle tricks can rarely be found anywhere, because carefully consider the loss of aperture when buying a teleconverter.
I will explain in more detail. We wanted to shoot the moon, so we took a 2x tele-converter and hooked it onto a 300mm F5.6 lens, after which the lens turned into a 600mm F11.2. If we shot the moon at 300mm F5.6 and at any one ISO value, let them have a shutter speed of 1 / 80s. Shooting the same moon at 600mm F11.2, we get an exposure of 1 / 20s. Difference in shutter speed is 4 times, and the difference in focal length is 2 times. And for a long focal length it is very critical and we cannot do without a tripod. About the importance excerpts at large focal lengths, you can read in the article how take pictures with hand.
Types of Teleconverters
Converters for cameras are mainly of two types - with autofocus support and without autofocus support... Both types can be used equally well for photographing. The only thing is that converters without autofocus support will not allow you to get autofocus with your lens. Nikon has another type of converters that support the communication of the camera with the lens, but for lenses with autofocus but without a focus motor, they cannot provide autofocus. Also, good teleconverters write in EXIF image data the increased value of the focal length and aperture, because the camera understands that the aperture is quite small when using the tele-converter, and the focal length is large.
There are converters that are installed in front of the lens as an attachment. Most often, such converters make a wider viewing angle. Often used on camcorders. Converters can be installed on the lens sequentially and you can achieve a super huge increase in focal length. Also, many cameras cannot focus properly with apertures below 5.6 - read about this in the specifications of your camera. For instance, Nikon D4 can focus on apertures up to 8.0
A good teleconverter is quite expensive, because it can change the focal lengths of all your lenses. Sometimes it’s better to buy a good telephoto lens right away than a cheap telephoto lens and a cheap teleconverter. Typically, a teleconverter enhances the disadvantages of lenses, especially you need to watch to enhance aberration and sharpening. Also, the teleconverter can change the settings white balance - change the color range that the lens gives. But, at the same time, the teleconverter can save the image from the lens from excessive distortion.
How much the teleconverter affects the quality of the photo, let's look at a real example of a teleconverter
Teleconverter Soligor AF PRO tele-converter AFd 1.4x N / AFd review
Let us now familiarize ourselves with the work of the tele-converter in practice, and at the same time draw for ourselves several conclusions about the quality of my Soligor 1.4X AF / D APO. This teleconverter showed good picture quality when working with different lenses.
Below are the crop (cuttings) of the parts of the image in the proportions of 1 to 1, so that you can judge the sharpness and HA.
The test was carried out with a tripod, focusing through Live View, several test shots were taken and the best ones were chosen to achieve the most objective output. The shooting was done using the remote control ML-L3... As you can see, the sharpness has suffered. Also, keep in mind that when you change the focal length, the composition of the frame and metering change. exposure will be different, because automation can show a decrease excerpts not exactly 2 times, but more or less.
Virtue This teleconverter is the fact that with it it will focus almost all lenses without a built-in AF motor, and all lenses with a built-in AF-S motor. I used this teleconverter with a non-motorized lens without any problems Nikon 50mm F1.8D AF. The teleconverter has practically no effect on the focusing speed, just like on the correct focusing. The teleconverter also transfers the desired value from the camera through the diaphragm jump lever. The converter very easily becomes and is removed from the lens and camera, well assembled, small and weighty.
The disadvantage This teleconverter is not the ability to multiply the focal length and aperture by 1.4 to transfer them to the camera, because the camera sees that it simply has a native lens installed without any converter. Also, the lenses give off a slightly yellow color, this distorts the native color rendition of the lens.
Here are the prices for the 'native' teleconverters:
All prices on TC-20E
Teleconverter - very useful tool for the photographerthat needs long focal lengths. You need to remember, in addition to increasing the focal length of any lens, the teleconverter reduces aperture the lens. Teleconverter Soligor 1.4X AFD APO (from this review) allows you to automatically focus on any Nikon AF and AF-S lens and has good performance.
If you have a question - ask in the comments. Thanks for attention. Arkady Shapoval.