How teleconverter works. Teleconverter Review Soligor AF PRO 1.4x
Teleconverter 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 a converter behaves very differently, it is convenient to say that the teleconverter 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 tele lens 55-200mm, and you need a much closer approximation. There are two ways out – either buy a new lens or buy a converter. With a teleconverter with a multiplicity of 2x, you can achieve a focal length of 400mm with the same lens. It is very convenient. Teleconverter can be used with any lens. If you have several lenses, you can increase the focal length of any of them.
How does teleconverter work?
Teleconverter actually magnifies the image from the center of the picture (from the center of the lens). This results in a visible increase in focal length. A teleconverter is installed between the camera and the lens. Usually, I install the teleconverter on the lens, and then install the bundle onto 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 mount connector as the lens.
Teleconverters are mainly characterized by multiplicity of increase. For example, the most common teleconverters are 1.4x, 2x, 3x. This means that when using a lens with a converter, the focal length of such a bundle will increase by 1.4 or 2 or 3 times, depending on the teleconverter.
If I use a teleconverter with a multiplicity of 1.4x and with a lens of 50-200mm, then the result will be a lens with a focal length of 70-280mm. And if you use a 2X converter with a 70-300mm lens, you will get a 140-600mm lens. A 600mm is really impressive.
Attention, please note that increasing the focal length, you thereby reduce the value of the relative aperture. If the teleconverter magnification is 2x, then besides increasing the focal length of the lens twice, the f / number will increase by 2 times. And the attention, the trick is that the difference in strength will not change by 2 times, but by 2 feet – that is, 4 times.
Therefore, a teleconverter with a multiplicity of 1.4x reduces the aperture ratio by 2 times (the exposure, other things being equal, drops by 1 stop). A teleconverter with a multiplicity of 2X reduces the aperture ratio by 4 times (the exposure, all other things being equal, drops by 2 feet). A teleconverter in 3X reduces the aperture ratio by 9 times (the exposure 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 the luminosity decreases by a factor of 9. The drop in luminosity is equal to the square of the multiplex of the teleconverter, for example, with a multiplicity of 1.7X, the luminosity decreases 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, so be careful about losing aperture when you buy a teleconverter.
I will explain in more detail. We wanted to shoot the moon, so we took a 2x teleconverter and hooked it onto a 300mm F5.6 lens, after which the lens turned into 600mm F11.2. If we were shooting the moon at 300mm F5.6 and on any one ISO value, let them have an exposure of 1 / 80s. Removing the same moon at 600mm F11.2, we get an exposure of 1 / 20s. The difference in exposure is 4 times, and the difference in focal length – 2 times. And for a long focal length, this is very critical and we cannot do without a tripod. About the importance of exposure at long focal lengths you can read in the article how to take pictures with hands.
Converters for cameras are mainly of two types – with support for autofocus and without support for autofocus. Both types can be used equally well for taking photos. The only thing is that converters without auto focus will not allow automatic focusing with your lens. Nikon has one more type of converters that support camera and lens communication, but for autofocus lenses, but without a focus motor, they cannot provide auto focus. Also, good teleconverters record the magnified focal length and aperture values into EXIF data, because the camera understands that the aperture is rather small when using a teleconverter, and the focal length is large.