A teleconverter, also known as a telephoto extender, is a lens attachment that fits between your camera and your lens, and increases the effective focal length of your lens. Teleconverters are a popular accessory for photographers looking to get a little more reach without buying a new, longer lens. Here's a closer look at how teleconverters work and how to use them on your camera.

When you attach a teleconverter to your lens, it multiplies the focal length of your lens by a factor of 1.4x, 1.7x, or 2x (depending on the type of teleconverter you're using). For example, if you have a 100mm lens and attach a 1.4x teleconverter, your lens will now have an effective focal length of 140mm. This can be useful for a variety of situations, such as sports photography, wildlife photography, or any other situation where you need to get closer to your subject without physically moving closer.

One thing to keep in mind when using a teleconverter is that it will also decrease the amount of light that reaches your camera's sensor, which can result in a decrease in image quality. This is because the teleconverter acts as an additional element in your lens, which can cause some light loss. To compensate for this, you'll need to use a wider aperture (smaller f-stop number) or increase your ISO.

Another thing to consider when using a teleconverter is that it will reduce the maximum aperture of your lens. For example, if you have a lens with a maximum aperture of f/2.8 and attach a 1.4x teleconverter, your lens will now have a maximum aperture of f/4 (since 1.4 x 2.8 = 3.92, which rounds down to 4). This can be an issue if you're trying to shoot in low light conditions, as you'll need to use a higher ISO or slower shutter speed to compensate for the loss of light.

Overall, teleconverters can be a useful tool for photographers looking to increase the focal length of their lenses without buying new ones. Just keep in mind that they can impact image quality and maximum aperture, and be prepared to make some adjustments to your camera settings to compensate for these changes.