Long telephoto lenses can be some of the most expensive out there, and when you need multiple focal lengths, the cost can quickly become prohibitive. Teleconverters offer a way to get more reach from lenses you already own, but they also come with drawbacks you should be aware of. This excellent, in-depth video discusses teleconverters, their pros and cons, and when they are appropriate to use.
Coming to you from Jan Wegener, this great video discusses the use of teleconverters. Teleconverters almost always come in two options: 1.4x and 2x, which denote the factor by which they increase the focal length of whatever lens you attach them to. This can be a quite affordable way to get significantly more reach out of your lenses, but it is important to be aware of the drawbacks as well. First, a 1.4x teleconverter decreases your maximum aperture by one stop, while a 2x teleconverter decreases it by two stops. Second, you can generally expect to lose some autofocus performance and image quality, particularly when using a 2x teleconverter. And with the high resolutions of many modern sensors, you may decide that simply cropping in post is the better option. Check out the video above for the full rundown from Wegener.