We've gone over zoom and telephoto lenses in the past and today I'd like to focus on a lens of a similar fashion, the teleconverter lens --sometimes also known as an extender or multiplier. They can multiply the focal length of a lens by 1.4 to 2 times. But like any piece of equipment, there are pros and cons to choosing a teleconverter over a zoom or telephoto lens.
The obvious, and most important, pro is increased focal length. A 1.4x converter will give you an extra 40%, while a 2x converter gives you 100% more focal length. When you're not so close to your subject, it will come out much clearer with the converter. Teleconverters are also much lighter. A telephoto lens is awesome, but have you held one in your hand? They add quite a bit of weight to your lens bag. Lastly, they can actually come in handy if you don't have a macro lens and want –and can— get in closer to your subject.
One major disadvantage is light. When you use a teleconverter lens, less light gets in and your max aperture will be decreased. The more you multiply the focal length, the more the aperture decreases. So it might be better to choose a 1.4x than a 2x converter. Just like with any lens that increases focal length, you have to worry about camera shake. You can solve the problem by increasing shutter speed and using a tripod. Converters also slow down camera focus speed, especially in lower lighting. Switch to manual mode to help. And finally, the image quality will be reduced so opt for higher quality converters to keep image quality up.