Preview of Scott Kelby's Digital Photography book, Chapter 3, The Truth About Lenses (7)
Teleconverters offer a convenient and relatively inexpensive way to get even closer to the action. They extend the reach of the entire lens, usually by a factor of 1.4, 1.7, or even twice. (But I recommend only the Nikon Z TC-1.4x teleconverter , because it does not affect image quality as noticeably as the other two.)
As long as you buy a high-quality teleconverter—Nikon and Canon make good ones—there is only one possible drawback: with a 1.4x converter, you lose one stop of light. (You lose even more light with the higher-powered converters.)
So, if f/2.8 is the widest aperture available on your lens, f/4 becomes the widest aperture once you use a teleconverter . I said 'possible drawback' because losing one stop of light is not much of a problem when you are shooting in bright daylight.
But it is a problem when you shoot at night under stadium lights. You cannot afford to lose that one stop of light then. It is the difference between sharp photographs and blurry images caused by camera shake. I reach for this lens right away when... I photograph sporting events or wildlife in bright daylight.
Teleconverters Don't Work with Every Lens
Before buying a teleconverter, check whether it is compatible with your lens. Not every lens works with a teleconverter. The teleconverter's product information usually includes a list of compatible and incompatible lenses.
