Teleconverters
You can get a teleconverter lens that is placed between your lens
and the camera body that will give you 1x or even 2x magnification.
If you put a 2x teleconverter on a 200mm lens, you instantly have a
400mm lens. However, you lose light, meaning suddenly your
widest aperture for that lens jumps from f/2.8 to f/3.5 or higher. I
have these, but every time I use them I swear I will never use them
again. It is very, very difficult to improve on a lens just as it is, which
is why the lens was made just that way in the first place – optimum.
Put anything on the front or back of it and you are (IMO) just taking
a good or great lens and turning it into an average (or worse) a
poor lens. I seldom ever, ever use one and don’t suggest them. Of
course, they are not for macro work but for distance photography. If
I was shooting birds I would probably have to use them.