Extension Tubes
I have scads of them but seldom use them. They are used to give
you greater magnification for a given lens but they always suck light
out of your shot anytime you use them and I seldom feel it is worth
it. In other words, if you have a f/2.8 lens and add an extension
tube between the lens and the camera body, you will get greater
magnification but lose one or more f-stops. Tubes degrade the
image, at least with large apertures (wide open). Suddenly you
have an f/2.8 lens that now is a f/3.5 lens or whatever f-stop. I
seldom use them and am not happy with the results when I do.