Best answer: A conversion (extension) tube's main purpose is for macro-photography. It allows you to get within a few mm of your subject and capture the tiniest details. The "downside" of such macro-photography is the extremely limited depth of field. One millimeter off, and your subject is blurred. For that reason, a small but steady tripod is necessary unless you have surgeon's hands and can keep the lens totally still.
On the other hand, a teleconverter changes the "zoom" area of a lens. For example, if you have a 24 - 105 mm zoom lens, adding a 2x teleconverter will give you essentially a 48 - 210 mm zoom lens. The downside of this is that it also cuts you aperture in half. Say your lens is an f/4, with a 2x teleconverter, you now have an f/8, thus requiring a pretty bright day for any types of action shots. While you can "zoom" in on subjects with your teleconverter, the closest distance allowed to your subject is also increased respectively, but your depth of field is not quite as critical as with a conversion (extension) tube. For example, if your normal lens allows you to get within 6 feet of your subject, if you add the teleconverter, it will require you to get back, perhaps 10-12 feet.
Back in the early1950s, when I first started in photography, I had no money for extension tubes, so I covered a toilet paper tube with black paper on the inside and placed my lens in front of it, while I held the contraption to my camera. I got some really nice shots. Of course, I shot B&W film because it was cheaper, and I developed it myself in the bathtub. Those were the days.
As to the EFS mounts, I do not know if this tube set can be used on it.
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