extension tubes...care to explain?

Could anyone please provide me with a quick explanation of the use of extension tubes? I tried searching but the term is used VERY frequently on the forum that I ended up with a LOT of results...

From what I gather, an extension tube is sort of like a TC, but uses no glass right? How does this work? Do you lose IQ, lens features (AF) etc?

Just a basic rundown/explanation is fine...any negative attributes to using ext. tubes?

An extension tube is used to reduce the focusing distance of a lens. There is no glass, but usually there is the electrical connections for the lens controls. There is no loss of IQ with a tube. The only down side to adding a tube is the loss of focus at infinity.

And you lose some light so your shutter speeds will slow down a stop or two maybe 3 depending on how much extension you have in place.

You lose the infinity focusing
You get less light
You do lose image quality, because the lens you're tubing is not designed for macro and the aberrations are not corrected for that range of focus.

But you can still shoot small stuff.

So it sounds like they are primarily for macro use then?

thnks!!!

They are pretty much exclusively for macro work...with the notable exception of being used with the 400mm f/5.6L lens....that lens has a very long minimum focus distance...many birders use a tube with it to bring the focus distance down when shooting close in at backyard feeders and such.

suomi7777 wrote in post #2317434
So it sounds like they are primarily for macro use then?

That is EXACTLY what extension tubes are for. An extension tube merely moves the lens away from the camera body so that you can focus on subjects that are closer than the lens could focus on when then lens is mounted directly to the body.

An extension tube is simply a hollow light-tight tube with male and female lens mount rings. For modern automated cameras, extension tubes also provide a set of electrical connections through the tubes to keep the lens "alive" and communicating with the camera.

To put it another way, an extension tube is a substitute for a longer focussing tube on your lens.

perfect...thanks everyone for your input.

I'm going to get me a set of extention tubes but it's not because I'm going to start doing macro work. I'm getting them so that I can get closer to my subjects with the longer (i.e. telephoto) lenses that I have.