Help understanding extension tubes

[dawnwithacamera]

Hi Guys:

I just got my first set of extension tubes, from Opteka. They are 13mm, 21mm and 31mm. I bought them thinking that they would extend the range of my lenses, ie making my 75-300 and 75-365mm. Thus elimanating the need, for now, to get a longer lens. When I tried them out, I couldn't see thru them for distance. They only worked for macro shots. Did I not understand the uses of extension tubes? I thought I could use them both ways. Any explanation in short and slow words would be most appreciated.

Thanks

[edbayani]

extension tubes are only for close up shots (macro). you can focus closer to the subject. it cannot be used as telephoto or wideangle adapters which are lenses that can be screwed in front or the rear of the lens. extension tubes are really just tubes, no glass inside. the purpose is to make the lens farther away from the sensor so you can come closer to the subject. once you screw the tubes on, you cannot focus far objects.

[dawnwithacamera]

Thanks for clearing that up for me. I began to suspect that was the case. Well, I wanted to get into more macro photography, and I guess I can.

[inkista]

Extending the range of a telephoto lens requires a teleconverter, which has glass in it. Be aware that using a tc will reduce the maximum aperture of your lens, though. A 1.4x tc robs you of a stop and a 2x tc will rob you of two stops. And most dSLRs stop autofocusing when the lens's max. aperture hits f/8.

In other words, don't use a 1.4x tc on anything slower than f/4. And don't use a 2x tc on anything slower than f/2.8.