I've been using extension tubes lately, and I thought I'd share my impressions. I'd love to hear your impressions too! (The following text was taken from comments on this picture.) Extension tubes are tubes that fit between your lens and your camera, effectively making your lens longer, and increasing the distance from the lens elements in front and the sensor on your camera in back. Increasing this distance means the image spreads out more before it gets to your sensor, increasing the size of the image on the sensor. They are handy for making macro shots bigger. I have a set of 3 which all fit together to make different magnifications. There were a few things I didn't know about these tubes before I bought them. First,the image gets dimmer as it spreads out, so you need to increase the aperture or the exposure. Also, you lose the ability to focus farther out. With all three tubes in, my maximum focusing distance on my 100mm, with the lens set to infinity, is about 6 inches. Lastly, the tubes change the balance of the camera so that it's harder to steady on a tripod. The camera sometimes seems to sway with its own rhythm. With my xsi, the autofocus technically does work with the extension tubes in place. Maybe it depends on the model of camera, or maybe my autofocus was off a bit and I just couldn't tell. I just tried it with my 18-55 lens. With a short tube, the maximum focusing distance was about 12 inches(!), but within that distance, the AF seemed to work. Also, if you are not on a tripod, that swaying effect probably won't happen. I mostly use the tubes to get farther away from my subject while keeping the image big, which can be an advantage when focus stacking (by decreasing the angular disparity caused by re-focusing). For that reason, most of my recently posted macro shots were taken using extension tubes. I usually have to try different combinations of tubes to find the one that gives the framing I'm looking for at the farthest distance from the subject with the lens set to about infinity. Other than that use for macro shots, I'm not really sure they add much as compared to just cropping the picture. That suggests a good comparison test -- cropped macro vs. macro with extension tubes. Also, I'm not sure what making the tubes longer does to depth of field, but sometimes it seems pretty shallow. I've always used the tubes with a tripod. I'm not sure how they would work with handheld. My guess is that not being able to focus very far away would be kind of awkward. I have no idea what the tubes would do to image stabilization. I hope you find this post helpful. If you have any experiences with extension tubes, I'd love to hear them!
