When you focusing a lens, the farther the lens from image sensor, the closer the focus . But the distance between lens and sensor is limited, then there is a limit how close we can focus the lens on your subject .

By adding extension tube between camera body to the lens, we can increase the distance between lens and image sensor, so it can focus much closer than normal . With this capability, the subject will looks much bigger.

Extension tube is shaped like a hollow tube, no contents inside. Usually have some size , the larger / thicker tube, the more space and has a greater magnification. If the size of extension equal to the lens focal length, you can get 1:1 magnification a real macro lens.

For example if using a lens with 65mm focus length (if you have a zoom lens, then zoom to 65mm), then by stacking three tubes (31 +21 +13 mm) and you will get 1:1 magnification.

Extension tubes can be stacked to obtain a longer distance . For photography of small objects, using lens with a long focal length is recommended so that there is enough distance between the camera and your subject and make the background more blurred.

The advantages of this simple accessories compared with the close-up filter or converter is, the image quality will be maintained because there is no optical elements inside the tube. The drawback, using extension tube means less light entering camera censor. The longer, the more light is reduced , then it is more suitable for outdoor using when the weather is sunny, or use the help of a tripod . The other drawback is that we can not focus the lens to infinity (which is far away).

When buying an extension tube, it’s recommended to buy a tube which has TTL function (through the lens) and autofocus . Thus , we can take pictures freely like not using a tube extension . If you don’t have that two features, you have to moving your camera to get focus and have to adjusting the light and dark setting by yourself. Make sure this accessories fit for your camera brand.

Below is an example of a photo using an extension tube.