Extension Tubes Overview ¹
An extension tube is simply a hollow cylinder that fits in between your camera and lens, causing the lens to move farther from the sensor. This additional distance allows your lens to focus more closely, which in turn provides more magnification capability. Unlike most lens accessories, extension tubes don’t add any extra optics, and are therefore relatively inexpensive, simple devices.
|Choose a Magnification:||1:2 (0.5X)||1:1 (1.0X)|
|Note: Diagram assumes that the lens is symmetric (pupil magnification = 1)|
An extension tube increases lens magnification by an amount equal to the extension distance divided by the lens focal length. For example, adding a 25 mm extension tube to a 50 mm lens will give a magnification gain of 0.5X. Therefore, if the lens’s original magnification was 0.15X, then the new magnification will be 0.15X+0.5X=0.65X. The closest focusing distance will also decrease to ~210 mm.
|0.15X Max Magnification|
with typical 50 mm lens
|0.65X Max Magnification|
after 25 mm extension tube
|Note: Shown using a full frame camera and a Canon EF 50 mm f/1.4 lens|
All camera lenses have some amount of native extension, which is used to focus on everyday objects. Lenses with closer focusing distances usually have more native extension, but these will also benefit less from extension tubes. Try experimenting with different lenses to see how extension affects magnification.
- • Extension tubes work best with short to medium focal lengths, they are less effective with telephoto lenses
- • Extra magnification also magnifies camera shake as well as the subject, tripod use is recommended
- • Be sure to use the smallest aperture (largest number) on your lens to give you adequate depth-of-field for better quality images
- • Each ring brings you closer to the subject as you increase the distance between lens and camera
- • Different lens lengths will require a different distance to be used from the subject, if the subject is not in focus move the camera closer or further from the subject until the subject comes into focus
- • The effectiveness of extension tubes decreases as focal length increases. You will need to be careful when working with extreme wide-angle lenses as the focusing distance required may be closer to the lens than physically possible (ie you’d hit the front lens element before you achieve focus).
For More information on Macro Extension Tube usage and calculations, please check the links below:
- • ¹ Macro Extension Tubes & Close-Up Lenses – Cambridge In Colour
- • The Ultimate Guide to Extension Tubes – Shutter Muse
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