The Caruba Extension Tube for Sony does not have any optical elements, which makes it possible to photograph subjects larger and from a closer distance without changing the quality of the image. The extension tube has a chrome mount and is compatible with Sony A lenses. Features such as auto focus and TTL light metering continue to work as usual. However, it is recommended to focus manually, as focus is very tight.
Ideal for macro photography
Every lens has a minimum focusing distance. If you put an extension tube, or so called spacer ring, between the lens and the camera body, the minimum focusing distance becomes smaller. The greater the focal length of the extension tube, the closer you can get. This is perfect for macro photography or for creating special close-ups.
How does a spacer work?
A spacer ring increases the distance between the image sensor of the camera and the rear lens of the lens. This shortens the focusing distance of the lens, making it possible to focus closer on the subject. As a result, the subject is projected onto the sensor larger than it would be without a spacer ring. A spacer ring increases the magnification factor of a lens. This can be calculated using the following formula.
Maximum magnification with a spacer ring = lens magnification factor + (mm spacer ring / focal length)
For example, you have an 85mm lens with a magnification factor of 0.13. With the 25mm spacer ring the magnification factor of the lens becomes as follows.
maximum magnification with 25mm ring = 0.13 + (25 / 85) = 0.13 + 0.29 = 0.42