Lens Basics – Extension Rings

By January 28, 2014January 24th, 2022Image Acquisition

In this post, we will be covering an essential lens add-on used in Vision and photography called the extension tube or extension ring. Most commonly used lenses are either fixed focal (having a minimum working distance) or vari-focal. An extension ring is an accessory used in between the connection of a lens to a camera. The purpose of this addition is to primarily move the lens away from the image plane (virtual object plane) in order to increase the focus and magnification.

In other words an extension tube is used primarily for two purposes:

  1. To view a smaller field of object view using a longer focal length, with the working distance remaining constant.
  2. To reduce the working distance between object and lens while using a longer focal length lens.

The disadvantage of extension rings is that they reduce the amount of light reaching the lens, hence necessitating a greater exposure setting. This can have a significant impact on image quality and is not recommended where light sensitivity and accuracy are demanding. For further details and inquiries,  do contact us at [email protected]

One Comment

  • Hi Nirmit, glad you find the blogs useful. Thanks for your comment – you’re right that the Depth of Field will also be reduced with the use of Extension Rings, thus causing mounting challenges.

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