Different telescopes can have very different back focus distances. In most telescopes the focal plane is deliberately moved further out, allowing users to attach cameras and other accessories more easily.
Refractors always have a rather long back focus since they are usually used with a star diagonal or erecting prism.
The Problem:
As a result of this you often cannot directly focus the telescope if you do not use it with the above mentioned accessories. You would have to move the focuser further out, but you reach the end of the focus travel before reaching a focused image.
The Solution:
An extension tube bridges the gap between the focuser and the focal plane. It is the ideal solution whenever the focus lies further outside than you can reach with the focuser.
The eyepiece is clamped firmly but without scratches through a brass compression ring. The advantage is that eyepieces are held more securely and the risk of the eyepiece being tilted out of the optical axis is minimized.
The extension tube is machined from solid aluminium. It is black anodized.
The advantages at a glance:
- Designed in Portugal, made with high precision in China.
- 2'' spring ring clamp
- 2'' filter thread in the bottom
Special feature of this extension: There is a recess at the top for the clamping screw of short 2"/1.25" reducers. For example, the extension sleeve fits perfectly with the Omegon Alpha Crayford focuser 2" for Newtonian telescopes.
