Celestron Luminos 2.5x Barlow Lens 2

Telescope magnification multiplier

The Celestron Luminos 2.5x Barlow Lens fits between a telescope and its eyepiece to increase magnification by 2.5 times. It accepts both 2 inch and 1.25 inch eyepieces, giving owners of either barrel size a simple way to extend their existing collection. The four-element apochromatic design is fully multi-coated to preserve light transmission and colour fidelity.

Optical limits and field flatness

Magnification rises by a fixed factor of 2.5, so eye relief and exit pupil shrink proportionally with every eyepiece used. The apochromatic correction controls chromatic aberration across the visible spectrum, but the overall field stop remains set by the eyepiece itself. Image brightness drops as the effective focal ratio increases, which can make faint deep-sky objects harder to detect.

Threaded installation and common issues

The lens barrel threads directly into the 2 inch eyepiece holder and includes a 1.25 inch adapter ring for smaller eyepieces. No tools are required, but the adapter must be seated squarely to avoid tilt-induced astigmatism. Over-tightening the locking screws can mar the eyepiece barrel, while under-tightening lets the heavy assembly shift during slewing. Users who need a 1.25 inch nosepiece without the 2 inch body cannot separate the two parts.