How to Focus a Lensometer

A lensometer is essentially a modified microscope used for reading lens strength.

A lensometer is a device similar to a microscope that is used to measure the strength and quality of lenses used in eye glasses. Lensometers must be calibrated prior to use. An uncalibrated lensometer will not accurately measure the lens prescription. Images called mires are used for focusing purposes. The lensometer focus can be adjusted at the eye piece (for calibration) and the diopter dial (for measuring lenses).

Instructions

1. Calibrate the lensometer. Set the diopter knob to zero and adjust the eye piece until the mires come into clear focus.

2. Place both lenses on the lensometer so that the curve of the lens points up.

3. Center the right lens under the lensometer lens. Adjust the placement until the mires are centered. Slip the lens clips at the lens edges to hold the lens in place.

4. Adjust the focus of the lensometer with the diopter knob. Do not adjust the eye piece. The mires will come into clear focus.

References

• Root Atlas: Using a Lensometer to Check Glasses
• Ohio State University: Lensometry
• Jomton Online: Introduction to Lensometry