The focimeter is a necessary tool for any optician. It responds to the need to have stable reference samples that allow each optician to offer, on the one hand, optically excellent lenses and, on the other, to demonstrate the precision and reliability of the instrumentation in the event of disputes and complaints. The legislation currently in force for consumer protection presupposes that the accuracy and reliability of the instrument, the procedures and the registrations that are performed in the verification process must be demonstrated.
It must become a good habit for the optician to periodically check the accuracy of such an important instrument as the frontometer. You must have the warning to record the calibration operation and its result, for itself, but above all as a caution in cases of unpleasant disputes.
The calibration set for front focometers is equipped with 12 samples suitable to cover the whole range of powers of the lenses of common ophthalmic use. The interval with neighboring steps is designed to ensure control of all measurable powers. The lenses are made with quality optical glass and with technologies used exclusively for the realization of fine optics. For the unambiguous identification of the pieces and for their protection, the lenses are inserted in a plastic frame on which the nominal power and the serial number of the set are engraved.
For cylindrical lenses this data is engraved directly on the lens glass.
The series is made of 12 lenses. There are
5 negative spherical lenses of nominal power −5,−10, −15, −20, −25 dioptres (symbol D),
5 positive spherical lenses of nominal +5, +10, +15, +20, +25 D,
1 cylindrical lens of nominal power Cyl +5 D,
1 prismatic lens of nominal power 5 prismatic dioptres.
From February 2018 the focimeter set has added also other 4 prismatic lenses, saying nominal power 2, 10, 15, 20 prismatic dioptres.
This is to comply with ISO requirements. In particular ISO 9342-1:2005 specifies requirements for test lenses for the calibration of focimeters that are used for the measurement of spectacle form lenses.
ISO 9342-1:2005 applies to focimeters meeting the requirements of ISO 8598.
The spherical lenses are made of K5 glass, 25 mm in diameter; they are mounted in a plastic frame where the identification mark is engraved.
The cylindrical lenses are made of C B23-59 glass, 60 x 40 mm2 in size. The prismatic lenses are made of K5 glass, 26 x 50 mm2 in size. All the marks are engraved on the glass.
Each lens is identified, one by one, by means of its nominal power in dioptres and its own serial number.
METHOD AND MEASURING INSTRUMENTS LENSES
The ophthalmic power is obtained from the geometrical and physical characteristics of the lenses.
For more details about our focimeter calibration set, please refer to the PDF document shown on the bottom of this page.
The technical report, for each focimeter calibration set sold, has been prepared by the National Institute of Applied Optics in Florence, and it is part of the focimeter set supply.
This document is written according to the international optical rules. Each focimeter set has a progressive number; every lens of this set is measured, attesting its dioptric value, its tolerance and the method used for its measurement.
The Focimeter calibration set is accompanied by a robust and elegant carrying case.
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