Carl Zeiss AG, Manufacturer;  Hirst Contact Lens Limited, Other contributor; 

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Maker and Role
Carl Zeiss AG, Manufacturer
Hirst Contact Lens Limited, Other contributor
Production Date
Keratometer. This instrument was designed to measure the radius of curvature of the cornea. Hirst later adapted it through the addition of a prism so that the posterior curve of a contact lens could be measured accurately. The lens with its concave surface facing down was placed on the prism centrally so the beam of light coming from the light source of the Keratometer could reflect off the contact lens. Looking through the eye piece the radius of curvature could be read off the scale from the small circular window above the eye piece.
Part 1: This keratometer has been modified by Hirst to serve a different purpose. Firstly - the headrest has been positioned backwards. Secondly, a glass prism has been attached to the headrest with metal pieces and screws. The headrest stand at the back of the object is made from two cylindrical metal posts with adjustment knobs. There is one horizontal flat bar in the middle for the chin rest and a horizontal bar with a semi-circle in the centre for the head at the top. The keratometer is grey plastic and a horizontal barrel shape. Its support is composed of two cylindrical black metal posts with a flat platform with curved edges in the middle. One post is attached to the keratometer on one end and on the other end the second post is attached to the base, forming a stepped appearance. There is an eyepiece at the front with two glass circular windows. There is a switch to the right, and bilateral cream adjustment knobs on either side. Underneath this is a metal cylindrical piece with yellow tape holding a cream-coloured component in place. This is the axis rotating handle. There is a second wider metal cylinder below the keratometer to the rear. This is where the light source is attached. This is a detachable part, allowing the light bulb to be replaced [Part 3]. There is a label on the side of the unit which reads “Serviced by / Optical Instrument Services / 40 Edward Street, Lincoln / Canterbury (03 325-2538)” and on the end of the object is “CARL / ZEISS / 84476 / West Germany” printed in black.
The object has a black square platform which slides from side to side, with a cream-coloured toggle switch to control it. There is a circular item in the centre of the platform with a cream coloured lid which reads “CARL / ZEISS / Nr 108551 / Germany”. There is also a shallow white plastic cylinder to the back right of the platform.
Part 2: There is a separate grey metal power supply unit with a textured surface. On the front is a black plastic socket. There is a white power cable and a two-pronged plug at the back. The pins are positioned in opposing directions, one horizontal and one vertical. There is a gold label on the top which is partially illegible, “Electri[…]”.
Part 3: This is a cylindrical metal piece which connects to the keratometer. The original light bulb is broken.
Part 4: This is a replacement bulb. It is not original to the object.
Other Name
Processed Material/Metal
Processed Material/Glass
Processed Material/Synthetic/Plastic
Signature/Marks and Type
Electri[…] Label
Serviced by / Optical Instrument Services / 40 Edward Street, Lincoln / Canterbury (03 325-2538) Label
CARL / ZEISS / 84476 / West Germany Printed
CARL / ZEISS / Nr 108551 / Germany Printed
Accession No
Credit Line
Carl Zeiss AG et al. 1950. Keratometer, 2018.1.17. The Museum of Transport and Technology (MOTAT).

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