Optical Patents

© Brooke Clarke 2015

Geneva Lens Measure


I good friend is an optical engineer and some of his passion for optics has rubbed off on me.  Recently I've been studying the Camera Obscura and as part of that trying to learn about the lenses they use (Wiki: History of photographic lens design, Photographic lens designs).  But I suspect I'll be adding patents for other types of things.


1840 (Wiki: Petzval Portrait Lens, history) - New Lomo version

65729 Lens for Photographic Portraiture, J.H. Dallmeyer, June 11 1867, 359/707; 359/786; 359/791 - (Wiki: Rectilinear lensRapid Rectilinear) minimize barrel & pincushion distortion (Wiki)

Photographic lens, Mar 12, 1889, 359/775; 359/81 - (Wiki: Double Guass)
435271 Photographic Objective, E. Abbe & Paul Rudolph (Carl Zeiss),  Aug 26, 1890 - spherical & chromatic abberation correction (Wiki:
492335 Photographic Objective, Albert B. Parvin, Feb 21, 1893, 359/740 359/795 -
528155 Lens for Optical Purposes, Carl P. Goerz & Emil Von Höegh, - free of spherical, chromatic and astigmatic abberations for phototgraphic purposes
540122 Lens, Harold Dennis Taylor (Wiki Cooke & Sons), May 28 1895, 359/786; 359/740 - flat image plane for photography
540339 Object Glass for Telescopes, Harold Dennis Taylor (Cooke & Sons), Jun 4, 1895, 359/793 - color ocrrected air spaced triplet
568052 Lens, Harold Dennis Taylor (Cooke & Sons), Sep 22, 1896, 359/787; 359/740; 359/785 - a flat image free of marginal astigmatism for photography

1896 (Wiki: Zeiss Planar by
Paul Rudolph)
1908 (Wiki: Zeiss Tessar by
Paul Rudolph)

Photographic Objective, Paul Rudolph (Carl Zeiss), May 5 1908,
1013849 Short-base range-finder, Harold Dennis Taylor (Cooke & Sons), Jan 2, 1912, 356/13 - doublet & meniscus lenses = telephoto lens
1361207 Lens, Warmisham Arthur (Taylor & Hobson), Dec 7, 1920, 359/775 - improvement on the (Wiki: Cooke triplet)
1998704 Photographic objective, Ludwig Bertele, Zeiss, Apr 23, 1935, 359/787 - (Wiki: Zeiss Biogon)
2031792 Anastigmatic objective for photography and projection, Robert Richter, Zeiss Carl Fa, Feb 25, 1936, 359/737 -wide angle (Wiki: Topogon = B&L  Metrogon)

Geneva Lens Measure Wiki: Lens Clock

This serves that same function as a Spherometer (Wiki), but works differently.  The span between the measuring legs is smaller on the lens clock than on the Spherometer, so the lens clock will work on smaller diameter lenses.

The generic name:
Geneva Lens Measure
is on the dial along with the
manufacturer's name:
Chicago Dial Indicator Co.

The hollow sheet metal cap protects the points when the meter is not in use.

When the points are placed on a flat surface,
such as a 123 block or V Block, the needle turns about 3/4 of a circle and points to 0.
So the position of the needle in the photo shows the maximum negative reading it can make of just over -19 dioptre.  In a similar manner when the central pin is pressed the maximum indication is about +22 dioptre.

The separation of the outer points is 20.61mm

It turns out that in order to get the correct dioptre (Wiki) both the curvature of the lens and the refractive index of the lens material need to be known.  The Lens Measure actually measures the radius of curvature (positive or negative) and has a built in adjustment for the refractive index of the glass.  So when measuring plastic reading glasses or a magnifying glass the displayed result is wrong.

Magnifying glass (Wiki) FL = 6.75" (0.171 meters = 5.8 dioptre).  Reads +3.2 and +3.2 dioptre (sum = 6.4 off by 0.6).
I don't know if the range of adjustment in the Lens Measure is large enough to include the refractive index of plastic.

The Wiki Lens Clock web page explains how to convert
the reading when the refractive index (Wiki) is different from the factory set value of 1.523 (crown flint glass).
Geneva Lens Measure 425 = 1
Geneva Lens Measure

Scroll down on the FOB WATCH SPHEROMETER web page for information on the Lens Clock and how to use Gullstrand's Equation to work with the lens clock.  On line Gullstrand's Equation Calculator -

Measure the positive or negative curvature of a lens in dioptre.
R = (W2 + 4 * H2 / (8* H)
R is radius
W = horizontal distance between outer 2 points
H = + or - height difference between center point and outer points
The Radius will be given in the same units as W and H.  To get dioptre the radius should be measured in meters, then Dioptre = 1/R (meters)

The power of a lens is equal to (n-1) * R where n is the refractive index (see link above for dioptre and the formula in the curvature section).

  703725 Lens-measuring instrument, Franklin Hardinge (famous lathe maker), Jul 1, 1902, 33/507 - dial gauge type
1093307 Spherometer, Joseph Becker, Apr 14, 1914, 33/501 -
1151635 Lens-measure, Austin T Webb, Aug 31, 1915, 33/507 - dial gauge type
1637408 Curvature-measuring device, Bugbee Jr Lucian W, Continental Optical Corp, Aug 2, 1927, 33/507, 116/299 - looks like micrometer with 3-point end
2855687 Measuring instruments, Price George B, Oct 14, 1958, 33/838, 33/709, 33/555.3 -




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