Unknown, 1625 c.25
Louwman Collection of Historic Telescopes Arrow right Arrow left

photo - whole telescope
Basic Info

Maker: Unknown

Year: 1625 c.25

Year Range: -

Year Notes:

Manufacturing Location:


Signature Notes:


No stand present.

Collection: Louwman Collection of Historic Telescopes

Accession #: LC 18


Project investigation, and Boerhaave exhibit.

Bolt & Korey, "The world's oldest telescopes," in THE ORIGIN OF THE TELESCOPE (Amsterdam 2011), p. 246.

Louwman, P.J.K., and Zuidervaart, H.J., "A Certain Instrument to See Far: Four Centuries of Styling the Telescope Illustrated by a Selection of Treasures from the Louwman Collection of Historic Telescopes". Wassenaar, 2009. p. 59.

Louwman, P.J.K., and Zuidervaart, H.J., "A Certain Instrument for Seeing Far: Four Centuries of Styling the Telescope Illustrated by a Selection of Treasures from the Louwman Collection of Historic Telescopes". Wassenaar, 2013. p. 37.

Public Notes:

Tubes made of thick metal and outer tube covered in old brown calf leather, inner tube has brown paper. Both tubes of tin. Objective is replaced, it has the wrong focal length and is very fuzzy. Eyepiece is plano concave. It is not confirmed but it is suspected that it is from Belgium or Germany, earlier from weapons dealer. Very old-- could be pre-1620.

"German (?) telescope with tubes made of thick sheet iron.
The main tube (with a length of 16 cm, Ø 3 cm) is covered with brown leather, blind-stamped with simple fillets, representing a line with four outfacing triangular motifs. The leather handgrip of the drawtube has the same diameter as the barrel. Length 16.5-29 cm. A virtually illegible inscription in iron-gallnut ink is written on the tube, probably the signature of a former owner. When the instrument is photographed in infrared light, it appears that the ink is not carbonaceous, so that the signature doesn’t stand out. The edge of the double convex objective (Ø 2.5 cm) is irregularly formed. Its glass has many air-bubbles. The (not original?) plano-concave eye lens is retained behind a 3.0 x 0.2 cm brass ring collar. Presumably first half of the seventeenth century" (Louwman and Zuidervaart, 2013).

Main tube length is 167 mm, first draw tube is 180 mm (160 mm when optically working). Main tube diameter is 31.4 mm, first draw diameter 25.3 mm, and tube 1 ferrule / ring diameter is 31.3 mm. Inner diam draw = ca. 16 mm; tin thickness = ca. 1.2 mm.

Objective notes: Objective diaphragm made of paper, held in place by paper ring on inside with writing (see borescope film). Starside convex; if eyeside plano, focal length would be twice the measured amount; if eyeside instead equally biconvex, then computed focal length would match measured focal length. When tubes are separated, with significant gap between them, image of distant object can be formed. Separation of lenses when focused at infinity: 570mm. Given measured objective focal length of 653 mm (using a comparative magnification method), this implies a negative lens eyepiece with a focal length of 83 mm.

Length (open): 327

Length (closed): 290


Exit pupil:

Object status:

Optical Basics

Objective type: singlet

Optical style galilean and terrestrial

Physical style spyglass

Functional style

Materials: leather, glass, unknown, gold tooling, iron, pasteboard

Optical/Lab Data

Drawtube data:

Drawtube notes:

Objective Data

CA curvature (diopters): CB curvature (diopters): PD lens power (diopters): fD focal length (mm): t thickness (mm): free aperture (mm): full aperture (mm): nD refractive index: ν Abbe No.:
Lens 1 1.53 653.00 25.40 16.00



Eyepiece 1
fD focal length (mm): free aperture (mm): full aperture (mm): s spacing (mm): CA curvature (diopters): CB curvature (diopters): M magnification: FOV field of view (degrees): Thickness:
Lens 1 83.00 24.40 7.90 1.04