Maker: Bourgeois, Jacques / Boulliau, Ismael / Beeckman, Isaac

Year:

Year Range: 1650-1700

Year Notes:

Manufacturing Location: France / the Netherlands

Signature: IB

Signature Notes:

Inscriptions:

No stand present.

Collection: Louwman Collection of Historic Telescopes

Accession #: LC 21

Sources:

Tiemen Cocquyt, "400 Years of Telescopes" booklet, Zeeuws Museum, 2008. Item 4;

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. 60.

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". Wasscnaar, 2013. p. 39

Project Investigation.

Public Notes:

"Telescope made of sheet iron. The main tube (length 12 cm) is wrapped with pasteboard and covered with gold-embossed thick brown leather. Signed in the leather cover with the signature ‘I.B.’ and above the letters a star. Three (uncovered) drawtubes. Maximum optical length 56 cm, Ø 2.8 cm. Opening of the diaphragm Ø 1.5 cm. Presumably mid-seventeenth century.

In the Willach Collection in Switzerland, there is a five-draw telescope with black and green covered pasteboard tubes, bearing the identical signature: ‘I.B. with a star above the letters’ (Willach no. 2622). Also the pattern of the gold tooling on the two telescopes is nearly identical, so there can be hardly any doubt that they are made in the same workshop. Willach ascribes his telescope – which has a compound eye-piece – to France or Italy .

From the seventeenth century , there are several candidates for the signature ‘I.B’. We know for instance that telescopes have been produced for Isaac Beeckman in the Netherlands, or for Ismael Boulliau in France. But probably the best candidate for the maker of these telescopes is Jacques Bourgeois, Miroittier et lunetier du Royat the Rue St. Denis in Paris. He published in 1645 a small booklet on telescopes, entitled: Advis aux curieux de la conservation de leur veue. Sur les lunettes dyoptiques; nouvellement mises en usage pour lutilite publique. In this book Bourgeois proposed for ordinary spectacles the use of a convex-concave lens, later called the meniscus lens. Bourgeois signed his booklet with the identical signature ‘I.B.’"(Louwmann, and Zuidervaart, 2013).

Good, crisp, clear image when focused. Optical separation of lenses is 580 mm, meaning ocular focal length is 94 mm.

Draw Tube Notes:
Main tube is thicker in middle covered by leather: 31.5 mm. Main tube, tube 1, and tube 3 have metal aperture stop reinforcing rings. Tubes 3 and 4 have ferrules. Observation, October 9, 2015: photos indicate that metal tubes alternate overlapping orientations, enabling tubes to rotate without catching on each other.

Objective Notes:
Objective held in place with split ring. Starside is convex, eyeside is nearly plano. Ronchigram shows perfect shape in central portion. Likely a replacement.

Eyepiece Notes:
Eyepiece held in place with split ring. Eyeside has central well. Irregularly shaped. Not polished at edges. Likely original. Central well aperture is 19.8 mm. Free aperture from paper ring is 9.5 mm. Lens thickness is 1.9 mm.

Length (open): 560

Length (closed): 140

F-ratio:

Exit pupil:

Object status:

Objective type: singlet

Optical style galilean

Physical style spyglass

Functional style

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

Drawtube data:

Drawtube notes:

Objective Data

Eyepieces

Notes: