Huygens, Christiaan, 1656
Louwman Collection of Historic Telescopes Arrow right Arrow left

photo - objective
Basic Info

Maker: Huygens, Christiaan

Year: 1656

Year Range: -

Year Notes:

Manufacturing Location: the Netherlands

Signature: CHR. HVGENIVS. Ao. 1656 - PED II

Signature Notes:


No stand present.

Collection: Louwman Collection of Historic Telescopes

Accession #: LC 30


Louwman Catalogue, p. 46.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.60.

Public Notes:

"Objective lens, polished by Christiaan Huygens, signed: ‘CHR. HVGENIVS Ao 1656 – PED II’ [= 11 feet or 335 cm]. The actual focal length has been determined in the optical laboratory of Rolf Willach as 365 cm. Biconvex lens Ø 6.2 cm. Radius of curvature: on the front side (with inscription) 400 cm; on the back 408 cm. Maximum thickness: 0.34 cm. Colour: grey-green. Many small bubbles in the lens. A paper diaphragm with an opening of 3.4 cm belonging to this glass has been preserved as well" (Louwman, and Zuidervaart, 2013).

Objective Notes:

This lens sits in a pasteboard well with a paper diaphragm on the reverse. The outer diam of the cell is 75.9 mm. There is writing on the black underside of diaphragm. Measured focal length of 3450 mm for outer edge (70% zone) at 5460 mm. After removing the stop blocking the central portion of the lens, and placing the lens in its original holder, which reduces the aperture from 62.3 mm to 30.9 mm, allowing only the central rays to pass through, the focal length increases significantly to 3635 mm. Ronchigrams show significant spherical aberration outside the zone of the original aperture stop, as expected. Objective is nearly equally biconvex, with the starside registering just over 4100 mm radius of curvature, the eyeside is typically a little shallower at 4150-4200 mm, when using a 40mm spherometer bell. A smaller spherometer bell (12.5 mm) showed a surprising variation from +-spot to spot, not just from center to edge. The 25 mm bell showed starside c 3500 mm (+/- 150), eyeside shallower but ranging from 3400 to 4000. The 12.5 mm bell reveals confusing data, all concave readings.

Length (open):

Length (closed):


Exit pupil:

Object status:

Optical Basics

Objective type: singlet

Optical style

Physical style

Functional style

Materials: glass

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 3650.00 3.40 62.00 30.90