A Victorian marine four-draw telescope or spyglass dating from 1840-1870, masterfully crafted and signed by the noted Liverpool maker, Benjamin Wood. The telescope measures 39 cm when closed and extends to an impressive 67.5 cm, this heavy brass spyglass features a long integrated front sunshade section designed to reduce glare on bright open waters. Outfitted with an authentic internal field stop (diaphragm)—a classic optical feature of the era engineered to block edge distortion and deliver a crisp, focused central image, if you are unfamiliar with this feature, we describe it in more detail below.
The main barrel retains its original rich, dark stitched-leather sleeve, displaying honest age-related patination and character that only a century and a half of history can provide.
A magnificent display piece for maritime decor, studies, or collections of antique scientific instruments.
In good working order but sold strictly as a historic collectible artifact.
Benjamin Wood was a known 19th-century optical, mathematical, and nautical instrument maker based in Liverpool, a major maritime hub supplying officers and ships with navigation and sighting equipment at the time.
The field stop was used for a number of reasons:
1. Eliminating Optical Aberrations (Sharpening the Image)
Early lenses, especially simple or early achromatic doublets from the 18th and 19th centuries suffered heavily from spherical aberration and distortion near their outer edges. By placing a physical restriction or "stop" inside the optical path, the telescope blocked out the distorted light rays coming through the perimeter of the lenses, forcing the viewer to use only the central, highest-quality portion of the glass. This drastically improved image sharpness and contrast.
2. Reducing Glare and Stray Light
Light bouncing around inside the empty metal or wooden draw-tubes creates internal reflections, washing out the image with a hazy glare. Internal baffles and stops acted as traps to absorb or block stray, off-axis light, ensuring that only the focused light making up the actual image reached the eye.
3. Defining the Edge of the Field of View
The stop acts as the physical plane where the image comes into focus. Without it, the edges of the view would feather out into a blurry, distorted mess. While it creates a "restricted" or tunnel-like view by modern standards, it gave historical observers a clean, sharply bounded circular frame.
