Huet 8x40 Roof

Mfr: Huet, Paris, France

Date: circa 1953

AFOV: ~88 degrees

TFOV: 11 degrees

Eye Relief: ~12mm

Prisms: roof

Serial Number: 00.425

This is an unusual 8x40 roof prism binocular with an ultra wide field of view.  Made for the French Navy in the 1950's, it is partially rubber armored and has fixed focus eyepieces with a linear reticle on the right side.  The prisms appear to be a two piece Abbe Konig (Koenig) type, shown in the photos above both in the cage assembly and apart.  There is a slight offset in the optical axis from the eyepiece to the objective.  This prism type is also found in Hensoldt and Zeiss models.  The optics have dark blue coatings and the roof prisms likely do not have phase compensating coatings.  The resulting optical image is slightly yellow and not as bright or sharp as in the finest porro prism designs (the optics in my sample may be slightly dirty).  On the positive side, the field of view is huge and fairly well corrected.  Distortion and astigmatism are low except close to the edge.  Unfortunately, the fixed focus and limited eye relief cause problems for eyeglass wearers.  Otherwise, this is a great binocular for wide angle connoisseurs.

This Huet 8x40 invites comparison to the classic Zeiss ultra wide angle Deltar/Deltarem which has very similar specifications but is a porro prism design.  The more modern Huet has essentially the same field of view but has noticeably less astigmatism and better edge sharpness.  Also, I prefer the distortion characteristics of the Huet.  The Deltarem, however,  has better contrast and sharpness at the center of the field.

Note: the eyepieces actually have a limited adjustment.  Under the rubber, the eyepieces can be turned with great difficulty.  This was probably for factory adjustment as it is not easy to do in the field.  I have been told that removing an O-ring on the eyepiece allows it to turn more freely (see picture below).  The eyepiece can be unscrewed all the way off to access the O-ring around its barrel.  Also, the tension on the interpupilary distance can easily be adjusted by turning a knob on the lower hinge.

To remove the prism cover plate, unscrew the retaining ring on its perimeter.  Note there is a square key screw on the prism plate which does not need to be removed, this provides access to a dry air port.  To access the prism assembly, remove the three screws which have washers (see arrows on photo above, do not remove the other screws which hold the prism cage together).

This model is pictured in Hans Seeger's gray book (2nd edition), Abb.264.