Ross Stepmur 10×50

Specifications:

Objective diameter (according to spec):  50 mm
Effective objective diameter (measured): 48 mm
Magnification:  10x
Exit pupil (according to spec): 5 mm
Effective exit pupil (measured): 4.8 mm
IPD: 55  – 74 mm
Usable eye relief (measured from rim of eyecup): 5 mm
RFOV:  7  degrees = 123 m
AFOV (measured, rounded): 65 degrees
Minimum focus distance (estimate): 19 m
Focus type: CF (direction of rotation from close to infinity: < anticlockwise)
Range of diopter adjustment (estimate): +/- 4 dpt*
Excess travel of focus wheel beyond infinity position (estimate): 6 dpt*
Prism system:  Porro II
Waterproof: no
Weight (measured, with eyepiece cover and strap): 1‘028 g
Made in: England UK

 
Remarks:

Made around 1960 by the British optics company Ross in London, this binocular with a wide angle of view (with 7 degrees, it beats most most current 10×50  binoculars) features Porro II prisms, which were more common before the arrival of today’s highly effective antireflection coatings. The ease of view (“Einblickverhalten”) is only good if you observe without eyeglasses, the short eye relief poses a problem for spectacle wearers. The image is relatively bright, but sharpness and contrast are not at par with the best binoculars of the period.  Moreoever, Ross seems to have been a bit “generous” with its specifications (cf. size of objective diameter and exit pupil).