Barr and Stroud Rangefinders

Barr and Stroud manufactured a large and evolving family of optical rangefinders, primarily coincidence models to several navies, notably the Royal Navy and the Japanese navy.

Early Development

The first Barr and Stroud instruments were developed in the 1890s in response to a call for rangetaking equipment meeting novel and somewhat loose and humble requirements of accuracy and maximum range. Based on their acceptance, a burgeoning relationship with the Royal Navy saw Barr and Stroud's line of instruments accepted to the near exclusion of all other types and manufacture. Over time, the number and base length of the instruments offered for each capital ship grew and grew, and the ships regarded as platforms for rangefinders grew down into the largest destroyers by the end of the war.

Part of what made Barr and Stroud a desireable supplier was that the firm's own fire control instruments were often the means by which the range cuts recorded on the devices were communicated throughout the ship.

Lessons Taken

The Royal Navy ultimately decided that the F.Q. type rangefinders were superiour to the F.T. types.

Nomenclature

Barr and Stroud's rangefinders, their mountings and associated appliances had an arcane naming scheme. Each had a two letter prefix and a numeric suffix. The first letter generally indicated the type of device ("F" for rangefinder, "M" for mounting, etc), and the second letter the basic sub-type or design principle. The numbers seemed to reflect finer differences.

Rangefinder Models

The rangefinder designations were all prefaced by "F" to indicate rangefinder, followed by "A", "Q", "T", or "X" to indicate basic design, and finally a numeric code to indicate model.

Most rangefinders had a "finder" scope for help in locating the target. This was generally a small telescope of lower magnification and larger field than the RF itself. On Rfs intended for individual use, these were generally integral. On small RFs, this might just be an open sight. On larger models, they would be separate items, rigidly affixed in some manner to the mounting for use by another operator, typically the trainer. They would not follow the RF in pitch. On turret RFs, this was a periscope. (p. 76-77)

ivory scales for all but FQ, P.O.D. adjustment, universal couplings, (TBC p90-91)

F.A. 2

BL 4.5ft, focused by eye lens (p71)

scale can be illuminated at night by a light off a reflector, and is focusable by moving eye lens. (p. 73)

The finder was viewed through the lower concave half of the left eyepiece. The upper half showed the scale. Whole objective could slide back and forth to adjust for distance between user's eyes. Focussing of scale and finder was joint.(p77)

The device had an astigmatiser that was moved into or out of position by a slider on the lower right hand side of the rangefinder.(p85-86)

The working head affected the upper field (right objective). When the upper is to the right of lower, the range is more than that indicated by the scale. The guide, then, was that working the head was moving the top field in the same direction.(p91)

F.Q. 2

BL 2m, 9ft, 12ft (p71) The F.Q. 2 was a notable rangefinder in the years 1906-1916, as it was the model being delivered for ships such as Dreadnought through ....

scale can be illuminated at night by a light off a reflector, and is focusable, like the range eyepiece, by a scaled lever near the lens (p. 73, plate 2)

A finder was located right under the right eyepiece. The range eyepiece looked 45 degrees down, but the finder looked straight down and was focussed by a small nub on its eyepiece shaft.(plate2) Finder looked through the scale illumination window. a small circle in the eyepiece, when placed over the target, put it in the RF view.(p77-78)

The rangefinder had internal astigmatiser lenses that were moved into or out of position by a slider on the lower right hand side of the rangefinder.(p86-87)

The scale was a spiral one etched on a strips of non-transparent celluloid wrapped on a metal drum, illuminated on the face.(p90)

The working head affected the lower field (left objective). When the lower is to the left of upper, the range is more than that indicated by the scale. The guide, then, was that working the head was moving the lower field in the same direction.(p91-92)

F.T. 4

BL 80cm (p71)

scale can be illuminated at night by a light off a reflector, and is focusable by internal adjustment (not generally needed). Scale can be read through illuminating window, as well (p. 74)

Its finder was a small collimator located over the right eyepiece, easy to look into without much head movement.(p78)

The rangefinder had internal astigmatiser lenses that were moved into or out of position by a lever located on the left handle.(p86-87)

The working head was located near the right handle.(p88-89)

The working head affected the lower field (right objective). When the lower is to the right of upper, the range is more than that indicated by the scale. The working head moved the lower field in the same direction.(p92)

F.T. 8

BL 9ft, 20 mag, focused by moving eye lens plus the field lens (p71) variant 28 mag focused by moving eye plus field (p72)

variant having both 20 and 28 power (p72-73)

scale is illuminated a light (integral?). No means of direct daylight illumination, and is focusable by moving eye lens (p. 74-75)

As this device was adjusted by a separate operator, the finder was a tall periscope of adjustable height of 2.5 power "of large field" affixed to the mounting. Different head-pieces made it work whether trainer sat with his back to the target or stood facing it. The eyepiece had a focussing ring. (p79-80, plate VIII)

The rangefinder had internal astigmatiser lenses that were moved into or out of position by a slider on the lower right hand side of the rangefinder.(p86-87)

The working head was located on top of the rangefinder on the right side, so the rangetaker's right hand could rest comfortably atop the device as he worked. (p88-89)

The working head affected the upper field (right objective). When the upper is to the right of lower, the range is more than that indicated by the scale. The working head worked backwards; it moved the upper field in the opposite direction.(p92)

F.T. 17

BL 66cm and 80cm (p. 59) left lens is bottom in erect models. (p63)

17 mag focused by moving eye plus field (p72)

no step prism needed as in FQ 2, as vertical difference between beams is slight (p59)

scale is read by daylight through a window (some have lenses to concentrate light) or by a light at night, and is focusable by internal adjustment (not generally needed) (p. 75)

The finder was a simple, small collimator with crosshairs located above the right eyepiece.(p80-81)

The rangefinder had internal astigmatiser lenses that were moved into or out of position by a lever located on the left handle.(p86-87)

The working head was located near the right handle.(p88-89)

The working head affected the lower field (right objective). When the lower is to the right of upper, the range is more than that indicated by the scale. The working head moved the lower field in the same direction.(p92)

It could be used with an M.B. 4 mounting.(p160)

F.T. 23

BL 2m, upper image inverted (p62) 25 mag focused by moving eye plus field (p72)

scale read by small telescope with concave eyepiece as in FQ2, focused by moving the whole. read by daylight (lens focuses light and external reading) or external light at night (p76)

The finder was a simple, small collimator with crosshairs located above the right eyepiece.(p80-81)

The rangefinder had internal astigmatiser lenses near the objective lenses that were moved into or out of position by a lever located on the left handle.(p87-88)

The working head was located on top of the rangefinder on the right side, so the rangetaker's right hand could rest comfortably atop the device as he worked. (p88-89)

The working head affected the upper field (right objective). When the upper is to the right of lower, the range is more than that indicated by the scale. The working head worked backwards; the upper partial image moved in the opposite direction.(p92)

F.T. 24

BL 9 and 15 feet. (p71) 20 mag, focused by moving eye lens plus the field lens (p71) variant 28 mag focused by moving eye plus field (p72)

variant with swappable 20 and 28 mag (p72-73)

scale is illuminated a light at night, and is focusable by moving eye lens (p. 74-75)

As this device was adjusted by a separate operator, the finder was a tall periscope of adjustable height of 2.5 power "of large field" affixed to the mounting. Different head-pieces made it work whether trainer sat with his back to the target or stood facing it. The eyepiece had a focussing ring. (p79-80, plate VIII)

The rangefinder had internal astigmatiser lenses that were moved into or out of position by a slider on the lower right hand side of the rangefinder.(p86-87, as FT 8... may differ slightly)

The working head was located on top of the rangefinder on the right side, so the rangetaker's right hand could rest comfortably atop the device as he worked. (p88-89)

The working head affected the lower field (left objective). When the lower is to the left of upper, the range is more than that indicated by the scale. The guide, then, was that working the head was moving the lower field in the same direction.(p91-92)

F.T. 25

BL 9 and 15 feet. erect image. right lens is bottom. prisms larger than in 17 and 27 (p63) 20 mag, focused by moving eye lens plus the field lens (p71)

scale is illuminated by a light at night, and is focusable by moving eye lens (p. 74-75)

As these were mounted within the Gun Control Tower they had no separate finder. (p81)

The rangefinder had internal astigmatiser lenses that were moved into or out of position by a slider on the lower right hand side of the rangefinder.(p86-87, as FT 8... may differ slightly)

The working head was located on top of the rangefinder on the right side, so the rangetaker's right hand could rest comfortably atop the device as he worked. (p88-89)

The working head affected the lower field (left objective). When the lower is to the left of upper, the range is more than that indicated by the scale. The working head was "backwards", and moved the lower field in the opposite direction.(p91-92)

F.T. 27

The F.T. 27 was a compact, single observer rangefinder of 1m or 80cm base length, and was manufactured in great numbers, often for use on land. It could be operated in hand-held manner or affixed to a tripod mounting.

no step prism needed as in FQ 2, as vertical difference between beams is slight (p59)

in 80cm, where upper is inverted, lower erect (p60) infer: 1m model never inverted

left lens is bottom in erect models. (p63)

14 mag focused by moving eye plus field (p72)

scale is read by daylight through a window (some have lenses to concentrate light) or by a light at night, and is focusable by internal adjustment (not generally needed) (p. 75)

The finder on those with an erect upper image was a simple, small collimator with crosshairs located above the right eyepiece. Those 80cm models with an inverted upper had no finder, as they were intended for "shore use".(p80-81)

The rangefinder had internal astigmatiser lenses near the objective lenses that were moved into or out of position by a lever located on the left handle.(p87-88)

The working head was located near the right handle.(p88-89)

The working head affected the lower field (right objective). When the lower is to the right of upper, the range is more than that indicated by the scale. The working head moved the lower field in the same direction.(p92)

It could be used with an M.B. 4 (with or without the lower portion of an M.B. 6) or an M.B. 7 mounting. On destroyers, it might be on an M.H. 37 tripod mounting.(p160)

F.T. 28

Intended for aircraft (p76) BL 1m "eyepiece arranged trunnionally so as to facilitate observation upon aircraft" (p64)

No scale eyepiece, but can be read through a window similar to the FT 27. There is a separate range scale at the trunnion head of the mounting. No provision for night lighting (p76)

Could be placed, vertically on M.T. 3 and M.T. 4. The finder was a short telescope that could be adjusted in pitch and looked downward into a prism which would cast its gaze skyward without straining the neck. The image in the finder was erect. A focussing ring was on the eyepiece.(p81, plate 9)

There was no astigmatiser.(p88)

The working head was located on the mounting, reaching the rangefinder over a universal coupling (p89)

The working head affected the lower field (right objective). When the lower is to the right of upper, the range is more than that indicated by the scale. The working head worked backward; the lower partial image moved in the opposite direction.(p92-93)

F.T. 29

Intended for aircraft (p76) BL 2m "eyepiece arranged trunnionally so as to facilitate observation upon aircraft" (p64) 14 mag focused by moving eye plus field (p72)

No scale eyepiece, but can be read through a window similar to the FT 27. There is a separate range scale at the trunnion head of the mounting. No provision for night lighting (p76)

Could be placed on M.T. 6. The man elevating the trunnion faced the rangetaker and not the target as in the F.T. 28. The finder with crosswires was mounted on the trunnion and did not require gearing and prism as in the F.T. 28. The eyepiece was on the trunnion axis and so did not change position with elevation. Prisms within the finder altered the view upward 90 degrees. A selector switch swapped objective lenses to offer 3 mag and field of 14 degrees or 8 mags and field of 5.25 degrees. A focussing ring was on the eyepiece. (p82, plate 10)

The rangefinder had internal astigmatiser lenses near the objective lenses that were moved into or out of position by a lever located on the left handle.(p87-88)

The working head was located on the mounting, reaching the rangefinder over a universal coupling (p89)

The working head affected the lower field (right objective). When the lower is to the right of upper, the range is more than that indicated by the scale. The working head moved the lower field in the same direction.(p92)

F.X. 1

The upper field came from the right hand objective.(p155)

Rangefinder Mountings

Year	Model	Type	Suitable RFs	Notes
	M.B. 4	Belt and Rail	F.T. 17, F.T. 27
	M.B. 7	Belt	F.T. 27
	M.E. 3	Rail	F.T. 4
	M.B. 6		F.T. 27
	M.G. 3	Turret	F.T. 8
	M.G. 8		F.T. 24
	M.G. 11		F.T. 24
	M.H. 28	Tripod	F.T. 23
	M.H. 37		F.T. 27
	M.J. 1	Traversing	F.Q. 2
	M.J. 2		F.A. 2
	M.L. 10	Turret	F.T. 8, F.T. 24
	M.L. 11		F.T. 24
	M.L. 12		F.T. 24
	M.L. 13		F.T. 8, F.T. 24
	M.N. 1	Fixed	F.Q. 2
	M.N. 2		F.A. 2
	M.P. 2	Traversing	F.Q. 2	2 man
	M.P. 3		F.Q. 2	2 man
	M.Q. 1	Fixed	F.Q. 2
	M.Q. 10		F.T. 24
	M.T. 3	High Angle	F.T. 28
	M.T. 4		F.T. 28
	M.T. 6		F.T. 29
	M.W. 1	GCT	F.T. 24, F.T. 25

Associated Equipment

Year	Model	Type	Suitable RFs	Notes
	M.B. 4	Belt and Rail

See Also

• Rangefinder

Bibliography

• Template:BibRangeAndVision
• Template:BibUKHandbookBarrAndStroudRFs