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With-Browning 1870 Reflector - Godlee Observatory England
This description and images were kindly supplied by Jerry Grover to whom I am indebted. Click on any thumbnail image above for a larger view to open in a new window.
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Total body length = 855 mm, not including colimation screws on rear mirror cell.
Tube diameter at mirror end = 160 mm
Tube diameter at open end = 136 mm. This is the diameter of the whole length of the tube - it is increased by the mirror mounting casting at the mirror end.
Mirror diameter is 110 mm, in a heavy brass cell, held to the body with three knurled screws. There is a 'keyway' cut in the rim of the cell that has to align with a mark on the OTA - the three mounting screws are not symmetrical.
Centre of mounting trunion to mirror end of tube = 220 mm
Front end to centre of eyepiece = 200 mm
The finder is an odd one in that focus is adjusted by sliding the objective lens in and out, the eyepiece remaining fixed. It is 25m mm in diameter and 275 mm or so long, depending on how far focus is moved.
I believe this method of moving objective lens is called a 'trombone' because the way the tube slides in and out is like a trombone. There was, now missing, a little 'handle' attached to the objective tube, which ran in a slot in the body, and thus made it easy to adjust (and limited its travel).
The finder is mounted in the usual way with two brackets 110 mm apart.
Removing 3 milled screws around the OTA at the mirror end releases the mirror cell holder (made of brass), painted brown on the outside - the mirror cell itself (painted black) is held in place by the cylindrical threaded 'boss' screwed to the central threaded stud. Around this are 3 symetrically placed screws with pointed ends that bear on the cell itself for collimation. Why does the cylindrical threaded 'boss' have a groove in the end that bears on the outside of the end piece?
Weight of mirror in its cell is 2.35 kg, weight of end casting (brown) alone is 1.9 kg. Weight of complete assembly is 4.5 kg. I know this doesn't quite add up - error in use of kitchen scales!
The mirror bears no trace of signature, date or any identifying marks.
Suggests it is a run-of-the-mill standard production mirror. It is 25.5 mm thick and 113 mm diameter. The mirror surface is still very bright, but has been badly handled and is marked and 'scuffed' quite liberally. The mirror is restrained in the black cell by a narrow metal ring (held by 3 screws) around its outside edge. I must say that, although the rear of the mirror may be ground to a perfect plane, the base of the cell in which it sits is anything but smooth, as the pix show.
The mirror cell assembly mates with a brass ring which is attached to the OTA by 3 bolts with nuts inside the OTA. This brass ring is 18 mm in depth (ie along length of OTA) around the OTA and is 24mm in depth where the mirror cell assembly fits on. Will measure diameters later. This stepped brass ring forms a convenient fixed edge from which the following measurements are made.
To trunion centre 207 mm, to nearest edge of internal band (see below) in OTA 333mm to furthest edge of internal band (see below) in OTA 460mm to first screw of Browning signature plate 382 mm to second screw of Browning signature plate 440 mm to eyepiece centre 644 mm
Browning signature plate is held by 2 bolts with nuts inside OTA
Internal band in OTA. I think this shows up well enough in the pix - I cannot see any obvious reason for it being there!
The eyepiece is held to OTA by four nuts inside OTA, presumably on studs on the eyepiece underside, as no screw heads are visible.
Godlee Observatory Website: click here
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