Product Description
Here is another industry standard two-axis autocollimator manufactured by Davidson Optronics - the model D-638 Coordinate Measuring Autocollimator. Like the similar D-656, the instrument features a folded optical path so despite the 20” focal length of the objective, the entire collimator is only 12.75” long. The baseplate is very massive, 10.5” by 6” and incorporates both azimuth and elevation adjustments (plus or minus 2 degrees each direction) with super-fine adjustment screws. Instrument weight is over 21 pounds.
Specifications of the instrument include the following:
Accuracy: 0.5 arc seconds over any one arc minute, 3.0 arc seconds cumulative over the entire range of 20 arc minutes
Sensitivity: 0.1 arc second
Repeatability: Plus or minus 0.2 arc seconds
Total measuring range: 20 minutes of arc in elevation and azimuth
Dual Scale Readout: minutes scale and seconds scale at 0.2 seconds/div.
Reticle Pattern: Darkfield with illuminated concentric rings approximately at two minute intervals. No numbers in the field of view – all readouts are taken directly from the filar readout drums. Center dot approximately 10 arc seconds in diameter.
Objective Aperture: 2.375”
Reduced Measuring Range at long distances = plus or minus 10 minutes @ 30 feet, and plus or minus 2 minutes @ 125 feet.
Lamp: GE #328 lamp driven by external 115v line voltage regulating transformer
Unlike the D-656, the ocular micrometer of this instrument may be rotated through exactly 90 degrees – at either end of its excursion, it will read in azimuth or elevation. Reference mirrors can be as small as 1/2 inch. The readout dials for the filar ocular are a work of art – the finely divided scale is magnified by the cursor window, and there are fiducial lines one both the crown and underside of the window to eliminate parallax errors while taking readings. Each revolution of the knob directly moves the seconds scale. One revolution equals one minute and this in turn advances the minute drum one division, which is numbered from zero to twenty. For additional specifications please refer to the Davidson Optronics web page at:
http://www.davidsonoptronics.com/D-638.htm.
This instrument is in perfect functional condition, but it does have a few minor cosmetic blemishes in the paint finish here and there. Optically, the coating on the objective is very strong, and the lens is free of cleaning marks. However there are four small chips in the front objective, easily seen in the last photograph. They are relatively inconsequential as far as the accuracy of the instrument is concerned. There is no cabinet with the collimator, but we will supply a light source and line transformer (not illustrated).
We have a copy of the operation and maintenance manual available upon request.
Location Display 1-1
Photo set 942