Here is a vintage angle-reading attachment for K&E alignment telescopes. It will also fit other brands that have the industry-standard 2.25\" diameter barrel. This item was made in 1966 by the former Keuffel & Esser company of New Jersey. They are no longer in business; this item no longer produced. I consider this a rare item; I\'ve only come across this one example in 40 years of using optical tooling.
This item, still in its original box, is in excellent condition and shows little sign of use if any. The optical element is clean and unblemished; the mechanical finish is excellent but for one paint-flake (1 by 4 mm) on the exterior. Still evident is the K&E Quality Control sticker, dated 10/19/66.
From page 21 of K&E catalog #9, the description reads: \"This attachment fits over the objective end of a standard 71-2022 alignment telescope and converts it into an angle-reading type telescope.... the micrometers read directly to one second of arc over a range of 50 seconds at infinity only. Maximum usable distance for auto-collimation is approx 30 feet. Infinity setting on focusing knob approx 17 feet.\"This brief description is perhaps confusing, so I\'ll offer few words of explanation & caution:First, one must fit the alignment scope with an auto-collimation lamp such as #71-5511 and use it as an auto-collimator at infinity-focus to sense the tilt of plane-mirror targets. The micrometer drums (+/- 0.050\" range) cannot measure tilt at infinity; they measure lateral displacement at finite/near ranges only. Introducing this item fools the telescope... it has a weak negative lens which requires re-focusing of the scope to a 17-foot range to see targets at infinity (and maintain auto-collimation). What\'s special about 17 feet? It\'s actually 206 and 1/4 inches... a distance at which 1 mil (0.001\") on the micrometer drum is equal to 1 arc-second. How clever! FYI, here\'s the math... recall that there are 206265 arc-seconds in one radian. So, 1 part in 206265 is equal to 1 arc-second; so 1 mil in 206.265 inches is equal to 1 arc-second. The micrometer drums are graduated in mils. Ta-da!By-note: the maximum usable distance (cited as 30 ft) is dictated by one\'s ability to see the return reticle image in auto-collimation. This is dictated by the size and reflectivity of the mirror target, and the intensity of the light source; has nothing to do with this accessory.
Some dimensions of this item are:outside diameter: 2 and 1/2 inches,Height (length): 1 and 5/8ths inches,Clear aperture: about 1 and 3/4 inches,Weight: 11 ounces.
Thanks for looking.
