Note: Autocollimation with ultra-high resolution and stability using telephoto objective together with optical enlargement and beam drift compensation. 
An autocollimation (AC) setup with ultra-high resolution and stability for micro-angle measurement is presented.  The telephoto objective, which is characterized in long focal length at a compact structure size, and the optical enlargement unit, which can magnify the image displacement to improve its measurement resolution and accuracy, are used to obtain an ultra-high measurement resolution of the AC.  The common-path beam drift compensation is used to suppress the drift of measurement results, which is evident in the high-resolution AC, thus to obtain a high measurement stability.  Experimental results indicate that an effective resolution of better than 0.0005 arc sec (2.42 nrad) over a measurement range of ±30 arc sec and a 2-h stability of 0.0061 arc sec (29.57 nrad) can be achieved.