OPG offers a PTB traceable 1” diameter window with an approximate 30 arc minute wedge measured for exact value to better than 1 arc second on a Trioptics PrismMaster and a Certificate of that measurement. The window is used to calibrate the PSM detector to change to distance, measured in μm between the reflected spots from the front and rear surfaces of the uncoated window into minutes and seconds of arc.

The package includes an unmounted 25.4 mm diameter by 5 mm thick N-BK7 window with an approximate wedge between the surfaces of 30 arc minutes packaged in a clean room compatible box, a Certificate with the precise measured value of the wedge angle to less than 1 second of arc and a Certificate of Conformance. The package is priced at $460 plus $40 shipping and handling.

In the early days of the PSM there was only one camera available so it was easy to have an internal calibration to change the distance measured on the video screen converted into minutes and seconds of arc. With the variety of camera format now available it is no longer possible to assure the conversion from distance to angle, particularly when some customers change cameras as the technology improves.

We now use the Certified wedge to make the conversion from the μm shown on the screen to angle by simply placing the wedge in front of the PSM with no objective so there is collimated light coming from the objective port, and recording the distance between the spots reflected from the front and rear surfaces of the wedge. The angle, α, between the 2 spots is equal to 2*β*n where β is the angle of the wedge on the Certificate and n is the index of the N-BK7 at 636 nm, the wavelength of the PSM laser diode, 1.515.

For occasional measurements of angle, it is easier just to use the ratio of μm to angle using the wedge. For extended use of the PSM for angle measurement, the Calibration Factor on the Cal Tab can be adjusted so the μm reading converts directly into seconds or minutes of arc.

Disclaimer: All specifications and prices are subject to change.