New Assembly of LF Objective
After the first six months of commissiong of NICS, we recognize the necessity of a new mechanics for the lens of LF camera objective.
At end of February the camera was brought back to the IR Lab at Arcetri observatory and the mechanical assembly of the LF was thoroughly revised by P. Stefanini, especially improving the parallelism between the reference planes of the lens holders. New features are added to the system: a new holding system of the lens close to the detector (lens #4) and the adjustment of positions of the lens #2 and #3.
After these mechanical revisions we planned to test the camera in conditions of operativity, putting it in a dewar used for test and controlling alignment by interference of laser beam reflected at the surfaces of the lenses.
The arrangement of the experiment is showed in the next pictures:
In the following images we reported the thermal history of the systems and the variation of the interference pattern during the cooling (the only adjustment made is a shift of the optical axis, by a total of about 0.75 mm, following the contraction of the cold plate that support the LF camera).
|Pattern od interference at room temperature. The saturated points are due to the strong reflection of dewar window (right of center) and of last surface of lens #4 (center of the pattern). All systems of fringes are centered except for a very weak one that is centered in the high side of the figure (about at half way between centre and edge).|
|Pattern at about 200 K after a shift of 0.5 mm of the optical axis.|
|Pattern at about 150 K.|
|Pattern at 100 K after another shift of 0.25 mm|
|Pattern after 10 hours at 80 K (to be sure of uniformity of temperature in all parts of systems. We don't see any change in alignment of the various systems of fringe. The test is successfully passed!|