Gravitational eccentric correction optics (GECO): an optical-gravitational device to compensate for flexures in astronomical spectrographs.
Mechanical flexure is a source of major failures in astronomical spectrographs, for which the reimaging of a focal-plane pinhole has to be maintained in position within a fraction of a CCD pixel that has dimensions of the order of 15 microm. The d.o.lo.res. (an acronym for device optimized for low resolution) spectrograph for the Italian national telescope, Galileo, showed displacements of the image of the pinhole more than 10 times greater than expected. The mechanical failure was overcome by the insertion of a passive optical wedge that can add an out-of-phase circle to the flexure ellipse. The results encourage the use of the gravitational eccentric correction optics (GECO) optical-gravitational device in all astronomical observations made with the d.o.lo.res. spectrograph.
Image motion and flexure compensation of the FORS spectrographs
One of the most critical issues in designing a spectrograph is the motion of opto-mechanical components due to flexure especially when it will be mounted to the Cassegrain focus of a telescope. Image motion on the detector has to be kept small in order not to affect the value of the scientific data. The FORS spectrographs fulfil those requirements by a proper design and by a passive compensation of the instrumental flexure. Image motion of the 2 metric tons instrument could be reduced in this way to a tiny fraction of one pixel's size thus not affecting the data gathered with those spectrographs. It is tested and approved at a telescope simulator that all specifications regarding those motions are fully met. A fine tuning flexure compensation is built into the spectrograph's design and is tested on its tuning range which allows to adapt the compensation to effects eventually caused by the Cassegrain flange of the telescope.
On the ontology of particle mass and energy in special relativity
Einstein claimed that the fundamental dynamical insight of special relativity was the equivalence of mass and energy. I disagree. Not only are mass and energy not equivalent (whatever exactly that means) but talk of such equivalence obscures the real dynamical insight of special relativity, which concerns the nature of 4-forces and interactions more generally. In this paper I present and defend a new ontology of special relativistic particle dynamics that makes this insight perspicuous and I explain how alleged cases of mass–energy conversion can be accommodated within that ontology.