We are working on a design for a variable f-ratio telescope simulator to aid in testing new instruments in the lab prior to telescope commissioning. We are looking for partners to join with us to reduce costs for the optics etc, for example two sets of optics costs only 1.5x one set hence each is a lot cheaper. If we get 3-4 sets then we all pay maybe 30% of the original price. the details are given below in case you are interested in such a unit. =========================================================================== At the La Palma observatory we are working on the design of a Cassegrain telescope simulator for testing instruments. During this work we realized that a) It is possible to design a simulator which gives diffraction limited images over a 60mm diameter field of view over most of the range 330nm to 2.3mu. b) The optics can be used to simulate most astronomical cassegrain telescopes in the world. As we expect that other Observatories could have use of a simulator, it is obvious to ask if anyone out there is interested in joining. The discount when ordering more than one set of optics is very significant. The general layout of our system is as follows: A) An integrating sphere with a set of lamps. B) One or two filter wheels. C) Illumination optics for illumination of object plane. D) Object plane where masks and slits can be mounted. E) Field flattener for adapting simulator to individual telescopes (optional). F) Collimating lens (diameter ~50mm) G) A parallel beam space - here goes the stop for your telescope. H) Telecentric focusing lens with back focal distance of ~300mm (diam. ~100mm). The optics we are referring to here only concerns F) and H). The specks of the current base line design is: 1) F-ratios down to F8 (Will also work with F7 at reduced field). 2) Field of 60mm diameter. 3) Back focal distance of 300mm. 4) Exit pupil distance from 5m to infinity. 5) Wavelength range from 330nm to 2.3mu. 6) Magnification of 0.666. 7) Diffraction limited (Strehl ratio > 0.8) on axis for all wavelengths. 8) Diffraction limited at 400nm and out at F8 for the whole field. The reason why a (near) telecentric lens is needed is that the exit pupil is far away in a cassegrain telescope (a bit beoynd the secondary mirror - a telecentric lens has the exit pupil at infinity). This is essential for testing IR instruments, where the pupil must coincide with the cold stop. The wide wavelength range is achieved by using a combination of 5 materials in the collimating lens. In this way we can use the large and more expensive telecentric lens for testing both optical and near-IR instruments. Optics matching these specks are not available comercially and must be ordered as custom optics. The system is good enough to test the image quality at all wavelengths (aberrations, tilt of focal plane, detector resolution etc. etc.). There is some residual colour, notably below 450nm, implying that narrow band filters should be used here, when testing image quality. For Cassegrain telescopes (non Richey-Chretien) a coma plate may be introduced (not yet investigated). We are still at the point where adaptions could be made to make the optics comply with the requirements of your telescope. We intend to put more info on the web, once the design has progressed to a more final stage. We will aim at a cost for the optics of around 5000 USD and are at the moment trying to adapt the design accordingly (ellimination of flurides in the collimating lens - at the cost of IR coverage). If you are interested you may contact either of Michael Andersen andersen@not.iac.es Mariet Broxterman mbrox@ing.iac.es Colin Aspin caa@not.iac.es