A new echelle-mode grism combination, grisms 13+10, has been commissioned, to give medium resolution (R=4000) in the blue end of the optical spectrum. Grism 13 is normally used with an order sorting filter in 3rd order, but can also be used with a cross-disperser. Grisms 13+10 give a good alternative for grisms 9+10, as spacial overlap is not a problem for this new combination. For medium-resolution spectroscopy bluer than 4250Å this option is preferred over grisms 9+10. The orders of grism 13 are too long for the chip: the total wavelength coverage is 3350-3610 (5th order), 3720-4430, 4770-5830, 7020-8660 (2nd order). See
http://www.not.iac.es/new/technical/astronomical/instruments/alfosc/grisms/
Four cut-on filters (GG420, GG475, OG515, OG570) have been purchased which are needed for optimal use of the red part of the various wavelength regions offered by the grisms. These filters have been tested and documented, and can be requested for use. See
http://www.not.iac.es/technical/astronomical/instruments/alfosc/blockers.html