Posted by Richard Miles at 18:11 on 2013 Jul 29
Hi Eliot,Good to meet you at the BAA Exhibition in Manchester.There is only one V passband – that corresponding to the Johnson-V one. It is sometimes called the Vj passband.Nowadays you have the choice of having either the coloured glass one, which is a sandwich of discrete elements originally put forward my Mike Bessell, which are cemented together and mimics the original Johnson filter or a ‘dichroic’ version which comprises an optically flat piece of glass onto which very thin films of various thickness/composition are evaporated which then transmits the Johnson passband range.The coloured glass version should be coated to protect it from oxidising/hydrolysing in moist air, or sandwiched between plates of silica glass or the equivalent. As well as Astrodon, I see a company called Horiba Scientific do these:http://www.horiba.com/uk/scientific/products/optical-filters/optical-filters-by-application/optical-filters-astronomy/?gclid=CKnTw96V1bgCFYOWtAod6ngAmwbut careful – they are not protected and the BG12 component will degrade after a few years unless kept dry.US-based Optec Inc. do various V filters but are pricey:http://www.optecinc.com/astronomy/prices/astronomy_price_list.pdfRichard