http://tech.groups.yahoo.com/group/Astroimaging_filters/ Astroimaging Filters Wed, 18 Nov 2009 13:06:49 GMT Lawrence D. Lopez http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2071 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2071 Their were these laser scanners that computer identics was making. They had some filters made up. They worked fine straight ahead but off axis they would Tue, 27 Oct 2009 14:22:52 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2070 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2070 Hi, this filter will be returned for refund. I did an out-of-bandpass transmission test, 190-950nm. The file can be seen if file folder Filter tests, file Mon, 26 Oct 2009 23:20:54 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2069 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2069 Hi, I just couldn't resist the purchase of a $119 Omega 2" Hb filter sold on eBay. This filter is from a lot of 10, I purchased the first one, nine remain. Tue, 20 Oct 2009 22:51:58 GMT Richard Crisp http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2068 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2068 Of course that is only an approximation; not all rays have the same angle on the filter. the on-axis rays are perpendicular the chief ray angle for a extreme Tue, 20 Oct 2009 19:50:01 GMT Wolfgang Renz http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2067 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2067 Re: filters shifts to the red to compensate for fast optical systems ... If a NB filter has a flat top, the transmission profile is placed in a way that the Tue, 20 Oct 2009 17:57:23 GMT Richard Crisp http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2066 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2066 I don't know how that works: not all of the light rays are angled.... Astrodon says lots of things including things that are mutually contradictory; depending Tue, 20 Oct 2009 17:39:16 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2065 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2065 Hi Richard, I noticed that AstroDon says he shifts his filters somewhat to the red to compensate for fast optical systems. He claims that other manufacturers Tue, 20 Oct 2009 17:13:30 GMT Richard Crisp http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2064 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2064 mine has a 4.5nm stated bandpass I have used it with success on M57, M27, NGC7635 and M42 I plan to try with Thor's Helmet when it comes into position I had no Tue, 20 Oct 2009 16:48:05 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2063 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2063 Hi Richard, I have been doing a little reading where gas being expelled from Wolf-Rayet stars can exceed ~4000 km/s. That could cause a spectral shift of Fri, 16 Oct 2009 17:31:19 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2062 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2062 Hi, a week or so ago I was searching eBay for astronomy filters and saw a 37.5mm mounted Omega NIR 809nm filter that looked narrowband and only cost $37 + $5 Tue, 13 Oct 2009 18:44:11 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2061 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2061 Hi Richard, while my skies are cloudy, I have been able to image terrestrial objects ~2+ miles away. Even with a 1% ND filter in series with the Thorlabs 470nm Tue, 13 Oct 2009 17:38:06 GMT Richard Crisp http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2060 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2060 two comments: these low cost filters are often designed for creating monochromatic light rather than for imaging. To be useful for imaging there is a substrate Tue, 13 Oct 2009 15:35:57 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2059 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2059 Hi, I have tested the 1" Thorlabs 470nm 10nm (HeII) fitler. The chart can be seen in file folder Filter tests, file Thorlabs_HeII.xls. Notice that the filter Thu, 08 Oct 2009 21:43:09 GMT Richard Crisp http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2058 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2058 4.5nm ... From: ssb73q To: Astroimaging_filters@yahoogroups.com Sent: Thursday, October 08, 2009 12:07 PM Subject: [Astroimaging_filters] Re: Anybody here Thu, 08 Oct 2009 19:07:10 GMT ssb73q http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2057 http://tech.groups.yahoo.com/group/Astroimaging_filters/message/2057 Hi Richard, one additional thought. What is the bandpass of your HeII filter? Gas maybe being expelled from the Wolf so fast that your narrow bandpass HeII