Andrea B. Posted August 17, 2017 Share Posted August 17, 2017 We really need one.Could we get some optical company to manufacture a dichroic IR blocker to stack over our "leaky" dual bandpass filters?Is there some IR-blocking coating we can buy? Let's research this. Link to comment
Cadmium Posted August 17, 2017 Share Posted August 17, 2017 It would need to be dichroic, other than that I don't think anything like that exists.That is the idea of stacking with BG type glass (which includes S8612),but if the 'leak' of the 'dual band' is in the visual range then BG will not stop it (by 'dual band' I think you are referring to 'UV bandpass', is what Schott calls those).So if you find a dichroic filter that passes UV and blocks visual and IR, then there might be little point in stacking when you can do the whole job with a dichroic filter that cuts all visual and IR, like the Baader U and others. Link to comment
Andy Perrin Posted August 17, 2017 Share Posted August 17, 2017 So if you find a dichroic filter that passes UV and blocks visual and IR, then there might be little point in stacking when you can do the whole job with a dichroic filter that cuts all visual and IR, like the Baader U and others. I thought she had in mind that 308nm bandpass that JMC was fiddling with? It would indeed be nice to have it all in one filter, but those kind of specialty filters often have poor blocking in IR, etc. However another issue with having multiple stacked dichroics is that it seems like that would be positively begging for hotspots! Link to comment
OlDoinyo Posted August 18, 2017 Share Posted August 18, 2017 Dichroic filters are subject to angle artifacts (colored rings and bulls-eye) especially with wider angle optics. If you are using a telephoto lens, this should be less of a concern. The MidOpt SP644 http://midopt.com/filters/sp644/ might be something like what you are looking for, but it does cut some UV. Omega Optical's 380SP filter http://www.omegafilters.com/products/filters/shortpass/380sp.html might be closer to a stand-alone solution if it cuts red and IR, but the data supplied do not tell us. Omega also takes orders for custom dichroic filters. I do not know what this would cost. Link to comment
ulf Posted August 18, 2017 Share Posted August 18, 2017 When I follow the link above the Omega Optical's 380SP filter data tell this DETAILED SPECIFICATIONS BLOCKING ≥ OD4 395-475nm ≥ OD2 475-1100nm Not good. Link to comment
Andy Perrin Posted August 18, 2017 Share Posted August 18, 2017 Those wouldn't help with a 308nm (NOT 380nm!) band pass anyway. I did not transpose the digits -- he is interested in UVB. Link to comment
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