Archived posting to the Leica Users Group, 2007/02/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]There are a multiplicity of IR filters available, each with a different cutoff wavelength. A good web site explaining the differences is: http://maxmax.com/aXRayTechnical.htm The Hoya numbers are related to the cutoff wavelength, but as you can see from the chart at the bottom, the other numbers seem arbitrary (or the reason is lost). Certainly, the longer the cutoff wavelength, the more IR effect you get, and the longer the exposure. Here is an example I took with the Wratten 87 (795 nm), and the Hoya 72 (720 nm): 720 nm: http://gallery.leica-users.org/v/rjrose/IR/L1000503-b.jpg.html 795 nm: http://gallery.leica-users.org/v/rjrose/IR/L1000372-s.jpg.html Note that the 795 nm picture has slightly more contrast, the trees are a bit lighter, etc. I paid much less for the Hoya 72, BTW. I tried gel filters, but I get light flare coming from leaks around the filter holder. I got a 52mm, and use step rings to 46mm and 49mm. You can't use the lens hoods, however. I reformatted the chart from mammax.com, to be a bit more helpful: nm Wratten Hoya M&K 350 18A 620 29 675 70 720 89B 72 735 88 750 88A 780 78 795 87 830 93 850 87C 95 900 90 930 87B 1000 87A 100 1000 Kaya PF4 is 780nm Kaya PF2 is 830nm Kaya PF1 & PF3a is 1000nm Hoya RM72 is 720nm Hoya RM90 is 900nm Hoya RM100 is 1000nm M&K #078 is 780nm M&K #093 is 830nm M&K #095 is 850nm M&K 1000 is 1000nm Wratten 18A is 350nm Wratten 29 is 620nm Wratten 70 is 675nm Wratten 89B is 720nm Wratten 88 is 735nm Wratten 88A is 750nm Wratten 87 is 795nm Wratten 87C is 850nm Wratten 87B is 930nm Wratten 87A is 1000nm