I've used something similar, a short piece of rubber hose (the automotive kind), they are pretty matte and black. The only problem would be if you use a long section, it will bend easy, but on short lenghts, it is straight enough. The other advantage is that you can find it in a lot of diameters, and they are real cheap and easy to find. Just my 0.02 Calvin -----Original Message----- From: Mark Willis To: PICLIST@MITVMA.MIT.EDU Date: Sunday, October 11, 1998 9:39 PM Subject: Re: how to filter surounding light >If you use a lens to focus just the light from the area you want to >examine, and use matte black paint inside the focusing assembly (and >keep the lens clean), that should pretty much do it (look into how >astronomers get telescopes to reject surrounding light, basically this >is the same problem on a *very much* smaller scale ) > > Mark, mwillis@nwlink.com > >M van der Bilt wrote: >> >> Hello everybody >> I want to measure reflected light from an object with an photo diode >> but i don't want surrounding light to effect measurement . >> I thought of lighting the object with infrared light pulsed at a certain >> frequentie and detect the signal back and read the detected level. >> My fear is this way is sensitive for noise and i wand a high level >> resolution. >> Are there good filters that pass light at an certain wave length? >> an other way i thought of is to first measure surrounding light then light the >> object with an additional light source measure again and subtract the >> surrounding light from measurement with additional light >> this method has also risks like is the surrounding light changes >> Any body with suggestions or idea to this matter? >> >> Marcel >> Electonic Wokshop Scoop >> Amsterdam >> >> marbel@xs4all.nl