2 of 2
2
Spectral Analysis of IR LEDs and Filters
Posted: 19 January 2010 07:56 AM   [ Ignore ]   [ # 16 ]
Avatar
Rank
Joined  2008-12-04
Total Posts:  20
New Member

I got my interference filter today and I did some comparions on my FTIR-screen. I’m using a PS3-EYE and 940nm-LED’s. The interference-filter clearly gives the best results. I haven’t observed any frequency-shifts so far…

Image Attachments
comparison_chart.jpg
 Signature 

/* no comment */

Profile
 
 
Posted: 19 January 2010 04:31 PM   [ Ignore ]   [ # 17 ]
Rank
Joined  2009-12-15
Total Posts:  3
New Member

Just wanted to share - we are getting pretty good results with RG-830 glass-based longpass filter (NT32-758 at Edmund Optics) and Environmental Lights 850nm LEDs. Transmission uniformity at varying angles was a consideration for us, because we use a fisheye lens. Image is better now (and much less software processing is needed), there is a hotspot from projector, but we plan on using a different projector with a mirror.

Profile
 
 
Posted: 04 February 2010 06:22 PM   [ Ignore ]   [ # 18 ]
Avatar
Rank
Joined  2009-12-29
Total Posts:  27
New Member

a piece of green transparent acrylic and red transparent acrylic work phenominally well as an IR filter.  Better than a piece of exposed negative film.  pictures soon.  I bought 2” square samples for a dollar at a local plastics store.  No need for an expensive IR lens.  Really.

Profile
 
 
Posted: 06 February 2010 10:33 AM   [ Ignore ]   [ # 19 ]
Rank
Joined  2009-11-09
Total Posts:  13
New Member
Flyingpumpkin - 04 February 2010 06:22 PM

a piece of green transparent acrylic and red transparent acrylic work phenominally well as an IR filter.  Better than a piece of exposed negative film.  pictures soon.  I bought 2” square samples for a dollar at a local plastics store.  No need for an expensive IR lens.  Really.

Awesome! how thick were the acrylic? is the order (green first then red?) important? Possible to post some pics on how you fit them to your cam? I have most of the parts ready except for the filter.  :(

Would love to try this out.  Thanks for sharing.  smile

Profile
 
 
Posted: 13 February 2010 04:23 PM   [ Ignore ]   [ # 20 ]
Avatar
Rank
Joined  2009-12-29
Total Posts:  27
New Member

The order does not matter.  I bought 1/8” thick samples (a dollar a piece) at the local plastics store (canal plastics in NYC but I’m sure any place has this stuff).  Any thickness will do, going thicker is no advantage.
also, theatrical lighting gels are pretty good too and they are as thin as a piece of transparency film.  I added in a piece of blue but it didn’t make much difference.  the green covers the same range as the blue it seems.  Then the red filter blocks out the rest.

Profile
 
 
Posted: 28 February 2011 01:24 PM   [ Ignore ]   [ # 21 ]
Rank
Joined  2008-02-11
Total Posts:  33
Moderator

We have been doing a bit of testing to create a larger scale bandpass filter.
Some of the materials we have tested combine to make an excellent bandpass filter @ 850nm.

get a small sample of this:
http://www.eplastics.com/Plastic/Plexiglass_Acrylic_Sheet_Infrared_Transmitting/ACRY11460-125IRT24X48

to block out all visible light up to 750nm.

Then apply a piece of 3m P70 prestige to the back acrylic to block out Near IR from 900nm onwards.
http://solutions.3m.com/wps/portal/3M/en_US/Window_Film/Solutions/Markets-Products/Residential/Sun_Control_Window_Films/Prestige_Series/

These materials have the combined effect of creating an excellent band pass filter of 80nm wide with a peak @ 850nm. Plus they are relatively cheap or free if you just use samples to construct a camera filter.

 Signature 

Gestureworks
OpenExhibits

Profile
 
 
   
2 of 2
2