Need some advice to find a filter that blocks visible spectrum - Page 1
Forum section: electronics / repair

author: gg64
author_rank: Regular Contributor
timestamp: April 27, 2019, 12:04:17 pm
content: Need some advice to find a filter that blocks visible spectrum ?Hello internet,I need to take a picture of some intruders coming at our place (on a regular basis?), to allegedly steal diesel fuel.Anyway we bought a camera like this one (fivanus camera digital trail camera):https://www.amazon.fr/Fivanus-Surveillance-Imperm%C3%A9able-Photographique-Infrarouge/dp/B01MYV86K9/ref=cm_cr_arp_d_product_top?ie=UTF8Basically it is a "hunting" camera meant to take picture of animals.But the IR flash got a visible component when it works in the dark. Plus it make noise but my main concern is the visible part.I would address eventually the noise issue once (probably a relay inside it) once I fixed the dim light from it.Where could I find a filter that blocks visible spectrum ?I found some things but I would like to get some wise advice.Have a good day.

author: duak
author_rank: Super Contributor
timestamp: April 27, 2019, 05:50:15 pm
content: A Wratten 87 IR filter blocks visible light but is usually quite expensive. Photographic or movie supply shops often have large pieces of filter material called gels that could be combined to block visible light. I can't recommend anything because I don't know what you have available.A piece of unexposed but developed photographic color slide or reversal film passes IR and blocks visible light. Examples of this are Agfachrome, Fujichrome or Ektachrome. seehttps://en.wikipedia.org/wiki/Reversal_filmhttp://www.photocritic.org/articles/create-your-own-ir-pass-filterI understand that exposed and developed color print film also works but I do not have any experience with it.

author: Stray Electron
author_rank: Super Contributor
timestamp: April 27, 2019, 06:22:48 pm
content: Whatever filter you use needs to be matched to the camera or other viewing device that you're using so you need to first decide what kind of camera or viewer that you're going to use and find out what wavelengths it is sensitive to. The wavelength will also determine what kind of illumination you need to use.FWIW a visible light source shoulddiscouragethieves more than a non-visible one. OTOH if you're goal is the lure them in and then catch them in the act then a non-visible source would be best.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 28, 2019, 03:30:13 am
content: Presumably it makes a faint red light? This is typical of the NIR LEDs used for IR cameras. I assume it is just the tail end of the emissions spectrum being in the region eyes are barely sensitive.A pack of gels is a good place to start. You might find one that blocks the red but lets enough IR for the camera to function.If the light is as dim as the security cameras I have seen, another option would be to use a diffuser. In the ones I have seen you can basically only see the red if you can look right at the LEDs. Any diffusing or scattering that spreads out the source would drop it below the detection threshold.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 28, 2019, 04:24:27 am
content: Another option would be to bypass the flash altogether. I have made a flood for my security system using slightly longer wavelength IREDs which are totally invisible to me, unlike the faint red glow from the lights built into the camera. The camera has a somewhat lower response to these IREDs but it works.Assuming that your game camera has a shutter also the flood concept makes it really simple, just leave it on all the time. If you can't afford the power drain you can just substitute the flood for the flash.

author: soldar
author_rank: Super Contributor
timestamp: April 28, 2019, 08:23:38 am
content: Quote from: ejeffrey on April 28, 2019, 03:30:13 amI agree. In my security system I have cameras with those NIR LEDs and I also have plain illuminators, just the LEDs and no camera. If you put several illuminators with filters to diffuse the light they will be barely visible if at all and will provide very good illumination.Search ebay for "IR security illuminator" and you will find plenty at very low prices. Then just stick a filter in front.

author: Heartbreaker
author_rank: Unknown
timestamp: April 28, 2019, 09:30:42 pm
content: You could try experiment with multiple layers of black plastic bags. I used such bags several years ago, when I modified a camera in a Nokia 6230i by removing (breaking) the IR filter and installer two layers of plastic bags above the sensor and it worked flawlessly in near IR light. Today a random sample from the kitchen drawer looks very transparent to my Flir - YMMV.One word of warning if someone would try to reproducere my results - don’t. I burned through more than a handfull of cameraes before I got one working despite I knew what it looked like on the inside and I had the equipment to do so. The camara housing is ultrasonic welded and the chip is bonded right next to the outer wall of the housing. My problem was large enough to justefy the materiale and time spend, though.

author: gg64
author_rank: Regular Contributor
timestamp: April 28, 2019, 10:07:39 pm
content: Thank you guys for the replies.I will try and test the plastic bag see from there.And btw I just need to cover the LEDs not the CCD chip, just the IR emiter.

author: anewmanx
author_rank: Contributor
timestamp: April 28, 2019, 10:54:56 pm
content: Leave a barrel out marked diesel that has sugar mixed into it.

author: gg64
author_rank: Regular Contributor
timestamp: May 07, 2019, 11:15:42 am
content: Hey,I tried garbage bag it works but dims the IR flash a little, I need to find the sweet spot (configuration wise, near, middle and far).But this looks really promising.