Allow me to quote gravano:
“Place the camera in a way that it doesnt create a glare or use acrylic that doesnt glare hotspots or use a different projector that doesnt create hotspots or use an ir filter”.
I know this has been discussed before, but I just wanna clarify a few points, since this glare thing has been annoying me a lot:
- Camera placing
To avoid the glare, the camera would have to be angled, resulting in a distorted (trapezoidal) captured image. Isn’t that a problem?
- Special Acrylic
Never seen it. I would assume any clear smooth acrylic would create a hotspot.
- Different projector
This is probably a promissing direction, since my projector seem to emit a lot of IR (it’s an LCD based Sony VPL-ES1). Should I go for LED ou normal DLP? LED has the advantages of shorter throw distance, lower IR emission and cooler operation (important for a boxed setup). On the other hand, it’s produces less brightness and I’ve seen someone relating short throw distance with high latency, creating a responsiveness issue.
- IR filter
Yeah, I’m probably going for a bandpass filter as well, but I do have a doubt: I’ll be probably using SFH485Ps, which have a reported 80 nm spectral bandwidth. Should I go for a filter with an FWHM of 10 nm (less IR polution) or 40 nm (potentially brighter blobs)?
I hope your experiences can help me shed some light on those matters. Tks.
Take care.
hey… i faced the same problems when i began work on my multitouch...so i’ll try to explain them from the best of my understanding…
~ firstly… the distortion on the cam due to angled placement is not much of an issue unless the distortion is major.. (anything around 10-15 degrees shud be fine) cause u’ll be running the configapp.exe to calibrate the table and projection before you move on to the apps… so that would take care of the trapezoidal distortion… look up the wiki for tutorials on how to calibrate the cam using configapp.exe. i am personally using a setup with inverted projector and cam looking at angled mirrors at the base of the box. works just fine and the distortion in the image recieved from the cam is minimal (not more than 5-8 degree app)
~secondly.... even i dont know of any special acrylic… but what i am using in my setup is a layer of frosted 3M sticker that acts as mild diffuser and has grains that distribute the glare spot… and layer of garware drafting film… the film is milky white and has a matte finish on one side and glossy on the other… the glossy side is facing downwards… this cuts out major glare by reflecting it back…
~projector… well this surely helps in cutting down hotspots ...sepically when u’re projecting a white surface… i use a toshiba projector with almost no ir dessipation… well the problem of low brighness in a short throw led projector would be a major issue… it’ll restrict you to use the table in controlled light conditions. another option would be to use the projector inverted downwards placed at the edge of the table… (design considerations will have to be made for the table to make it not look popping out of the table) the projection being reflected using a mirror.... its also a possibilty (havent tried it but thought of it) to use a anti glare film on the mirror at the base of the box.... it just might cut down some galre and it is a better and cheaper option to apply film on a 1/4th size mirror than the full surface.
~ i am not really sure bout the bandpass filters… i am personally using 5 layers of 80% sun block film (ones’ used in tinting window glasses in buildings) on a sony dv handycam with night vision on.
I have a bandpass filter and I’m getting an infrared mirror (or hot mirror) for my projector. The idea is to put the infrared mirroring filter facing the bulb just in front/on top of the projector lens. RGB light will come through while infrared light will be blocked, hopefully eliminating my projector hotspot! Still waiting for it to arrive to confirm if it works. I just get a little glare/hotspot from the core of the bulb. It’s due to my projector pointing directly at the surface (projector is perpendicular to surface). Like others said, it can be fixed by angling the projector and modifying your keystone parameters. Thorlabs sells both bandpass filters and hot mirrors. After having spent $80 on a bandpass filter I lucked out and found a Tiffen Hot Mirror for $15 on ebay. It may not be as good as the Thorlabs one (haven’t found specs) but it’s worth a try for the price difference.
Great info up there, deej. Thanks, man. I’ll look into some of your solutions.
And Cirrus, what is the spectral bandwidth of your bandpass filter? I’m definitely getting one, but still not sure if I should go for a narrower (+-10 nm) or wider (+-40 nm) one.
And about the hot mirror, I’ll be looking forward to your results. I tried to get one, but the Rosco representative I have contact with suggested me the Thermashield, which is some kind of thick film that reflects infrared energy. It is considerably cheaper than the hot mirror, but I was a little disappointed with the results. Although some of the IR pollution coming out of the projector was removed, most of the hotspot is still there. I wonder if the hot mirror would do a better job.
Take care.
I got a narrow +-10 just because it was a little cheaper but in hindsight the +-40 should do the trick and improve camera response. I may order a 40 one in the future. Still waiting on the hot mirror...The specs for the Thorlabs hot mirror are really good.
Yeah, just saw those hot mirrors from Thorlabs. They do look good judging by the specs.
But there’s a catch: the biggest one I found has a diameter of only 2”, which is about the diameter of my projector lens hole (the lens sits inside the case). I’m afraid it could be dangerous to place the filter right atop the opening, because it would reflect IR light (heat) back to the projector lens, potentially creating a heat bomb.
That’s why I first tried the Thermashield, since it’s about 30 x 30 cm thus allowing it to be placed at a good distance from the projector.
How are you planning to overcome that issue? Or am I a little paranoid?
You know I hadn’t considered that, but you’re right the hot mirror will reflect the entire infrared spectrum. My projector doesn’t emit that much IR so it may not be an issue (but then again I’ve only been looking at NIR). I think it would take a really long time for it to actually harm the projector but it would be worthwhile to hear someone’s opinion who has a little more experience or knowledge about IR. I’ll do some tests when the mirror gets here. Worse case I’ll have some nice pictures of a molten projector
I am using a thorlabs bandpass filter and have no problems with hotspots anymore…
I orderd two versions, the 10 - and 40 nm width. The unibrain color doesn´t work
to well with the 10nm one, because two much light gets swallowed. The 40nm works nicely.
I also have the firefly MV, which is a lot more sensitive to ir light, I can use the 10nm filter
on that one without a problem…
What projector are you using, Tim?
And is your Firefly MV the BW version?
In case of using this camera, would you say the 10 nm is definitely a better choice?
Ok, too many questions…
Thanks heaps.
these are the ones I use, and they work pretty well. I would use the 40nm wide one, its a bit “safer” than the 10nm one.
Also depends on your camera though…
You have to choose the same wavelength as your Illuminators are, so if you have 880nm Illuminators, get the 880nm bandpassfilter..
@GFantini
I have an panasonic AX-100, which is really nice because it has lensshift (easier to setup), and also that 3m short throw projector
I am using the B/W version of the firefly MV
I am not to sure about the 10nm Filter anymore, it also depends on the kind of lens you are using, especially wide angle lenses are more
difficult to work with. So I am back to using the 40nm one with a 3.6mm lens. But if you are using a 5-8mm lens, 10nm might be good.
To play it safe, I would use the 40nm instead..
Thanks for the reply Tim.
If I am trying to block the hot spot using a bandpass filter isn’t the wave length of the IR coming from the projector more relevant than the illuminators?
Apologies if I’m being stupid, I’m looking for a filter to put directly in front of the projector lens.
Seeper, I think Tim was talking about the bandpass filter that would go over the camera. Putting a bandpass filter over the camera has really helped my setup and made the projector glare about 1/5 of what it was. There is still a tiny glare though about the size of a small finger. I was thinking of trying to put IR blocking film in front of the projector to see if that’ll cut the IR from the projector out; I haven’t tested this so it just depends whether it’ll affect the projected image or not.
If you’re looking for a filter for the projector you would want to look for a an IR cut filter that starts cutting IR as low as possible. So an IR cut filter starting at 800nm would be good and it should cut most IR out.
Well, I guess I just went the safest route: got both the 10 and 40nm filters. Checking out which works best myself.
I also got the PK20 led projector for a number of reasons: low IR emittance, cooler operation, small size, short throw distance, low cost and long lamp life. And regarding its low brightness, it shouldn’t be such an issue, since my table is only about 50 x 35 cm and will be mostly used in low ambient light (FTIR works best at this scenario anyway).
Thanks a lot for the advices, Tim (and rest of the guys). It surely has helped. I’ll post results when I get the parts.
Thanks cerupat I thought Tim was talking about the camera. I have a bandpass filter and film negative on my camera still got the hot spot.
Now time for a hot mirror in front of the projector I think. Anybody knows any competitive UK suppliers?
