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One Eyed Hopeful

Joined: Sat Jun 02, 2007 1:07 pm
Posts: 11
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Has anyone tried Infitec out? I was thinking of doing a two projector setup and am debating on either polarized lenses or Infitec. Any suggestions on what to go with?

Tue Jun 05, 2007 11:27 pm
One Eyed Hopeful

Joined: Wed May 02, 2007 12:17 am
Posts: 32
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Hey Leftler,

I haven't tried infitec but I did a bit of research into it to see how much it would cost etc. Advantages Disadvantages. As far as I can tell the technology is tightly controlled by Infitec Gmbh in germany. They are the only ones who can provide you with an interference filter to meet the requirements.

If you wanted to build your own interference filter it could end up costing a lot of money. Alternatively Infitec Gmbh will only provide a complete solution. This involves you sending them two projectors into which they will put two filters and calibrate a hardware color correction computer. This was quoted at it's absolute cheapest to be more than 2500 euro's assuming I provided everything else. Since I was interested in this more as a DIY end user it was not quite cheap enough.

I guess this leaves one with one option. to buy a pack of Infitec glasses cut one in half and use it for the projection filter... I have never actually handled a pair of infitec glasses so I don't know if the heat from a projector would damage the glasses. Anyways It's an option. One could also attempt to construct ones own infitec filters using a combination of holographic bandstop filters.

I don't know how much you know about interference technology works but basically it allows a certain band of frequencies to pass and blocks others. I'm not too familiar with my color frequency bands so bear with me as I explain the principle.

filter 1: allows 425-437, 455-467, 485-497
filter 2: allows 442-455, 472-485, 502-515

I know these numbers are not correct but it does show that the frequency spectrum of the lights do not directly overlap.

Let us proceed to look at the color frequency spectrum of an LCD projector. Every projector will have a different color spectrum this is why infitec works better on some projectors than others.

lcd transmission spectrum: 433-448, 463-478, 493-508

similarly one must also consider the actual light spectrum being generated from the light source.

ex) natural sun light: 300-700
proj light) for simplicity sake we will assume it is masked on all sides by the filter spectrum of the LCD. However often IR light is let through projection systems to reduce unnecessarily trapping heat inside.
431-450, 461-480, 491-510

So what you are left is a very sensitive overlap of the transmission spectrum which reduces the light through put drastically.

eye 1: 433-437, 463-467, 493-497
eye 2: 442-448, 472-478, 502-508

This means that if the projector is a 2000 lumen lcd projector (not sure how lumens are measured) I would expect the light output to reach each eye to be computed as follows.

((437-433)+(467-463)+(497-493))/((450-431)+(480-461)+(510-491)) * 2000 = 421 lumens

This however assumes that each subcomponent of each eyes frequency spectrum is transmitted in it's entirity. As far as I know from holographic bandstop filters each color would allow at best 85% transmission of other colors whilst blocking the desired color. By simply multiplying this out we would get 0.85*0.85*0.85=0.614125 this means at best 61% of the light that is not filtered out actually makes it through the filter. Now how many filters are there between us and each projector 2. so lets square that. 0.614125*0.614125 = 0.377149515625. So thats closer to 38%. So take the original lumens per eye and multiply by this factor and we get.

158 lumens

I realize this is only an example and not correct at all. But I think it illustrates one issue with infitec. Light efficiency is really not that optimal and you need a strong projector to make the most of it. By comparison a properly tuned polarized projector setup would allow closer to 900 lumens to each eye I would expect.

The final downside of Infitec would be the reduced color spectrum available. As far as I can tell this is compensated for using color correction hardware which reduces the available colors to be the same for each eye. I'm not entirely sure how this works. Without any color correction hardware one would expect to see one image that was slightly more blue and one image that was slightly more red.

One benefit of infitec is virtually no ghosting when a user tips his head. For single screen viewing this would not seem like such a big deal to me and you can position yourself in front of the screen to see it. For multi projector setup however infitec has a distinct advantage as it would facilitate cave type situations where polarization would not.
Another benefit of infitec is no silver screen!!

I am not entirely sure about anything I have said here but this is just my understanding. I am more than open to any corrections any one else may have with regards to how this works as it might shed some positively light on the matter.

Wed Jun 06, 2007 6:19 am
One Eyed Hopeful

Joined: Sat Jun 02, 2007 1:07 pm
Posts: 11
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Thanks for the info, that helps a lot.

Also if you are curious, I remember what a lumen is from High School Science.

The brightness 1 candle will project on to a 1 meter square at 1 meter away.

Thu Jun 07, 2007 2:29 pm
Binocular Vision CONFIRMED!

Joined: Thu Jun 07, 2007 2:29 pm
Posts: 258
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That seems not really true. And it would be very subjective to types of "candles".

Quote from wiki:
"If a light source emits one candela of luminous intensity into a solid angle of one steradian, the total luminous flux emitted into that solid angle is one lumen."

That seems at least better defined.

But perhaps Wiki is wrong (impossible!) :)

ps: maybe your definition is a rather close approximation? Don't feel like calculating it really..

Thu Jun 07, 2007 2:49 pm
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