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RSS >  a4tech pk-335MB ir filter?
Volans #1 14/11/2007 - 09h21

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Hallo all, and thank you for this wonderful piece of sotware.
 I tried freetrack 2.1 with a three point cap mount and a A4tech PK-335MB web camera. I bought this camera at 15 euro, and works  very well with freetrack: 28 constant fps and 0-8 jitter.

 However seems to work best with visible light leds, when I tried with ir leds they are seen by the camera very poor, and when I obturated the lens with magnetic disc (from a floppy) camera couldn't see ir leds at all.
 Well, I thought that must be an ir filter somewhere, so I disassembled the camera, but can not find it...at least he didn't popped into my eyes. I searched the net but couldn't find any relevant info.

So, can anyone, please give me a clue? Does this model have an ir filter? If so, where is it, and how can be removed? Thanks in advance.
 If it help, I can post some pictures with camera disassembled.
Volans #2 14/11/2007 - 09h27

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tristan68 #3 14/11/2007 - 10h45

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Hello volans.

On the first picture i see a plastic block on the far right side of the picture. This plastic block screws on the printed circuit board and the lens is screwed in it.

Does this plastic block have a tiny piece of glass in it ?

If yes , then this piece of glass is the IR filter. Just pop it out and reassemble your webcam.

If no , then the ir filter is probably integrated in the lens assembly, and will be much more difficult to extract.


cya
Volans #4 14/11/2007 - 10h57

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thanks for the quick answer. Unfotrunatly that block(cilinder) of plastic is empty, hollow I mean. It is nothing more than a tranzition piece: the base is to be screwed onto camera circuit board and the other end suport the lens assembly....
 So, the ir filter can be incapsulated in the lens cilinder?...this is sad, because the lens capsule is soldered, does not have any screw, so must be cut....
Still, on top of the cmos sensor is a tiny glass piece, very thin, that appears to be glued by the cmos. I think (never saw any cmos sensor untill now) that is placed there for sensor protection, but can be an ir filter?...
Deimos #5 14/11/2007 - 12h40

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The glass piece on the sensor is probably just for its protection.
The filter might be inside the tube holding all the lens, or even on one of them as a coating, not a separate element.
If you look hold the lens against a strong light source, like a window and see that the reflection in the lens has an orange-red hue, it might mean that the IR filter is put directly on the lens - just like in labtec (and  logitech too i think) cameras.
Removing it might be a bit hard, but not impossible, look here:
http://freetrack.online.fr/forum/index.php?showtopic=329

It seems to me that the silver part of the lens casing is glued to the black part, so you might try opening it there, instead of cutting it - if it's been put together somehow, then there must be a way to take it apart without such measures as cutting ;)
Just make sure that you don't lose any of the lens and remember how to put them back when you open it up.

To check where the filter was in my camera, i tried a experiment:
Try connecting the camera to the computer with its lens on, and putting an object illuminated by a strong both visible and IR light source, like a halogen lamp. If you then put a visible light filter in front of it (two layers of black parts of photographic film will be ok), the picture should be totally dark, since both IR and visible light are now mostly filtered out. If its not, make sure that the lamp isn't shining directly into the camera. Now, remove the lens, leaving the camera in the same place, in front of the illuminated object. Of course you won't see any details now, but the picture will be bright. Now cover the sensor with the visible light filter - if the picture doesn't go very dark, it means that the IR light didn't get filtered out, so the filter is in the lens. If the picture goes totally dark, then the filter seems to be on the sensor cover.

Good luck.
Volans #6 14/11/2007 - 21h47

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Deimos, how can I thank you for your excelent advice????
 Well, I made a differential diagnose and realise that the ir filter is placed in the lens cilinder (and the tiny glass ontop of the cmos is only for mechanical protection, does not filter any ir). Crossing my fingers, and with a bit of luck I removed the ir filter. maybe someone will came across the same problem, so here is a little detail:
- first, I separate the black tube (contains the lens)  from the silver part of the lens casing. Those were joined with some glue, so I force them a little.
- next, the black cilinder (by the way this one is made from alluminium painted black). So, this "cilinder" is made from two parts, one screwed into the other, but also glued, this mean that one can not simply unscrew them. With a sharp tool ( eg. a knife ) and sand paper I dislocate the glue, ant then I was able to unscrew them. This way, the first lens is exposed.
 - under the first lens (from exterior to interior) lay the ir filter, which is a thin square piece of glass, with an orange-red hue. Remove it at once (very easy to remove, it is holded in place only by the first lens, who is on top of it.)
- reassemble the camera. I put a piece of magnetic disk (from a floppy) in front of the objective, and now only seeing the ir leds. In freetrack works like a charm, w. 28 constant fps and 0-9 jitter. It has only one drawback: although I can manually set up the exposure to zero, it won't remember the setting next time, so every time I use freetrack I had to adjust the exposure slider. Otherwise, highly recomnded, for it price.
 Thank you Deimos and tristan68 for your kind support.

Pictures:

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Deimos #7 15/11/2007 - 12h25

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Always glad to help :D
Btw, how about eighter making this tread sticky, or creating a new IR conversion instruction tread for this cam, and making that one sticky?
Having few IR conversion guides here, in this forum will surely help other - current and potential Freetrack users.
tristan68 #8 15/11/2007 - 12h40

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WTG volans ! well done

@deimos :

Thanks for your info, help is much appreciated  :)

About your suggestion to create a few conversion guides , we're working on it  ^^

stay tuned

cya
Kestrel #9 16/11/2007 - 03h34

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Volans @ 14/11/2007 - 22h47 a dit:

It has only one drawback: although I can manually set up the exposure to zero, it won't remember the setting next time, so every time I use freetrack I had to adjust the exposure slider.



Use 'Force Exposure' in Freetrack to automatically set the exposure for you.
Volans #10 17/11/2007 - 10h39

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Thanks!. Now it work excellent... One might use as well a handy tool to enable the grayed autoexposure setting: "enable button".
 I am now a happy user of freetracK!
Kestrel #11 18/11/2007 - 01h04

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Volans @ 17/11/2007 - 11h39 a dit:

One might use as well a handy tool to enable the grayed autoexposure setting: "enable button".



Doesn't the checkbox option in ForceExposure do that?

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