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Dusted Sensor and other cybernetic friends...

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#1 Plank

  • Posts: 2835
  • LocationNew Zealand.

Posted 27 September 2016 - 22:22

Sony Ps3 eye Camera.  Dust on the sensor issues.


Avid D.I.Y headtracker wants the IR filter removed....


Crack open camera lens, remove IR filter.



Sensors can see infra red, we can't, so we don't need the camera to see in that spectrum.

But wait IR leds need to be seen by the camera so we take the IR filter out.

Great. Good work. Top marks.




we do let DUST in. 


and this is hard to detect when your camera is up and running.

Does your tracking "freak out" every now and then?

and no amount of fiddling will fix it?


Well try this:


Open the Cl -eye folder and run CL -eye test.


Remove band pass filters. 

Set the camera to normal brightness etc.

Aim camera at blank sheet of clean white paper. ( aprox 100mm away is fine.)

Notice any small dark smudges?

Move the camera around, if the smudge moves, it's on the paper.

Find a not moving smudge.


Whip out a going IR led and Aim it at that dark smudge, quite close to the camera.


Does the IR led suddenly get LARGER and/or Distorted?


You may have dust on your sensor.


and that will ruin your head tracking at that teeny tiny spot on the sensor.


Attached File  Cl eye test.jpg   576.47KB   0 downloads


The above pic is of my camera pointing at a white sheet of paper reasonably well lit.


It took me at least FOUR goes to get the TINY specs of dust off the sensor.

( unplug camera, unscrew lens housing. ( two screws on back of P.C.B, brush off dust, refit lens, plug in and test....)


Looks quite clean? I think so too.


I did have to use a pair of binoculars to see the specs but once I got the hang of

seeing them, blinking heck, they were like boulders on a billiard table.


To clean them off I used a really fine clean paintbrush. Synthetic sable I think.


Now the interesting thing is that this spec of dust on the sensor only really ruins the

tracking if the sensor and spec of dust and IR led happen to be perfectly lined up.


Waving your head around a metre away from the camera with your hat clip widget

probably WILL NOT DETECT the dust spec. Until you get it BANG ON, then it will.

and this is not easy to do on purpose but you can do it accidentally every now and then

while looking every way at once to see if Ice_age is on your tail...


Dust can get your killed!


Don't be a chump like me and put up with random tracking.


Check for dust!






PS. An after thought. The back of the lens can have dust on it too. This is less problematic but never the less...

Hold the lens pointing UP ( the back of the lens is down the front is up. ) now brush any dust off.

Holding the lens in this way will stop dust settling back onto the rear element. ( the one you just cleaned. )

It's all to do with gravity.




NEVER BLOW ON ANYTHING. You are just spreading moisture from your lungs everywhere. 

If you must blow things off use clean canned air.... or a blower bulb.

but really you are just blowing dust everywhere....

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#2 Plank

  • Posts: 2835
  • LocationNew Zealand.

Posted 28 September 2016 - 12:31

Dear chaps,


The reason why dust etc that effects the vision of your camera is such a bother is for this specific reason.


The CENTRE of the IR target is calculated by the BLOB of pixels it can see.


This centre is used to calculate where you should be looking.


If for some reason the blob of pixels radically changes SHAPE then a NEW CENTRE is calculated.

And this will be in a different position. Which inturn will shift your POV very quickly to this new position.


So you when get a very short fast shift of view ( A Shimmy? ).

lets say when panning left. it might be short and annoying.

Then when you pan back right , the way you came, you can run over it again

and the same thing happens. ( Shimmy left, shimmy right... )


If for some reason you get multiple recentres in quick succcession you will get your POV

flickering all over the place. ( Erk! no!!!)


So, if you are lucky and use Freetrack you can look at your IR leds in the camera view

and study the little crosses that are the centres of your IR LED's.


When in game you notice a hicup or worse, flicking view, shimmy etc.


Alt tab into freetrack

Or better still set it up on a second monitor,

and check the little crosses a the same point you were at in game.

Do the crosses jump around?

If they do then hello! you have recentering itis. or a Shimmy spot or a tiny nightclub for dancing recentres...




Attached File  Free track IR centres.jpg   267.02KB   0 downloads



As you can see in this picture I have regular nice round blobs of pixles that are the IR LED's.


The centres of those are the little crosses.


If I cast my head around a bit I can closely scrutinise the shape of the pixel clumps.

If they change dramatically over a very short distance of movement I can be sure

that I will get a POV flicker in game.


This is where the dust ties back in.


The dust on the sensor changes the shape of the blob of pixels and so changes where the

centre is. Causing pov shimmy.  ( Yes I know I said this before...)


So there you go. Something I learned this evening while experimenting.



POV Shimmy? Check your IR LED pixel blobs.  and then the little crosses.






PS. Freetrack really is good. It might be the best but it's a very clever and well thought out bit of kit.

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#3 Plank

  • Posts: 2835
  • LocationNew Zealand.

Posted 29 September 2016 - 07:44

Dear chaps,


I discovered another dust particle on my sensor.


( Good grief does this never end?)


Attached File  FT dust on sensor.jpg   315.99KB   0 downloads


The left IR target image is being interrupted by the dust mote.


As you can see the Cross in now not in the centre of the IR image and so my POV has been disturbed.


Finding this little blighter on purpose is quite tricky but the effect of finding it accidentally is very noticeable.


And keeping them out is an issue. Maybe a bath of alcohol or something might be the trick?


If I had know this was such a big deal I might no have opened the lense up in the first place.

And just worked around the IR filter... Never mind.


I will try again to clean it off.




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