Re: RBT Mounts "Back in Black"

[P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

Larry Berlin writes

David Stuckey writes
>When he put these in his projector (RBT) the autofocus had a hard time
>deciding where it should be and there was also some transmission of 
>visible light to the screen as the white mounts are not completely opaque. 
>Therefore I assume that black opaque mounts prevent infra red transmission
>from the lamps and into the focus sensing mechanism.

You mention the white part of the mounts are not completely opaque and
therefore transmit some visible light. This makes sense but I think the
the black opaque mounts prevent more the visible part of the spectrum 
from interfering with the IR sensor rather than the IR radiation. This
might sound puzzling but really isn't. Even thou the sensor is sensitive to
IR radiation, the intense visible radiation being passed is overriding the
weaker IR emitter signal. The IR radiation is partially reflected by the
white part and to a much greater degree by the heat absorbing glass. There
shouldn't be much near-IR at this point, which is what the sensor is 
sensitive to. As for very far-IR that is another story. In any case it 
shouldn't be the white part of the mounts job, to withstand the intense
IR radiation of the lamp.

Larry Berlin responds to David Stuckey's post  
>*************  This is what I guessed from Dr. T's experiment when the
>black melted before the white even though it faced away from the lamp. The
>infrared goes right through the white to a significant degree, making the
>use of black on the far side even more likely to cause problems. They need
>a far more reflective surface in front of the slides to prevent 
>transmission of the heat. The white plastic doesn't reflect enough of it
>away and it isn't opaque enough by itself to be a good slide holder in
>projection. 

Yes the infrared does go thru to a significant degree in the above case but
in this case the HAG was taken out to see the effect. The white plastic
is not up to blocking this intense IR radiation. If the HAG is in good
condition and in place the white mount even if it's opaque will block 
quite a bit of IR.

>**************  The black part can't be a radiator unless it is free of
>incoming radiation. Since the white is essentially trasparent at least to
>infrared, the black side is definitely at risk. Remember that in the
>projector, heat build up as well as radiation directly from the lamp causes
>a wash of infrared from many directions (meaning that *during projection*
>the black is more absorber than radiator). Only adequate protection with
>heat filters and air circulation can protect the slides and their mounts.

Actually all bodies are continually absorbing and radiating radiant energy.
The effect of making it black (and rough also to increase surface area)
is to increase both its absorbing and radiating patterns. The key to
if there is to be a heat gain, loss, or equilbrium is as I mentioned before
the nature of the body (black or white, smooth or rough etc.) and the 
difference between its temperature and surrounding temperature. In
electrical circuits, heat sinks are good absorbers and radiators of 
heat buildup and if properly designed will maintain an equilbrium
temperature and thus no heat build up. Same thing with motorcycle engines.
As to the infrared a wash in many directions, I think it would be more
hotter as you get closer to the lamp. After saying all that I am not
purporting that making the mount black on one side would be an effective
radiator. As you mention the only adequate protection is with heat filters
and air circulation and not colors on mounts. I agree 100% on that point.
We should be free to use whatever color we want! ;-)

>One other item that pertains only to the overheated mounts. There was some
>research done a couple years ago into all industrial pigments for toxicity
>levels. It was discovered that there are safe and non-toxic forms for ALL
>colors EXCEPT BLACK. This means that if your black mounted slide starts
>melting, stay far away from any of the fumes! It is far more likely to be
>toxic than any other color.(not that plastic is good for you in any
>color!)

NOW you tell me. I wonder if all those experiments melting black plastic
had any effect on me! Is that why I like to kiddd? Is that why I like 3D!?

Gabriel fuming about all those toxic stuff in black pigments.







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