P3D Re: FWD: TDC Model 116 and 716 Projectors

[Tom Hubin <thubin@xxxxxxxxx>]

Dr. George A. Themelis wrote:
> 
> Message from Gary Nored, rejected because of HTLM code...
> 
> ---
> A few years back there was a thread regarding which of these two
> projectors is the brightest. The results of much discussion and
> calculation left open the possibility that the Model 116 _might_ be
> the brighter of the two.
> 
> At last we have a meaningful comparison of the two. For the moment I
> have both the TDC 116 (500 watts) and the TDC 716 (750 watts), both
> with 4 inch, f 3.5 lenses. Sure enough, the Model 716 is 1/2 stop
> brighter. It's also 50 percent hotter, and somewhat noisier.  Both
> machines produce bright, clear images. The 716 might have the edge in
> situations where the ambient light was high, but without having the
> two of them side by side, one would be hard put to tell the difference
> in the projected image.
> 
> Gary Nored

Hello Gary,

I have some cautions for you. I do not disagree with your results but if
you want to settle a dispute you need to make sure your experiment is
valid.

Make sure you used the proper lamps for each projector. Not just the
correct wattage. The filament dimensions and centering must be correct.
The lamps should also be nearly new to do a fair comparison. The TDC116
was designed for the 500 watt CZX lamp. The TDC716 was designed for the
750 watt DDB lamp.

Half a stop is 41% brighter which is very close to 50%. With what
precision did you do the measurement?

Anyway, if the optical power of the TDC716 is not close to 50% more than
the TDC116 then the filament size is likely the culprit. The lamp
filament is imaged at (or near) the projection lens entrance pupil. The
8mm square filament of the 500 watt CZX lamp fits neatly within the
projection lens with the corners of the filament image just touching the
aperture edges. So no light is clipped by the projection lens aperture. 

The 750 watt DDB filament is larger than 8mm square. I don't recall the
exact dimensions but I think it is 10mm square. The condenser optics are
the same for both projectors. The result is that the image of the DDB
lamp filament is too large to completely enter the projection lens. The
corners of the filament image are clipped so some light is lost. You
would only have to clip 6% of the filament image area to go from the
desired 50% increase (0.58 stop) to your measured 41% increase (0.50
stop).   

This is all pretty consistant with your findings and my calculations and
findings.

I suspect the debate may have involved using 750 watt halogen BTP lamps
for the TDC716. In either of these projectors, the 500 watt CZX lamp
will outperform the 750 watt BTP lamp. The BTP lamp has a 10mm x 14mm
filament. The filament image is much too large for the projection lens.
Lots of light is clipped. So you get 50% more heat and less light for
your effort. In that case the TDC116 will produce a brighter image than
the TDC716 but the real culprit is the wrong lamp for the TDC716.

I did some research using a couple of lamps for some TDC116 and TDC716
projectors. The results are in my report at
http://www.clark.net/pub/thubin/aosd/photo3d/ir_study.txt.

Tom Hubin
thubin@xxxxxxxxx
AO Systems Design


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