P3D Re: Halogen bulbs for projectors

[dalia miller <ddd@xxxxxxxxxxxx>]

Dalia wrote:

Tom, I'm surprised that you didn't use a 500w halogen in the experiment
with the 500w incandescent. Using a 750w halogen may raise more issues than
you would want.  Perhaps you didn't have a halogen 500w.  I'd try that
comparison first and then I'd do another test:  I would switch  the halogen
and incandescent and see if the results are the same.  You never know if
the condensors, polarizing filters are identical on each side. I believe
that would be more of an accurate test.  And if any engineeers out theere
have more suggestions, let us know.  

Why don't you just order a bulb from us and do some experimenting.  We once
discussed your doing a piece for INSIDE 3D??  I'll even give you a discount
on the bulb for the effort. Please contact me off-line.
>


Tom wrote:
>
>I did a simple demo at a PSSP meeting last year. No meters used. I put a
>new CZX 500W and a new BTP 750W in a TDC 116 projector. Then projected
>an empty slide mount onto the white wall about 3 feet away. I blocked
>one projection lens at a time and let folks vote on which side was
>brighter. The difference was obvious and all chose the 500W as brighter
>than the 750W. The next half hour or so was devoted to lecturing on how
>the lamp filament, condenser optics, slide, and projection lens aperture
>combine to give the brightness.

Dalia wrote:

>>   I did do some very primitive testing a while ago with a Stereomatic 500
>> after I changed out the mirrors (didn't change the condensors) and replaced
>> the polarizers in each projector.  We measured the amount of light that
>> bounced off the screen with one of Andrew's fancy fancy light meters - and
>> the halogen bulbs produced a slightly brighter image.  It was not
>> appreciably brighter and I can't remember how much more candle power was
>> detected.
>> 
>> My conclusion at that time was:  the halogen is only slightly brighter but
>> the bulb's  longevity made the bulbs much more desirable.  Please note that
>> I didn't test the bulb's longevity myself, we used the specs for the bulb.

Tom wrote:
>My conclusion is similar to yours, although I could find no suitable 500
>watt halogen lamp at that time. What I concluded was that the
>substituted 750 watt BTP produced about 50% more heat and over 50% more
>light than the original 500 watt CZX lamp. The extra heat was damaging
>slides due to inadequate heat absorbing glass. The extra light was not
>making it through the projection lens because the BTP filament was so
>much larger than the CZX filament.
>   
>The condenser optics is such that the 33mm diameter of the projection
>lens is imaged onto the filament as a 10mm diameter circle. This is like
>having a 10mm diameter aperture at the filament. Any part of the
>filament that is outside this 10mm diameter cannot contribute any light.
>The TDC116 condenser optics was designed with an 8mm square CZX filament
>in mind. Too much of the light from the 10mm X 14mm BTP filament is
>clipped by this 10mm diameter circle.
>
>When making substitutions, keep in mind that increasing wattage usually
>results in proportionately increased heat. Increasing lamp wattage,
>without dissipating the extra heat, is not a good idea if you value your
>slides.
>
>If the replacement filament is larger then the system is designed for,
>you will lose light at the projection lens. This is not harmful but can
>account for surprising light losses. This is what happened with the CZX,
>DDB, and BTP lamps. We expected the BTP 750W to be brighter than the DDB
>750W, or at least the same, but it was actually dimmer than the CZX 500W
>lamp.
>
>I am curious about the filament dimensions for the 500W Halogen that
>Dalia sells. Can somebody measure it with a simple metric ruler?
>
>It is curious that I had to speak to factory engineers to get the
>filament dimesions or measure them myself. That data seems to be
>unpublished. It is no wonder that folks ignore that when making
>substitutions. Yet it is just as important as the other data.

(deleted)

Dalia wrote:

Tom, I'm surprised that you didn't use a 500w halogen in the experiment
with the 500w incandescent. Using a 750w halogen may raise more issues than
you would want.  Perhaps you didn't have one.  I'd try that first and then
I'd do another thing:  I would switch  the halogen and incandescent and see
if the results are the same.  You never know if the condensors, polarizing
filters are identical on each side. That would be more of an accurate test.
Why don't you just order a bulb from us and do some experiment.  I'll even
give you a discount for the effort.
>

Dalia
ddd@xxxxxxxxxxxx
stereo supplies for the photographer
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http://www.3dstereo.com