Re: Slide projector melting my 35mm slides -- any advice?
- From: Dick Alvarez <alvarez@xxxxxxxxxx>
- Date: Fri, 13 Aug 2010 09:19:14 +0000 (UTC)
Jessica Lonkin <candogeewhiz@xxxxxxxxxxxxxxxx> wrote:
<<My aunt says that when the slide projector bulb gets
old it gets really hot.>>
That seems unlikely unless the lamp somehow fails
physically, as by an internal support breaking, or the air
flow is partially obstructed.
In an ordinary projector, the condenser lens directs
the light fairly uniformly through the slide aperture, and
then images the lamp filament in the objective lens (the
projection lens at the front of the projector). The
objective lens images the slide on the screen.
If somehow the condenser lens manages to image the lamp
filament in or near the slide aperture, it will melt the
slide. Probably a clue to that would be very uneven
illumination of the picture on the screen.
The condenser lens generally consists of two thick
plano-convex lens elements, with the convex surfaces
facing each other and very close together. If one or both
condenser lens elements is out of its proper position, for
example if the condenser lens was removed for cleaning and
then one or both of its elements was installed
incorrectly, that could image the lamp filaments in or
near the slide aperture, and thus melt the slides.
Probably it also would be evident by inspection of the
lens positions.
If the slide carrier somehow is too far forward, as
from breakage or improper assembly after cleaning, then it
might still be possible to focus the objective lens on the
slide, but the lamp filament might be imaged in or near
the slide aperture, and thus melt the slide.
If the lamp socket somehow broke loose mechanically and
is in the wrong position, or if the wrong type of lamp is
being used, that could cause the same effect.
Typically, the lamp bulb includes a hemispherical
reflector behind the lamp filament. Some projectors use
an external reflector behind the lamp bulb. The reflector
is designed to image the lamp filament coils between the
physical lamp filament coils, and thus give the appearance
of twice as many lamp filament coils, and thus almost
double the picture brightness. If that reflector somehow
is in the wrong position, that could cause the condenser
lens to image half of the lamp filament coils in or near
the slide aperture, and thus melt the slide.
If the fan air intake port is partially blocked, the
projector can over-heat. For example, if the projector is
placed on a paper or magazine, the fan can suck the paper
up against the air intake port. In one case, the lamp
bulb exploded. The condenser lens survived, and it
protected the slide and the objective lens from
destruction. With no slide in the projector, check the
air outlet port for sufficient air flow and reasonable
outlet air temperature.
So I suggest looking inside the projector, and checking
the following, beginning at the back of the projector:
(1) external reflector, if present; (2) proper lamp
model; (3) lamp internal integrity (not broken
internally); (4) lamp socket not broken loose from its
proper position; (5) all condenser lens elements in their
proper positions, and pointing in their proper directions;
(6) the slide carrier in its proper position; (7) the air
intake port not obstructed.
.
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- From: Jessica Lonkin
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