P3D Microscope and projector filament spacing( Was white LEDefficiency)

[Peter Homer <P.J.Homer@xxxxxxxxxxxxx>]

Tom Hubbin

>First problem is that the filament spacing is ill defined. For example,
>the CZX 500 watt lamp used in the TDC116 has a filament coil arranged
>like an 8mm square. There is little free space between the coils and no
>spec on how that should be done. So any reflected light that gets
>between the coils is by luck and not by design.

>
>To get around the coil spacing problem I offset the filament. I have a
>1.7mm x 0.5mm filament coil in a 20w, 12v Halogen lamp that I use for
>microscope illumination. I offset the filament by 0.6mm. The reflected
>filament and the forward filament look like a pair of side by side
>filaments that now occupy 1.7mm x 1.2mm. I use a simple 50mm radius
>mirror. This is nearly as good as afocal because the mirror radius is
>much longer that the filament size.

But you can do this with other projectors if not with the  TD116  its even
possible with the FED to offset its original large filaments  so that the
reflected image appears between the actual filaments or if converted to 24v
halogen the inverted reflected image is above the filament.  Adjusting a
projector filament is very similar to setting up Nelsonian or critical
illumination with a microscope lamp. Because you cannot focus a projector
condensor the way you can a microscope condensor you need to fit a pinhole
in the slide holder to increase the depth of field (and reduce light
intensity)
so that the filaments can be imaged on a diffusing screen fitted over the
objective lens. Colin Clay described this in an article in the UK
stereoscopic society journal. In normal use the filaments  are actualy
defocused as you can do with a microscope by adjusting the condenser after
centring the filament and irises to give Kohler illumination.

I was interested to read that your microsocpe lamp has a reflected image of
the filament presumably produced by a mirror, because I have seldom come
across this in a microscope lamp myself and have often wondered why not as
it should give near double the light. Even a Gillert and Sibert "conference
microscope" we have at work which is also a microprojector does not have a
mirror, we have another which is actualy just an atatchment for a
conventional projector which will have a mirror and the same goes for other
microprojector atatchments for projectors.
The only purpose built microprojector I know of with a mirror was the old
Flatters and Garnet instrument which was a dedicated device and would need
to be fitted with a tube and eyepiece to be used as a normal microscope the
way the Gillert and Sibert could be.       P.J.Homer