Adrian Tuddenham wrote in message
nvalid.invalid...
N_Cook wrote:
Adrian Tuddenham wrote in message
valid.invalid...
N_Cook wrote:
As though the red of the colour wheel has gone dark with age.
Instead of
vibrant red it is dull red/brown. Improved a bit with up to the
limits
changes to the colour matrix, now dull red rather than dark brown
for a
saturated red input . Not a leads problem , computer in and then
computer
out to a monitor is fine. Video source is similarly affected. No
loose
leads
inside. "Service" manual has no schematic of course.
Is there a generic cause to this as it seems quite common across
different
makes and models?
Is there any easy way to look at the colour wheel and see if the
filter
really is the problem.
Could it be the lamp failing in some strange way? You can get a rough
idea of the spectrum if there is some light spillage which has not
come
through the colour wheel (reflections coming out of ventilation slots
in
the projector, for instance). Take one of the clear CDs that is used
to
protect the bottom of a pack and, taking care not to get any
fingerprints on the disc, hold it so that the tip of your nose is
poking
through the centre hole. Close one eye and move your head so that the
light from the lamp appears above the top edge of the disc.
If the light source appears sufficiently small, you should see a clear
spectrum with a good quantity of each colour.
--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
What an intriguing test, I'll make sure no one can see me while doing
it,
they may phone up the funny-farm.
(look, the loon has taken to playing CDs with his nose)
I once demonstrated it at a coffe morning of the Bath Royal Literary &
Scientific Institution. After handing out half a dozen discs, I had a
great time watching them trying it out (pity I didn't take a
photograph).
The lamp spillage looks normal white but
if such a spectrum test shows an absence of red it would be useful
elimination test.
I would have thought that a normal-looking white would suggest that the
lamp is OK - although I suppose there is a faint possibility that some
sort of filtering or correction system could be upset by the absence of
some parts of the spectrum which are too narrow to affect the overall
appearance.
Would your "CD" difraction grating disc yest work with any
lamp souurce for comparison say car headlight or a xenon floodlight bulb
just to see what a complete spectrum would look like with such a disc.
It works with any source, but the image you view should be as small as
possible if you want to see any detail of lines or holes in the
spectrum. You can either mask-down a large source or stand a distance
away from it.
I've just tried the test with my own projector and the lamphouse spill
shows a fairly continuous band with a couple of strong lines in the
green and one in the cyan. I have tried to photograph it for you, but
the bands don't show up:
http://www.poppyrecords.co.uk/other/...BAT01_1122.JPG
With the screen set to 'black', the residual light coming through the
lens appears a bit stronger in the red region and the lines are not
noticeable, so I suspect there is some correction going on.
The light seen through one of the other vents appears to be a very
strange magenta-ish colour (too diffuse to analyse with the CD). I
would guess that this is coming out of the back of the lamp and is the
unwanted transmission from a dichroic mirror.
--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
I suppose those discs are rejects from the pitting stage so never go on to
the matalising stage.
I tried with some LEDs , the most convincing was "point source" non diffused
blue, just a slight bit of green in the spectrum with the blue. Even orange
lens over a neon was quite convincing. The more light the less convincing
presumably because the eye is overloaded with the most prominent allowing
the minor spectra components to be more prominent
Through one section of the fan louvres you can see part of the dichroic
mirror and that is distinctly red when the lamp is on , I wonder if the
dichroic plating? can break down over time and stop reflecting red and
absorbing it instead, ie passing red and infra-red light.
If I get inside again I may try mounting a piece of mirror in the lamp light
path and try reflecting a red LED laser into the light tunnel and
colourwheel and see if that brings up the red component/s of the image