I am making the MkIII - using the kit - I am not
able to remove a spider like pattern from the screen
- I have removed the reflector and condenser
- moved the lamp - moved the mirror - used the lens
out of my OHP - moved the frensle lens -
I have not seen this in any of my home made projectors
and OHPs yet -
I have though it was my light because every thing else
has been moved or replaced - but I moved the light
and it did not change the spider pattern -
here is a pic - I changed the brightness and stuff to
bring out the pattern
able to remove a spider like pattern from the screen
- I have removed the reflector and condenser
- moved the lamp - moved the mirror - used the lens
out of my OHP - moved the frensle lens -
I have not seen this in any of my home made projectors
and OHPs yet -
I have though it was my light because every thing else
has been moved or replaced - but I moved the light
and it did not change the spider pattern -
here is a pic - I changed the brightness and stuff to
bring out the pattern
Attachments
reflector issue
Whats the shape of your reflector? My guess is the reflector is folding light in a way that overlapps at certain angles.
Whats the shape of your reflector? My guess is the reflector is folding light in a way that overlapps at certain angles.
I tried lots of things - I still have it with or with out
the reflector - I had a mirror and removed it by using
the MkIII like a OHP with the light out of the top
- still have it - I got a sheet of glass thats as thick
as your pinky finger over the frensnel - I think it may
be what it is - It came with the kit - I am going to get
a thin piece of glass to see - the one from my OHP
is two small
the glass is the only thing that has not been checked
the reflector - I had a mirror and removed it by using
the MkIII like a OHP with the light out of the top
- still have it - I got a sheet of glass thats as thick
as your pinky finger over the frensnel - I think it may
be what it is - It came with the kit - I am going to get
a thin piece of glass to see - the one from my OHP
is two small
the glass is the only thing that has not been checked
I found out that glass blocks some UV but not
all - and I guess the thicker the more it blocks
but also more light
Its my frensnel - its got to be - with or with out
the glass its still there - the frensnel came pre
cut - its a split frensnel - and I use some black
on the sides to join them - ring lines face-ing
I made sure it was lined up - using the center rings
I tried flipping it over - and the pattern it different
- could I have got if off center just a hair, and it do this???
fresnel problem
If it is the fresnel, the alternating bright /dark angles going out from the middle are an interference pattern.
Does the fresnel look warped or buckled in any way? Does it lie flat? Could it have been on something hot or had something very heavy on it that would flatten the grooves?
Is this the fresnel between the LCD and the final lens? try raising or lowering it a bit. Does that change the pattern?
If it is the fresnel, the alternating bright /dark angles going out from the middle are an interference pattern.
Does the fresnel look warped or buckled in any way? Does it lie flat? Could it have been on something hot or had something very heavy on it that would flatten the grooves?
Is this the fresnel between the LCD and the final lens? try raising or lowering it a bit. Does that change the pattern?
the arms come from the center like a octopus
its not
warped and not burnt and lies flat - its new
yes - the arms move -
the fresnel is between the LCD and the light - I tried
moving it up and down and was never able to
remove the arms - even tried tilting it, the arms
move with the tilt
no - its some 3M OHP
frensel - I think, it had a 3M sticker on it, and its huge
it came with the MkIII kit, if I remember right it said
220mm - both look the same, and look cut from the
same joined OHP frensel but a big one
quote:
try raising or lowering it a bit. Does that
change the pattern?
yes - the arms move -
Light does like to wave! hehe couldn't resist.
So you are saying without this fresnel you get a clear projection but with it you get the "arms". Seems like a bum lens to me! return it.
try raising or lowering it a bit. Does that
change the pattern?
yes - the arms move -
Light does like to wave! hehe couldn't resist.
So you are saying without this fresnel you get a clear projection but with it you get the "arms". Seems like a bum lens to me! return it.
3 things i see is whats causing this if its the frensel.
1) The rings are miss matched
2) The top frensel has a different ring count or pitch then the bottom.
3) Crushed rings. Who ever cut this may have crushed the rings from clamping, (though you would see the crushed rings on your screen).
I can prety much garentee you that its either 1 or 2.
A warped frensel wont do this, it will simply give you a dirty looking light on the edges, and the edges will be out of focus. (on a triplet is best for testing, though just use your eyes by looking at the frensel lol).
Trev🙂
1) The rings are miss matched
2) The top frensel has a different ring count or pitch then the bottom.
3) Crushed rings. Who ever cut this may have crushed the rings from clamping, (though you would see the crushed rings on your screen).
I can prety much garentee you that its either 1 or 2.
A warped frensel wont do this, it will simply give you a dirty looking light on the edges, and the edges will be out of focus. (on a triplet is best for testing, though just use your eyes by looking at the frensel lol).
Trev🙂
I just had the same thing
They are interference patterns between the two fresnel's rings, that only show up if the light between the fresnels is perfectly parallel.
I found two different cures:
1) Raise the fresnels about 5 mm above the focal length from the lamp arc, so the light between the fresnels is not perfectly parallel.
or
2) Seperate the two fresnels by at least 1 cm.
They are interference patterns between the two fresnel's rings, that only show up if the light between the fresnels is perfectly parallel.
I found two different cures:
1) Raise the fresnels about 5 mm above the focal length from the lamp arc, so the light between the fresnels is not perfectly parallel.
or
2) Seperate the two fresnels by at least 1 cm.
I separated the 2 fresnels and tried sliding them back
and forth over each other - gently so not to scratch them,
I was able to get it just by placing one of them off center
I tried even lining up the cut marks in the edge of the
fresnels and tapeing them together - it did no good
thanks everybody
and forth over each other - gently so not to scratch them,
I was able to get it just by placing one of them off center
I tried even lining up the cut marks in the edge of the
fresnels and tapeing them together - it did no good
later I may try - I seam to have lost just a hair of brightness
thanks everybody
I had the exact problem when I put both fresnels (unsplit) before the lcd panel in my pj. (I am not uing an ohp, but am putting everything in an enclosure.) I pulled out the 330mm fresnel and put it in front of the lcd (now a split fesnel setup) and the spider light rays disappeared.
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