My projector is now pretty much built but there is a small hotspot in the middle of the image, its not very big but still quite noticable especially in darker scenes.
I have tried moving the rear fresnel back and forth and also moved the condencer forward a bit, that didnt help. I cant move the condenser any further towards the buld as its as close as it will go. I also tried removing the reflector totally and you still get the hot spot. I really cant think what else it could be?
can anyone help?
I have tried moving the rear fresnel back and forth and also moved the condencer forward a bit, that didnt help. I cant move the condenser any further towards the buld as its as close as it will go. I also tried removing the reflector totally and you still get the hot spot. I really cant think what else it could be?
can anyone help?
Does the hotspot move when you move the screen (LCD)? if so it is burned into the LCD, otherwise it is the light distribution......at least thats how I see it...
Hi Phil,
What's the specs on the condensor lens? Are you sure the hotspot isn't being caused by it? I suggest you trying removing it and see what happens, perhaps it's focal length is too long.
What's the specs on the condensor lens? Are you sure the hotspot isn't being caused by it? I suggest you trying removing it and see what happens, perhaps it's focal length is too long.
well, took my projector apart again today and checked the LCD, there is definatly no problems with the LCD.
In answer to quins question the condenser lens is 90mm diameter and 240mm focal length. My condenser fresnel is 220mm focal length, do you think this could be causing a problem with both their focal lengths being quite close?
Also, i have tried removing the condenser but you get a crappy image, really dull and only bright in the middle, i dont have a decent reflector its way to small.
you can see in the picture below. I have also tried removing the reflector completly and you still get the small hot spot on the image.
In answer to quins question the condenser lens is 90mm diameter and 240mm focal length. My condenser fresnel is 220mm focal length, do you think this could be causing a problem with both their focal lengths being quite close?
Also, i have tried removing the condenser but you get a crappy image, really dull and only bright in the middle, i dont have a decent reflector its way to small.
you can see in the picture below. I have also tried removing the reflector completly and you still get the small hot spot on the image.
An externally hosted image should be here but it was not working when we last tested it.
I just checked this image and you can see the bright spot. Its bit brighter on his nose and just a bit to the left and right of his nose out as far as his eyes.
its diff to see on photos as the camera doesnt pick up the light so well anyway but this is the best shot i have of the bright area.
its diff to see on photos as the camera doesnt pick up the light so well anyway but this is the best shot i have of the bright area.
An externally hosted image should be here but it was not working when we last tested it.
I think you'll find the condensor focal length is far too long, it will be focussing the light almost to a point at where the fresnel is situated, this isn't the way it's meant to work! My understanding of it is that you wan't a much smaller focal length, so the light is focussed to a point way before the rear fresnel, so that it 'spreads' back out again and hits the entire rear fresnel.
Someone else is welcome to correct me, but I don't think there is an aweful lot you can do with that lens mate.
My next step would be to run it without the condensor so you can elimate any problems that might cause, then start altering the distance of reflector to bulb to try and elimate the hotspot being caused it. One problem at a time 🙂
Someone else is welcome to correct me, but I don't think there is an aweful lot you can do with that lens mate.
My next step would be to run it without the condensor so you can elimate any problems that might cause, then start altering the distance of reflector to bulb to try and elimate the hotspot being caused it. One problem at a time 🙂
I doubt its the condenser having a focal too long cos we never place a condenser at its focal from the bulbs arc, its always closer. Normally a condenser that has a focal thats too short would do it, but not one with a long focal.
I say its the middle of you lcd running far too hot. If thats not the problem then i say its that little light unit you made thats causing a reflection brighter on the center of the lcd then what the rest of the light thats coming out from the bulb.
An overheated lcd will turn white then black, and it normally starts in the center.
Trev🙂
I say its the middle of you lcd running far too hot. If thats not the problem then i say its that little light unit you made thats causing a reflection brighter on the center of the lcd then what the rest of the light thats coming out from the bulb.
An overheated lcd will turn white then black, and it normally starts in the center.
Trev🙂
Quin, When you initially turn on the lamp you can see where the light cone is hitting the fresnel, it hits it perfectly at about the rear fresnel focal length so all the light is hitting the rear fresnel. Also the hot spot it definatly not being caused by the reflector, i said that i took it out and the hot spot is just the same.
ace, its definatly not a problem with the LCD overheating, i have turned on the unit and fidled with the rear fresnel moving it up and down and if i just look down at the LCD you can see the little bright spot moving up and down as well. So i know its not a problem with the LCD.
If it was a problem with the light box, should i spray the whole inside of it black with some high temp paint? that should stop most of the reflections inside.
Thanks for the help guys, if anyone has anymore ideas let me know, its the only prob i have with my projector and its buggine me lol
ace, its definatly not a problem with the LCD overheating, i have turned on the unit and fidled with the rear fresnel moving it up and down and if i just look down at the LCD you can see the little bright spot moving up and down as well. So i know its not a problem with the LCD.
If it was a problem with the light box, should i spray the whole inside of it black with some high temp paint? that should stop most of the reflections inside.
Thanks for the help guys, if anyone has anymore ideas let me know, its the only prob i have with my projector and its buggine me lol
To try to find out firstly if it is the light box, take the light box away and have the bare bulb running without anything around it. if it is the light box try to find out where the reflection is coming from and make the changes acordingly in a new design 😉 .
If its not the light box i can prety much bet money on it that its heat, have you felt the center of the lcd and is it the same temp as the outside? Btw an lcd should not feel hot, anything over warm will cause the lcd to darken or discolour.
To me i think you have a stray reflection thats causing an area of the lcd to run too hot, so in a way its both, if not, one or the other.
Is the lcd brand new?
Trev🙂
The LCD monitor is far from new lol, very old but no dead pixels and was in very very good condition when i brought it, im 110% sure its not the LCD causing the bright spot. I took the picture below by putting the semi transparent white sheets from the LCD monitor over the LCD which i found shows the bright spot very well. The photos view is looking down at the LCD between the fresnels. I had to take the photo when the projector had only just been turned on so that the bulb wasnt to bright to take the pic yet.
It looks like the bulb arc is focusing on the back of the LCD but still kind of managing to successfully spread the light cone out over the whole LCD, i have a feeling that because the rear fresnel FL (220mm) and the condenser FL (240mm) are similar that it might be focusing the bulb arc on the back of the LCD a bit.
It looks like the bulb arc is focusing on the back of the LCD but still kind of managing to successfully spread the light cone out over the whole LCD, i have a feeling that because the rear fresnel FL (220mm) and the condenser FL (240mm) are similar that it might be focusing the bulb arc on the back of the LCD a bit.
An externally hosted image should be here but it was not working when we last tested it.
Hmmm ok, i take it that, that pic was taken from the light side and not the projection lens side? If so thats the right way to do it, atleast that looks like what you've done lol.
I think the next thing would be to try the system without the light cage and just have the bare bulb. See what that does.
Trev🙂
I think the next thing would be to try the system without the light cage and just have the bare bulb. See what that does.
Trev🙂
yep thats how the pic was taken.
If i remove the front of my light box so that its just the bulb with the really crap small reflector at the back i just get a dim image which is only bright in a circle with diameter no bigger than 1/3 the total width of the projected image so there is no was to actually make out the light spot with that setup. I would need to get a proper reflector to be able to try it that way..... this is proving to be a right pain in the tits lol.....
i also toyed with the (bad) idea of just holding something between the the lenses or lamp or anything to try and dim the middle of the image a bit... not very good solution or very good results lol...
i wonder if you can get software for the PC to adjust brightness levels of small sections of the screen to try and even out the light heh heh.... prob also not a very good idea.
maybe if i get another reflector and still use the condenser then it willlight the rest of the image a bit more and then you wont notice the brighter spot on the image anymore? do you think that might work?
If i remove the front of my light box so that its just the bulb with the really crap small reflector at the back i just get a dim image which is only bright in a circle with diameter no bigger than 1/3 the total width of the projected image so there is no was to actually make out the light spot with that setup. I would need to get a proper reflector to be able to try it that way..... this is proving to be a right pain in the tits lol.....
i also toyed with the (bad) idea of just holding something between the the lenses or lamp or anything to try and dim the middle of the image a bit... not very good solution or very good results lol...
i wonder if you can get software for the PC to adjust brightness levels of small sections of the screen to try and even out the light heh heh.... prob also not a very good idea.
maybe if i get another reflector and still use the condenser then it willlight the rest of the image a bit more and then you wont notice the brighter spot on the image anymore? do you think that might work?
its def not prob with the reflector as such, if i remove the reflector the bright spot is still there just the same amount, i just thought a better reflector might make the area around the dot brighter and the area in the middle might stay the same lol... i have a slightly bigger reflector on order to see how it works out.
it's got to be the reflector, mate. to prove/disprove this, can you put a piece of black cardboard or paper in front of your rear fresnel and take a pic of the light hitting it?
all else fails, can you just run your bulb without anything behind/infront of it?
all else fails, can you just run your bulb without anything behind/infront of it?
but surley if i have removed the reflector completly and the light spot is still there and looks just the same then is cant be a problem with the reflector??
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