I noticed that there is a bright spot in the middle of a projected image, it is clearly visible looking at the area above the fresnels with panel removed, see attached picture.
This occurs on two OHP's that I have.
Is this normal? Are there any replacement fresnels that would either eliminate this effect or reduce it?
(I read on another thread someone else was experiencing the same thing, thought I would post a new thread rather than hijack a current one)
This occurs on two OHP's that I have.
Is this normal? Are there any replacement fresnels that would either eliminate this effect or reduce it?
(I read on another thread someone else was experiencing the same thing, thought I would post a new thread rather than hijack a current one)
Attachments
Yeah my stuff is SMOKING!!!!
And yes I did warp back to the past to post this message, only because the forum has gotten so big in the next 17 yrs which makes it very difficult to find the answers we need.
Now back to the real world, I thought the light would show up better in the picture if I blew a little smoke over the fresnels, and that isn't difficult to do in my case considering the way I abuse my body with nicotine.... As for the date, duh no excuse.
The result of that intense beam of light eminating from the center is what is disturbing, it leaves a golf ball image on the screen, very noticable at times.
I was hoping that someone would have a solution to this, I am surprised that I haven't seen it mentioned more often.
I just picked up a 15" panel, and am will be replacing the current halogen with a MH bulb, any chance that these upgrades, oh yeah and the triplets will reduce this effect?
TIA
And yes I did warp back to the past to post this message, only because the forum has gotten so big in the next 17 yrs which makes it very difficult to find the answers we need.
Now back to the real world, I thought the light would show up better in the picture if I blew a little smoke over the fresnels, and that isn't difficult to do in my case considering the way I abuse my body with nicotine.... As for the date, duh no excuse.
The result of that intense beam of light eminating from the center is what is disturbing, it leaves a golf ball image on the screen, very noticable at times.
I was hoping that someone would have a solution to this, I am surprised that I haven't seen it mentioned more often.
I just picked up a 15" panel, and am will be replacing the current halogen with a MH bulb, any chance that these upgrades, oh yeah and the triplets will reduce this effect?
TIA
So am I to assume that this spot in the middle of the screen is normal using this method of projection? That this is totally unavoidable, no matter what is done?
How about if using another method to project? Like a Mk 3 or one of the other designs I have seen, do they also suffer from the spot?
Could it be that the stock fresnels grrove pitch is not dense enough?
I have a 15 inch panel stripped and ready to go, I need to order new 15" fresnels and build a box opposed to using the overhead. Before I 'blindly' puchase more parts I would like to see if there is something that can eliminate or reduce the spot!
One of the reasons I chose to build my own projector is because of the cost of replacement bulbs on the commercial ones, images I have seen of peoples diy projectors range from garbage to excellent. Of course wanting to do this, means that I have paid more attention to the excellent results, not once have I seen anyone say that although the picture is great, the spot is still in the center of the screen.......
(sorry for the length of the message, I would normally let this stuff flow in a thread, but my messages have to be approved first)
How about if using another method to project? Like a Mk 3 or one of the other designs I have seen, do they also suffer from the spot?
Could it be that the stock fresnels grrove pitch is not dense enough?
I have a 15 inch panel stripped and ready to go, I need to order new 15" fresnels and build a box opposed to using the overhead. Before I 'blindly' puchase more parts I would like to see if there is something that can eliminate or reduce the spot!
One of the reasons I chose to build my own projector is because of the cost of replacement bulbs on the commercial ones, images I have seen of peoples diy projectors range from garbage to excellent. Of course wanting to do this, means that I have paid more attention to the excellent results, not once have I seen anyone say that although the picture is great, the spot is still in the center of the screen.......
(sorry for the length of the message, I would normally let this stuff flow in a thread, but my messages have to be approved first)
I dont see no spot in the picture. Maybe take a pic of the screen...
Looking at an angle, fresnels always have bright patterns. I assume you dont mean that.
Maybe the fresnel is upside down or the bulb has been adjusted closer. If the bulb is inside the FL it will only properly light the middle. The outer grooves will point past the bulb.
Looking at an angle, fresnels always have bright patterns. I assume you dont mean that.
Maybe the fresnel is upside down or the bulb has been adjusted closer. If the bulb is inside the FL it will only properly light the middle. The outer grooves will point past the bulb.
The beam of light is clearly visible in the picture I have already supplied. The golf ball size is in reference to the projected image.
I have found other people mention the same symptom since posting the original message in the thread, (different terminology, same problem).
However I haven't found anyone who has suggested a solution to it I suspect that those who do not see the brighter spot in their images either have poorer quality screens, bad eyes or better quality lenses, bulbs, panels etc...
The overall quality of the image is not acceptable to me, it is good compared to some of the pictures I have seen posted, just not good enough.
I have already stripped a 15" panel, MH light/ballast on the way, and lenses were ordered a couple of days ago. I am concerned that even with building a projector from scratch, that the bright spot in the middle may still be there.
That is why I waited to order the lenses, I suspect it is caused by the way light is bent by the ribs in the fresnel, the center rib having different properties than the others is causing this. There may be lenses out there that have a "modified" center, or perhaps a more dense pattern will reduce the effect.
For anyone that is interested this bright spot in the middle was experienced with two different OHP's one used folded light the other direct, same condition exisited.
I have found other people mention the same symptom since posting the original message in the thread, (different terminology, same problem).
However I haven't found anyone who has suggested a solution to it I suspect that those who do not see the brighter spot in their images either have poorer quality screens, bad eyes or better quality lenses, bulbs, panels etc...
The overall quality of the image is not acceptable to me, it is good compared to some of the pictures I have seen posted, just not good enough.
I have already stripped a 15" panel, MH light/ballast on the way, and lenses were ordered a couple of days ago. I am concerned that even with building a projector from scratch, that the bright spot in the middle may still be there.
That is why I waited to order the lenses, I suspect it is caused by the way light is bent by the ribs in the fresnel, the center rib having different properties than the others is causing this. There may be lenses out there that have a "modified" center, or perhaps a more dense pattern will reduce the effect.
For anyone that is interested this bright spot in the middle was experienced with two different OHP's one used folded light the other direct, same condition exisited.
Tez, if you want us to diagnose your problem then you should supply use with as much info as possible. Giving us one pic and saying here is the problem, if you can’t see it it’s not my problem, isn’t very helpful. Going by the responses in this thread, I don’t think anyone else can see it either. So at this point I’m afraid that I can’t help you.
DJ
DJ
I still can’t see anything wrong, looks perfect too me lol.
That spot shouldn’t be there. Make sure that the correct lamp/reflector are in the ohp. It looks like the same light pattern you get from a cheap parabolic reflector in a flashlight, someone may have retro-fitted a new lamp/reflector. Having the Fresnel the wrong way around may cause this spot at the screen but causing a spot that close to the fresnel makes me suspect that it is coming from behind it, maybe the distance from the lamp to the fresnel has been changed.
DJ
That spot shouldn’t be there. Make sure that the correct lamp/reflector are in the ohp. It looks like the same light pattern you get from a cheap parabolic reflector in a flashlight, someone may have retro-fitted a new lamp/reflector. Having the Fresnel the wrong way around may cause this spot at the screen but causing a spot that close to the fresnel makes me suspect that it is coming from behind it, maybe the distance from the lamp to the fresnel has been changed.
DJ
Bear in mind that this occurs on TWO OHP's of different brands...
The Elmo has had two different bulbs, both are ENX's these come with built in reflectors. (folded light)
The Apollo has only been tested with the one bulb, I gave up at this point and decided that starting from scratch is the way to go.
Thanks for the response!
The Elmo has had two different bulbs, both are ENX's these come with built in reflectors. (folded light)
The Apollo has only been tested with the one bulb, I gave up at this point and decided that starting from scratch is the way to go.
Thanks for the response!
What is common?
If its there with 2 different projectors, what part of the system is not changing? Maybe its a problem with your projection panel. If you slide the panel off center is the spot still in the same place?
If you put 1" bars under each side of the panel to raise it does the spot change? Useing a weaker light source, put a paper in between the projection panel and the meniscus lens. Is the spot there? Try it projecting without the panel.
Have a look at the tip of the bulb. Is it smooth or is there a pinch ball on the end?
Isolate what part of the system is causing it by removing other parts as above.
If its there with 2 different projectors, what part of the system is not changing? Maybe its a problem with your projection panel. If you slide the panel off center is the spot still in the same place?
If you put 1" bars under each side of the panel to raise it does the spot change? Useing a weaker light source, put a paper in between the projection panel and the meniscus lens. Is the spot there? Try it projecting without the panel.
Have a look at the tip of the bulb. Is it smooth or is there a pinch ball on the end?
Isolate what part of the system is causing it by removing other parts as above.
Me2! said:
The electrical outlet, the table they are placed on, and the screen.
We can eliminate the table and the screen, the bright spot will project on the wall as well. I'll check the current.....
Yes, it will still be projected to the center of the screen, I think the panel has nothing to do with it because the spot is there regardless. Maybe a better panel could diffuse the spot better....
I have used two seperate projectors with three differnt bulbs.....
I was starting to think this was "normal' using this kind of projector/panel, if the image you are projecting is your windows desktop/explorer etc. it isn't so bad, it is very noticable projecting TV/DVD images. Having said that, it is still there with NO image projected, just harder to see, (I used tinted glass).
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