I was reading in an optics book a week or two ago and found this interesting image. It looks to me as though as long as you have good optics, it doesn't matter if you have a point source of light or not, as long as you set your focal lengths up properly to do the right convergence at the right distances. If nothing else, I think this image is a great explanation of how focus works and what the different lenses do.
Comments? This image almost makes me want to go flourescent (or halogen array), and just make sure I spend the time to get my optics calculations correct.
Keep imagining!
--Clint
Comments? This image almost makes me want to go flourescent (or halogen array), and just make sure I spend the time to get my optics calculations correct.
Keep imagining!
--Clint
Attachments
Theoretically, yes, it is true. and smaller LCDs can use big (flouroscent) light sources. BUT, the projection lens is big relative to the LCD size. If you are using a 'not-so-point-light-source', you are going to need a larger projection lens, like those page magnifier in 100" TV 😀
or like this one: http://www.diyaudio.com/forums/showthread.php?postid=194830#post194830
or like this one: http://www.diyaudio.com/forums/showthread.php?postid=194830#post194830
18 wheeler
heya bud sorry but i strongly disagree with your theory are u talkiong condensers or projection lenses? if u are talking condensers u are right but projection lens nope lol im doing a little research on this and to be honest for a ohp a large light source is better than a point
Trev
heya bud sorry but i strongly disagree with your theory are u talkiong condensers or projection lenses? if u are talking condensers u are right but projection lens nope lol im doing a little research on this and to be honest for a ohp a large light source is better than a point
Trev
Okay...
So if large sources of light can be used just as well, what's the big deal that everyone has made about not being able to use large-arc-tubes because they're not a point source? It really doesn't seem like it matters. Am I just challenging a non-existant belief here? But as someone who has only been on these boards for six months or so, I was under the impression that everyone's general belief was that you need as close to a point source of light as possible.
It definately DOES seem like the less-point-source you are, the more careful you need to be about focus (I.E. if you had a true point source of light you would never need to focus your projector), but it doesn't seem like it matters as long as you do your math right.
Respectfully,
clint
So if large sources of light can be used just as well, what's the big deal that everyone has made about not being able to use large-arc-tubes because they're not a point source? It really doesn't seem like it matters. Am I just challenging a non-existant belief here? But as someone who has only been on these boards for six months or so, I was under the impression that everyone's general belief was that you need as close to a point source of light as possible.
It definately DOES seem like the less-point-source you are, the more careful you need to be about focus (I.E. if you had a true point source of light you would never need to focus your projector), but it doesn't seem like it matters as long as you do your math right.
Respectfully,
clint
HanClinto:
Whats the name of your optics book?
Also, do you have some optics and a non-point light source that you could use to test?
I would REALLY like to use one of those 1000w metal halide weed lights off ebay.
Whats the name of your optics book?
Also, do you have some optics and a non-point light source that you could use to test?
I would REALLY like to use one of those 1000w metal halide weed lights off ebay.
well this is my theory anyway with light im taking concetrated light like a point sorce and a small parobollic reflector the wide u make the beam the less intense it gets, now the narrower the beam is the further the light will trvel with more intensity that is why a small lcd can get brighter than a 15inch with the same light sorce, i have tested it and its logical, just take a torch that is all u need to play with to find out.
Now this is what i believe will work for the 15inch thingy on a ohp.
Ok throw that small point sorce away u are making the beam too wide and loosing too much light that way aslso beleive it or not u will get more screen door as the light is hitting the screen door at an angle so it lights up more, and more heat and glare, the straiter the beams of light is the further it can travel also wich means more intensity and more lumens not to mention a sharper image.
The fix, ok get a 400w double ender if need be or a single depending on what fits and make sure the bulb is tubular not the shape of a normal bulb cos that will loose u light too cos it will be too far away from the reflector, i have made a reflector for a bulb that has a long burning ark, my bloody halogen lol and with abit of tuning here and there u get the hot spots out, the reflector is what gives them to u, now if the burning arc of the bulb is brighter than the reflected light from the reflector the bulb needs to go closer and the reflector tuned so u are counciling out the bright buring arc of the bulb i have done this and it works. the reflector is not a normal shape i might add either but when u look into it u can see the bulb reflect both sides of it with the light off
The reason to use a bigger arc bulb is to make the beam more narrow that way giving u a straiter beam and a much brighter light, however with this idea u will need a condenser the size of your bulb but if u do it right with a 400w mh i doubt u will even need one unless u want some magnified light
Trev
Now this is what i believe will work for the 15inch thingy on a ohp.
Ok throw that small point sorce away u are making the beam too wide and loosing too much light that way aslso beleive it or not u will get more screen door as the light is hitting the screen door at an angle so it lights up more, and more heat and glare, the straiter the beams of light is the further it can travel also wich means more intensity and more lumens not to mention a sharper image.
The fix, ok get a 400w double ender if need be or a single depending on what fits and make sure the bulb is tubular not the shape of a normal bulb cos that will loose u light too cos it will be too far away from the reflector, i have made a reflector for a bulb that has a long burning ark, my bloody halogen lol and with abit of tuning here and there u get the hot spots out, the reflector is what gives them to u, now if the burning arc of the bulb is brighter than the reflected light from the reflector the bulb needs to go closer and the reflector tuned so u are counciling out the bright buring arc of the bulb i have done this and it works. the reflector is not a normal shape i might add either but when u look into it u can see the bulb reflect both sides of it with the light off
The reason to use a bigger arc bulb is to make the beam more narrow that way giving u a straiter beam and a much brighter light, however with this idea u will need a condenser the size of your bulb but if u do it right with a 400w mh i doubt u will even need one unless u want some magnified light
Trev
Psionic
I don't have the book here at work with me, but I'll get it over the weekend. Hopefully I'll remember to post the name on Monday -- it really is an amazingly practical book in the realm of optics. It even has a whole chaper on projection! (old-school slide stuff is what it is geared towards, but everything still applies for video projection). It seems like an old book from the '60's, I'll try and post the name. It's a fairly thin quick read -- probably less than 200 pages. It's packed with good stuff though.
No, unfortunately I don't have a good workshop this summer to do optics testing in. That's one reason why I posted, I want to know what more experienced people know in this area. If I find out anything though, I'll post it here.
Keep imagining!
clint
I don't have the book here at work with me, but I'll get it over the weekend. Hopefully I'll remember to post the name on Monday -- it really is an amazingly practical book in the realm of optics. It even has a whole chaper on projection! (old-school slide stuff is what it is geared towards, but everything still applies for video projection). It seems like an old book from the '60's, I'll try and post the name. It's a fairly thin quick read -- probably less than 200 pages. It's packed with good stuff though.
No, unfortunately I don't have a good workshop this summer to do optics testing in. That's one reason why I posted, I want to know what more experienced people know in this area. If I find out anything though, I'll post it here.
Keep imagining!
clint
Re: Okay...
That was because all those non point light sources have been tried and failed (in larger LCD application). a couple months ago, YWH posted a couple of light sources that he or his friends tried and failed.
ace, I firmly believe the projection lens is the key to bigger light sources. reasons? the relative size between those 5" LCDs and the projection lenses, and the existing of 100" TV. condensor lens collect light toward the LCD, but the projection lens determine how much light can arrive at the screen. I cannot say either one is not important.
HanClinto said:
That was because all those non point light sources have been tried and failed (in larger LCD application). a couple months ago, YWH posted a couple of light sources that he or his friends tried and failed.
ace, I firmly believe the projection lens is the key to bigger light sources. reasons? the relative size between those 5" LCDs and the projection lenses, and the existing of 100" TV. condensor lens collect light toward the LCD, but the projection lens determine how much light can arrive at the screen. I cannot say either one is not important.
18wheeler
yess u are right the projection lenses in ohp,s are way to small for my liking, they should be atleast 4inches in diameter to get a significant gain in picture brightness, a condenser however makes a huge difference in brightness by it just being bigger, it collects more light to throw at the screen concentrated and thats what u want for starters, as for the non point source not working for others i dont see what they did wrong, mines not a point source and i got mine bright as, its all to do with how u collect the light and how good the reflector is, those reflectors u get for 400w mh are crap they are designed to throw the light out in a big area not to a concentrated place and furthermore the materials they use are no where near as shiny enough and u cant get close enough to a decent reflector with a standard mh bulb, u need a tube type bulb or it wont work lol
Trev
p.s i wish u was here so i could prove the case cos im crappy at explaining things on here but it does work
yess u are right the projection lenses in ohp,s are way to small for my liking, they should be atleast 4inches in diameter to get a significant gain in picture brightness, a condenser however makes a huge difference in brightness by it just being bigger, it collects more light to throw at the screen concentrated and thats what u want for starters, as for the non point source not working for others i dont see what they did wrong, mines not a point source and i got mine bright as, its all to do with how u collect the light and how good the reflector is, those reflectors u get for 400w mh are crap they are designed to throw the light out in a big area not to a concentrated place and furthermore the materials they use are no where near as shiny enough and u cant get close enough to a decent reflector with a standard mh bulb, u need a tube type bulb or it wont work lol
Trev
p.s i wish u was here so i could prove the case cos im crappy at explaining things on here but it does work
18wheeler
the focal of the condenser has alot to do with succes too just as much as the projection lens
Trev
the focal of the condenser has alot to do with succes too just as much as the projection lens
Trev
18wheeler
this type of reflector is perfect for a ohp check it out
http://www.insidesun.com/cgi-bin/ws...y&setup_value=1&cleanup=n&item_id=IS-400M-C-1
this type of reflector is perfect for a ohp check it out
http://www.insidesun.com/cgi-bin/ws...y&setup_value=1&cleanup=n&item_id=IS-400M-C-1
yeah psonic that was just for the pic not the price lol i wouldnt pay that for a reflector i made mine for free, that relfector is more for a wide beam of light when i made mine i made it so u can only see the bulb either side of it reflecting twice so it is a more narrow beam not like the one in the pic that u see the bulb reflected more than twice, i did other things to it to as in shape to cut out the hot spots and to maximise the brightness and intensity
One of the major secrets to gettting the light intense and bright is the reflector, if that is no good u got a bung projector my son lol
ill try to scale mine up for a 250w or a 400w for somone to try.
Trev
One of the major secrets to gettting the light intense and bright is the reflector, if that is no good u got a bung projector my son lol
ill try to scale mine up for a 250w or a 400w for somone to try.
Trev
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