I don't think that the polarizing filters are the whole problem here. They are just there to make sure that the light that goes through is parallel, because it gives better performance from the LCD. I think this is right, isn't it true that if light goes through the LCD at different angles the contrast is reduced, because of several different rays of light going through the screen?
Anyway, even without the polarizing filter, the basic design of an LCD means that any light not hitting it as a parallel beam will be attenuated. The way an LCD works is to rotate a tiny structure (in each pixel) so that light can go straight through, when a voltage is applied. If you go to the amazing www.howstuffworks.com, you can get a better idea, probably with some nice flash animations.
On another note, if anybody's still interested in CRT (and if they are give me a heads-up), here are some links.
Once again, www.howstuffworks.com has a good video of someone shooting a CRT, and it doesn't blow up. Magic eh?
Good links for the inner detailed workings of TVs here:
http://www.bithose.com/serfaq/sam/tvfaq.htm
as does this:
http://www.lesbell.com.au/Home.nsf/...052599676c7ff16c4a2569250042e7f0?OpenDocument
and this:
http://sure.org.ru/docs/hardware/pcrepair/chap33.html
You can read into a lot of these for some very good information, like sticking a raw RGB/composite signal into a TV without a composite input.
And the next door neighbour's got their washing machine on so that's my queue to go - the whole floor is vibrating, she must have knickers like tents.
Anyway, even without the polarizing filter, the basic design of an LCD means that any light not hitting it as a parallel beam will be attenuated. The way an LCD works is to rotate a tiny structure (in each pixel) so that light can go straight through, when a voltage is applied. If you go to the amazing www.howstuffworks.com, you can get a better idea, probably with some nice flash animations.
On another note, if anybody's still interested in CRT (and if they are give me a heads-up), here are some links.
Once again, www.howstuffworks.com has a good video of someone shooting a CRT, and it doesn't blow up. Magic eh?
Good links for the inner detailed workings of TVs here:
http://www.bithose.com/serfaq/sam/tvfaq.htm
as does this:
http://www.lesbell.com.au/Home.nsf/...052599676c7ff16c4a2569250042e7f0?OpenDocument
and this:
http://sure.org.ru/docs/hardware/pcrepair/chap33.html
You can read into a lot of these for some very good information, like sticking a raw RGB/composite signal into a TV without a composite input.
And the next door neighbour's got their washing machine on so that's my queue to go - the whole floor is vibrating, she must have knickers like tents.
tech head,
OHP's will work fine as they are, and building a projector like an OHP will also work great! I was just trying stir the DIY Kool-Aid, and I didn't even know what flavor it was 😉 .
SuperDave,
I made a baby step with the MV bulb issues. I took my Delta 20 lens apart and removed the middle lens (looks to be a very short focal length DCX lens with one side much flatter than the other...almost a PCX lens). I then placed it between the bulb and the fresnel/LCD, and this greatly improved the intensity and spread of light across the LCD. Without a suitable reflector, I am still losing at least 75% of the light to scatter 🙁 . Hopefully this will help you out if you decide to upgrade the bulb in your OHP.
Scot_lad,
You weren't kidding about that www.howstuffworks.com website. What a great resource! I just spent an hour reading about LCD's, CRT's, and Stirling engines.
OK, I need to get back to studying. I have 8 finals/boards over the next 10 days 😱 . Good luck, everybody.
-f4
OHP's will work fine as they are, and building a projector like an OHP will also work great! I was just trying stir the DIY Kool-Aid, and I didn't even know what flavor it was 😉 .
SuperDave,
I made a baby step with the MV bulb issues. I took my Delta 20 lens apart and removed the middle lens (looks to be a very short focal length DCX lens with one side much flatter than the other...almost a PCX lens). I then placed it between the bulb and the fresnel/LCD, and this greatly improved the intensity and spread of light across the LCD. Without a suitable reflector, I am still losing at least 75% of the light to scatter 🙁 . Hopefully this will help you out if you decide to upgrade the bulb in your OHP.
Scot_lad,
You weren't kidding about that www.howstuffworks.com website. What a great resource! I just spent an hour reading about LCD's, CRT's, and Stirling engines.
OK, I need to get back to studying. I have 8 finals/boards over the next 10 days 😱 . Good luck, everybody.
-f4
fender4,
you mentioned using a 0.8" hi-res lcd panel,
would the small size of the panel be an issue?
isn't it true that the larger the lcd panel the more the light can pass through? Is it possible to converge all the light to pass through this small area?
Thanks in advance...🙂
you mentioned using a 0.8" hi-res lcd panel,
would the small size of the panel be an issue?
isn't it true that the larger the lcd panel the more the light can pass through? Is it possible to converge all the light to pass through this small area?
Thanks in advance...🙂
IV'E BEEN FOLLOWING THIS PROJECT FOR SOME TIME NOW,
WHILE YOUR ON THE SUBJECT OF PARRALEL LIGHT TAKE A LOOK
AT THIS PAGE I FOUND IT MAY BE OF SOME HELP,IF ANYONE CAN
UNDERSTAND IT
ITS IN PDF FORMAT SO YOU WILL NEED ACROBAT READER
http://www.fresnel-optics.com/pdf/condenser_lenses.PDF
WHILE YOUR ON THE SUBJECT OF PARRALEL LIGHT TAKE A LOOK
AT THIS PAGE I FOUND IT MAY BE OF SOME HELP,IF ANYONE CAN
UNDERSTAND IT
ITS IN PDF FORMAT SO YOU WILL NEED ACROBAT READER
http://www.fresnel-optics.com/pdf/condenser_lenses.PDF
CRT route
Thanks för the links Scot_lad 🙂
I´m catching up on how a CRT works but the progress is slow 🙁
And no word from the university . . . . 🙁
What do You think about using the electronics from a PC monitor and feed 3 proper projection tubes with it?
Is there any simularity bethween a prpjection tube and a monitor tube when it komes to voltidge and current and stuff?
I guess it is a long shoot but I´m throing it out on the thread anyways 🙂
Bye for now
Thanks för the links Scot_lad 🙂
I´m catching up on how a CRT works but the progress is slow 🙁
And no word from the university . . . . 🙁
What do You think about using the electronics from a PC monitor and feed 3 proper projection tubes with it?
Is there any simularity bethween a prpjection tube and a monitor tube when it komes to voltidge and current and stuff?
I guess it is a long shoot but I´m throing it out on the thread anyways 🙂
Bye for now
hey all. been gone a while. been busy watching movies and making crazy plans for the future. diy projectors have become an addiction. not altogether DIY anymore, but man.....
anyways, where to begin. lets see.
yeah, with the fresnels, the lcd has to come after the fresnels. its not that bad a problem though: as long as the light is within a certain viewing angle %, there should be no (or near enough so) attenuation. its really not a problem.
ballasted light systems rock. MV sounds great. personally, i'm a big fan of metal halide. 400 watt metal halide is freaking beautiful. really. theres nothing like seeing a wall light up.
someone was talking about heat in light bulbs. well, conservation of energy states that any energy being put in and not coming out is having to go somewhere. theres just about two forms: light and heat. bulbs which produce more light for the same wattage are also more heat efficient. whoot to that.
so back to metal halides. they have BAR NONE the best efficiency around. is heat still a problem? oh yes. 400 watts will never be non-trivial. but with 3 times the efficiency of fluorescents.... well... damn. check out metal halide. yes, they need a $60 - $70 ballast. but bulbs are only $30 and last 20,000 hours. compare at $215 for the various 575 watt short arc bulbs a lot of your projectors are probably using (that last at most 1000 hours). the advantage is crystal clear.
and for the FREAKS in the audience, you can even get 10,000 K color temperature bulbs. 😀 😀
i really wanna start poking people towards elliptical mirrors. they are the ****. they're hard to build and probably nigh impossible to find, but hot damn are they ever perfect. it'd be a DIY project in and of itself to make them, but so worth it. basically, you'd put a light at one foci, put a panel between the two foci and have a projection lense system around the other foci. perfection.
custom lenses suck. i've been *** deal in optical design. it sucks. avoid if possible. if your really serious, go buy a book.
as a final note, a good projection screen is ESSENTIAL. i'm running **** right now and barely hacking it. i moved my system temporarily over to a real projection screen and nearly wet myself all over again. my oh my.
oh, yeah, for anyone really really really interested in how to take apart a vg150, look here. warning: 24 megs.
whew
good to be back
myren
anyways, where to begin. lets see.
yeah, with the fresnels, the lcd has to come after the fresnels. its not that bad a problem though: as long as the light is within a certain viewing angle %, there should be no (or near enough so) attenuation. its really not a problem.
ballasted light systems rock. MV sounds great. personally, i'm a big fan of metal halide. 400 watt metal halide is freaking beautiful. really. theres nothing like seeing a wall light up.
someone was talking about heat in light bulbs. well, conservation of energy states that any energy being put in and not coming out is having to go somewhere. theres just about two forms: light and heat. bulbs which produce more light for the same wattage are also more heat efficient. whoot to that.
so back to metal halides. they have BAR NONE the best efficiency around. is heat still a problem? oh yes. 400 watts will never be non-trivial. but with 3 times the efficiency of fluorescents.... well... damn. check out metal halide. yes, they need a $60 - $70 ballast. but bulbs are only $30 and last 20,000 hours. compare at $215 for the various 575 watt short arc bulbs a lot of your projectors are probably using (that last at most 1000 hours). the advantage is crystal clear.
and for the FREAKS in the audience, you can even get 10,000 K color temperature bulbs. 😀 😀
i really wanna start poking people towards elliptical mirrors. they are the ****. they're hard to build and probably nigh impossible to find, but hot damn are they ever perfect. it'd be a DIY project in and of itself to make them, but so worth it. basically, you'd put a light at one foci, put a panel between the two foci and have a projection lense system around the other foci. perfection.
custom lenses suck. i've been *** deal in optical design. it sucks. avoid if possible. if your really serious, go buy a book.
as a final note, a good projection screen is ESSENTIAL. i'm running **** right now and barely hacking it. i moved my system temporarily over to a real projection screen and nearly wet myself all over again. my oh my.
oh, yeah, for anyone really really really interested in how to take apart a vg150, look here. warning: 24 megs.
whew
good to be back
myren
Hey
Hey Myren, welcome back. I've been waiting for for VG150 pics for like weeks now 🙂 Too bad, I think I've already decided to with projection panels, even though I already have a vg150 in my hands. It looks just too sweet and innocent to to take it apart and do rude things to it 🙂 I'm just going sell it, I'm not too happy with its color rendtion abilites, and can't justify $320 for it (I bought it before my little vg150 for $230 post). If I cant get perfect picture quality, I think LCD panels are a sweeter spot on the price vs performance curve.... Gotta go, I have two midterms to study for 🙂
Hey Myren, welcome back. I've been waiting for for VG150 pics for like weeks now 🙂 Too bad, I think I've already decided to with projection panels, even though I already have a vg150 in my hands. It looks just too sweet and innocent to to take it apart and do rude things to it 🙂 I'm just going sell it, I'm not too happy with its color rendtion abilites, and can't justify $320 for it (I bought it before my little vg150 for $230 post). If I cant get perfect picture quality, I think LCD panels are a sweeter spot on the price vs performance curve.... Gotta go, I have two midterms to study for 🙂
ravide,
I was referring to the 0.8" LCDs that are used in many of the high-end commercial projectors. Unfortunately, these are unavailable to the DIYer, and if they were, they would probably be pricey. They would allow us to forego all of the fresnel optics by using a parallel light source all the way to the projection lens...nice, but not practical for us.
Myren,
Good to hear from you! Those MH bulbs are VERY nice...I've seen them on reef aquariums several times, and I don't think anything can beat their intensity, color, or efficiency. I'm trying the MV setup because it is so cheap (~$25 for bulb, ballast, and socket). If I can figure out a reflector, then I can upgrade to a metal halide if the MV doesn't work out. I think the bulbs have similar dimensions.
I have looked everywhere on the internet over the last few weeks for info on building an elliptical reflector, and I can't find anything useful. Can you point me to any resources? That is exactly what I need to make my MV bulb functional. Could a properly designed elliptical reflector eliminate the need for fresnels? I was assuming it would, but I'm not 100% sure.
Good luck everyone!
-f4
I was referring to the 0.8" LCDs that are used in many of the high-end commercial projectors. Unfortunately, these are unavailable to the DIYer, and if they were, they would probably be pricey. They would allow us to forego all of the fresnel optics by using a parallel light source all the way to the projection lens...nice, but not practical for us.
Myren,
Good to hear from you! Those MH bulbs are VERY nice...I've seen them on reef aquariums several times, and I don't think anything can beat their intensity, color, or efficiency. I'm trying the MV setup because it is so cheap (~$25 for bulb, ballast, and socket). If I can figure out a reflector, then I can upgrade to a metal halide if the MV doesn't work out. I think the bulbs have similar dimensions.
I have looked everywhere on the internet over the last few weeks for info on building an elliptical reflector, and I can't find anything useful. Can you point me to any resources? That is exactly what I need to make my MV bulb functional. Could a properly designed elliptical reflector eliminate the need for fresnels? I was assuming it would, but I'm not 100% sure.
Good luck everyone!
-f4
Arc
Hello
Well I have been working on my projector, rather then just make it for home use I have set myself the task of making a projector that can be used in a cinema type setup. I am looking into using carbon arcs for the light sorce, not the most practical by is very very very very very bright and fun to play with. Just a thought. I need a good reflector, not one with a hole it but one that the globe sits in front of, what can I do? The reflector is a huge part of making a sucessful DIY projector.
Hello
Well I have been working on my projector, rather then just make it for home use I have set myself the task of making a projector that can be used in a cinema type setup. I am looking into using carbon arcs for the light sorce, not the most practical by is very very very very very bright and fun to play with. Just a thought. I need a good reflector, not one with a hole it but one that the globe sits in front of, what can I do? The reflector is a huge part of making a sucessful DIY projector.
Hellfire
Hello,
Interesting questions, not sure where to start. The tubes in PC monitors and projectors are similar only in that they are tubes, which have the cathode, anode, etc. that all CRTs have. The one big difference between the two is that projector tubes are essentially single colour tubes which have different coloured phosphors. This means that there is no aperture grid or associated circuitry to align the RGB guns to the RGB pixels. In any case, there are no pixels on the projector tubes, just a mass of phosphors.
The voltages involved would be in roughly the same range, although the scan rate on a monitor would usually be much higher than on a TV. Scan rate affects things like the deflection coils. The inductive load in these coils increases with increasing frequency, so if they were designed for a TV, would not be able to handle the MUCH higher (sometimes 3x) frequencies for a monitor.
The same basic bits and pieces make up TVs and monitors, ie flyback transformers, etc. and these are present in all CRT systems, whether projector or monitor. But, all of these components are designed to work with each other, and overall with the tube itself. So I do not think you could use the PC electronics to drive three projection tubes. For a start, a projection tube itself costs upwards of £600, and that's for rear-projection. Front may be more. Secondly, to connect up all the components would be very complicated and time consuming. Not to mention dangerous. And you're not guaranteed a result at the end either. The flyback transformer is only designed to run one tube after all, whereas it would run three in a projector system. (the same one drives the three to make sure they're in sync I think)
So to answer your question, I don't think the PC monitor pieces would be ideally suited or powered for the projector. But it has crossed my mind to take the three tubes I have and build a system round it. I decided it was too complicated.
Sorry I cannot be more useful! I will look into this with my projector tubes and see how easy it would be to build a system round those.
Hello,
Interesting questions, not sure where to start. The tubes in PC monitors and projectors are similar only in that they are tubes, which have the cathode, anode, etc. that all CRTs have. The one big difference between the two is that projector tubes are essentially single colour tubes which have different coloured phosphors. This means that there is no aperture grid or associated circuitry to align the RGB guns to the RGB pixels. In any case, there are no pixels on the projector tubes, just a mass of phosphors.
The voltages involved would be in roughly the same range, although the scan rate on a monitor would usually be much higher than on a TV. Scan rate affects things like the deflection coils. The inductive load in these coils increases with increasing frequency, so if they were designed for a TV, would not be able to handle the MUCH higher (sometimes 3x) frequencies for a monitor.
The same basic bits and pieces make up TVs and monitors, ie flyback transformers, etc. and these are present in all CRT systems, whether projector or monitor. But, all of these components are designed to work with each other, and overall with the tube itself. So I do not think you could use the PC electronics to drive three projection tubes. For a start, a projection tube itself costs upwards of £600, and that's for rear-projection. Front may be more. Secondly, to connect up all the components would be very complicated and time consuming. Not to mention dangerous. And you're not guaranteed a result at the end either. The flyback transformer is only designed to run one tube after all, whereas it would run three in a projector system. (the same one drives the three to make sure they're in sync I think)
So to answer your question, I don't think the PC monitor pieces would be ideally suited or powered for the projector. But it has crossed my mind to take the three tubes I have and build a system round it. I decided it was too complicated.
Sorry I cannot be more useful! I will look into this with my projector tubes and see how easy it would be to build a system round those.
CRT route
Scot_lad
Don´t be sorry 🙂
I´m just throing out my ideas and hoping that something whill stick 🙂
I have plenty more so I´m not giving up that easy 🙂
Bye for now
Scot_lad
Don´t be sorry 🙂
I´m just throing out my ideas and hoping that something whill stick 🙂
I have plenty more so I´m not giving up that easy 🙂
Bye for now
focal-length
Ravide,
you're right, every time you change focal-length of the lens, automaticaly you should adjust all the distance (LCD to lens and lens to screen).
Any focal-length can be use, however if you use lens 1 with long focal-length, it will make greater distance between LCD to virtual image.
LCD to lens 1 distance should be greater than 2xf-length of lens 1 to produce shrinked virtual image.
You can try it in my diagram & calculation #2.
Lens 2 focal-length depend on how far and how big we want final image at the screen.
see you.
Ravide,
you're right, every time you change focal-length of the lens, automaticaly you should adjust all the distance (LCD to lens and lens to screen).
Any focal-length can be use, however if you use lens 1 with long focal-length, it will make greater distance between LCD to virtual image.
LCD to lens 1 distance should be greater than 2xf-length of lens 1 to produce shrinked virtual image.
You can try it in my diagram & calculation #2.
Lens 2 focal-length depend on how far and how big we want final image at the screen.
see you.
400 W MH bulb, ballast, reflector for $90 Too Big?
One of the more usual things you see at ebay. Looks like a good deal though.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2020161724
Has an electronic type ballast (quiet, important). Reflector is a bit large looking (17" x 10" x 7") especially for a projector panel. What do you think? I emailed the guy, he doesn't know crap about the bulb, expect for that its a mongel base and he says it can take any mongel base MH bulbs.
What do you guys think? A good deal? By the way, speaking of reflectors, why not just buy a whole fixture assembly that has a reflector built in. What I found here may not be a good example, but I'm sure there out there.
One of the more usual things you see at ebay. Looks like a good deal though.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2020161724
Has an electronic type ballast (quiet, important). Reflector is a bit large looking (17" x 10" x 7") especially for a projector panel. What do you think? I emailed the guy, he doesn't know crap about the bulb, expect for that its a mongel base and he says it can take any mongel base MH bulbs.
What do you guys think? A good deal? By the way, speaking of reflectors, why not just buy a whole fixture assembly that has a reflector built in. What I found here may not be a good example, but I'm sure there out there.
Attachments
Metal halide
Hi, I know for fact that ballasts are only suited for bulbs of one specific wattage. Thus you can not use ANY bulb with that ballast.
Hi, I know for fact that ballasts are only suited for bulbs of one specific wattage. Thus you can not use ANY bulb with that ballast.
Not much new
Well there is not much new... I tried using my Mercury Vapor - HomeDepot light last night but have the same problem as Fender...I lost amlost all light due to scatter. I mentioned the other day that this light is AMAZINGLY bright and causes the entire room to glow...but I just cant direct it through my panel.
The reflector that comes with the light (if you want to call it a reflector) covers only the back 1/4 of the light. The light fixture comes with a plastic cover to spread the light and I did not remove this as I would have to break it off and I didnt want to do that unitl I know I will use this lamp. I have some pictures I will attach and more I will provide a link to later that show some simple setups I had (dont laugh too much).
My biggest problem is the size of the bulb...This thing is huge!!! Its about 10 inches long. Are the MercuryHalide bulbs this big???
I would really like to get something quite a bit smaller.
Myren...how big is your light bulb and balast??? Do you have any pics of your setup....I to am using a gutted vg150. My current setup is far from the design I have in mind but it makes everything easily accessible.
OK...here are the pictures I mentioned...
pic1 -- you can see HOW BIG this light is... If I find a way to reflect the light proberly I can tear this apart and make it about 1/3 the size seen but it will still be quite large with a LONG bulb.
pic2 -- The LCD is screwed into the wood and my fresnel is taped to the wood (I know it's my white trash setup). You can see the light is going through but I am getting a very very faint picture on my wall after it goest through my lens (not seen). You can also see that most light is going everywhere but at the LCD.
pic3 -- another view.
pic4 -- I try covering the light assembly with my custom built cardboard cover (lol)...but it makes absolutely no difference (not that I really expected it to) but at least it doesnt light up the entire house now.
pic5 -- same as above but it didnt get any more light through the LCD.
SOMEONE PLEASE help us find a good/proper reflector for the HUGE lights...If we can properly focus the light coming from these lamps we will be set.
Later,
Dave
Well there is not much new... I tried using my Mercury Vapor - HomeDepot light last night but have the same problem as Fender...I lost amlost all light due to scatter. I mentioned the other day that this light is AMAZINGLY bright and causes the entire room to glow...but I just cant direct it through my panel.
The reflector that comes with the light (if you want to call it a reflector) covers only the back 1/4 of the light. The light fixture comes with a plastic cover to spread the light and I did not remove this as I would have to break it off and I didnt want to do that unitl I know I will use this lamp. I have some pictures I will attach and more I will provide a link to later that show some simple setups I had (dont laugh too much).
My biggest problem is the size of the bulb...This thing is huge!!! Its about 10 inches long. Are the MercuryHalide bulbs this big???
I would really like to get something quite a bit smaller.
Myren...how big is your light bulb and balast??? Do you have any pics of your setup....I to am using a gutted vg150. My current setup is far from the design I have in mind but it makes everything easily accessible.
OK...here are the pictures I mentioned...
pic1 -- you can see HOW BIG this light is... If I find a way to reflect the light proberly I can tear this apart and make it about 1/3 the size seen but it will still be quite large with a LONG bulb.
pic2 -- The LCD is screwed into the wood and my fresnel is taped to the wood (I know it's my white trash setup). You can see the light is going through but I am getting a very very faint picture on my wall after it goest through my lens (not seen). You can also see that most light is going everywhere but at the LCD.
pic3 -- another view.
pic4 -- I try covering the light assembly with my custom built cardboard cover (lol)...but it makes absolutely no difference (not that I really expected it to) but at least it doesnt light up the entire house now.
pic5 -- same as above but it didnt get any more light through the LCD.
SOMEONE PLEASE help us find a good/proper reflector for the HUGE lights...If we can properly focus the light coming from these lamps we will be set.
Later,
Dave
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Quick question
I just realized how long my previous post was...I thought it was going to put links to my images...
If I should not make posts this long or not include this many images please let me know. I hope I havent made this page a pain to load for those people with slow modems...I just wanted to post my progress...
again let me know if posts like the one above are appropriate or not.
Thanks,
Dave
I just realized how long my previous post was...I thought it was going to put links to my images...
If I should not make posts this long or not include this many images please let me know. I hope I havent made this page a pain to load for those people with slow modems...I just wanted to post my progress...
again let me know if posts like the one above are appropriate or not.
Thanks,
Dave
bulbsize
Hi Superdave,
in the end you will, just as me, have to put a "blind" over the bulb, so it is pointlike. Otherwise you will get an image, that is blurry on the edges. This blind (sheet of metal with a hole of approx 1 inch diameter in it) should be placed as close to the origin of light (the place inside the bulb where the arc is) as possible. Obviously you will lose a lot of light as you put the blind further away. Your bulb has a large glass sphere around the arc, thus you can not put a blind close to it. Page 76 of this thread shows my bulb, which is a HQI-TS. That is as small as it gets in floodlight-style (cheap) Metal-Halides. The HQI-T of equal wattage are screw-in type of bulbs and are probably twice as long as the HQI-TS. Don't ask me why. Since I get on all of your's nerves with that "blind"-thing I should add that this is what made the difference from acceptable to good image in my case. And it makes sence, too. Thats why I think you won't get around it. I should add, that I have a lens right behind that blind which spreads the light to the fresnel. That is the way the OHP I used was designed. (The OHP did not have a "blind", since it had a point-like lightsource to start with)
Hope any of this helps.
Frank Batzen
Hi Superdave,
in the end you will, just as me, have to put a "blind" over the bulb, so it is pointlike. Otherwise you will get an image, that is blurry on the edges. This blind (sheet of metal with a hole of approx 1 inch diameter in it) should be placed as close to the origin of light (the place inside the bulb where the arc is) as possible. Obviously you will lose a lot of light as you put the blind further away. Your bulb has a large glass sphere around the arc, thus you can not put a blind close to it. Page 76 of this thread shows my bulb, which is a HQI-TS. That is as small as it gets in floodlight-style (cheap) Metal-Halides. The HQI-T of equal wattage are screw-in type of bulbs and are probably twice as long as the HQI-TS. Don't ask me why. Since I get on all of your's nerves with that "blind"-thing I should add that this is what made the difference from acceptable to good image in my case. And it makes sence, too. Thats why I think you won't get around it. I should add, that I have a lens right behind that blind which spreads the light to the fresnel. That is the way the OHP I used was designed. (The OHP did not have a "blind", since it had a point-like lightsource to start with)
Hope any of this helps.
Frank Batzen
Those pics do look green...maybe a camera issue? I have the same light, and the light is DEFINITELY not green...very white with some blue. Here is an excerpt from an reef aquarium website (so take with a grain of salt 😉 ):
"When you see a bright light illuminating some industrial building and it has a decided bluish cast - that's mercury vapor. Mercury vapor lamps have an output spectra that is almost entirely blue-white, with very little red. Worse, the spectra is not continuous, there are spectral peaks at certain wavelengths. These lamps, although not useless - there is no doubt very good results can be obtained with them - are equivalent to cool white fluorescents."
(Source = http://www.killi.net/lighting/ )
The limited spectra is probably related to the low CRI of MV bulbs that has been mentioned before. I'm not sure how bad this will be for us...
Reflectors--The problem with some of the Grow light or aquarium reflectors is they might not be truly parabolic or elliptical. This would probably be OK, but for high efficiency and consistency, a high precision reflector is essential. A nice elliptical reflector could potentially focus the light from a size of the LCD to the size of the projection lens...just as a frenel does. A parabolic setup would allow the use of a single frensel to turn parallel rays into converging rays. Both setups would minimize light scatter/random angle light and therefore reduce any "washout".
jjasniew,
The MH fixture/ballast on ebay is interesting...pretty cheap, but no bulb. I think 250watt bulbs are not as common as 400watt (also, higher wattage bulbs are often cheaper!). You can get a new 400watt MH ballast for $45.00 here:
http://www.vitrex.net/~lighting/mh400ballast/mh400.htm
http://lighting.webpipe.net/ballast.htm
That's a pretty good deal!
SuperDave, those bulbs are large! I know that MH bulbs for reef aquariums can be smaller (cylindrical shapes). I think the glass envelope is only for UV filtering purposes...but I DON'T recommend removing it! That's a quick way to burn out your retinas and/or house. I agree with Myren...a good reflector is the key to success with any point source light. Oh yeah, there are two bolt/screws that hold the reflecor onto the fixture. I was able to remove it without damaging it, so that might help you out. Good luck with it.
-f4
"When you see a bright light illuminating some industrial building and it has a decided bluish cast - that's mercury vapor. Mercury vapor lamps have an output spectra that is almost entirely blue-white, with very little red. Worse, the spectra is not continuous, there are spectral peaks at certain wavelengths. These lamps, although not useless - there is no doubt very good results can be obtained with them - are equivalent to cool white fluorescents."
(Source = http://www.killi.net/lighting/ )
The limited spectra is probably related to the low CRI of MV bulbs that has been mentioned before. I'm not sure how bad this will be for us...
Reflectors--The problem with some of the Grow light or aquarium reflectors is they might not be truly parabolic or elliptical. This would probably be OK, but for high efficiency and consistency, a high precision reflector is essential. A nice elliptical reflector could potentially focus the light from a size of the LCD to the size of the projection lens...just as a frenel does. A parabolic setup would allow the use of a single frensel to turn parallel rays into converging rays. Both setups would minimize light scatter/random angle light and therefore reduce any "washout".
jjasniew,
The MH fixture/ballast on ebay is interesting...pretty cheap, but no bulb. I think 250watt bulbs are not as common as 400watt (also, higher wattage bulbs are often cheaper!). You can get a new 400watt MH ballast for $45.00 here:
http://www.vitrex.net/~lighting/mh400ballast/mh400.htm
http://lighting.webpipe.net/ballast.htm
That's a pretty good deal!
SuperDave, those bulbs are large! I know that MH bulbs for reef aquariums can be smaller (cylindrical shapes). I think the glass envelope is only for UV filtering purposes...but I DON'T recommend removing it! That's a quick way to burn out your retinas and/or house. I agree with Myren...a good reflector is the key to success with any point source light. Oh yeah, there are two bolt/screws that hold the reflecor onto the fixture. I was able to remove it without damaging it, so that might help you out. Good luck with it.
-f4
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