CRTs
I'm gonna have to have a look at that website with the CRT vs LCD people, 'cos I'm going in the direction of CRT. I've been thinking about it for a while and experimenting, sorry I've not had much time to place results plus I don't have many results anyway.
Basically, I'm using the same 5" lens to project, but using a 5" black and white CRT, with the brightness cranked up. Very 'Blue Peter' I know, but the results (even in black and white) are very surprising. The image was very bright and clear. My plan is to take an RGB output, split the sync signal off the green (or composite) output of something (ideally the PS2) and insert it into the decoder chip on the TV. This all sounds complicated but it's really easy. I can sort out some diagrams if anyone else is interested.
One thing to watch for with CRTs is they pack a hell of a kick due to the high capacitance effect of the tube. Don't touch it until it's discharged (either over time or with a giant resistor). I will place a load of links I have found later on tonight when I get home from work.
Can I get a heads-up on how many people are interested in this? The CRT cancels out a hell of a lot of issues that the LCD creates, albeit at the cost of creating a load of new CRT-specific issues. I'm currently looking for red green and blue filters for the monochrome screens, to produce a full colour image.
Sorry this email is probably a bit cryptic, I will write it properly later on when I get home.
Cheers,
Chris.
I'm gonna have to have a look at that website with the CRT vs LCD people, 'cos I'm going in the direction of CRT. I've been thinking about it for a while and experimenting, sorry I've not had much time to place results plus I don't have many results anyway.
Basically, I'm using the same 5" lens to project, but using a 5" black and white CRT, with the brightness cranked up. Very 'Blue Peter' I know, but the results (even in black and white) are very surprising. The image was very bright and clear. My plan is to take an RGB output, split the sync signal off the green (or composite) output of something (ideally the PS2) and insert it into the decoder chip on the TV. This all sounds complicated but it's really easy. I can sort out some diagrams if anyone else is interested.
One thing to watch for with CRTs is they pack a hell of a kick due to the high capacitance effect of the tube. Don't touch it until it's discharged (either over time or with a giant resistor). I will place a load of links I have found later on tonight when I get home from work.
Can I get a heads-up on how many people are interested in this? The CRT cancels out a hell of a lot of issues that the LCD creates, albeit at the cost of creating a load of new CRT-specific issues. I'm currently looking for red green and blue filters for the monochrome screens, to produce a full colour image.
Sorry this email is probably a bit cryptic, I will write it properly later on when I get home.
Cheers,
Chris.
CRT tubes, prices
Scot_lad,
I'm interested in the CRT projection, since it's hard to get LCD panels here for a reasonable price (no ebay-like sites). I think I have a better chance to find small size CRTs than a good lcd.
How do you tweak the contrast and brightness on the crt?
One more question: is is possible to use a 14" normal computer monitor CRT and increase the brightness on that? Then you don't have to use color filters, and I know that calibrating CRT projectors is not easy. You'll have to be able to move the 3 crt tubes on a horizontal and vertical axis until you have all 3 images projected to the same area, else it's gonna be blurry. Commercial crt projector suppliers even come to your house to have it done correctly for the first time, and you have to re-calibrate it every time you move you projector to a new location.
By using a color crt you get rid of all this.
Thanks in advance for the links and info 🙂
Gabriel
Scot_lad,
I'm interested in the CRT projection, since it's hard to get LCD panels here for a reasonable price (no ebay-like sites). I think I have a better chance to find small size CRTs than a good lcd.
How do you tweak the contrast and brightness on the crt?
One more question: is is possible to use a 14" normal computer monitor CRT and increase the brightness on that? Then you don't have to use color filters, and I know that calibrating CRT projectors is not easy. You'll have to be able to move the 3 crt tubes on a horizontal and vertical axis until you have all 3 images projected to the same area, else it's gonna be blurry. Commercial crt projector suppliers even come to your house to have it done correctly for the first time, and you have to re-calibrate it every time you move you projector to a new location.
By using a color crt you get rid of all this.
Thanks in advance for the links and info 🙂
Gabriel
jjasniew-
Please note that I've read conflicting reports on the response time of the KDS- I've read 11ms, and I've read 35. So I'm not exactly sure. It was more than fast enough for DVDs and TV, however. It's so frustrating having a panel in front of you that used to work, and you have NO IDEA how it could be fixed. The ribbon cable should still work by holding it in like I've tried a thousand times.
I am also wondering how Myren managed to relocate the board- and that's why I'm going to wait for pics and a detailed description of the process before I think about getting a viewsonic. And that's if this whole RMA thing works out. I'm tempted just to get a projection panel from Ebay- but the contrast ratio and response times aren't generally as good.
CRT projection definately has it's advantages, but the curved screen of most CRTs is the problem. My TV is almost bright enough to use, but I think I'd need a large glass lens (not fresnel), and a curved surface on which to project.
Please note that I've read conflicting reports on the response time of the KDS- I've read 11ms, and I've read 35. So I'm not exactly sure. It was more than fast enough for DVDs and TV, however. It's so frustrating having a panel in front of you that used to work, and you have NO IDEA how it could be fixed. The ribbon cable should still work by holding it in like I've tried a thousand times.
I am also wondering how Myren managed to relocate the board- and that's why I'm going to wait for pics and a detailed description of the process before I think about getting a viewsonic. And that's if this whole RMA thing works out. I'm tempted just to get a projection panel from Ebay- but the contrast ratio and response times aren't generally as good.
CRT projection definately has it's advantages, but the curved screen of most CRTs is the problem. My TV is almost bright enough to use, but I think I'd need a large glass lens (not fresnel), and a curved surface on which to project.
the viewsonic was quite nice with component respects. a bit more circuitry than i'd like, but it got the hell out my way nicely.
the main panel has a one inch wide PCB strip bordering it on two sides. Its fairly securely mounted on. Theres a ribbon cable coming off these mini-PCB strips that goes to the controller circuitry. You can just dangle the controller circuitry off the side.
photos included when i get my panel back. ups makes my blood boil.
the main panel has a one inch wide PCB strip bordering it on two sides. Its fairly securely mounted on. Theres a ribbon cable coming off these mini-PCB strips that goes to the controller circuitry. You can just dangle the controller circuitry off the side.
photos included when i get my panel back. ups makes my blood boil.
Lenses, forums, and a question
First, a plug: I highly recommend Surplus Shed as a source for projection lenses. I ordered the Delta TV projection lens from them on Thursday, and it arrived beautifully packed and in perfect condition on Saturday. Good lens, too. I'm not affiliated with them in any way, I just think good companies deserve to be known.
Second, there's a Yahoo group for DIY projectors here ... traffic is kind of low but I hope that some of this discussion can be moved there and it'll pick up. It's certainly a lot easier to follow various topics on a threaded discussion board than on a single 60+ page thread.
Finally, the question. I posted earlier (a few pages ago) about my specialized application. For this application, I need high magnification (about 15X) over a short distance (about a foot). The Delta lens I got, while nice, isn't quite powerful enough for the purpose. Can anyone offer any suggestions?
First, a plug: I highly recommend Surplus Shed as a source for projection lenses. I ordered the Delta TV projection lens from them on Thursday, and it arrived beautifully packed and in perfect condition on Saturday. Good lens, too. I'm not affiliated with them in any way, I just think good companies deserve to be known.
Second, there's a Yahoo group for DIY projectors here ... traffic is kind of low but I hope that some of this discussion can be moved there and it'll pick up. It's certainly a lot easier to follow various topics on a threaded discussion board than on a single 60+ page thread.
Finally, the question. I posted earlier (a few pages ago) about my specialized application. For this application, I need high magnification (about 15X) over a short distance (about a foot). The Delta lens I got, while nice, isn't quite powerful enough for the purpose. Can anyone offer any suggestions?
Hi.
I've read along since this thread was about 20 posts long. I've learned a lot and am constructing my own projector now. I'm using a Demolux Overheadprojector and an "NEC LCD 400V" TFT-Display from about 1998. The first piece of Information I would like to share is about the Reaction Time of TFT-Displays. The Reaction Time of mine is stated at 50ms, which in public opinion seems far too much for video applications. Before I disassembled it (pictures will be posted as soon as I can get a camera) I watched TV on it, connected to the VGA-out of my computer. Even watching soccer there was absolutely no pixel-smearing visible. Quintessentially I would say that you have to see how a display performs and not rely on the specs.
As several members of this board I also have a problem putting the PCBs out of the path of light. There are two ribbon cables which are about 4cm long. Much too little to go without elongation. It seems impossible to get suitable plugs for them (45 connections with .5mm pitch) so I will have to be quite intrusive. I will, probably tomorrow, use a 80 pin UDMA 100 harddisc cable and solder it to the PCBs to connect the controller board with the display. This is exactly whats going to go wrong 🙂. Up to this point building the projector has been a fun and easy task, but now its going to get serious. Axeman, I will be thinking of you 🙂
The Overheadprojector used to be a 250W halogen one, not too brite, a bulb at 15 EUR lasting just 50h and producing very yellow lite. So i gutted it and equipped it with a 400W Hqi discharge lamp, which used to light a tennis court. The heat is obviously less than that of a 500W halogen floodlight, but still very hot. I was planning on building the projector into the base of my bed, but desided on leaving it in the overheadprojector housing since i am not willing to sacrifice my life for a big screen. The cooling in the original housing is very efficient. Anyway, the wisdom I want to share about the lightsource (and I think Hqi is the only way to go, but that's just my oppinion) is basically that it works. 400W Hqi-bulbs are less then "point-lightsources" The area that lights up is about 6 squarecentimeters. When the light was set in the projector and I projected an image to the wall, the center of the image was sharp, but the vast majority of the image at the sides of the image was very blurry. First I thought it was because of the lightsource being not small enough (pointlike lightsource). But when I adjusted the distance of the lightsource to the fresnellens of the OHP the entire picture became very sharp.
With a normal metal halide OHP the bulb last about 2000h and cost about 250EUR! A new bulb for my setup will cost 75EUR new and a lot less used.
I think thats it for now, hopefully noone will be lost in this post.
g!zmo
I've read along since this thread was about 20 posts long. I've learned a lot and am constructing my own projector now. I'm using a Demolux Overheadprojector and an "NEC LCD 400V" TFT-Display from about 1998. The first piece of Information I would like to share is about the Reaction Time of TFT-Displays. The Reaction Time of mine is stated at 50ms, which in public opinion seems far too much for video applications. Before I disassembled it (pictures will be posted as soon as I can get a camera) I watched TV on it, connected to the VGA-out of my computer. Even watching soccer there was absolutely no pixel-smearing visible. Quintessentially I would say that you have to see how a display performs and not rely on the specs.
As several members of this board I also have a problem putting the PCBs out of the path of light. There are two ribbon cables which are about 4cm long. Much too little to go without elongation. It seems impossible to get suitable plugs for them (45 connections with .5mm pitch) so I will have to be quite intrusive. I will, probably tomorrow, use a 80 pin UDMA 100 harddisc cable and solder it to the PCBs to connect the controller board with the display. This is exactly whats going to go wrong 🙂. Up to this point building the projector has been a fun and easy task, but now its going to get serious. Axeman, I will be thinking of you 🙂
The Overheadprojector used to be a 250W halogen one, not too brite, a bulb at 15 EUR lasting just 50h and producing very yellow lite. So i gutted it and equipped it with a 400W Hqi discharge lamp, which used to light a tennis court. The heat is obviously less than that of a 500W halogen floodlight, but still very hot. I was planning on building the projector into the base of my bed, but desided on leaving it in the overheadprojector housing since i am not willing to sacrifice my life for a big screen. The cooling in the original housing is very efficient. Anyway, the wisdom I want to share about the lightsource (and I think Hqi is the only way to go, but that's just my oppinion) is basically that it works. 400W Hqi-bulbs are less then "point-lightsources" The area that lights up is about 6 squarecentimeters. When the light was set in the projector and I projected an image to the wall, the center of the image was sharp, but the vast majority of the image at the sides of the image was very blurry. First I thought it was because of the lightsource being not small enough (pointlike lightsource). But when I adjusted the distance of the lightsource to the fresnellens of the OHP the entire picture became very sharp.
With a normal metal halide OHP the bulb last about 2000h and cost about 250EUR! A new bulb for my setup will cost 75EUR new and a lot less used.
I think thats it for now, hopefully noone will be lost in this post.
g!zmo
Interesting URL for rear projection setup!
http://www.stewartfilm.com/product_information/projection_screens_17.html
http://www.stewartfilm.com/product_information/projection_screens_17.html
JonathanTheRed
Looks like you need an achromat with a focal length of about 19mm to achieve your goal. Given that the object to be magnified has to be located within 1-2 focal lengths of the lens, you need to find a large aperture lens with this short focal length to cover all your image.
Looks like you need an achromat with a focal length of about 19mm to achieve your goal. Given that the object to be magnified has to be located within 1-2 focal lengths of the lens, you need to find a large aperture lens with this short focal length to cover all your image.
CRTs and stuff
gabriel:
Using a 14" colour monitor would certainly solve a lot of problems, with colour definition, convergance, etc, but you would surely have to use a huge lens to get the 14" monitor projected onto the wall?
One good thing about black and white CRTs is that they don't have any pixels on them, they are effectively just a screen covered in phosphors. This gets rid of pixellation problems. Also, the constrast on these is brilliant.
To tweak the constrast/brightness, you can do one of several things, depending on your CRT. My experimental one has a chip inside it which I'm going to bastardise to increase the output voltage for driving the CRT, this isn't complicated I will place diagrams and stuff when I get them made. Which should be this or next week sometime.
Flipping the image horizontally and vertically is very simple indeed, all you need to do is reach inside the CRT and desolder and resolder the horizontal and vertical deflection coils with the opposite polarity. Very simple.
As far as convergence is concerned, don't believe what you hear, it is not nearly as difficult as the proffesionals would have you believe. For a start, you don't need vertical calibration, since they should all be on an identical horizontal axis (ie, aligned in the up/down direction). The only problem is aligning them in the left/right direction. This isn't difficult. If you really want to get clever, you could install a simple system to figure out the distance to the screen and converge the lenses yourself, I'm sure I could manage that right now without too much hassle.
But make sure you know what you're doing. Even with a small CRT, it holds big voltages. You may want to do a search for 'CRT safety' on the web for info about this.
Cheers.
gabriel:
Using a 14" colour monitor would certainly solve a lot of problems, with colour definition, convergance, etc, but you would surely have to use a huge lens to get the 14" monitor projected onto the wall?
One good thing about black and white CRTs is that they don't have any pixels on them, they are effectively just a screen covered in phosphors. This gets rid of pixellation problems. Also, the constrast on these is brilliant.
To tweak the constrast/brightness, you can do one of several things, depending on your CRT. My experimental one has a chip inside it which I'm going to bastardise to increase the output voltage for driving the CRT, this isn't complicated I will place diagrams and stuff when I get them made. Which should be this or next week sometime.
Flipping the image horizontally and vertically is very simple indeed, all you need to do is reach inside the CRT and desolder and resolder the horizontal and vertical deflection coils with the opposite polarity. Very simple.
As far as convergence is concerned, don't believe what you hear, it is not nearly as difficult as the proffesionals would have you believe. For a start, you don't need vertical calibration, since they should all be on an identical horizontal axis (ie, aligned in the up/down direction). The only problem is aligning them in the left/right direction. This isn't difficult. If you really want to get clever, you could install a simple system to figure out the distance to the screen and converge the lenses yourself, I'm sure I could manage that right now without too much hassle.
But make sure you know what you're doing. Even with a small CRT, it holds big voltages. You may want to do a search for 'CRT safety' on the web for info about this.
Cheers.
Displays
I was thinking (i can't remember if anyone has mentioned this in the thread) what about those tiny little displays that are in the viewfinders of camcorders. are they LCD or CRT? in newer cameras they are colour lcds (i think). they are as expensive as those small DLP's to buy them individually - but if someone had the oportuninty to buy a broken video camera (or three) and get the small displays working, then there would be no need for the high heat outputting lights...
just a thought
I was thinking (i can't remember if anyone has mentioned this in the thread) what about those tiny little displays that are in the viewfinders of camcorders. are they LCD or CRT? in newer cameras they are colour lcds (i think). they are as expensive as those small DLP's to buy them individually - but if someone had the oportuninty to buy a broken video camera (or three) and get the small displays working, then there would be no need for the high heat outputting lights...
just a thought
Field Fresnel lens
Scot_lad,
I was thinking about this, the big diagonal size of the 14" CRT should not be a problem. Just like using a fresnel for the equal spread of light between the light source and the LCD in the others' setups, a reversed fresnel can be used to collect the output from the LCD/CRT to focus and push it towards the projection lens. take a look at
http://www.fresnel-optics.com/pdf/condenser_lenses.PDF
they call this lens a "field lens". They also have some schematics to show how it works.
"Fresnel condenser lenses are used to collect and
collimate light nto the LCD panel, and field lenses focus the
LCD image to the projection lens system."
The only thing to do is to find a fresnel with 14" or 12" diagonal size. Probably a glass fresnel would give better image quality, but that's way too expensive.
So I think that placing such a condenser in front of my tweaked CRT tube would solve the size problem. I am also thinking about building a custom box/housing for the [CRT->Fresnel->Proj.lens] and other parts, I don't think that taking apart a crt monitor is a big task 🙂
Here in Europe many people place some sort of self-adhesive fresnels on the rear windshield of their cars (to see better who's coming from behind? 🙂 ) , I thought I could buy one and stick it to a glass sheet. Proper cooling (2 or 3 fans) should be more than enough to keep the whole setup from melting.
I am already searching for a 12" VGA or SVGA color monitor to start experimenting. Don't know what to say about the size of the finished projector.
Gabriel
Scot_lad,
I was thinking about this, the big diagonal size of the 14" CRT should not be a problem. Just like using a fresnel for the equal spread of light between the light source and the LCD in the others' setups, a reversed fresnel can be used to collect the output from the LCD/CRT to focus and push it towards the projection lens. take a look at
http://www.fresnel-optics.com/pdf/condenser_lenses.PDF
they call this lens a "field lens". They also have some schematics to show how it works.
"Fresnel condenser lenses are used to collect and
collimate light nto the LCD panel, and field lenses focus the
LCD image to the projection lens system."
The only thing to do is to find a fresnel with 14" or 12" diagonal size. Probably a glass fresnel would give better image quality, but that's way too expensive.
So I think that placing such a condenser in front of my tweaked CRT tube would solve the size problem. I am also thinking about building a custom box/housing for the [CRT->Fresnel->Proj.lens] and other parts, I don't think that taking apart a crt monitor is a big task 🙂
Here in Europe many people place some sort of self-adhesive fresnels on the rear windshield of their cars (to see better who's coming from behind? 🙂 ) , I thought I could buy one and stick it to a glass sheet. Proper cooling (2 or 3 fans) should be more than enough to keep the whole setup from melting.
I am already searching for a 12" VGA or SVGA color monitor to start experimenting. Don't know what to say about the size of the finished projector.
Gabriel
lense question
Hello,
It has been a long time since I have posted but I have been watching everyday. I just had a question about projection lenses. I have a 4" lcd from a psone. I was just wondering how large of a diameter should the projection lenses be? Do the delta projection lenses work good? And what is the forcal length, is it how far away it should be from the lcd?
Thanks a lot
Chris
Hello,
It has been a long time since I have posted but I have been watching everyday. I just had a question about projection lenses. I have a 4" lcd from a psone. I was just wondering how large of a diameter should the projection lenses be? Do the delta projection lenses work good? And what is the forcal length, is it how far away it should be from the lcd?
Thanks a lot
Chris
Hmm..
How the hell you boost CRT brightness?
Well CRT anyway is too hardcore for me so I won't be taking that route.. But anyway OHP projection lens works with 14" CRT as well than with 15" LCD. Just a suggestion..
I have nothing new.. Screen is still lying at the floor, hopefully I'll get it mounted this week.
Bläh bläh.. That's all.
How the hell you boost CRT brightness?
Well CRT anyway is too hardcore for me so I won't be taking that route.. But anyway OHP projection lens works with 14" CRT as well than with 15" LCD. Just a suggestion..
I have nothing new.. Screen is still lying at the floor, hopefully I'll get it mounted this week.
Bläh bläh.. That's all.
CRTs and Fresnals
Hey All,
I'm not sure about the CRT thing, I'm going for a small 5" LCD because I mainly want it for video / small size, but check this CRT link out, not sure how good it works though:
http://www.bstvcentral.b0x.com/
There are several people selling plans of how to turn a normal CRT tv / monitor into a projector, but the above is free.
Happy projecting,
James
Hey All,
I'm not sure about the CRT thing, I'm going for a small 5" LCD because I mainly want it for video / small size, but check this CRT link out, not sure how good it works though:
http://www.bstvcentral.b0x.com/
There are several people selling plans of how to turn a normal CRT tv / monitor into a projector, but the above is free.
Happy projecting,
James
Need a source for cheap First Surface Mirror/Sheet
Joe:
Great info on the Stewart Mirrors and the Fresnel lenses. I am still searching for a source of reasonably priced first surface mirrors, be it mylar or glass (probably has to take a mortgage on that one).
Joe:
Great info on the Stewart Mirrors and the Fresnel lenses. I am still searching for a source of reasonably priced first surface mirrors, be it mylar or glass (probably has to take a mortgage on that one).
Lokost
You can find reasonable priced front surface mirrors at most glass shops. Just call the local glass shop. I got a 32" X 22" for $24.00 US.
High quality too.
Tim
You can find reasonable priced front surface mirrors at most glass shops. Just call the local glass shop. I got a 32" X 22" for $24.00 US.
High quality too.
Tim
Front surface mirrors
Surplus Shed (www.surplushsed.com) sells front surface mirrors CHEAP! Look in their closeout section.
Surplus Shed (www.surplushsed.com) sells front surface mirrors CHEAP! Look in their closeout section.
Surplus Shed
Try
http://www.surplusshed.com/list.cfm?ID=L1812&Category=Lenses
for a lens that accomodates the smaller LCD panels.
These guy also have mirrors, as was mentioned.
Try
http://www.surplusshed.com/list.cfm?ID=L1812&Category=Lenses
for a lens that accomodates the smaller LCD panels.
These guy also have mirrors, as was mentioned.
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