| blueknyt |
Ive seen mention of slide projectors DIY but havent been able to find the thread on how these were built. Is it as simple as 2.5" LCD and guting a slide projector carriage assembly to fit the LCD where the slide would normaly go?
Also
call me stupid but talking about the differnt lenses kinda confusing me But:
Using PS1LCD what lenses do i need to put the projection on a wall 10' away, would any triplet do? does one need to use Both fesnel lenses infront and behind the LCD? when cutting the Fesnels the center has to be centered with the LCD and trim the outsides? and read somewhere about the lenses being split?
I am reading but not catching something right.
I can get my lighting for free, the only real cost is the LCD,Lenses,and UVfilter. is there a list of this parts somewhere, some of the links listed are dead.
whats the diff between a "Cold Mirror" an a "standard mirror?
im trying to build a unit in a minitower PC case, posibly using 2 mirrors in a Horse Shoe config from bottom to top and hanging it sideways
will try to attach a basic rep of my idea |
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| blueknyt |
in useing this equation from DIYprojectorcompany:
distance-FL : (from projector to screen) 120"
X
LCD Diag size 5"
/ (divided By)
Focal Length
= Projection diag size
Focal Length is what? what the lense puts out?
how far the lens has to be from the LCD to project the image?
a lens with 380mm FL has is only 14.96 inchs from wall? |
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| ancorp |
Hey,
Welcome to the forum:)
The focal lenght is pretty much the ammount of magnification... higher focal lenght, smaller image... and the lens is pretty much around the same distance from the lcd to the lens back as the focal length.
A cold mirror reflects the light but passes the heat throught, thus having heatsinks and fans on the back of the mirrors, it can really improve the cooling of your lcd.
Yes, the LCD has to be centered.
As for the rest, im sure other forum members can answer that better.
Good luck on your build.
Cheers,
Alex |
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| Guy Grotke |
In most designs, you need more distance between the LCD and the projection lens than you need between the lamp and the LCD. So your design will probably work better with the LCD horizontal between the two mirrors.
You can make a very simple projector using a CRT or backlit LCD and one positive lens. The distance between the LCD, lens, and screen all are described by this equation:
1/lens focal length = 1/LCD to lens + 1/lens to screen
Of course,all the dimensions have to be the same units. You can try plugging some numbers in to see what effect the focal length has. When you design a projector for a particular room, you can determine the lens to screen distance (throw distance) and then think about how much magnification you want. For example, if you use a 15" LCD and want a 90" image, then M = 90/15 = 6.
Then knowing M and the throw distance, use this:
lens fl = (throw distance) / (M+1)
That's enough for a very simple projector. If you get a very wide diameter lens, then it won't be too bad watching it in total darkness.
If you want a better projector, then you need to use a stripped LCD with a light condensor system. That usually consists of a metal halide lamp and some fresnel lenses which generate an even cone of light through the LCD that gets focussed right at the projection lens. This is a second projection system that follows the same rules, but is usually simplified by using two fresnels. The condensor fresnel gets light from a lamp located at the fresnel's focal distance. That makes parallel rays come out the other side. Then the light enters the field fresnel and gets focussed on the other side at that fresnel's focal distance. Hopefully, that point is inside the projection lens. The LCD can go between the fresnels or just after the field fresnel. To design a good projector, you need to find a combination of the two projection systems that puts the projection lens at the right distance from the LCD, and then gets the condensed light focussed at that same point.
Of course, you have to work with what is available! You won't find any 1280 by 1024 5" LCDs, 700 mm fl triplet lenses, etc. Lamps, reflectors, fresnels, LCDs, and projection lenses come in a limited number of sizes and specs. There are problems to solve like removing excess InfraRed and UltraViolet light from the lamp's light, and getting adequate cooling to heat-sensitive parts of your projector. |
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| CKSMartin |
Almost a year ago I dabbled with a slide projector turned TV projector. I found an old Kodak one-slide-at-time projector on ebay. Using a dremel I expanded the top slot and was able to slide a LCd 2" tv panel into place and then ran a ran on top, sucking the heat out from the bulb.
The bulb itself is encased in an aluminum box enclosure, with a single convex lense. The light then focuses through the LCd monitor and out an adjustable lense. I used a PC cooling fan, to try and cool the LCD.
Problem was I got a circular projection, not square, and I got these rolling bands of color on the picture- I think it was a bad power supply, but I wondered if the heat had somehow damged the LCD.
Can the light hitting the LCD panel generate heat? Ir is the heat strictly emitted from the light?
Whole thing was about the size of a toaster.
Got busy and boxed it up. Been thinking about dragging it back out. |
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| blueknyt |
Thank you for your responses, i willdo my best to Not be dense, and try to ask the questions in a way to understand things better.
ok, i guess the FL/lens terms im missunderstanding, how do you decypher this info on the lenses?
which numbers mean what?
granted my mental math sucks, but my calculator works fine. so following the formula is ok aslong as i understand what the formula is asking FL seems to mean differnt things (hence missing the connection)
ive seen what folks use, but not understanding how they decided what to use and how to set it up
I guess my design is an offshoot of the Pico model. i do want to keep it compact as posible as it will hang from ceiling in the back of the room. I do understand alittle about the fresnels now, so i have revamped my first design Input on the idea would be most welcome
(helpful online converter http://www.convert-me.com/en/convert/length )
perhaps im not using the correct search words
thanks again |
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| Guy Grotke |
First let me comment on your new design picture: The fresnels need to be much closer to the LCD. You may find fresnels that will both go 10 to 25 mm below the LCD. Or you may find fresnels that require the lower condensor fresnel to be 10 to 25 mm below the LCD, and the upper field fresnel 10 to 25 mm above the LCD. Depends on the focal length of the field fresnel compared to the LCD to projection lens distance.
Now regarding the numbers you see printed on projection lenses. There are usually two numbers:
fl = Focal Length sometimes in mm, sometimes in inches. This is the distance between an object and the center of the lens, if you were focussing an image of the object on a screen an infinite distance away. Conversely, if you point the lens at an object very far away, like the sun, then this is the distance between the center of the lens and the image you can form with it. (ie. burning ants) Sometimes also called EFL (Effective Focal Length)
f (usually in an italic font) = The f-stop of the lens, which comes from photography. It is a number generally between 1.0 and 22 which is determined by:
f = Focal Length / diameter
This is a measure of how much light the lens will collect from a diffuse object, which is pretty much meaningless for projection where we use a condensor system to direct all the light into the lens.
BFL = back focal length, which is just EFL - about half the length of the lens. Makes it easier to measure distances from the lens.
The number you almost never see is the field angle, which is very important for projection! Large format designs (ie 15-17" LCDs) need lenses with field angles > 30 degrees. If the field angle is not wide enough, then your corners are too dim or cut off. |
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| blueknyt |
CKSMartin thanks for sharing,
unless im wrong in my understanding (recently aquired) light emittedfrom a bulb doesnt travel parallel when hiting the LCD initialy, but the LCD DOES filter the light parrallel. so the use of the fresnel lens is to grab the Radiant light waves and redirect them in a parallel fasion through the LCD in an even pattern, however the heat from the bulb would warp the fresnel so one would need a glass buffer/heat dam to insulate the Fresnel while allowing the light to pass.
ok im also guessing the light source doesnt have to be close to the LCD aslong as a certain amount of Pattern Focused light reaches the LCD. IE bulb, UV glass, fresnel, mirror, fresnel, LCD triplet
so then i just need to learn how to read the lenses and understand what thier values mean |
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| Guy Grotke |
Light is generally radiated in all directions from an arc lamp. A fresnel at the right distance from the arc will capture part of that light and refract it into roughly parallel rays on its other side. If the fresnel is closer to the lamp, it will capture more of the light, just because it intersects more of the rays. This only works up to a point. If the angle of the rays to the corners gets above 45 degrees, then most of it will be reflected from the fresnel surface. If you change to a fresnel with a longer focal length, (and move it out to that distance from the lamp arc), then it will capture fewer of the rays.
Some designs use a pre-condensor lens right up against the lamp to capture even more rays and direct them all to the fresnel. Either way, if you have a spherical reflector behind the lamp, more of the light will get to the fresnel.
Light going through an LCD doesn't have to be parallel. LCDs have a viewing angle which describes the useful cone the light through a pixel can travel. In my projector, I have both fresnels together on the lamp side of the LCD. So the light travels through the LCD as a converging cone. |
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| CKSMartin |
The slide projector I chose had no fan built in it, and the lens by the light was fairly thick. I assumed that since slide didn't melt in the thing, an LCD in the same location wouldn't gather any heat either.
However, in re-thinking things, it dawned on me that you don't leave slides in the projector for hours on end, so maybe my LCD is going to be subjected to lots of heat. Now I'm scared to run the thing, as the fan I have pulling heat off, is over the bulb and not the LCD. |
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| blueknyt |
Ok, useing one of those little TV's, how did you get the AV signal to it? other then the antenna? i figured strip down the unit and solder a coax to antenna and tune the Little TV to ch3 like you would for VCR use, connect the VCR to the new coax and there you go. is this what you did?
Ok, moved the Fresnels, what finnal projection lens would you recomend for this type of setup to project 10-12' |
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| Guy Grotke |
I would recommend something around 220 mm fl, to give you a nice bright 62" screen image. But maybe you want a bigger, not so bright image with big visible pixels: A 150 mm fl lens would give you about a 95" screen image.
All the math you need to calculate this yourself is already in this thread. |
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| CKSMartin |
For my stalled project I used an old LCD cam corder monitor- it is basicaly a tv with no tuner, that attaches to a plate that fits on the shoe mount of the tripod, so that you have a color monitor behind your tripod-mounted camcorder, studio style.
I got it way back in 1992, and it was pretty good picture back then. I had it laying around in a box somewhere, and decided to use it.
I'm sure the picture won't be that great, but if it's at least drive in quality, my little girl will be thrilled. |
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| blueknyt |
Ok guy Grotke.
i think i finnaly got it, lets see if this tracks
Projection Size(diag) is found as follows
dist - FL X LCD diag / FL all messurements in MM
[10'] 3048mm - 220mm X [7"] 178mm / 220mm = 2288mm [90"]
did i miss anything?
and the FL is the distance between the Subject(LCD) to the back side of the projection lens?
220mm = 8.6"
150mm = 5.9"
IE LCD -> ||<---8.6"--->)=0 <--- lens |
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| Guy Grotke |
The curvature and material of a positive lens determines the focal length. This is a measure of the "strength" of the lens. If you put a point source light on the left side of the lens, right at the focal length, then a beam of parallel rays will come out of the right side of the lens. If you moved that point source light farther away from the lens to the left, then the light coming out the right side would have the shape of a cone. As the light got farther awayto the left, the point on the right where the cone focussed would get closer to the focal length of the lens. When the distance to the light is very far away (ie. like the sun), then the cone of light on the right side will focus at the focal length of the lens.
In a telescope, the stars are effectively at an infinite distance, so their image will be focussed at the focal length from the lens. In a projector, neither the object (the LCD) nor the screen are at an infinite distance. That's why neither one is at the focal length. For every lens to screen distance, there is an LCD to lens distance that will give you a focussed image. The relationship between those two distances is determined by the strength of the projection lens:
1/focal length = 1/LCD to lens + 1/lens to screen
The magnification of an object to give you an image is the product of the two distances:
M = (lens to screen) / (LCD to lens)
So if you wanted a 70" image from a 7" LCD, then the magnification (M) would be 10. Let's say you want a 10 foot throw distance (lens to screen).
focal length = (lens to screen) / (M + 1)
focal length = 120 inches / (10 + 1) = 10.91 inches
10.91 inches * 25.4 mm / inch = 277 mm fl projection lens
You can also calculate the distance from the LCD to the lens:
10 = (lens to screen) / (LCD to lens) so
Lcd to lens = lens to screen / 10 = 12 inches |
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| blueknyt |
ok, just shorted another brain cell, yall can laugh any time now hell i expect it.
I am really trying to grasp it, but i guess im not seeing it the way your intending.
i cant even think of another way reword or discribe in a way to get us on the same page. |
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| Guy Grotke |
Sorry, I was just trying to explain why the distance between the lens and the LCD is not the same as the focal length of the lens. Then I just got inspired and threw in all the rest of the math you need to design a projector. But you can just give us a few of your projector design goals and i will try to point you to specific lenses, fresnels, lamps, etc. that would work.
You can make a projector with a long throw or a short throw, big image or small image, big LCD or small LCD, and everything inbetween. You have to start somewhere. For me that "somewhere" was the shape of my media room. I wanted a 95" image with a 14 foot throw distance. I also wanted to take advantage of 15" XGA LCD monitors for under $200. I had room for a very big upright box projector. So those four things pretty much determined all the dimensions and lens focal lengths in my projector.
So what do you want your projector to do? Games & video, or computer monitor? 4:3 normal TV or 16:9 HDTV? Is there a particular throw distance you need? A particular screen image size? Does it need to fit in a small box? Do you already have some parts? Time to get out the tape measure... |
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| blueknyt |
Ok, i live in a mobilehome (singlewide trailer) my living room is 15'x11'6" i want is small so i can hang it from ceiling in the rear of the room, was thinking of a Minitower PC case as the Baseline Box. but setting it so its on one side or the other (laying down)
(also want to build one with a 2" LCD and a slide projector but very few folks have done this and my understanding of DIYPJ's needs alittle more expanding before i make my own footprints there)
the distance will be aprox in the 12' range from projector to screen
i have some fresnels coming and couple projection tV lenses (mainly to eperiment with they were cheap enough) as well as fans and posible case(has alot of plastic on it kinda hesitant)
http://cgi.ebay.com/ws/eBayISAPI.dl...me=STRK:MEWA:IT
i work at an airport and have access to the lighting parts i need for nothing. gonna start with a 250W MH setup for its size mainly
i do not have as of yet IR filter, UV filter, Condenser lens, or (not sure what i need) [HOT or Cold] mirror or the LCD. i want to use a small LCD like a 5" to 7" either PSlcd or lilliputt, but 50-100$ to strip down a unit is kinda hard to swallow, But while battling that with my wallet hand (i will beat it soon) im trying to learn and understand.
I try again, the FL is the distance of source from backside of lens that gives a parallel (beam) refraction on oposite side?
0 ===||=== VS 0=||>-<
if i still missed it just patt me on head say try again. |
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| blueknyt |
:eek: wait wait, i tink i finnaly got it (Visual aid helped)
the focal length is the distance from the lens to where the REFRACTION comes to a point at the tip of the cone
A)====>B A being the lens & B is the tip of the cone of refracted light
a 220mm fl lens would be 220mm between A and B right? right? tell me i got it now :bawling: |
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| Guy Grotke |
>the FL is the distance of source from backside of lens that gives a parallel (beam) refraction on oposite side?
>the focal length is the distance from the lens to where the REFRACTION comes to a point at the tip of the cone
Yes, both of these are correct. Assuming a 220 mm focal length lens:
The first one describes light coming from a point source, spreading over the 220 mm to the lens. The lens refracts the cone of light into a parallel beam coming out the other side.
The second one describes a parallel beam hitting a lens and getting refracted to a cone with the tip 220 mm from the lens.
If you build a projector with a pair of fresnel lenses, then the condensor fresnel (nearer to the lamp) is doing case 1. The field fresnel (nearer to the projection lens) is doing case 2. |
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| Guy Grotke |
One thing you left out: What size image are you going for? Lots of people try for 100" diagonal, but that might just be a bit too big for a 250 Watt lamp. Smaller is brighter. You should measure the wall (or screen area) you plan to use in both vertical and horizontal directions. Then we can figure out what you can use from 12 feet to get that image.
Lilliputs and PSones are both small format LCDs, but they are very different in terms of price and resolution. Do you have the $$$ for a Lilliput 800 by 480? Much more than a PSone, but also much higher quality. |
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| blueknyt |
im not overly greedy 90" is fine thats still what 7' diag?
ok, so it depends on HOW the lens is used as to the source being the parallel in to cone or the source being the Cone in to parallel out the focal point is still the same messurement 220mm from lens to Cone point for a 220mm lens
doing snoopy dance.:D |
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| Guy Grotke |
DIYprojectorCompany.com has a lens you could use. It has a focal length of 217.6 mm to 229.5 mm. Using a 5" LCD from 12 feet, this would give you a 79 inch image on the screen.
With that size image, a 250 Watt MH lamp would be fine. The distance between the LCD and the projection lens will be around 231 mm. I would recommend a 200 mm fl fresnel 10 to 15 mm before the LCD, and a 220 mm fl fresnel about 15 mm after the LCD. |
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| blueknyt |
ill most likly pic up one of the lenses you recomend, but i was wondering if projection TV lenses work too, like these
http://cgi.ebay.com/ws/eBayISAPI.dl...me=STRK:MEWA:IT
got these for 19.99 shiped. figure at worse use parts for condensor lens infront of bulb. |
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| Guy Grotke |
Usually they have such a short focal length that you have to put them right up against the CRT or LCD. That means the lens has to be at least as wide as your LCD. This may be possible with a 5" LCD. I guess you will find out!
The lenses may be acrylic, which would melt if you tried to use them as condensor lenses. |
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| blueknyt |
yeah, thats what i thought, well, i got one Hipgear 2.5lcd controler comeing 24$ and one PSone screen new sealed 35$ and went ahead and grabed one of the lenses you posted
http://www.surplusshed.com/pages/item/l3311.html 15$
Ill be grabing the LightEngine parts nextweek from work when my electrician coworker comes back (think i have him hooked on the project too)
think the only parts left are reflector behind bulb, mirror to bounce light to fresnel (cold or hot?)
UV and IR filters
Idea's? |
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| Guy Grotke |
If you want to bounce the light off it, then it has to be a cold mirror. The only reasonably priced cold mirror I have found is surplusshed's $5 4.75" diameter cold mirror. All the rest I have found are much much more.
Hot mirrors are much easier to use, since you can fit a small one into a straight light path. There are also lots of sources for cheap and not-so-bad hot mirrors.
For UV filtering, you can buy UV filter sheets at some of the DIY projector web stores for <$10, or you can just use Lexan XL10 to support your fresnels. Lexan XL10 is sold at Home Depot as window glass replacement and has a great UV blocker built in. |
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| blueknyt |
| so then, your not using a Hot mirror to reflect the Driver light(light for LCD) but bounce the HEAT Rad back, so this could be placed just before the 45* cold mirror bounces the light to the fresnels for the LCD. then use the Lexan to filter UV at the fresnel. |
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| Guy Grotke |
Yes, that is how hot and cold mirrors work. But you don't really need both. If you put a good hot mirror across the light path, then you don't need a cold mirror. You could use a first surface mirror (or even a standard mirror before the LCD), which is much cheaper than a cold mirror. (Also you have to keep in mind that every mirror will lose about 10% of the visible light. )
On the other hand, if you can actually fit a cold mirror in the light path, and find one you can afford, then that has some real advantage over using a hot mirror: You get to direct all the heat to the area behind the cold mirror, where it can be absorbed by a heatsink and then removed by a fan.
In my projector, I use hot mirror to bounce the IR back toward the lamp, and I use Lexan XL10 to support my fresnels which acts as a UV filter. |
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| blueknyt |
Ok, got my 210mm lens from surplusshed, and 2 unlabled fresnels
still waiting on my PSone LCD,
Got my Hipgear 2.5" LCD controler but havent found a slideprojector to my liking yet. cant see spending more then 10$ on something im going to gut anyway. but then, ill find somthing.
I still have the 3 projectionscreen lenses, any ideas on tap for them? |
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| jfguay2 |
I am a newbie and was trying to project a stripped 2.5 lcd from a hip gear onto a OHP Porta Scribe G-100, that has a 600 w halogen bulb.
It's not showing much on the wall , I can barely see an image.
Am I doing something wrong? or is this OHP simply not powerful enough in terms of lumens? I am awaiting to get an old projector slide to try in into but in the meantime, I wanted to see the results on the Porta Scribe.
Can anybody help? I am also waiting for a 15 inch Benq fp557s, that I will strip and put on the OHP. Will it work?
Thank you all for your input
JF:bigeyes: |
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| Clinton |
Are you masking around the LCD? If not this would be the cause, you'll be loosing too much light. You also need to have it right in the center of the fresnel.
Clinton |
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| blueknyt |
| wow a 2.5" on an overhead? i would think you would need to build a stand to raise it about half way just for the lens to see it. |
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| Guy Grotke |
Think about it: Your OHP lights at least a 100 square inch area, but your LCD has only about 3 square inches. So less than 3% of the light output even gets to the LCD to begin with!
Then the LCD absorbs 50% of the light because it has the wrong polarization. Then the color filters absorb about 66% of what is left.
If you blow it up to more than a 15 inch image, I bet it is so dim you can't see it at all.
It makes much more sense to start with a slide projector if you want to use a 2.5" LCD. |
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