Hi Noodles,
Yup, that's what I saw when I checked out their site. However, I bought a Laserdisk from them through Ebay, and asked what hi-res panels they have (I had seen some good reviews of them on the earlier thread).
They had no high-res ones available, but threw in a Spectra C for $75. The price might have gone up recently, but give them a shot - they seem to be good guys.
Bill.
Yup, that's what I saw when I checked out their site. However, I bought a Laserdisk from them through Ebay, and asked what hi-res panels they have (I had seen some good reviews of them on the earlier thread).
They had no high-res ones available, but threw in a Spectra C for $75. The price might have gone up recently, but give them a shot - they seem to be good guys.
Bill.
More changes, still no better...
I've found a reflector for the 400 W MH bulb. It's an A15 highbay reflector, which certainly puts much more light in a single direction. I also found that if I lower the bulb deeper into the base of the reflector, light output is significantly better.
But my screen image is still very dim. Something's very wrong. I feel that I've got all the right components to do this right, but using them wrong.
The Focal lenght of the Fresnel is about 8.5" (the distance from the panel to a surface where the image of the sun is tightest)
The focusing distance for a 12' throw is about12.5" from the LCD to the lens head.
Here's a pic of the revised set up. Any ideas? Suggestions? Obvious oversights?
Thanks,
dave.
I've found a reflector for the 400 W MH bulb. It's an A15 highbay reflector, which certainly puts much more light in a single direction. I also found that if I lower the bulb deeper into the base of the reflector, light output is significantly better.
But my screen image is still very dim. Something's very wrong. I feel that I've got all the right components to do this right, but using them wrong.
The Focal lenght of the Fresnel is about 8.5" (the distance from the panel to a surface where the image of the sun is tightest)
The focusing distance for a 12' throw is about12.5" from the LCD to the lens head.
Here's a pic of the revised set up. Any ideas? Suggestions? Obvious oversights?
Thanks,
dave.
Attachments
Another thought...
The Top surface of the OHP I'm using is a frame with the fresnel mounted about 1" below a plate glass surface, upon which the LCD lies.
Gunwan instructed me to put the LCD as close to the Fresnel as possible. Is this 1" an issue? Because it's part of the original OHP setup, I was thinking it's OK to keep this configuration.
And another thing... The fresnel itself is plastic, so I'm concerned about keeping it too close to the light source (heat...)
And yet another thing... The recent discussion around condenser lenses is interesting, but I'm confused by those that say the best thing is to have a set of fresnel/condenser from a single OHP. My OPH doesn't seem to have this condenser lens. The head is a pari of lenses, about 1/2" apart, but I thought the multple lens setup is just to reduce spherical abberations.
More thoughts???
dave.
The Top surface of the OHP I'm using is a frame with the fresnel mounted about 1" below a plate glass surface, upon which the LCD lies.
Gunwan instructed me to put the LCD as close to the Fresnel as possible. Is this 1" an issue? Because it's part of the original OHP setup, I was thinking it's OK to keep this configuration.
And another thing... The fresnel itself is plastic, so I'm concerned about keeping it too close to the light source (heat...)
And yet another thing... The recent discussion around condenser lenses is interesting, but I'm confused by those that say the best thing is to have a set of fresnel/condenser from a single OHP. My OPH doesn't seem to have this condenser lens. The head is a pari of lenses, about 1/2" apart, but I thought the multple lens setup is just to reduce spherical abberations.
More thoughts???
dave.
Hi Dave,
Is your reflector elliptical or parabolic?
It looks paraboic(ish) and I am assuming that it is throwing out a parallel beam of light.
If this is the case, then don't put anything (except some decent UV & possibly IR blocking glass) between the light source and the LCD. The first measurement to make with this arrangement is to see how much light is getting through the LCD. There should be loads.
Next: use a single fresnel lens (not the fresnel doublet from an OHP - they are designed to focus a point source of lifght back to another point source; you only need to beam parallel light into a cone).
If you put this on top of your LCD as close to the LCD as is possible without getting moire, the light from the LCD should all get beamed into a cone without much distortion at the corners etc. Generally, you want the rough side of the fresnel facing the panel, and you want the fresnel to have as long a focal length as possible while being compatible with your objective. The ones from OHPs have the right focal length, but I'm not sure of their optical quality...
Ok, with your fresnel in place, take a piece of paper and find the apex of the light cone. This is where your objective should go (roughly). You want it so that as you move the objective up and down to focus it, the light from the cone stays within the diameter of the lens. As soon as the diameter of the cone at the point where it hits the lens is bigger than the diameter of the lens, you are losing much light.
If the fresnel and objective are compatible, then you will be able to achieve this easily. If they are mismatched, then one or other will have to change (or, you could put corrective lenses in between, but this gets messy...)
An alternative to this, assuming your reflector is parabolic, is to put the top half of a fresnel doublet under the LCD as if it were a regular OHP. Depending on your panel characteristics, you might get less light or contrast or both.
The caveat about matching the fresnel and objective still applies though... (If your optics are from an OHP, then no problem.)
The thing about condensers only applies to the use of an elliptical reflector to produce a point source of light - a virtual bulb - that is more efficient than using the bulb alone.
Here, a condenser is needed at the focal point of the elliptical reflector to produce divergence characteristics that are compatible with the fresnel DOUBLET. (You DO use the full doublet in this case to re-converge the diverging rays from the reflector/condenser back to the objective).
Hope this helps.
Bill.
Is your reflector elliptical or parabolic?
It looks paraboic(ish) and I am assuming that it is throwing out a parallel beam of light.
If this is the case, then don't put anything (except some decent UV & possibly IR blocking glass) between the light source and the LCD. The first measurement to make with this arrangement is to see how much light is getting through the LCD. There should be loads.
Next: use a single fresnel lens (not the fresnel doublet from an OHP - they are designed to focus a point source of lifght back to another point source; you only need to beam parallel light into a cone).
If you put this on top of your LCD as close to the LCD as is possible without getting moire, the light from the LCD should all get beamed into a cone without much distortion at the corners etc. Generally, you want the rough side of the fresnel facing the panel, and you want the fresnel to have as long a focal length as possible while being compatible with your objective. The ones from OHPs have the right focal length, but I'm not sure of their optical quality...
Ok, with your fresnel in place, take a piece of paper and find the apex of the light cone. This is where your objective should go (roughly). You want it so that as you move the objective up and down to focus it, the light from the cone stays within the diameter of the lens. As soon as the diameter of the cone at the point where it hits the lens is bigger than the diameter of the lens, you are losing much light.
If the fresnel and objective are compatible, then you will be able to achieve this easily. If they are mismatched, then one or other will have to change (or, you could put corrective lenses in between, but this gets messy...)
An alternative to this, assuming your reflector is parabolic, is to put the top half of a fresnel doublet under the LCD as if it were a regular OHP. Depending on your panel characteristics, you might get less light or contrast or both.
The caveat about matching the fresnel and objective still applies though... (If your optics are from an OHP, then no problem.)
The thing about condensers only applies to the use of an elliptical reflector to produce a point source of light - a virtual bulb - that is more efficient than using the bulb alone.
Here, a condenser is needed at the focal point of the elliptical reflector to produce divergence characteristics that are compatible with the fresnel DOUBLET. (You DO use the full doublet in this case to re-converge the diverging rays from the reflector/condenser back to the objective).
Hope this helps.
Bill.
To all those with doubts.
There's nothing wrong with my Panel or Overhead....NOTHING, they work together as well as it is possible, they image i got on page 22 was because the panel was not centered on the OHP, and after i raised it about 3 mm off the fresnel, that effect disappeared.
I believe that i need an LCD, a really good, Small, and high res. ( at least SVGA) lcd, to keep me going in this field. Before a NEW LCD is released, there's no point of trying new designs, they all will be huge.
I know Marklar and Undream got nice results, mine were not worse. But their designs are a bit too large for me. VERY nice work though, keep it up, guys!!
And if anyone else is still in doubts about my panel or Overhead, i can take screen shots, but i will need to get a digital camera, and so on and so on...
thanks
aleksey
There's nothing wrong with my Panel or Overhead....NOTHING, they work together as well as it is possible, they image i got on page 22 was because the panel was not centered on the OHP, and after i raised it about 3 mm off the fresnel, that effect disappeared.
I believe that i need an LCD, a really good, Small, and high res. ( at least SVGA) lcd, to keep me going in this field. Before a NEW LCD is released, there's no point of trying new designs, they all will be huge.
I know Marklar and Undream got nice results, mine were not worse. But their designs are a bit too large for me. VERY nice work though, keep it up, guys!!
And if anyone else is still in doubts about my panel or Overhead, i can take screen shots, but i will need to get a digital camera, and so on and so on...
thanks
aleksey
I'm *still* stuck on the reflector, unfortunately. I just plain and simple can't find one. I need some help! I've exhausted all the local electrical supply stores looking for something reasonably priced, and have come up empty handed. Maybe someone else out there with more local resources can help me out?
Under preliminary tests of my roughly made cut mirror reflector that I spent 8 bucks on, I don't think its going to work well enough.
Under preliminary tests of my roughly made cut mirror reflector that I spent 8 bucks on, I don't think its going to work well enough.
Hi Undream,
Why not try out Mycamel's idea of creating (using a simple template) a plaster mold and then either build up a reflector from layers of tinfoil wrapped around it and epoxied together, or, use a bit of brute force to wrap a suitably cut sheet of 1mm aluminium foil into something suitable that could be held together again by epoxy, or bolts or even pot rivets?
Alternatively, there seem to be plenty of reflectors from stage-lights etc on ebay. The 6" ones are too small for the big 400W MH bulbs, but you might be able to find an 8" one that would fit.
Bill.
Why not try out Mycamel's idea of creating (using a simple template) a plaster mold and then either build up a reflector from layers of tinfoil wrapped around it and epoxied together, or, use a bit of brute force to wrap a suitably cut sheet of 1mm aluminium foil into something suitable that could be held together again by epoxy, or bolts or even pot rivets?
Alternatively, there seem to be plenty of reflectors from stage-lights etc on ebay. The 6" ones are too small for the big 400W MH bulbs, but you might be able to find an 8" one that would fit.
Bill.
Also, what is your light path? If you are trying to duplicate Marklar's setup, the demands on a reflector will be much higher than if you want to use a more parallel beam of light:
The Marklar setup used an elliptical reflector + condensor to emulate a virtual bulb. This allowed him to use his conventional OHP optics.
This elliptical arrangement is not easy to make unless you ter Mycamel's arrangement. A roughly parabolic reflector would be much easier to get going. This would get the light going in a roughly parallel beam. As long as the lighting is even, this is enough.
Then, all you need is a SINGLE fresnel lens - either above or below your panel - depending on taste. The single fresnel will take the parallel beam and converge it into a cone.
The doublet fresnel from an OHP is purely designed to take a point source of light, and focus it back into a point image. If you are using a doublet, and your reflector arrangement is not generating a compatible point source, then that is your problem.
Check out my previous reply to daveb for more details on the setup.
Bill.
The Marklar setup used an elliptical reflector + condensor to emulate a virtual bulb. This allowed him to use his conventional OHP optics.
This elliptical arrangement is not easy to make unless you ter Mycamel's arrangement. A roughly parabolic reflector would be much easier to get going. This would get the light going in a roughly parallel beam. As long as the lighting is even, this is enough.
Then, all you need is a SINGLE fresnel lens - either above or below your panel - depending on taste. The single fresnel will take the parallel beam and converge it into a cone.
The doublet fresnel from an OHP is purely designed to take a point source of light, and focus it back into a point image. If you are using a doublet, and your reflector arrangement is not generating a compatible point source, then that is your problem.
Check out my previous reply to daveb for more details on the setup.
Bill.
FINALLY
No-one here probably remembers me but nevermind....
Finally finished uni, saved up and bought some bits and pieces, current set up:
LCD - Infocus 550LS (640x480 though it actually seems to do 800x600)
LIGHT - 400w Metal Halide (tubular bulb) with a SON T ballast
Lenses - 2 Fresnel and 2 glass lenses
Not sure what the lenses are called, lens one is flat one 1 side and curved on the other while lens 2 was from an OHP
It goes LIGHT - LENS1 - FRESNEL - LCD PANEL - Fresnel or LEN2
using the second fresnel i get a brighter image and it's bloody huge though a little out of focus in places (i'll try and get photos)
Lens 1 has the curve facing the bulb, i though this would disperse the light out in all directions.....
a little bit lost so any help, pointers or just plain taking the **** would be appreciated 🙂
Thanks
No-one here probably remembers me but nevermind....
Finally finished uni, saved up and bought some bits and pieces, current set up:
LCD - Infocus 550LS (640x480 though it actually seems to do 800x600)
LIGHT - 400w Metal Halide (tubular bulb) with a SON T ballast
Lenses - 2 Fresnel and 2 glass lenses
Not sure what the lenses are called, lens one is flat one 1 side and curved on the other while lens 2 was from an OHP
It goes LIGHT - LENS1 - FRESNEL - LCD PANEL - Fresnel or LEN2
using the second fresnel i get a brighter image and it's bloody huge though a little out of focus in places (i'll try and get photos)
Lens 1 has the curve facing the bulb, i though this would disperse the light out in all directions.....
a little bit lost so any help, pointers or just plain taking the **** would be appreciated 🙂
Thanks
Hi Forrest,
Check out your alignments and light path.
The light coming from your first fresnel (assuming it is a singlet) should be parallel. The second fresnel should be as close to the LCD as possible - check out which way round you have it. If it is close, and it is the right way around, there should be no distortion.
If your image is too big, then you might have an issue with focal length - even if the fresnel & objective are matched (see prev posts), if the focal lengths are too short, you will get mega zoom.
You might want to try a concave lens close after your objective to reduce zooming a little.
Bill.
Check out your alignments and light path.
The light coming from your first fresnel (assuming it is a singlet) should be parallel. The second fresnel should be as close to the LCD as possible - check out which way round you have it. If it is close, and it is the right way around, there should be no distortion.
If your image is too big, then you might have an issue with focal length - even if the fresnel & objective are matched (see prev posts), if the focal lengths are too short, you will get mega zoom.
You might want to try a concave lens close after your objective to reduce zooming a little.
Bill.
You do realize that forrest is using a lcd projector and not a panel right? It is an older infocus and from what I've read it only does 640*480 res which is still pretty good. The replacement bulbs for it should be fairly cheap as it just uses a 400w halogen bulb. Although replacing it with a small metal halide would be cool.
reflector idea
Has anyone thought of using the reflector side off a automotive fog light as their reflector? Just think of the times you get blined by them when you drive down the street. Now, Imagine it with a metal halide bulb in it.
I've been looking at these reflectors and they seem like they would work well since they are very reflective and they are available anywhere from 3" to 8" across (baja style) or even larger.
My SHARPVISION projector uses a 6.4" screen (800x600) and the reflector from the metal halide buld assembly is no larger than 3" across and the lens the light shines through is no larger than 2" so I dont think you need to use huge bucket style reflectors.
just a thought
ap0the0sis
Has anyone thought of using the reflector side off a automotive fog light as their reflector? Just think of the times you get blined by them when you drive down the street. Now, Imagine it with a metal halide bulb in it.
I've been looking at these reflectors and they seem like they would work well since they are very reflective and they are available anywhere from 3" to 8" across (baja style) or even larger.
My SHARPVISION projector uses a 6.4" screen (800x600) and the reflector from the metal halide buld assembly is no larger than 3" across and the lens the light shines through is no larger than 2" so I dont think you need to use huge bucket style reflectors.
just a thought
ap0the0sis
The reflector in a fog light will do one of two things.....melt or be crap. Most nowadays are plastic with a chrome interior finish......and are rated for 100W tops....even the baja ones. The metal ones will have the same problem.....they are thin guage metal and the mirror surface isnt as good as commercial reflectors. Again they were designed for lower wattage bulbs. Where are you going to get a 400W MH bulb to put in one? I havent seen any 400 watters compact enough to fit in a fog light to begin with......the enclosure will most definitly melt or at the least deform.
Daveb,
You said that your objective lens to LCD distance is 12.5" and your fresnel fl. is 8.5", supposed your reflector is parabolic type, you will get parallel light coming out from it, then it hits the fresnel, light output coming out from fresnel will be condensed to small point at fresnel focal length=8.5" in front of it. Your obj. lens is at 12.5", it's to far!
The best lens position is shorter than 8.5", try it with white hard paper as small screen, draw a circle on it with diameter=lens dia., put it in front of the fresnel, move it back and forth until the light beam covered the circle, that is the best location for your lens.
Since you already had the reflector,
first, adjust the light bulb up&down, until the light beam covered all side of the fresnel panel and
second, adjust fresnel panel position, until the light beam covered the whole objective lens.
Hope it will work. Good luck.
Woneill,
OHP fresnel can do parallel light to cone, just think it as a doublet lens, parallel beam will be focused to it's focal length.
OHP fresnel has shorter fl. than one face fresnel. (usually 12"). We can use all type of fresnel as long as it has a tight and tiny groove circle (means good quality)and a focal length we need.
Guys,
Is this the perfect reflector setup we need?
Correct me, if I'm wrong.
You said that your objective lens to LCD distance is 12.5" and your fresnel fl. is 8.5", supposed your reflector is parabolic type, you will get parallel light coming out from it, then it hits the fresnel, light output coming out from fresnel will be condensed to small point at fresnel focal length=8.5" in front of it. Your obj. lens is at 12.5", it's to far!
The best lens position is shorter than 8.5", try it with white hard paper as small screen, draw a circle on it with diameter=lens dia., put it in front of the fresnel, move it back and forth until the light beam covered the circle, that is the best location for your lens.
Since you already had the reflector,
first, adjust the light bulb up&down, until the light beam covered all side of the fresnel panel and
second, adjust fresnel panel position, until the light beam covered the whole objective lens.
Hope it will work. Good luck.
Woneill,
OHP fresnel can do parallel light to cone, just think it as a doublet lens, parallel beam will be focused to it's focal length.
OHP fresnel has shorter fl. than one face fresnel. (usually 12"). We can use all type of fresnel as long as it has a tight and tiny groove circle (means good quality)and a focal length we need.
Guys,
Is this the perfect reflector setup we need?
Correct me, if I'm wrong.
Attachments
Hi Gunawan,
Your setup looks good to me!!!
For the fresnel thing, though, there is a problem using two fresnels as a DCV lens: Fresnels are usually specifically designed to have the light source and image at specific points that are fixed within a small margin. These points are called conjugates.
If you take a fresnel that is designed to have parallel light hitting one face (conjugate at infinity), and instead place a point source at its focal length, it will work, but there will be distortion and scattering. Similarly, if you take a fresnel that is expecting a point source of light at its focal length (conjugate at its focal length) and hit it with a parallel beam, you will again get a working lens, but with distortion and scattering.
The biggest problem with fresnels is internal reflection. And if they have a wide aperture and short focal length, they must be used as intended otherwise you will lose much quality.
This is the reason why they use two fresnels in an ohp, and is why the rough sides face each other - the flat side is intended to project/receive light at its focal length, and the rough side is intended to project/receive a parallel beam.
Thus in the OHP, the bottom flat side is expecting to receive diverging light from a point source bulb and converge it into a parallel beam which is fed into the rough side of the second fresnel which then converges it into a converging beam.
It WILL work as a regular DCV lens, but it is best used as intended...
See the fresnel-tech PDF for more info on fresnels:
http://www.fresneltech.com/pdf/FresnelLenses.pdf
Bill.
Your setup looks good to me!!!
For the fresnel thing, though, there is a problem using two fresnels as a DCV lens: Fresnels are usually specifically designed to have the light source and image at specific points that are fixed within a small margin. These points are called conjugates.
If you take a fresnel that is designed to have parallel light hitting one face (conjugate at infinity), and instead place a point source at its focal length, it will work, but there will be distortion and scattering. Similarly, if you take a fresnel that is expecting a point source of light at its focal length (conjugate at its focal length) and hit it with a parallel beam, you will again get a working lens, but with distortion and scattering.
The biggest problem with fresnels is internal reflection. And if they have a wide aperture and short focal length, they must be used as intended otherwise you will lose much quality.
This is the reason why they use two fresnels in an ohp, and is why the rough sides face each other - the flat side is intended to project/receive light at its focal length, and the rough side is intended to project/receive a parallel beam.
Thus in the OHP, the bottom flat side is expecting to receive diverging light from a point source bulb and converge it into a parallel beam which is fed into the rough side of the second fresnel which then converges it into a converging beam.
It WILL work as a regular DCV lens, but it is best used as intended...
See the fresnel-tech PDF for more info on fresnels:
http://www.fresneltech.com/pdf/FresnelLenses.pdf
Bill.
Some new numbers...
Gunwan,
Frustrated with the setup, I took the fresnel outside to the sunlight to reconfirm its focal length. As it turns out, I was finding an IMAGE of the sun (and the surrounding Gazebo) at about 8.5". I thought this is what I needed. But then I remembered all those summer afternoons frying ants on the driveway with a handheld magnifying glass, and thought (hey, shouldn't I be burning a hole in this cardboard?" So I move it a few inches close, and voila! at about 5.5", I'm burning a hole!
So, now I know that one of my problems is that my focal length of the main fresnel is really 5.5".
So I realized that if I'm using the filiment of the 400 W MH bulb as the "point source", I need to have the fresnel 5.5 inches from the filiment. But the bulb iteslf is so large I can't get that close.
So I've taken the reflector off again, put the bulb back to horizontal, and moved the fresnel down to 5.5". Still no brighter.
This is getting VERY frustrating. Now, maybe I need to cut back the reflector to accommodate the horizontal bulb, then flip over the fresnel to re-focus the light.
So here's my latest connundrum: You've suggested putting the objective lens inside the focal length of the fresnel. but I belive I'm constrained in this distance: The distnace between the object and the lens MUST be 12.5" in order to cast an image to the wall 12" away. I don't believe I have any latitude in this distance, unless I completely change my objective lens(es).
If it'll help, I'll post a couple of pix tonight of the lens head configuration.
And another question: In your diagram just posted, there's a small convex lens just beside the light bulb: if this diagram is to scale, then it's INSIDE the MH bulb. I don't understand...
dave.
Gunwan,
Frustrated with the setup, I took the fresnel outside to the sunlight to reconfirm its focal length. As it turns out, I was finding an IMAGE of the sun (and the surrounding Gazebo) at about 8.5". I thought this is what I needed. But then I remembered all those summer afternoons frying ants on the driveway with a handheld magnifying glass, and thought (hey, shouldn't I be burning a hole in this cardboard?" So I move it a few inches close, and voila! at about 5.5", I'm burning a hole!
So, now I know that one of my problems is that my focal length of the main fresnel is really 5.5".
So I realized that if I'm using the filiment of the 400 W MH bulb as the "point source", I need to have the fresnel 5.5 inches from the filiment. But the bulb iteslf is so large I can't get that close.
So I've taken the reflector off again, put the bulb back to horizontal, and moved the fresnel down to 5.5". Still no brighter.
This is getting VERY frustrating. Now, maybe I need to cut back the reflector to accommodate the horizontal bulb, then flip over the fresnel to re-focus the light.
So here's my latest connundrum: You've suggested putting the objective lens inside the focal length of the fresnel. but I belive I'm constrained in this distance: The distnace between the object and the lens MUST be 12.5" in order to cast an image to the wall 12" away. I don't believe I have any latitude in this distance, unless I completely change my objective lens(es).
If it'll help, I'll post a couple of pix tonight of the lens head configuration.
And another question: In your diagram just posted, there's a small convex lens just beside the light bulb: if this diagram is to scale, then it's INSIDE the MH bulb. I don't understand...
dave.
optics software
i found some optics software, if anyone is interesting it is at:
http://www.astrion.de/download/download.html
i found some optics software, if anyone is interesting it is at:
http://www.astrion.de/download/download.html
If anyone answer this, i'd be appreciative;
In a commercial LCD projector unit (or the majority of them anyways), how does the unit know if the lamp is on? is there an optical sensor, sensitive to light? or it is measured electronically.
Im asking as I wish to retrofit a LCD projector with a cheaper metal halide.
cheers,
jon
In a commercial LCD projector unit (or the majority of them anyways), how does the unit know if the lamp is on? is there an optical sensor, sensitive to light? or it is measured electronically.
Im asking as I wish to retrofit a LCD projector with a cheaper metal halide.
cheers,
jon
check out alternative light sources.....we've discussed this a lot in that thread.....some use a simple photocell to determine if its on....other's dont do anything at all. Projectors dont usually go into any elaborate methods for determining it.....usually the ballast is simply switched on via a relay, no complex circuitry is usually needed there.