I am about to purchase my Fresnel Lense Set from diyprojectorcompany.com and I want to make sure that I am getting the right stuff.
The set I plan to get:
Groove Pitch: 0.5 grooves/mm
Rear Lens Focal Length: 8.67" (~220mm)
Front Lens Focal Length: 13" (~330mm)
Is this pretty much the best match for the copy lens?
Also I will need to get a condensor/reflector that will work with this set up. Any recommendations and where to get them from? I will probably use the 250w MH kit from diyprojectorcompany as well.
Thanks!
The set I plan to get:
Groove Pitch: 0.5 grooves/mm
Rear Lens Focal Length: 8.67" (~220mm)
Front Lens Focal Length: 13" (~330mm)
Is this pretty much the best match for the copy lens?
Also I will need to get a condensor/reflector that will work with this set up. Any recommendations and where to get them from? I will probably use the 250w MH kit from diyprojectorcompany as well.
Thanks!
that's the right fresnel set
That should work just fine with a 240 mm fl lens. At a 10 foot throw distance, the LCD to lens distance will be around 260 mm. You can put both fresnels about 40 mm before the LCD and you will get a very bright image.
That should work just fine with a 240 mm fl lens. At a 10 foot throw distance, the LCD to lens distance will be around 260 mm. You can put both fresnels about 40 mm before the LCD and you will get a very bright image.
looks good to me
You can try all those distances out before committing it to a box. Just toss together a temporary "bench model" using duct tape, sticks, etc. to hold everything in place while you project an image the real throw distance. You can even make a mockup LCD using some transparency film printed with a lot of fine text, to verify your focussing.
People use split designs because they have too short a focal length field fresnel for their projection lens. With a 330 mm fl field fresnel and a 240 mm fl projection lens, you have room to spare to use a non-split design. Unless you need to do optical keystone correction, you should avoid a split design. The field fresnel in a split design can only hurt the image quality, not help it!
To combine the fresnels you just put them together in the same holder with their centers aligned and the grooved sides facing each other.
BTW: What were you thinking of doing to remove heat from the light? If you use a cold mirror instead of that first surface mirror, then most of the IR will pass through the mirror where it can be absorbed by a heat sink and then removed by an air stream.
You can try all those distances out before committing it to a box. Just toss together a temporary "bench model" using duct tape, sticks, etc. to hold everything in place while you project an image the real throw distance. You can even make a mockup LCD using some transparency film printed with a lot of fine text, to verify your focussing.
People use split designs because they have too short a focal length field fresnel for their projection lens. With a 330 mm fl field fresnel and a 240 mm fl projection lens, you have room to spare to use a non-split design. Unless you need to do optical keystone correction, you should avoid a split design. The field fresnel in a split design can only hurt the image quality, not help it!
To combine the fresnels you just put them together in the same holder with their centers aligned and the grooved sides facing each other.
BTW: What were you thinking of doing to remove heat from the light? If you use a cold mirror instead of that first surface mirror, then most of the IR will pass through the mirror where it can be absorbed by a heat sink and then removed by an air stream.
I appreciate your help Guy Grotke.
I planned on using the same type of cooling that Hillbilly used. Two 120mm fans blowing on the light. Will that be enough? Do I still need a UV filter or IR filter? Would the circular cold mirror work from diyprojectorcompany?
Also, do you know where I could get a condenser and reflector that will work with this?
I planned on using the same type of cooling that Hillbilly used. Two 120mm fans blowing on the light. Will that be enough? Do I still need a UV filter or IR filter? Would the circular cold mirror work from diyprojectorcompany?
Also, do you know where I could get a condenser and reflector that will work with this?
cooling, filtering, & condensing
That fan setup should be good, but you still need IR and UV filtering. If you can fit the whole light cone from the pre-condensor lens to the fresnel into the 4.75" diameter cold mirror, then that would be great. Try making some full-scale drawings to see if that is possible. I think you can also get them from surplusshed.com for a bit less. If it won't fit, then there are some hot mirrors available from the various DIY online stores: DIYbuildergroup.com, lumenlab.com, diyprojectorcompany.com. Hot mirrors are easier to fit since they just go straight across the light path. (Or you could buy or piece together a larger cold mirror.)
For UV filtering, you can buy UV filter sheets or UV glass from most of the DIY online stores. Or you can just go to Home Depot and buy a piece of Lexan XL10. The lexan is also very good for supporting your fresnels, since it is so strong.
DIYbuilderGroup.com has some condensor lenses in their online store. The owner also says he is expecting condensors and reflectors from the manufacturer in another couple of weeks.
That fan setup should be good, but you still need IR and UV filtering. If you can fit the whole light cone from the pre-condensor lens to the fresnel into the 4.75" diameter cold mirror, then that would be great. Try making some full-scale drawings to see if that is possible. I think you can also get them from surplusshed.com for a bit less. If it won't fit, then there are some hot mirrors available from the various DIY online stores: DIYbuildergroup.com, lumenlab.com, diyprojectorcompany.com. Hot mirrors are easier to fit since they just go straight across the light path. (Or you could buy or piece together a larger cold mirror.)
For UV filtering, you can buy UV filter sheets or UV glass from most of the DIY online stores. Or you can just go to Home Depot and buy a piece of Lexan XL10. The lexan is also very good for supporting your fresnels, since it is so strong.
DIYbuilderGroup.com has some condensor lenses in their online store. The owner also says he is expecting condensors and reflectors from the manufacturer in another couple of weeks.
Re: cooling, filtering, & condensing
Hey Guy,
My bulb is a Philips CDM-T 150w with UV filter. Do I still need to put more UV filtering to my project?
Greetings
Guy Grotke said:
Hey Guy,
My bulb is a Philips CDM-T 150w with UV filter. Do I still need to put more UV filtering to my project?
Greetings
Re: cooling, filtering, & condensing
Do you mean instead of using a FS mirror to bounce the light, I would use the cold mirror instead?
Guy Grotke said:
Do you mean instead of using a FS mirror to bounce the light, I would use the cold mirror instead?
two replies
mengalva:
I think if you can find specs for that lamp, it will say the UV stop glass only absorbs 90% of the UV. That will help prevent skin and eye burns, but over time it will still wreck your LCD color filters and yellow your acrylic fresnels. Lexan XL10 or one of the flexible UV filter sheets will remove >99.9% of the remaining UV.
Lexan polycarbonate and acrylic (ie. Plexiglas) are both good UV absorbers (ie. 90%), but in that process it damages the plastic. The "XL" and some other types of Lexan have a special UV blocking layer on one or both sides to prevent solar UV from turning the lexan window yellow. That layer is the 99.9% UV filter. If you use Lexan, make sure you put that layer facing the lamp.
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skiguy411:
Yes, you can use a cold mirror to bounce the visible light to the fresnel. The IR goes right through the cold mirror. You put a black metal surface a few cm behind the cold mirror and blow air over it to remove the heat. Works great! But you have to have a cold mirror that is big enough to reflect all the visible light. As soon as you look for bigger than those surplus 4.75" diameter, the price goes way up. If you can cut glass, the cheapest way to get a bigger cold mirror would be to cut some round 4.75" mirrors square and piece them together.
The other option is to use a hot mirror. These look like transparent glass but they reflect IR. You have to put one of these right across the light path. The visible light goes through but the IR gets reflected. Hot mirror is easier to use than cold mirror since the reflection angle does not matter so much.
mengalva:
I think if you can find specs for that lamp, it will say the UV stop glass only absorbs 90% of the UV. That will help prevent skin and eye burns, but over time it will still wreck your LCD color filters and yellow your acrylic fresnels. Lexan XL10 or one of the flexible UV filter sheets will remove >99.9% of the remaining UV.
Lexan polycarbonate and acrylic (ie. Plexiglas) are both good UV absorbers (ie. 90%), but in that process it damages the plastic. The "XL" and some other types of Lexan have a special UV blocking layer on one or both sides to prevent solar UV from turning the lexan window yellow. That layer is the 99.9% UV filter. If you use Lexan, make sure you put that layer facing the lamp.
**********************************
skiguy411:
Yes, you can use a cold mirror to bounce the visible light to the fresnel. The IR goes right through the cold mirror. You put a black metal surface a few cm behind the cold mirror and blow air over it to remove the heat. Works great! But you have to have a cold mirror that is big enough to reflect all the visible light. As soon as you look for bigger than those surplus 4.75" diameter, the price goes way up. If you can cut glass, the cheapest way to get a bigger cold mirror would be to cut some round 4.75" mirrors square and piece them together.
The other option is to use a hot mirror. These look like transparent glass but they reflect IR. You have to put one of these right across the light path. The visible light goes through but the IR gets reflected. Hot mirror is easier to use than cold mirror since the reflection angle does not matter so much.
I understand now. I don't think I could make a full size drawing right now as I don't have the measurements of the parts and not really sure how to calculate the light cone. How would I go about doing that?
I should have my LCD by this week and my light kit next week. Ill try to order the frenels, copy lens, and the Lexan XL10 by next week.
I should have my LCD by this week and my light kit next week. Ill try to order the frenels, copy lens, and the Lexan XL10 by next week.
full-scale drawing
If you know the distance between the pre-condensor lens and the fresnel, the diagonal size of the fresnel, and the diameter of the lens, that is all you need. You just draw the lens and the fresnel as straight parallel lines on the paper, seperated by their known distance and centered on the horizontal axis. Then you draw a line from the upper end of the lens to the upper end of the fresnel, and a line between the lower ends. That is the cone of light, represented in two dimensions.
Then you can see how to fit a 45 degree cold mirror (or any mirror really) in that path to bend it 90 degrees. Pretty simple. Keep in mind that the pre-condensor lens can't block the reflected light, so it can't be too close to the mirror. The size of the required mirror will surprise you. It has to be much longer than it is wide.
If you know the distance between the pre-condensor lens and the fresnel, the diagonal size of the fresnel, and the diameter of the lens, that is all you need. You just draw the lens and the fresnel as straight parallel lines on the paper, seperated by their known distance and centered on the horizontal axis. Then you draw a line from the upper end of the lens to the upper end of the fresnel, and a line between the lower ends. That is the cone of light, represented in two dimensions.
Then you can see how to fit a 45 degree cold mirror (or any mirror really) in that path to bend it 90 degrees. Pretty simple. Keep in mind that the pre-condensor lens can't block the reflected light, so it can't be too close to the mirror. The size of the required mirror will surprise you. It has to be much longer than it is wide.
What do you think about the Spherical Reflector (ladle) from diyprojectorcompany.com? How will that work with my setup?
soup ladle
I think it is better than no reflector at all. (Although some will argue with that. 😀 )
Pros: You get more light through your LCD. It only costs $7.95 + shipping. It will fit their lamp without modification. The cutout is large enough that you can get a lot of airflow around the lamp. Having somthing made of metal between the lamp and your box prevents charring the nearby wood.
Cons: Stainless steel is only 60-65% reflective. All the light that is reflected will go through the lamp arc, heating it so it may have a shorter life. (But replacement lamps are only $30.)
There are better solutions. Polished aluminum or aluminum on glass is a much better reflector. Polished silver is even better, so you can make a soup ladle much better by getting it silver plated. (Much more expensive option!) You could wait a week or two for DIYBuilderGroup to get their reflectors to see if you want a real optical aluminized glass reflector. Or you can shop around to see what else you can find now. If you can find a dichroic spherical reflector that fits your lamp and pre-condensor lens, that would be ideal. They do exist but they cost a lot more. (Dichroic means it reflects visible light but transmits IR, which cures the arc heating problem.)
I think it is better than no reflector at all. (Although some will argue with that. 😀 )
Pros: You get more light through your LCD. It only costs $7.95 + shipping. It will fit their lamp without modification. The cutout is large enough that you can get a lot of airflow around the lamp. Having somthing made of metal between the lamp and your box prevents charring the nearby wood.
Cons: Stainless steel is only 60-65% reflective. All the light that is reflected will go through the lamp arc, heating it so it may have a shorter life. (But replacement lamps are only $30.)
There are better solutions. Polished aluminum or aluminum on glass is a much better reflector. Polished silver is even better, so you can make a soup ladle much better by getting it silver plated. (Much more expensive option!) You could wait a week or two for DIYBuilderGroup to get their reflectors to see if you want a real optical aluminized glass reflector. Or you can shop around to see what else you can find now. If you can find a dichroic spherical reflector that fits your lamp and pre-condensor lens, that would be ideal. They do exist but they cost a lot more. (Dichroic means it reflects visible light but transmits IR, which cures the arc heating problem.)
I see now. I'll probably just go with the ladle.
One last question (maybe 🙂) Is there a certain thing I need to look for in the condensor? Or will just any one do?
Could this one work or should I wait for the other one to come in stock?
95mm x 150mm BK7 High Quality DCX Condenser Lens
Thanks you so much Guy Grotke.
One last question (maybe 🙂) Is there a certain thing I need to look for in the condensor? Or will just any one do?
Could this one work or should I wait for the other one to come in stock?
95mm x 150mm BK7 High Quality DCX Condenser Lens
Thanks you so much Guy Grotke.
DIYbuildergroup condensors
The condensor JCB has on order is optimised for 15" and 17" LCDs with a 220 mm fl condensor fresnel. From your past posts in this thread, I think you are using a 7" LCD with a 330 mm fl condensor fresnel. So that condensor may not be right for your projector. (You might still want to use his spherical reflector, though, if the price is right.) You really need to find a condensor with the right size and focal length so you can put it within a couple of centimeters of your lamp (to capture as much light as possible), and still have the resulting output cone of light fit your condensor fresnel.
Read this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=51658&perpage=10&pagenumber=1
There is a discussion about pre-condensor lens selection there, with a simple graphical method for determining the spacing between lamp, lens, and fresnel. I recommend you make a full-scale drawing for each potential condensor lens to see how it would fit in your projector. This only takes a few minutes. (Keep in mind: Ray angles above 45 degrees from the lamp arc to the edges of the pre-condensor lens are not useful, since too much of that light gets reflected at the glass surface.)
The condensor JCB has on order is optimised for 15" and 17" LCDs with a 220 mm fl condensor fresnel. From your past posts in this thread, I think you are using a 7" LCD with a 330 mm fl condensor fresnel. So that condensor may not be right for your projector. (You might still want to use his spherical reflector, though, if the price is right.) You really need to find a condensor with the right size and focal length so you can put it within a couple of centimeters of your lamp (to capture as much light as possible), and still have the resulting output cone of light fit your condensor fresnel.
Read this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=51658&perpage=10&pagenumber=1
There is a discussion about pre-condensor lens selection there, with a simple graphical method for determining the spacing between lamp, lens, and fresnel. I recommend you make a full-scale drawing for each potential condensor lens to see how it would fit in your projector. This only takes a few minutes. (Keep in mind: Ray angles above 45 degrees from the lamp arc to the edges of the pre-condensor lens are not useful, since too much of that light gets reflected at the glass surface.)
Ace sent me an email and said he had fresnels that were 210 bottom focal x 310 top focal. Also had a reflector and 80mm diam, 89mm focal condenser. Would those work better than the ones from diyprojectorcompany?
better match for 7" LCD
I think Ace specializes in 7" projector designs, so I am sure the optics he would sell you for a 7" LCD would all work together. The only problem you will have is paying for shipping from Spain.
Please post here to let us know how the ordering, shipping, & customs process goes. Both Ace and Exclusiv-online are in Europe and they have some interesting stuff. I would like to know how difficult & expensive it is to get in into the US.
I think Ace specializes in 7" projector designs, so I am sure the optics he would sell you for a 7" LCD would all work together. The only problem you will have is paying for shipping from Spain.
Please post here to let us know how the ordering, shipping, & customs process goes. Both Ace and Exclusiv-online are in Europe and they have some interesting stuff. I would like to know how difficult & expensive it is to get in into the US.
Guy I punched some numbers and found that DBG's condensor was FAR from an optimized condensor. It only adds about 10% more light...an optimized should add a lot more than that...
Do you know of any math that canback up your "optimized" statement? Because im not buying it...
Do you know of any math that canback up your "optimized" statement? Because im not buying it...
"non-optimized pre-condensor"
I'm not too surprised by that. (Although I have moderator status on their forum, I don't work for DIYBuildergroup, so I look at their store products with the same scepticism I look at other DIY projector store's products.) By "optimized for 15 inch" I just meant that JCB had determined expeimentally that his lens worked with 15" and 17" LCDs using a 220 mm fl condensor fresnel and a Ushio T15-size lamp. I did not mean to imply that it was the optimal pre-condensor for that design.
What I was trying to suggest (rather unsuccessfully, I guess) is that a pre-condensor that works under those conditions probably won't work for very different conditions, (ie. a 7" LCD with a 330 mm fl condensor fresnel).
As for math, I like the graphical ray method for working out pre-condensor lens behavior. It just gives me a better intuitive feel for what different parameter changes do to the end result. That is why I suggest that people try it: So they really understand what is happening to the light, instead of just plugging numbers into an equation.
Based on that understanding, I think the low yield with DIYbuildergroup's pre-condensor is not so much a problem with the lens. The problem is that a lamp 220 mm from a 220 mm fl 15" wide fresnel is already getting most of the light possible. (With a 17" wide fresnel it gets even more.) When you add a pre-condensor lens you can capture a bit more, but you can't get beyond that because if you decrease the focal length by much or increase the diameter, then the rays at the edges go past the critical angle. Then they mostly get reflected off the surface of the lens. If the math doesn't take that into account...
Another limitation is the lamp outer diameter. If you are using a T15-size lamp then you can't get a pre-condensor lens any closer that 15/16" from the arc center. If you have a T6-size lamp, then it can be 6/16" from the arc center. That makes a huge difference in picking a pre-condensor lens.
So given a T15-size lamp and a 15" diagonal width 220 mm fl fresnel, what do you think would be optimal?
I'm not too surprised by that. (Although I have moderator status on their forum, I don't work for DIYBuildergroup, so I look at their store products with the same scepticism I look at other DIY projector store's products.) By "optimized for 15 inch" I just meant that JCB had determined expeimentally that his lens worked with 15" and 17" LCDs using a 220 mm fl condensor fresnel and a Ushio T15-size lamp. I did not mean to imply that it was the optimal pre-condensor for that design.
What I was trying to suggest (rather unsuccessfully, I guess) is that a pre-condensor that works under those conditions probably won't work for very different conditions, (ie. a 7" LCD with a 330 mm fl condensor fresnel).
As for math, I like the graphical ray method for working out pre-condensor lens behavior. It just gives me a better intuitive feel for what different parameter changes do to the end result. That is why I suggest that people try it: So they really understand what is happening to the light, instead of just plugging numbers into an equation.
Based on that understanding, I think the low yield with DIYbuildergroup's pre-condensor is not so much a problem with the lens. The problem is that a lamp 220 mm from a 220 mm fl 15" wide fresnel is already getting most of the light possible. (With a 17" wide fresnel it gets even more.) When you add a pre-condensor lens you can capture a bit more, but you can't get beyond that because if you decrease the focal length by much or increase the diameter, then the rays at the edges go past the critical angle. Then they mostly get reflected off the surface of the lens. If the math doesn't take that into account...
Another limitation is the lamp outer diameter. If you are using a T15-size lamp then you can't get a pre-condensor lens any closer that 15/16" from the arc center. If you have a T6-size lamp, then it can be 6/16" from the arc center. That makes a huge difference in picking a pre-condensor lens.
So given a T15-size lamp and a 15" diagonal width 220 mm fl fresnel, what do you think would be optimal?
Guy,
I read over your other post on condensors, and you described a way of drawing the condensor...
I made an excel program that will plot the condensor and normal light fields real quick...I think I interperted your instructions wrong because when I fit a 100mm diam condensor with 200mm FL into a 15" light path it is actually worse, the usable angle of light is less.
Well heres a picture, I must be drawing it wrong cause this doesnt make sense.
My Light angle for the 15" panel by itself is 82 degrees, with the condensor it is narrowed to 28 degrees.
I read over your other post on condensors, and you described a way of drawing the condensor...
I made an excel program that will plot the condensor and normal light fields real quick...I think I interperted your instructions wrong because when I fit a 100mm diam condensor with 200mm FL into a 15" light path it is actually worse, the usable angle of light is less.
Well heres a picture, I must be drawing it wrong cause this doesnt make sense.
My Light angle for the 15" panel by itself is 82 degrees, with the condensor it is narrowed to 28 degrees.
An externally hosted image should be here but it was not working when we last tested it.
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