Although I'm sure this is covered some where on this forum, I did some searching and couldn't find it. So here goes.
If I understand the project right you have these parts in this order.
1. Light
2. fresnel lense (for straitening the light)
3. lcd screen
4. fresnel lense (for focusing the light)
5. projector lense (for projecting the light)
Questions:
1. some designs I've seen seem to omit the second fresnel lens...is that just an oversight, is it not nessicary or is it because of a propert of one of the other two lenses?
2. If I have a fresnel lense with a 200mm focal length, does that mean that a) my first fresnel lense should be 200mm from the light source, b) my second fresnel lense FL should be equal to the FL of the projector lense?
3. How do these lenses sound?
Fresnel Lenses:
260mm x 260mm
Transmittance: high
Thickness: 1.8mm
Weight: 160 grams
Material: optical acrylic
Groove pitch: 0.2mm
Focal length: 200mm (7.874")
Projector Lense:
FOCAL LENGTH: 7.8"
SPEED: F:6.6
BARREL DIA.: 2-7/16"
BARREL LENGTH: 2-7/16"
If I understand the project right you have these parts in this order.
1. Light
2. fresnel lense (for straitening the light)
3. lcd screen
4. fresnel lense (for focusing the light)
5. projector lense (for projecting the light)
Questions:
1. some designs I've seen seem to omit the second fresnel lens...is that just an oversight, is it not nessicary or is it because of a propert of one of the other two lenses?
2. If I have a fresnel lense with a 200mm focal length, does that mean that a) my first fresnel lense should be 200mm from the light source, b) my second fresnel lense FL should be equal to the FL of the projector lense?
3. How do these lenses sound?
Fresnel Lenses:
260mm x 260mm
Transmittance: high
Thickness: 1.8mm
Weight: 160 grams
Material: optical acrylic
Groove pitch: 0.2mm
Focal length: 200mm (7.874")
Projector Lense:
FOCAL LENGTH: 7.8"
SPEED: F:6.6
BARREL DIA.: 2-7/16"
BARREL LENGTH: 2-7/16"
Attachments
I see alot of you guys are recomending a projection lense that is about 320mm FL.
I planning on building my projector with a 15" screen.
What do you think about this lense
PROJ. LENS, Focal length 9.0" 2-11/16" diameter
I bought 2 fresnel lenses, (by mistake I thought they were somehting other than what they were)
They ended up being http://3dlens.com/pagemagnifier.htm , which kinda ticks me off that I bought that. any way. Does any one know where to buy the 3dlens.com's A260, in the US so I can avoid paying the $25 shipping. Also do you guys think that the A260 is a good lense for this set up?
I planning on building my projector with a 15" screen.
What do you think about this lense
PROJ. LENS, Focal length 9.0" 2-11/16" diameter
I bought 2 fresnel lenses, (by mistake I thought they were somehting other than what they were)
They ended up being http://3dlens.com/pagemagnifier.htm , which kinda ticks me off that I bought that. any way. Does any one know where to buy the 3dlens.com's A260, in the US so I can avoid paying the $25 shipping. Also do you guys think that the A260 is a good lense for this set up?
The lenses at 3dlens are ok. they do have minor imperfections and cromatic abberation. Not bad enough to ruin the image but it does waste some light.
I think they are working on better methods because their groove pitch is shrinking. I assume their newer equipment will also be used to make the OHP fresnels in the future.
Not sure where lumenlab or Alan get theirs. Check them out too.
I think they are working on better methods because their groove pitch is shrinking. I assume their newer equipment will also be used to make the OHP fresnels in the future.
Not sure where lumenlab or Alan get theirs. Check them out too.
questions & answers
Questions:
1. some designs I've seen seem to omit the second fresnel lens...is that just an oversight, is it not nessicary or is it because of a propert of one of the other two lenses?
You could use a single fresnel that has the same focal length as the combination of the two normally used, but it is not a good idea because fresnels do not work very well unless you have parallel light on the ringed side and the lamp or projection lens near the focal length from the smooth side. But sometimes you can get a pair of fresnels (ie. a 220 mm fl & a 330 mm fl) glued together, so they work very well but look like one fresnel. When you do have two fresnels, you can put them both at least 20 mm before the LCD, or you can split them up. Then the condensor fresnel goes at least 20 mm before the LCD and the field fresnel goes 20 - 30 mm after the LCD. Unsplit looks better. Split lets you do some optical keystone correction, if needed.
2. If I have a fresnel lense with a 200mm focal length, does that mean that a) my first fresnel lense should be 200mm from the light source, b) my second fresnel lense FL should be equal to the FL of the projector lense?
a) That is a good starting point, but you can adjust this distance later by a few millimeters to get the light going into the projection lens.
b) No, the LCD to lens distance will be more than the focal length of the projection lens, since your screen will not be on the moon! For a 10 foot throw distance and a 320 mm fl triplet, the LCD to lens distance would be 357.5 mm. Ideally, your field fresnel would be (357.5 + 20) = 377.5 mm fl for an unsplit design, or (357.5 - 20) = 337.5 for a split design. Either one of those would focus the lamp arc image right into the center of the projection lens. But I don't think you can find a 377 or a 337 mm fl fresnel!
Use a 330 mm fl fresnel. If you need to do optical keystone correction, then build the split design with the 200 mm fl fresnel 20 mm before the LCD and the 330 mm fl fresnel 30 mm after the LCD. If your projector can be positioned so the projection lens is at the same height as the middle of the screen, then build the unsplit design with both fresnels 20 mm before the LCD.
Once you have it together enough to project an image, you can tune the optics by adjusting the lamp to condensor fresnel a bit to get the light all going into the projection lens.
3) Have fun!
Questions:
1. some designs I've seen seem to omit the second fresnel lens...is that just an oversight, is it not nessicary or is it because of a propert of one of the other two lenses?
You could use a single fresnel that has the same focal length as the combination of the two normally used, but it is not a good idea because fresnels do not work very well unless you have parallel light on the ringed side and the lamp or projection lens near the focal length from the smooth side. But sometimes you can get a pair of fresnels (ie. a 220 mm fl & a 330 mm fl) glued together, so they work very well but look like one fresnel. When you do have two fresnels, you can put them both at least 20 mm before the LCD, or you can split them up. Then the condensor fresnel goes at least 20 mm before the LCD and the field fresnel goes 20 - 30 mm after the LCD. Unsplit looks better. Split lets you do some optical keystone correction, if needed.
2. If I have a fresnel lense with a 200mm focal length, does that mean that a) my first fresnel lense should be 200mm from the light source, b) my second fresnel lense FL should be equal to the FL of the projector lense?
a) That is a good starting point, but you can adjust this distance later by a few millimeters to get the light going into the projection lens.
b) No, the LCD to lens distance will be more than the focal length of the projection lens, since your screen will not be on the moon! For a 10 foot throw distance and a 320 mm fl triplet, the LCD to lens distance would be 357.5 mm. Ideally, your field fresnel would be (357.5 + 20) = 377.5 mm fl for an unsplit design, or (357.5 - 20) = 337.5 for a split design. Either one of those would focus the lamp arc image right into the center of the projection lens. But I don't think you can find a 377 or a 337 mm fl fresnel!
Use a 330 mm fl fresnel. If you need to do optical keystone correction, then build the split design with the 200 mm fl fresnel 20 mm before the LCD and the 330 mm fl fresnel 30 mm after the LCD. If your projector can be positioned so the projection lens is at the same height as the middle of the screen, then build the unsplit design with both fresnels 20 mm before the LCD.
Once you have it together enough to project an image, you can tune the optics by adjusting the lamp to condensor fresnel a bit to get the light all going into the projection lens.
3) Have fun!
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