Ok hi all,
This is no joke, I have found THE answer to large fresnel buying..... well sort of, heres the problem:
I bought two of these like sold Here (shop around, I got mine for $45 each and they are 14 inches X 18 inches)
But well .... the focal lenghts are LONG, really long.... like 3 + feet long.
Now unless im doing this all wrong as this is my first attempt at a projector (17inch lcd) I cant get these lenses to work.
I really dont care if my projector is 6 feet long due to focal lengths, but well using the fujinon lense I cant get anything to focus. The fresnel focal length and projector lense length dont line up.
Anyone know of a lense that will work?
Have I stumbled onto THE new supplier of fresnel stuff?
Or did I just waste 90 bucks lol
Thanks for any help
This is no joke, I have found THE answer to large fresnel buying..... well sort of, heres the problem:
I bought two of these like sold Here (shop around, I got mine for $45 each and they are 14 inches X 18 inches)
But well .... the focal lenghts are LONG, really long.... like 3 + feet long.
Now unless im doing this all wrong as this is my first attempt at a projector (17inch lcd) I cant get these lenses to work.
I really dont care if my projector is 6 feet long due to focal lengths, but well using the fujinon lense I cant get anything to focus. The fresnel focal length and projector lense length dont line up.
Anyone know of a lense that will work?
Have I stumbled onto THE new supplier of fresnel stuff?
Or did I just waste 90 bucks lol
Thanks for any help
Fujinon lens? Which one? The copy lens or the Projection Lens? The copy lens should focus most of the image (if not all - brainchild I think you were testing one of these?) But the Fujinon Projection lens is not meant for an image source bigger than 4 or 5" I think. And won't focus much of a full 17" panel.
Not sure about the fresnels... But they CAN work, it's just finding the right projection lens for your focal lengths.
Not sure about the fresnels... But they CAN work, it's just finding the right projection lens for your focal lengths.
What is the groove count on these fresnels? Did you split it? I think that would be a good thing with these big boys. I can't believe they're so cheap.
Cruser might have some good input here. Even if the groove count is low they'd work behind the lcd.
I'd like to see some pictures of YOUR big fresnel Gonthorn, if you have the ability.
Cruser might have some good input here. Even if the groove count is low they'd work behind the lcd.
I'd like to see some pictures of YOUR big fresnel Gonthorn, if you have the ability.
The problem is this:
let say that the focal of your fresnells are 40 inch, then without condsor you need to place the arc (lamp) at 40 inch from the first fresnell to get parallel beams out. Then when you place the second fresnell, the light will be collected at 40 inch on the other side. The (picture) focal of your fuji-lens is way smaller. You have to place that at a distance from the tft wich is the same as the focal length of the lens (maybe slightely further away). For a picture to be bright both light as picture focals have to be roughly the same. This is not the case so horrible dark picture. And as people already sayed, you need a larger focal lens (400mm) to get the complete 17" tft on. If you want to shorten the focal lenght of the second fresnell (behind the tft) you can place a second one (same focal) touching it and it will reduce the focal length by 50% (1/f=1/f1+1/f2). But i don't know if that is wise to do.
let say that the focal of your fresnells are 40 inch, then without condsor you need to place the arc (lamp) at 40 inch from the first fresnell to get parallel beams out. Then when you place the second fresnell, the light will be collected at 40 inch on the other side. The (picture) focal of your fuji-lens is way smaller. You have to place that at a distance from the tft wich is the same as the focal length of the lens (maybe slightely further away). For a picture to be bright both light as picture focals have to be roughly the same. This is not the case so horrible dark picture. And as people already sayed, you need a larger focal lens (400mm) to get the complete 17" tft on. If you want to shorten the focal lenght of the second fresnell (behind the tft) you can place a second one (same focal) touching it and it will reduce the focal length by 50% (1/f=1/f1+1/f2). But i don't know if that is wise to do.
The groove count is very very high, it has the most grooves I have ever seen, my attempt to count gets me 64 grooves per inch. Let me get some pictures of it later.
I will also try to get an actual focal length. I really hope they will work, guess its just finding a lense to do it. the fujinon copy lense isnt, any suggestions on a good lense that will capture a full 17inch lcd?
I will also try to get an actual focal length. I really hope they will work, guess its just finding a lense to do it. the fujinon copy lense isnt, any suggestions on a good lense that will capture a full 17inch lcd?
1- 64 grooves per inch is NOT very high.
2- The fujinon has a 240mm focal length. How in the world are you gonna use them with those fresnels even if the fujinon could focus a full 17" screen.
My advice to you is SEARCH. All of this has been covered many, many times. I'm not trying to be a *****... just saying. Even the cheap EXTRA large fresnels you mentioned have already been talked about.
search
JCB
____________________
www.diybuildergroup.com
TONIGHT!
2- The fujinon has a 240mm focal length. How in the world are you gonna use them with those fresnels even if the fujinon could focus a full 17" screen.
My advice to you is SEARCH. All of this has been covered many, many times. I'm not trying to be a *****... just saying. Even the cheap EXTRA large fresnels you mentioned have already been talked about.
search
JCB
____________________
www.diybuildergroup.com
TONIGHT!
Ok its all fixed, that is its doable 
Using a telescope lens with 900mm FL I can get the image focused between the fresnels. So im off to build my projector, it will be built into a cabinet so the 7 foot size is not an issue.
For those interested I took a chance and it turned out ok (on a 17inch lcd that is)
parts:
2 fresnels as seen above
1 900mm FL lens (surplus shed)
1 17inch lcd its Acer panel (au optronics 16ms response, 1280 x 1024 .... this its AL1721 only needs 1 cable lengthened, 7 pin .5mm pitch, looks easy enough.
1 500 watt halogen light source
wish me luck
Using a telescope lens with 900mm FL I can get the image focused between the fresnels. So im off to build my projector, it will be built into a cabinet so the 7 foot size is not an issue.
For those interested I took a chance and it turned out ok (on a 17inch lcd that is)
parts:
2 fresnels as seen above
1 900mm FL lens (surplus shed)
1 17inch lcd its Acer panel (au optronics 16ms response, 1280 x 1024 .... this its AL1721 only needs 1 cable lengthened, 7 pin .5mm pitch, looks easy enough.
1 500 watt halogen light source
wish me luck
Large Fresnel Lenses
I wish I had seen this thread sooner. I have some 14x14 fresnel lenses (good for up to a 17" LCD) with the correct focal length of 13" (about 330mm I think) and with a groove count of approximately 2 per mm. I'm putting this together as a group order, so it's not a profit thing - everyone pays exactly what the lens costs to make. You can view/join the fresnel order at http://www.diylabs.org/projector/parts.htm by clicking on "Fresnel Lenses".
As an asside... MAN those are some huge fresnel lenses that other website offers. I might someday buy one just for the heck of having it - you could probably make a pretty sweet solar grill using one outdoors!
I wish I had seen this thread sooner. I have some 14x14 fresnel lenses (good for up to a 17" LCD) with the correct focal length of 13" (about 330mm I think) and with a groove count of approximately 2 per mm. I'm putting this together as a group order, so it's not a profit thing - everyone pays exactly what the lens costs to make. You can view/join the fresnel order at http://www.diylabs.org/projector/parts.htm by clicking on "Fresnel Lenses".
As an asside... MAN those are some huge fresnel lenses that other website offers. I might someday buy one just for the heck of having it - you could probably make a pretty sweet solar grill using one outdoors!
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