Hi Guys,
After off from this forum for around 8 months, I saw many success project and many new ideas, one of this is split fresnel.
The idea is using 2 fresnel before and after lcd panel. Actually this already discussed long time ago buried in DIY Video Projector part 1!
Here is one of the link I remember:
www.fresneloptics.com/pdf/condenser_lenses.PDF
What is new for me is really spliting one panel into two, that never thought before!
Many of you got good result doing this, but there are some confusion hanging around.
I try to explain it as far as I know, correct me if I'm wrong.
Here is:
To get the optimum result, we should follow certain rules:
1. lamp position should at the focal length of fresnel #1, to produce parallel rays.
2. fresnel #1 to lcd panel to fresnel #2 is up to your need, because we deal with parallel rays that no effect (ideally), but better is close together to reduce light lost.
3. objective lens position should inside light beam produced by fresnel #2, it's slightly shorter than focal length of fresnel #2.Why? because if we put the lens longer than fl. of fresnel #2, we lost the light beam, otherwise if we put the lens much shorter, it will generate hotspot.
The tricky part is how to choose all parts to get the best result.
Fresnel #1 is easy, because it's only need to adjust the lamp position, but to reduce light lost, the reflector should reflect all the light to the fresnel.
Fresnel #2, it's depend on th lens we use or vise-versa, let say: if we want 110inch diagonal projected image size at a distance of 10ft, we need objective lens with focal length = 12inch and lcd to lens distance is 13inch, so we need fresnel #2 with focal length more than 13 inch or around 15inch (depend on the lens diameter).
That's all for now, see you.
Gunawan.
After off from this forum for around 8 months, I saw many success project and many new ideas, one of this is split fresnel.
The idea is using 2 fresnel before and after lcd panel. Actually this already discussed long time ago buried in DIY Video Projector part 1!
Here is one of the link I remember:
www.fresneloptics.com/pdf/condenser_lenses.PDF
What is new for me is really spliting one panel into two, that never thought before!
Many of you got good result doing this, but there are some confusion hanging around.
I try to explain it as far as I know, correct me if I'm wrong.
Here is:
To get the optimum result, we should follow certain rules:
1. lamp position should at the focal length of fresnel #1, to produce parallel rays.
2. fresnel #1 to lcd panel to fresnel #2 is up to your need, because we deal with parallel rays that no effect (ideally), but better is close together to reduce light lost.
3. objective lens position should inside light beam produced by fresnel #2, it's slightly shorter than focal length of fresnel #2.Why? because if we put the lens longer than fl. of fresnel #2, we lost the light beam, otherwise if we put the lens much shorter, it will generate hotspot.
The tricky part is how to choose all parts to get the best result.
Fresnel #1 is easy, because it's only need to adjust the lamp position, but to reduce light lost, the reflector should reflect all the light to the fresnel.
Fresnel #2, it's depend on th lens we use or vise-versa, let say: if we want 110inch diagonal projected image size at a distance of 10ft, we need objective lens with focal length = 12inch and lcd to lens distance is 13inch, so we need fresnel #2 with focal length more than 13 inch or around 15inch (depend on the lens diameter).
That's all for now, see you.
Gunawan.
Attachments
I'm confused as to why splitting the fresnel would enhance the quality or brightness of the resulting image. Could you help me figure that part out?
Parallel Light
I think the theory is that the regular "double fresnel lens before lcd" method results in light hitting the lcd at a slight angle (20 degress?). If you split the fresnel and place the lcd between the 2 halfs, the light hits exactly perpendicular to the lcd plane. If the light is parallel when passing through the lcd, is there an increase in the amount of light that passes through the lcd? Some folks say that it is considerably brighter this way.
I have not tested it as there is a considerable distance from the plane of my LCD and where I can place the screen side of the split fresnel lens.
Ken
I think the theory is that the regular "double fresnel lens before lcd" method results in light hitting the lcd at a slight angle (20 degress?). If you split the fresnel and place the lcd between the 2 halfs, the light hits exactly perpendicular to the lcd plane. If the light is parallel when passing through the lcd, is there an increase in the amount of light that passes through the lcd? Some folks say that it is considerably brighter this way.
I have not tested it as there is a considerable distance from the plane of my LCD and where I can place the screen side of the split fresnel lens.
Ken
hm yes i see that now. i will try it out. split my fresnel too a week ago to increase the focal length and light output by using just one. i hope to get my beamer ready this weekend, so i can post some results. if not, i will need a better fresnel. and bigger oh yeah!
Diylabs,Nitemare,
if you placed the fresnel #1 at the right position (depend on it's focal length) as my faq above, sure it can enhance the brightness (see good explanation by Mavmesa above).
If you get better brightness, your projection image must be better too, right?
To achieve the best result, you need better quality for fresnel #2 (means: no blurry, scratch or bend and the important thing is more dense in circular grooves), because it's placed in front of your LCD panel, don't forget check it's focal length too!
For fresnel #2 : " you don't feel it's there, but you see it bends all the light to your objective lens".
see you.
Gunawan.
if you placed the fresnel #1 at the right position (depend on it's focal length) as my faq above, sure it can enhance the brightness (see good explanation by Mavmesa above).
If you get better brightness, your projection image must be better too, right?
To achieve the best result, you need better quality for fresnel #2 (means: no blurry, scratch or bend and the important thing is more dense in circular grooves), because it's placed in front of your LCD panel, don't forget check it's focal length too!
For fresnel #2 : " you don't feel it's there, but you see it bends all the light to your objective lens".
see you.
Gunawan.
Yeah I was wondering if the fresnel #2 would affect the quality of the projection, but you already answered that for me. I used to have an InFocus 750 for a while, and it has two fresnel halves built in like that. They didn't have as high of a groove count as my fresnel lenses do, but they still produced a picture that looked great. I think that as long as you place the #2 fresnel at the right exact spot that you could eliminate any defects in the image. Also, maybe we should put that fresnel between 2 thin sheets of glass to keep it perfectly straight and protect from scratches.
yes it has to be straight. but i have to experiment some more until i get it right. but i think i need a better fresnel. one that is biger than my TFT lcd. i got a viewsonic vg150 15" and the fresnel i got is a little bit smaller. but if i am informed correct it needs to be bigger tha the lcd. it won't be easy finding such a fresnel here in europe...
The largest fresnel lens that I've been able to find is the 12.2"x12.2" that I carry. Unfortunately they are made with the corners missing like most of the fresnel lenses are, so there's no way that I know of to get one that will cover the entire surface. I have seen single fresnel lenses that are large enough for 15" monitors, but as I recall they were very expensive (~$100) and you'd need two of them, so I doubt they would be of interest.
So far my advise to everyone with a 15" LCD is to simply get a 12x12 fresnel and then use the resizing menu on your LCD module to make the image fit inside of the fresnel's surface area if the missing corners really gets annoying. Usually it doesn't interfere with anything though.
So far my advise to everyone with a 15" LCD is to simply get a 12x12 fresnel and then use the resizing menu on your LCD module to make the image fit inside of the fresnel's surface area if the missing corners really gets annoying. Usually it doesn't interfere with anything though.
hm i am having trouble picturing the problem with these corners. lcds are sized in the ration 4:3. so if a 12"x12" fits a lcd on the long side, just move it in the middle of the fresnel to place it between those cut corners...
btw how much would it be for a shipment to europe, germany?
i am interessted in those super trasnparent new fresnel you got there...
btw how much would it be for a shipment to europe, germany?
i am interessted in those super trasnparent new fresnel you got there...
Fresnel Lens International Shipping
The corners cut out just a tiny bit of the image in each corner of the LCD. You can easily slide the LCD up a bit so that you're only missing the top corners since your "start" button is in the lower corners.
Shipping to Germany costs $16 for 4-10 day airmail for this fresnel lens. Email me at diylabs@hotmail.com if you are interested in anything. You can also check out my website at www.diylabs.org
The corners cut out just a tiny bit of the image in each corner of the LCD. You can easily slide the LCD up a bit so that you're only missing the top corners since your "start" button is in the lower corners.
Shipping to Germany costs $16 for 4-10 day airmail for this fresnel lens. Email me at diylabs@hotmail.com if you are interested in anything. You can also check out my website at www.diylabs.org
Re: Parallel Light
Hmmm,
Mav...do you know if split fresnel will make the picture brighter? because I watched a few movies on a not split fresnel and during 50% dark scenes (meaning there is light but not a bright scene), I cant really see the persons face.
What about the sharpness of the pic? When I used the lcd, and adjusted the lens, one part of the screen was sharp while the other part was not, then when I moved the lens a little that part was sharp then the other part was not.
Uh...dont know how to rephrase that 🙁
Mavmesa said:
Hmmm,
Mav...do you know if split fresnel will make the picture brighter? because I watched a few movies on a not split fresnel and during 50% dark scenes (meaning there is light but not a bright scene), I cant really see the persons face.
What about the sharpness of the pic? When I used the lcd, and adjusted the lens, one part of the screen was sharp while the other part was not, then when I moved the lens a little that part was sharp then the other part was not.
Uh...dont know how to rephrase that 🙁
sharpness??
I think we are running a conversation over two threads.
I fixed the sharpness by sandwiching my fresnel between two plates of glass to flatten it. Alan's tripett is pretty sharp focus, the center will be in better focus for very small detail (that is related to fresnel rings, i think). You probably need to turn down the image contrast. I found that this improve "Matrix" for me. I expect more brightness when I get the new fresnel.
As to the effect that splitting the fresnel has on brightness. I just asked that question on the other thread about "the goodness of split fresnels". I want to be sure I am not promoting a false idea.
Mavmesa
I think we are running a conversation over two threads.
I fixed the sharpness by sandwiching my fresnel between two plates of glass to flatten it. Alan's tripett is pretty sharp focus, the center will be in better focus for very small detail (that is related to fresnel rings, i think). You probably need to turn down the image contrast. I found that this improve "Matrix" for me. I expect more brightness when I get the new fresnel.
As to the effect that splitting the fresnel has on brightness. I just asked that question on the other thread about "the goodness of split fresnels". I want to be sure I am not promoting a false idea.
Mavmesa
Re: Fresnel Lens International Shipping
Or if possible... you can change the horizontal size of the lcd, then you will see the whole image 🙂
diylabs said:
Or if possible... you can change the horizontal size of the lcd, then you will see the whole image 🙂
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