Hi guys,
I 've got this dude from the begining ...
Does Condenser lens alters in anyway the correct distance between the arc (source point) and the fresnel ?
Example: we have a first fresnel with a focal lenght of 8.6" so the arc or point source must be exactly at 8.6" from the fresnel to get parallel light out to the panel.
But using a condenser lens, the light reachs the fresnel now at a diferent angle so, doesn it alter this distance ?
How can we calculate the exact distance to put the point source ?
In the next image I try to explain what I mean.
I 've got this dude from the begining ...
Does Condenser lens alters in anyway the correct distance between the arc (source point) and the fresnel ?
Example: we have a first fresnel with a focal lenght of 8.6" so the arc or point source must be exactly at 8.6" from the fresnel to get parallel light out to the panel.
But using a condenser lens, the light reachs the fresnel now at a diferent angle so, doesn it alter this distance ?
How can we calculate the exact distance to put the point source ?
In the next image I try to explain what I mean.
Attachments
A Meniscus Lens will change the focal length of your fresnels. Plano Convex lenses also effect the focals. And DCX will not effect the focal length.
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If you want to know what the focal length of the lenses as a pair is, which will be the distance your fresnel needs to be from the arc, can be found using the equation:
1/ft=1/f1+1/f2
ft = focal total
f1 = focal of first lens(order doesn't matter)
f2 = focal of second lens(order doesn't matter)
One th lenses that will shorten the focal length, use the positive focal length. If a lens lengthens it, plug in the negitive focal length into that equation.
Hope I've helped!
1/ft=1/f1+1/f2
ft = focal total
f1 = focal of first lens(order doesn't matter)
f2 = focal of second lens(order doesn't matter)
One th lenses that will shorten the focal length, use the positive focal length. If a lens lengthens it, plug in the negitive focal length into that equation.
Hope I've helped!
This applie's only for thin lenses touching each other. For lenses further away you need a more difficult equation.
The Gullstrand's Equation
Onthis page under "MULTI LENSES FOCAL LENGTH CALCULATION" you can calculate the focal length for multpiple lenses.
I am a chemist student but i don't get it. I understant that you can calculate the new focal lenght only, from where is this new focal lenght? I believe it is from the principle plain (see first link) but how do you calculate that distance? I am confused?
Anyone?????
The Gullstrand's Equation
Onthis page under "MULTI LENSES FOCAL LENGTH CALCULATION" you can calculate the focal length for multpiple lenses.
I am a chemist student but i don't get it. I understant that you can calculate the new focal lenght only, from where is this new focal lenght? I believe it is from the principle plain (see first link) but how do you calculate that distance? I am confused?
Anyone?????
Al
Heya buddy, this all depends on a few things, we have a focal on our condenser, we have a focal on the frensel and a focal on the reflector.
Dweils calculation is fairly correct, but one thing that no body takes into acount is power of a lens, and this makes a big diff to where a frensel should be placed.
On a general rule using a spherical reflector, with the bulb at its focal, the condenser tuned to spread the amount of light needed over a given area, all you should realy need to do is measure the frensels focal from just infront of the condenser back to how far the frensels focal is. This is what i do and works every time, most condensers have alot of power, they are designed for this, especially the shorter focal condensers, ie: 100mm fl.
Alot has to do with the lights angles also, its not just about the lenses you choose, if you have a reflector that has a long focal length then your light will be in a long ray fashion. if your reflector has a short focal then your rays will be in a wide ray fashion. Another thing is the depth of a spherical reflector, the deeper the reflector is the wider the rays are, the shallower, the longer they become, but this isnt as important as the focal and realy the focal is all we need to go by. This can afect how a condenser can perform,and will result in differnt results on your projected image. If the rays are too wide you will see a haze in your projected image, if the light is too narrow well then we get hotspots, so its not just the condenser that we have to worry about its also the reflector, and they must be perfectly matched for the ultimate performace and a colour correct image.
The stated above also can fool with the frensel, the rays going to the frensel should also be closely matched, if not we will get the haze, and loss of light, also this can alter how the frensel will perform and can cause headaches with our frensels focal point. Its probally where most dont understand how their frensels focal can be so out, its realy not the frensels focal but the angle of the rays that are out.
So just to finnish up, it takes experimenting, unless you get custom designed optics your optics will never be fully correct, but imo now days alot of us have optics that are close and are yealding great results. I normally just focus the frensel to the condenser i choose, focus it to the front of the condenser, not far infront of it, and it yealds me great results. Try to find a condenser thats just abit smaller then your frensels focal and your light rays from the condenser will be fairly spot on to the frensels focal angles, thats if you choose the right reflector ofcourse. The best focals to use for spherical reflector on a ohp setup is between 25mm - 35mm, anymore or any less and results will be disapointing, but ofcourse there are ways to fix these problems with a condenser, and thats where if you are using the wrong gear, projector designing and building can become a pain
Trev
Heya buddy, this all depends on a few things, we have a focal on our condenser, we have a focal on the frensel and a focal on the reflector.
Dweils calculation is fairly correct, but one thing that no body takes into acount is power of a lens, and this makes a big diff to where a frensel should be placed.
On a general rule using a spherical reflector, with the bulb at its focal, the condenser tuned to spread the amount of light needed over a given area, all you should realy need to do is measure the frensels focal from just infront of the condenser back to how far the frensels focal is. This is what i do and works every time, most condensers have alot of power, they are designed for this, especially the shorter focal condensers, ie: 100mm fl.
Alot has to do with the lights angles also, its not just about the lenses you choose, if you have a reflector that has a long focal length then your light will be in a long ray fashion. if your reflector has a short focal then your rays will be in a wide ray fashion. Another thing is the depth of a spherical reflector, the deeper the reflector is the wider the rays are, the shallower, the longer they become, but this isnt as important as the focal and realy the focal is all we need to go by. This can afect how a condenser can perform,and will result in differnt results on your projected image. If the rays are too wide you will see a haze in your projected image, if the light is too narrow well then we get hotspots, so its not just the condenser that we have to worry about its also the reflector, and they must be perfectly matched for the ultimate performace and a colour correct image.
The stated above also can fool with the frensel, the rays going to the frensel should also be closely matched, if not we will get the haze, and loss of light, also this can alter how the frensel will perform and can cause headaches with our frensels focal point. Its probally where most dont understand how their frensels focal can be so out, its realy not the frensels focal but the angle of the rays that are out.
So just to finnish up, it takes experimenting, unless you get custom designed optics your optics will never be fully correct, but imo now days alot of us have optics that are close and are yealding great results. I normally just focus the frensel to the condenser i choose, focus it to the front of the condenser, not far infront of it, and it yealds me great results. Try to find a condenser thats just abit smaller then your frensels focal and your light rays from the condenser will be fairly spot on to the frensels focal angles, thats if you choose the right reflector ofcourse. The best focals to use for spherical reflector on a ohp setup is between 25mm - 35mm, anymore or any less and results will be disapointing, but ofcourse there are ways to fix these problems with a condenser, and thats where if you are using the wrong gear, projector designing and building can become a pain
Trev
I don't believe trying is the only option. We have math to help us with this kind of stuff. Maybe we should fill in data from already build projectors and see what rolls out of the formula i posted. Maybe then i understand how it works and we can just calculate futher projects.
Thanks guys !
It is more dificult that I assumed to be at the beginning !!
My current setup is a DIY Labs Condenser (I dont know the FL) and a Surplus Shed OHP unsplitted Fresnel (280mm and 320mm FL) and I did have to put the source point at 460mm !! from the fresnell in order to get the light concentrated in the 60mm DIY labs triplet at 350mm.
My next step is to use a 240mm FL Fujinon Copy Lens and split the fresnel to sandwich the panel and I need to assure the light will pass perfectly parallel through the panel and converge in a point now at 260mm.
So I need to know if I can put all together in a PC cabinet.
Does any body have measured results using the DIY labs Condenser and Fresnel gear with the fujinon copy lens ?
Thank you all !!
It is more dificult that I assumed to be at the beginning !!
My current setup is a DIY Labs Condenser (I dont know the FL) and a Surplus Shed OHP unsplitted Fresnel (280mm and 320mm FL) and I did have to put the source point at 460mm !! from the fresnell in order to get the light concentrated in the 60mm DIY labs triplet at 350mm.
My next step is to use a 240mm FL Fujinon Copy Lens and split the fresnel to sandwich the panel and I need to assure the light will pass perfectly parallel through the panel and converge in a point now at 260mm.
So I need to know if I can put all together in a PC cabinet.
Does any body have measured results using the DIY labs Condenser and Fresnel gear with the fujinon copy lens ?
Thank you all !!
Hi guys !
Let´s pretend we have this options:
For a condenser lens:
---------------------------
DIYLabs 60mm Diameter 110mm FL Condenser
SurplusShed 90mm Diameter 103mm FL Plano Convex (L4702)
SurplusShed 79mm Diameter 89mm FL Plano Convex (L4375)
For the first Fresnel:
-------------------------
210mm FL Fresnel
280mm FL Fresnel
320mm FL Fresnel
To simplify the question lets assume there is no reflector in the setup.
My questions are:
1) Can I use the SurplusShed's PCXs as condenser lens in order to take advantage of a bigger diameter ?
2) How to calculate (in theory) the maximum distances between the fresnel / condenser / arc to get collimated out from the fresnel ?
Ace:
Does that means that if I choose the 280mm Fresnel I can put any condenser at exactly 280mm from the fresnel (from condenser back to fresnel front) ?
But what about the arc/condenser distance ?
I just need to know if such lenses will fit in my current avalaible space before buying.
Thanks a lot guys !!
Let´s pretend we have this options:
For a condenser lens:
---------------------------
DIYLabs 60mm Diameter 110mm FL Condenser
SurplusShed 90mm Diameter 103mm FL Plano Convex (L4702)
SurplusShed 79mm Diameter 89mm FL Plano Convex (L4375)
For the first Fresnel:
-------------------------
210mm FL Fresnel
280mm FL Fresnel
320mm FL Fresnel
To simplify the question lets assume there is no reflector in the setup.
My questions are:
1) Can I use the SurplusShed's PCXs as condenser lens in order to take advantage of a bigger diameter ?
2) How to calculate (in theory) the maximum distances between the fresnel / condenser / arc to get collimated out from the fresnel ?
Ace:
Does that means that if I choose the 280mm Fresnel I can put any condenser at exactly 280mm from the fresnel (from condenser back to fresnel front) ?
But what about the arc/condenser distance ?
I just need to know if such lenses will fit in my current avalaible space before buying.
Thanks a lot guys !!
bfourcade said:
Lets start with the question I DO know.
If you have a fresnel with a focal of 280 mm and you place the arc at 280 mm you will get parallel beams out of the first fresnel (what you want), but when you use a condensor this distance chances and you have to calculate the new distance. This is a black hole, because the exact calcultation has not been done.
I am working on it, but my results need some testing.
What of type condesor you need? I don't no, depents on you panel size. A short focal can decrease the size of your total projector, but this can only be used when with that condesor your TFT is completely lid. I would go for the largest diameter, because the focals are quite the same.
With the fresnels i can't help you. Short focal will probably decr easy the projctor size also.
When i use the equations from the site from my above post -
With a 110 fl condesor and a 210 mm fresnel - you will need to place the condensor 2,4 cm away from the arc and the fresnell 18 cm from the condesor to get parallel beams. IF my calculations are right.
I would really like to test my findings, so who can give me there focal lengths of there condesor and fresnell so i can calculate the distance between the lenses and see if my calculations are right!
I just want to mention that you must first of all decide the focus of the fresnell and objectlens this two must match each other. When you have the fresnellens and the objectlens, adjust the focus of the objectlens so you get a sharp picture on the screen, then move the lightsource without a condensor so you fill the objectlens with light, this is the right distance the lightsource should be at. After you have done all this you can add a condensorlens, but you can´t calulate a condensorlens strength before this.
mathias - once you have adjusted the distances bewteen the light source, fresnel lens and projection/object lens correctly, won't the addition of a condensor lens change the how the light is transmitted from the light source onto the fresnel lens, or will it just concentrate the light from the light source onto the fresnel lens? 😕
What I understand you must move the lightsource closer to the fresnellens with a condensor, to get the same light angle as before, but I can have wrong.
Can someone confirm whether that is the case? - if you have a setup that works ... then add a condensor, the light source will need to be moved closer to the fresnel lens to capture all of the light from the condensor.
Sorry - this has been answered by ACE in another thread :
http://www.diyaudio.com/forums/showthread.php?s=&threadid=23596&highlight=condensor+distance
http://www.diyaudio.com/forums/showthread.php?s=&threadid=23596&highlight=condensor+distance
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