DJ_holmes,
Did you ever get your corner problem solved. Here is a rule of thumb that you need to understand. The lens must be able to focus the LCD from corner to corner without the fresnel. IF it can't do that then it doesn't have a wide enough FOV. So then you have to get another lens or use a smaller LCD. If it almost works then you can make the adjustment stated below.
The fresnel is only to help guide the light so you have brightness. As long as it is behind the LCD. In front as with a split system you introduce a very complex set of problems because the fresnel becomes part of the objective lens system and it is not designed or corrected to work together. Plus the fresnel is not suited for imaging only guiding light.
There is a way you may be able to get better edge focus with your first lens but you will have to project a bigger image and thus it will be less bright.
When you move the projector further away from the wall the lens will focus further away from the LCD so since the LCD stays the same size it uses less FOV from the lens.
Hezz
Did you ever get your corner problem solved. Here is a rule of thumb that you need to understand. The lens must be able to focus the LCD from corner to corner without the fresnel. IF it can't do that then it doesn't have a wide enough FOV. So then you have to get another lens or use a smaller LCD. If it almost works then you can make the adjustment stated below.
The fresnel is only to help guide the light so you have brightness. As long as it is behind the LCD. In front as with a split system you introduce a very complex set of problems because the fresnel becomes part of the objective lens system and it is not designed or corrected to work together. Plus the fresnel is not suited for imaging only guiding light.
There is a way you may be able to get better edge focus with your first lens but you will have to project a bigger image and thus it will be less bright.
When you move the projector further away from the wall the lens will focus further away from the LCD so since the LCD stays the same size it uses less FOV from the lens.
Hezz
thanx for the headz up bruv. but your forgetting that essentially a fresnel is like a large flat magnifying glass...if can affect corners if it was large enough..........look bruv forget all that nonsense..i got a 15" benq 395mm large fresnel and 150w hqi even a box ALL i need to do is cut the fresnel and fit and adjust it will take about 5 hours to finish....I PROMISE YOU I WILL HAVE CORNER FOCUS or i will break the bloody ting!!! on a mission like 007!!!
pics as soon as i finish...i put it off a bit cos i had to cut fresnel (i'm scared) but i bought a tool soo only a matter of time....2morrow??
😀 😀 😀 😀 😉 🙂 🙂 🙁 🙁 🙁 😱 😱
pics as soon as i finish...i put it off a bit cos i had to cut fresnel (i'm scared) but i bought a tool soo only a matter of time....2morrow??
😀 😀 😀 😀 😉 🙂 🙂 🙁 🙁 🙁 😱 😱
Hezz said:
this is not correct. farther the wall, closer the lcd from the triplet.
Let me tell you, you are confusing two terms; FOV is the circle on the object plane where the field angle intersets with. FOV is a superfice wile field angle (somewhere read FOV angle) is the angle from the triplet to the max object size. It is the field angle what is constant on a lens by construction. The FOV is apllication dependent, throw dependent. just let you know it, guy grotke explainetit to me, i also confused two terms before.
I asked to the owner of this varifocal if he could get the field angle value from the seller, i think it is interesting spec to be known. Maybe you don´t find it interesting but fo me is as interesting as the focal lengh.
Rox,
I think you are misunderstanding what I am saying. The lens field of view does not change. But when the objective is further away from the LCD is uses less of the usable FOV. Assuming that it's size does not change.
DJ,
You are correct and yet you are wrong. Only if the fresnel is between the image and the objective lens will it expand or compress the actual image. When it is behind you are only effecting the light intensity of the image, and which light ray angles have higher intensity. Now to some degree increased light will make things focus better if there is so little light that there is not enough photon density. This is becasue the lens scatters the light rays to some extent and the more dense the light rays the more they blend together.
Hezz
I think you are misunderstanding what I am saying. The lens field of view does not change. But when the objective is further away from the LCD is uses less of the usable FOV. Assuming that it's size does not change.
DJ,
You are correct and yet you are wrong. Only if the fresnel is between the image and the objective lens will it expand or compress the actual image. When it is behind you are only effecting the light intensity of the image, and which light ray angles have higher intensity. Now to some degree increased light will make things focus better if there is so little light that there is not enough photon density. This is becasue the lens scatters the light rays to some extent and the more dense the light rays the more they blend together.
Hezz
Hezz said:
sorry, i thought you were speaking about the increasing the throw (this would mean the triplet would go closer form the lcd)
about the FOV, yes you are right a lcd farther from the triplet would need smaller FOV than the same lcd if was closer from the triplet. But I repeat what said on previous post, do not mix the FOV and the FIELD ANGLE. FOV is dependent of the aplication but FIELD ANGLE is always the same.
FOV= circle on the object plane where the image would be focused. (farther object would have larger circle) this circle is measured by milimeters (is de diameter of the circle).
FIELD ANGLE= the angle on the triplet that would see the FOV. this is measured on degrees, even if in the reallity there is a solid angle (3D angle cone) it is measured like if it were plane in degrees.
the field angle is one of the specs given by the anufacturer as it is constant, just like the focal lengh. The FOV is not posible to define as spec because it depends on the throw... if we know the FIELD ANGLE we can work out what FOV has our design.
Do you see the difference now?
Rox,
I understand completely what you are saying and forgive me for not being more precise but these two concepts amount to the same thing. They are essentially different ways of describing the same thing.
Let me describe it another way. THe field angle does not change but the FOV area changes depending on the distance of the object to the lens.
Ok I still disagree with you on the throw issue since my imperical observations conflict with what you claim. The same lens can be used to generate a range of throw distances by moving the lens and object further from the wall. You are claiming that enlarging the image size requires moving the lens closer to the object (LCD). But this is not the case for the same lens. If you move the lens closer to the LCD the image will not be in focus. You therefore have to move both the object (LCD) and the lens further away from the wall. When you do this the lens focuses at a greater distance from the object (LCD).
For a given FL there is a relationship between the object to lens distance and the lens to image distance. When you increase the lens to wall distance you must also increase the lens to object distance to keep the image in focus.
IF you do not believe me ok. But you will see when you get your gear. The problem is that you are misapplying simple geometric and mathmatical relationships.
Hezz
I understand completely what you are saying and forgive me for not being more precise but these two concepts amount to the same thing. They are essentially different ways of describing the same thing.
Let me describe it another way. THe field angle does not change but the FOV area changes depending on the distance of the object to the lens.
Ok I still disagree with you on the throw issue since my imperical observations conflict with what you claim. The same lens can be used to generate a range of throw distances by moving the lens and object further from the wall. You are claiming that enlarging the image size requires moving the lens closer to the object (LCD). But this is not the case for the same lens. If you move the lens closer to the LCD the image will not be in focus. You therefore have to move both the object (LCD) and the lens further away from the wall. When you do this the lens focuses at a greater distance from the object (LCD).
For a given FL there is a relationship between the object to lens distance and the lens to image distance. When you increase the lens to wall distance you must also increase the lens to object distance to keep the image in focus.
IF you do not believe me ok. But you will see when you get your gear. The problem is that you are misapplying simple geometric and mathmatical relationships.
Hezz
Hezz said:
i have already checked it, but knew it before tested.
HEZZ sayd; "For a given FL there is a relationship between the object to lens distance and the lens to image distance".
Could you tell me this relation?
Yes,
In non mathmatical terms,
The system is in focus when all of the paraxial light rays and non paraxial light rays align at the object and image plane. When this occurs all of the refracted light rays are at a certain angle in relation to each other. The point where these refracted light ray angles focus is the only ray angle position where the system will focus for this lens. In order for the system to stay in focus these angles must be maintained exactly. Therefore the ratio of lens to object distance and lens to image is distance must always stay the same to maintain the correct refracted ray angle alignment. So if you move the lens back to create a larger image you must also move the object plane further from the lens to maintain this ratio. Otherwise the system will be out of focus.
There is a simple equation to calculate FL or magnification in a system. This equation which is something like FL is equal to lens to object distance times lens to image distance over lens to object distance plus lens to image distance.
This equation is good for calculating basic magnification. But it does not predict the way the lens behaves when it moves. It also does not take into consideration how thick or multiple lenses behave.
If you want to be able to design a projector completely on paper first you have to understand a lot more about optics and it is a very in depth topic that will require some study time. Also because a lot of aspects cannot be easily diagrammed a lot of the diagrams can be misleading.
Hezz
In non mathmatical terms,
The system is in focus when all of the paraxial light rays and non paraxial light rays align at the object and image plane. When this occurs all of the refracted light rays are at a certain angle in relation to each other. The point where these refracted light ray angles focus is the only ray angle position where the system will focus for this lens. In order for the system to stay in focus these angles must be maintained exactly. Therefore the ratio of lens to object distance and lens to image is distance must always stay the same to maintain the correct refracted ray angle alignment. So if you move the lens back to create a larger image you must also move the object plane further from the lens to maintain this ratio. Otherwise the system will be out of focus.
There is a simple equation to calculate FL or magnification in a system. This equation which is something like FL is equal to lens to object distance times lens to image distance over lens to object distance plus lens to image distance.
This equation is good for calculating basic magnification. But it does not predict the way the lens behaves when it moves. It also does not take into consideration how thick or multiple lenses behave.
If you want to be able to design a projector completely on paper first you have to understand a lot more about optics and it is a very in depth topic that will require some study time. Also because a lot of aspects cannot be easily diagrammed a lot of the diagrams can be misleading.
Hezz
Hezz said:
i only asked you the relation 😀.
well the relation is thisone; 1/F=1/D + 1/T
where: F=Focal, D=object-lens dist, T=throw
You knew this formula?
Rox,
In my studies in the past I have come across several equations but I don't remember equations so I would have to do a lot of searching to find one for you and I don't have the time to do that. If I knew off the top of my head I would tell you. I think that the problems come in when trying to equate a static system to a dynamic one.
I'm not really sure that my above description makes total sense. But I suggest that you get a inexpensive multiple element lens and experiment with it. THen perhaps with more information you can design your dream projector with the final parts that you want.
Hezz
In my studies in the past I have come across several equations but I don't remember equations so I would have to do a lot of searching to find one for you and I don't have the time to do that. If I knew off the top of my head I would tell you. I think that the problems come in when trying to equate a static system to a dynamic one.
I'm not really sure that my above description makes total sense. But I suggest that you get a inexpensive multiple element lens and experiment with it. THen perhaps with more information you can design your dream projector with the final parts that you want.
Hezz
well, this equation i gave you is the only one. The others come out of this (if you play a bit with maths).
This equation says where will be the image focused, depending on the object placement (triplet position, "dinamic" as you say) and focal of triplet.
Now i would like you to play with any values and then see what happens when you increase the throw. (you said the object triplet distance would increase as well, it is not what the equation says).
Still hold on your statement?
This equation says where will be the image focused, depending on the object placement (triplet position, "dinamic" as you say) and focal of triplet.
Now i would like you to play with any values and then see what happens when you increase the throw. (you said the object triplet distance would increase as well, it is not what the equation says).
Still hold on your statement?
Rox,
WHen you get further into optics you will find that they have what is called 1st order optics and 2nd order optics and so on up to about 4th or 5th order optics.
All of these orders of optics are mathmatical ways of describing light and optical behavior. Remember that light is considered to be both a particle and a wave.
The 1st order optical equations are the simplest and make gross assumptions about a system they assume that light rays are only particles and that simple and theoretical ideal lens geometries exist.
These equations are the ones you will see on website that are trying to explain first principles. In real life such 1st order situations rarely exist.
They are useful as a starting point for simple systems. The problem is that you are not going to find these more advanced methods anywhere on a website. They are in college level textbooks that cost a lot of money. And require higher levels of math.
Now you are asking me to give you math reasons for our argument over this one concept in question. Frankly I am at the limit of my knowledge in beng able to explain it and cannot from a math point of view. But I have to stick with my empirical experimentation knowing that these are the real way that things are behaving.
Now, I am sure that it is likely that there is nothing wrong with your math but what the equation you are using does not describe is when you take a lens system of a fixed FL and force it to work as if it were a lens with another FL. Which is what you are doing when you try to create a different image size with the same lens.
Hezz
WHen you get further into optics you will find that they have what is called 1st order optics and 2nd order optics and so on up to about 4th or 5th order optics.
All of these orders of optics are mathmatical ways of describing light and optical behavior. Remember that light is considered to be both a particle and a wave.
The 1st order optical equations are the simplest and make gross assumptions about a system they assume that light rays are only particles and that simple and theoretical ideal lens geometries exist.
These equations are the ones you will see on website that are trying to explain first principles. In real life such 1st order situations rarely exist.
They are useful as a starting point for simple systems. The problem is that you are not going to find these more advanced methods anywhere on a website. They are in college level textbooks that cost a lot of money. And require higher levels of math.
Now you are asking me to give you math reasons for our argument over this one concept in question. Frankly I am at the limit of my knowledge in beng able to explain it and cannot from a math point of view. But I have to stick with my empirical experimentation knowing that these are the real way that things are behaving.
Now, I am sure that it is likely that there is nothing wrong with your math but what the equation you are using does not describe is when you take a lens system of a fixed FL and force it to work as if it were a lens with another FL. Which is what you are doing when you try to create a different image size with the same lens.
Hezz
Hezz said:
The lens equation i told you is the ideal. I know the lens sistem we have is real and it will not be a s accurate as the ecuation, but roughly it will act as the equation. (mean if there is an increment on the trhow, there must be a decrement on the objet to lens distance)
I can focus and magnify to any image size that i like with my 32cm fixed focal. It only depends on the throw, there is no forcing any focal lenght. I can explain it to you in terms of math.
I don´t still understand why do you say your test show you the trhow and the object distance needs to increase both at once (this is not possible, not if you have a varifocal at least) maybe you did a two very close test so the increment /decremnt were imperceptible, you could try it once more but with a trhow increment of 2X and then see what happens with the object-lens dist? (guy grotke, ace,... will tell you the same thing, you are on error with your statement)
I have considered the possibility that my methods were not detailed enough and that I had mixed up the end for end orientation of the lens but when I tried the experiment the second time I got the same results. The measurements were far enough apart as not to confuse them. The first time was with about a 7 foot lens throw and the second a 11 foot throw. The differences in the lens to object distances were on the order of 2 - 3 inches so close measurements were not really an issue.
Hezz
Hezz
Hezz said:
the trhow change from 7 to 11 foot is more than enough to notice the movement on the triplet.
So you mean that 7 foot throw had X objet to lens distance and then 11 foot throw had X+2,5" new placemnt?
(both increased as you said previosly?)
this goes against lens teory. check it once agan or ask it to someone else please.
the easyest way to test this is with the projection lens in your hand (any lens works, singlet, doublet, triplet... ) take a white paper and focus the light of the window on the paper, then you can focus the outside of the window (trees, buildings, street...) the diference of focusing the window or the outside is like if you had increased the throw (actually the projection is reversed, the light is being projected on the paper, but the optical law is exactly the same for both cases)
wou will notice focusing farther objets (trees, buildings, clouds...) does the lens paper distance decrease. Have a try and tell us results. 😀
wou will notice focusing farther objets (trees, buildings, clouds...) does the lens paper distance decrease. Have a try and tell us results. 😀
ROX,
The first time that I did the test I was unsure of my results because I found out later that the lens focused from different distances depending on which end is towards the object. How do you account for that as that violates the theory as well as the total FL is the same regardless of which orientation that the lens is.
Because of this I did the test again being very sure that I kept the lens in the same orientation so as not to invalidate the test by having inconsistant setup.
THe second time I got about the same results. WIth the 11 foot throw distance the lens focused at about 3 inches further away from the objective plane than with the 7 foot throw distance.
I suppose that it is possible that I was mistaken and could make the test again but I am too lazy to do that right now. I am going to get my projector together and then if the lens does not satisfy me I will attempt to design a perfect for the situation lens and build it by hand.
Maybe in the future when I get more time I could design you a best possible lens configuration for your setup. THen you would have an ideal lens as a reference to help you select the best surplus or retail lens.
The thing is that the triplet that I designed was easy to do because it was a scaled and tweaked version of a high quality wide angle triplet.
WHat I would like to do eventually is design a high quality large format wide angle lens that can use plastic lenses. THese are easier and cheaper to manufacture by hand. But the lens system needs more elements than a glass one because there are far fewer choices of optical grade plastic and a narrower range of dispersion properties.
Hezz
The first time that I did the test I was unsure of my results because I found out later that the lens focused from different distances depending on which end is towards the object. How do you account for that as that violates the theory as well as the total FL is the same regardless of which orientation that the lens is.
Because of this I did the test again being very sure that I kept the lens in the same orientation so as not to invalidate the test by having inconsistant setup.
THe second time I got about the same results. WIth the 11 foot throw distance the lens focused at about 3 inches further away from the objective plane than with the 7 foot throw distance.
I suppose that it is possible that I was mistaken and could make the test again but I am too lazy to do that right now. I am going to get my projector together and then if the lens does not satisfy me I will attempt to design a perfect for the situation lens and build it by hand.
Maybe in the future when I get more time I could design you a best possible lens configuration for your setup. THen you would have an ideal lens as a reference to help you select the best surplus or retail lens.
The thing is that the triplet that I designed was easy to do because it was a scaled and tweaked version of a high quality wide angle triplet.
WHat I would like to do eventually is design a high quality large format wide angle lens that can use plastic lenses. THese are easier and cheaper to manufacture by hand. But the lens system needs more elements than a glass one because there are far fewer choices of optical grade plastic and a narrower range of dispersion properties.
Hezz
Hezz said:
It is not my case. All my lens follow the lens equation just fine (even when i project images with my fresnell lens). I´m lazy as well, but taking the lens on your hand and a paper isn´t too much work. (you can take a condensor lens singlet or any kind of lens, the projected image on the paper won´t be very good but should be enought to check the equation is ok).
about reversing the triplet and finding the distance to object is different, it does not violate the equation, i found this issue as well, but then found the cause as well. it is the optical center of the lens that is not at the fisical center, this way when you turn it around, the equivalent thin lens has been moved so it fill focus as if the throw had changed. Then if you want the same trhow, need to compensate that distance from the fisical center to the optical center so the optical center is where it was before turning it around. (on the 135 triplet, the optical center is 1,5cm closer to the rear lens from the fisical center so when you turn it around, you need to move 3cm =1,5*2 closer to the object).
Also would like to say that the throw and the object distance are meassured from the two planes to the OPTICAL CENTER, so if we don´t know where it is, our meassuremnts will be not accurated.
If you check on the forums, you will see people talking about increasing throw does reduce the other distance. No one said what you noticed. I doubt that you cold find a equation where sais what you are saing. (your lens is fixed focal, isn´t it?
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