I just downloaded the free version, and I swear you are a rocket scientist now. Jeesh, where do I put what in what slot. I'm like a virgin on his first outing. 
Ok, what if I put these lenses together, where do I put the numbers, that will tell me the fl etc. Trying to make a triplet. Thanks Chad
http://www.surplusshed.com/pages/item/l3490.html
http://www.surplusshed.com/pages/item/l1836.html
Ok, what if I put these lenses together, where do I put the numbers, that will tell me the fl etc. Trying to make a triplet. Thanks Chad
http://www.surplusshed.com/pages/item/l3490.html
http://www.surplusshed.com/pages/item/l1836.html
Ok, found some lenses I want to try. Although not the same one's . Guy, not sure on the clearness of the lens, but here are the specs
580 positive, -635 for the middle, 580 positive again for rear, and each spaced at 20mm. This is saying it gives a 520.6mm EFL. Now, the question is, how do I know if they will match up together as far as how far apart to put them. I mean, if I put them like this, is it guarenteed to work? Or is it kinda luck draw?
580 positive, -635 for the middle, 580 positive again for rear, and each spaced at 20mm. This is saying it gives a 520.6mm EFL. Now, the question is, how do I know if they will match up together as far as how far apart to put them. I mean, if I put them like this, is it guarenteed to work? Or is it kinda luck draw?
OSLO
All I have done is to play around with OSLO a bit. I think you could read the manual, and maybe a good optics book to start. OSLO is just a tool to automate the calculations. You do have to tell it what to model!
You can start with the object. Fill in the object size with half the diagonal length of your LCD. So for a 15" LCD, that would be 7.5" * 25.4 mm / inch. That will get it sending rays from the corner of the LCD screen to the center of the lens. You also need to play with the different surface specifiers so the ray crosses the central axis at the middle lens in the triplet. You have to enter air spaces in the surface list, as well as glass spaces. The first entry will be your LCD-to-lens distance, then the thickness of the first lens, then the distance between lenses, etc.
Next, you fill in lens curve and material data. The size of the lens is the radius, so you put in 50 mm for a 100 mm diameter lens. The curves are pretty easy. They are just the radius in mm of the sphere that forms the lens curve. Positive numbers curve one way and negative curve the other. Start with thick lenses until you get the curves about right. Then you can make them thinner. That way you don't get impossible pairs of curves. I use a big number like 99999 for a flat surface.
The material is more problematic. Even if you have a lens, you may not know what kind of glass it is. If you are trying to design something new, then picking the right two or three different glasses are a big factor in the performance of the triplet. Telescope Optics by Rutten & van Venrooij discusses this at great length. You might want to start with the OSLO triplet example, and then adjust the curves, diameters, and spacing to see what they do.
If you had the paid version of OSLO, you could select the lens materials, diameters, curves, and spacing, and then tell the program to optimize it. It would adjust some or all of those parameters until it got a combination that met your performance requirements. Since you have the free version, you get to try small changes and then check what it did each time.
I find it helps to model a single lens by itself before I add other lenses. That way I can get a particular focal length.
I like to look at the spot size graph to gauge the performance. That summarizes all the different aberrations into a single size for each distance from the center. You want the spot size to stay below some limit over the whole image size. It may wriggle up and down, but the point where it crosses your design limit is the useful Field Of View for your lens.
All I have done is to play around with OSLO a bit. I think you could read the manual, and maybe a good optics book to start. OSLO is just a tool to automate the calculations. You do have to tell it what to model!
You can start with the object. Fill in the object size with half the diagonal length of your LCD. So for a 15" LCD, that would be 7.5" * 25.4 mm / inch. That will get it sending rays from the corner of the LCD screen to the center of the lens. You also need to play with the different surface specifiers so the ray crosses the central axis at the middle lens in the triplet. You have to enter air spaces in the surface list, as well as glass spaces. The first entry will be your LCD-to-lens distance, then the thickness of the first lens, then the distance between lenses, etc.
Next, you fill in lens curve and material data. The size of the lens is the radius, so you put in 50 mm for a 100 mm diameter lens. The curves are pretty easy. They are just the radius in mm of the sphere that forms the lens curve. Positive numbers curve one way and negative curve the other. Start with thick lenses until you get the curves about right. Then you can make them thinner. That way you don't get impossible pairs of curves. I use a big number like 99999 for a flat surface.
The material is more problematic. Even if you have a lens, you may not know what kind of glass it is. If you are trying to design something new, then picking the right two or three different glasses are a big factor in the performance of the triplet. Telescope Optics by Rutten & van Venrooij discusses this at great length. You might want to start with the OSLO triplet example, and then adjust the curves, diameters, and spacing to see what they do.
If you had the paid version of OSLO, you could select the lens materials, diameters, curves, and spacing, and then tell the program to optimize it. It would adjust some or all of those parameters until it got a combination that met your performance requirements. Since you have the free version, you get to try small changes and then check what it did each time.
I find it helps to model a single lens by itself before I add other lenses. That way I can get a particular focal length.
I like to look at the spot size graph to gauge the performance. That summarizes all the different aberrations into a single size for each distance from the center. You want the spot size to stay below some limit over the whole image size. It may wriggle up and down, but the point where it crosses your design limit is the useful Field Of View for your lens.
surplus lens DIY triplet
BTW: Triplet design starts with the performance requirements, and ends with the lens data. Not the other way around.
If you start with some random surplus lenses, the chance of ending up with a useful triplet is around 0%. I tried lots of surplus shed lens combinations (with the actual lenses before I got OSLO), and I never got anything worth using.
You would be much better off looking for a triplet that was optimized for a similar application, and is now surplus. The "similar application" depends on the size of your LCD. Slide projector lenses are good for 2-3" LCDs. Copy machine lenses work well for 5-7" LCDs. (Surplus shed often has these.) Overhead projector lenses and opaque projector lenses are good for 8-15" LCDs. You find these at office equipment recyclers, school district surplus sales, eBay, etc.
BTW: Triplet design starts with the performance requirements, and ends with the lens data. Not the other way around.
If you start with some random surplus lenses, the chance of ending up with a useful triplet is around 0%. I tried lots of surplus shed lens combinations (with the actual lenses before I got OSLO), and I never got anything worth using.
You would be much better off looking for a triplet that was optimized for a similar application, and is now surplus. The "similar application" depends on the size of your LCD. Slide projector lenses are good for 2-3" LCDs. Copy machine lenses work well for 5-7" LCDs. (Surplus shed often has these.) Overhead projector lenses and opaque projector lenses are good for 8-15" LCDs. You find these at office equipment recyclers, school district surplus sales, eBay, etc.
Thanks for helping me on that. I wasn't sure if I needed all the other info, like thickness, glass type etc. I also emailed a place that offers a triplet just like I want, but haven't heard anything yet. It will be much easier if I can find one the perfect size/ wouldn't we all. Anyways, thanks for your help. for now i will just have to use my 500mm doublet. I believe from my calculations, it is using 2 1000mm fl lenses at 2mm apart from eachother. What I like about them, is that they are pretty flat. That seems to help keep the image projected focused all the way across. Just wanted to see if a triplet will even be better. Thanks again.
triplet
I think a triplet could be designed to have less chromatic aberration over the useful field of view. If your screen image has blue and red color fringes around white letters on a black background, then you could get rid of those.
It could also be optimised for focussing flat objects on a flat screen.
But it really comes down to what you want to do with your projector: If you just want to watch video, then it doesn't make a lot of sense to pay a lot more for sharper focussed screendoor between the pixels. If you want to use it as a computer monitor, then you need to get a really good lens.
But you should keep in mind that building a custom triplet will cost you hundreds of hours of work and maybe thousands of dollars. I see very nice opaque projector triplets on eBay all the time, and they go for <$100 US plus shipping. The most common are 18" (457 mm), but I also see 22" (558 mm).
I think a triplet could be designed to have less chromatic aberration over the useful field of view. If your screen image has blue and red color fringes around white letters on a black background, then you could get rid of those.
It could also be optimised for focussing flat objects on a flat screen.
But it really comes down to what you want to do with your projector: If you just want to watch video, then it doesn't make a lot of sense to pay a lot more for sharper focussed screendoor between the pixels. If you want to use it as a computer monitor, then you need to get a really good lens.
But you should keep in mind that building a custom triplet will cost you hundreds of hours of work and maybe thousands of dollars. I see very nice opaque projector triplets on eBay all the time, and they go for <$100 US plus shipping. The most common are 18" (457 mm), but I also see 22" (558 mm).
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