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Lenses with antireflection coating are the best, but more expensive. Tell him or her it is for a projector lens, so you need uncut unmounted lenses. The pair of uncoated lenses should not cost anymore than their discount eyeglasses price.
Is there any difference between "zoom" lens and standered? Or is it just getting the correct focal lengths for each lens? Keep checking back i will post my results on the design that you specified. Im in the middle of midterms so it may be a week or more tell i post again. Creating two reference planes for the front and back of the lens will help with aligning them to create the triplet.
Is it possible to build a triplet apochromatic refractor?
Spherical aberration is the largest cause of distortion on this lens but it is not the only cause. So unless you already know the focal length of your lens, you should measure it. You’ll need a piece of paper, a ruler, and a distant light source such as a lamp across the room .
And once the DIY project is completed, you’ll have your very own telescope with which to observe the stars and planets. Just by inspection of the layout, the caustic for both the on-axis and off-axis seem to be free of coma and spherical which plauged the us earlier. After performing the optimization the off-axis spot size has been reduced by a factor of 3.3.
Thread: how to build Cooke triplet ??
The good thing about building a small refractor telescope is that they’re light and portable, making them idea for taking to dark-sky sites. We create a merit function using the Zemax Optimization Wizard with attempts to minimize the root-mean-squared spot size radius calculated from the centroid, with 3 rings and 6 arms. We also insert an optimization operand, EFFL, to control the effective focal length of 50 mm. The 2D Layout shown below shows significant coma aberration in the caustic of the off-axis fields.
What I am saying is that using trial and error by mixing four lenses together is realistically going to be very difficult because you don't have enough lens values or time to look at every combination. Granted you could build the lens with stock lenses but it would perform lower than an optimized one of simpler design. What makes it high end is that it is optimized to the point where it can no longer be improved without making the system more complex by adding more elements or by adding aspheric surfaces. This lens if built to spec would outperform any four element system that you could put together without going through the same computer optimization. In years past it took engineers months doing hundreds of calculations to approach a design like this but a computer can do millions of calculations in only a second or two.
Ade Advanced Optics 10x21TB-A Triplet Professional Loupes
The heart of any refractor is its convex glass objective lens, which is mounted close to the front of the hollow telescope tube. A triple convertible lens is a lens that provides three focal lengths in one. The front element has one focal length, the rear element a different focal length, and by screwing them together the whole intact lens has a shorter focal length. For example, some Schneider Symmars from the early 1950s and before were designed like this. Triple convertible lenses can have other designs as well.
The other parts of the scope are made from plastic pipe that can be bought from a builder’s merchant for around £20, or donated by a friendly plumber. This is the kind of lens we will be building for our refractor. The aperture of the objective is larger than that of your naked eye, which means it can capture more light. The eyepiece usually has a much shorter focal length, which means that the final image is magnified. If you don’t have one, a 1.25-inch Plössl eyepiece will cost you around £25.
First Results: Optical Aberrations
While spherical aberration dominates the on-axis field. Mark, you have exhumed an ancient thread, so I don't know if you'll get many answers. I have never tried to use an ordinary triplet lens as a macro lens, but here is some speculation. The Cooke Triplet was the basis of all of the high speed lenses used in 35mm photography.
Fully coated anti-reflective optics so the light doesn't bounce off the lens and instead gets directed to your eye. Then aim the lens at a distant object – the view through a window works well – and move the lens back and forth until a focused, upside down image of the outside world appears. There are a number of surplus companies offering mounted telescope objectives – see Surplus Shed, for example. These lenses, which can be cemented together or separated by a small gap, are called ‘achromatic’ objectives. It is possible to correct all seven first- and third-order aberrations exactly to zero in a Cooke Triplet, however in practice this is not done. Third-order aberrations are non-zero to balance the higher-order aberrations.
Loupe by Bausch & Lomb, 14x Hastings Triplet Magnifier
The equation is placed into a function called ‘GetBackRadius’ which calculates the value when given a set of parameters, such as the thickness of the lens, refractive index of the material, etc. We can call the function repeatedly for different parameters. The patent completely describes the three lenses but we are going to make it a bit more interesting by calculating the radius of the back of the lens from the focal length. To do that we need to use the lensmaker’s equation. The loupe frame and lens barrel are all flat matte black to prevent interference from reflected light. Measuring the distance between the glass of the lens and the card gives you an approximate value for its focal length, which will help you design the rest of the telescope.
Although functional, the preceding lens still doesn’t have a mechanism for adjustable focus. Let’s look at a few approaches to solve that problem. The first approach is to “recycle” the helical focuser from an old lens. Mounts and filter threads can be attached with Super Glue if necessary. This lens also includes an old iris diaphragm I found for $3 at a local surplus shop. Attaching rings from junk filters to both the focuser and the diaphragm will allow you to use them in an interchangeable system.
Comfort– Comfort is the other primary factor we took into consideration when evaluating triplet lenses. After all, the more comfortable a triplet lenses is, the less likely you will dislike it. To overcome this, modern telescopes have ‘doublet’ lenses that use two different glass elements to bring most of the colours to focus at the same point.
Please look at the anamorphic thread to see how some of those lenses were actually made in the past. Here is a picture of a computer optimized wide angle cooke triplet which should work with LCD of 17 inch wide screen format. It has 450 mm FL and 40 degrees total field of vision. I will post design information and the lens can be scaled down for use with 15 inch LCD and lower FL. Find an optician who will sell you two 75 mm diameter +0.75 Diopter lenses.
Here is a zip file which is a microsoft word document that has the technical drawings and spacing information for this lens design. If anyone out there needs this file in another word processor format just ask and I can probably put it in any major format as long as the wordprocessor can insert EMF format. If I've done this correctly...it is a 15" LCD to be projected....approx 10 foot projected image...and 16 foot distance to the screen...which suggests a 21.3" focal length. Of course, you can also find more creative ways to mount your optics, such as using a 2 inch steel electrical conduit with a screw-in coupler to make a functioning focuser.
Best triplet lenses Reviews
I'm using a 15" LCD and have a 220mm fl and a 317mm fl fresnel lenses. The screen I'm projecting to is huge...approx 122". The focusing duplet I have is way off base...image is 2-3 times bigger than the screen when projected from 16 feet. If I were going to build a duplet from eyeglass lenses, can you offer this noob a bit of help on the diopter needed and spacing. AS can be seen in this spot diagram for the glass 40 degree triplet it can focus down to about 44 microns of spot size on the paraxial axis.
(Lenses designed with this have a 30 degree field of view.) I usually just use the chart at the bottom of the page. I know that a 1000 mm + 1000 mm duplet works very well with a 15" LCD. The field angle is about 32 degrees. With a shorter focal length and a 15" LCD, the field angle increases so it may not work as well. If you use a smaller LCD, then the field angle may decrease. You could try making one with off-the-shelf CR-39 plastic lenses to see if it works for your projector.
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I have compared it to a four element optimized glass tessar lens and the tessar is slightly better giving a 32 micron spot for the paraxial axis. For most application the slight improvement of the tessar over the cooke triplet does not justify the cost and added complexity. For us it shouldn't matter too much as the cooke has twice the on-axis resolution that we need. When a lens is used to focus parallel rays of light, the focal length is the distance from the lens to the point of focus. This means that for a single element camera lens, the focal length determines the distance the lens needs to be from the film or sensor.
When a lens designer starts a design, he has a set of goals. Telescope objective designers don't care how their lens performs with light entering at a 20 degree angle, because it will be mounted in a long tube with a tiny eyepiece at the other end. Rays coming in at more than 1 degree will never make it to the eyepiece. A particular telescope objective might work okay with a 20 degree off-axis ray, but it might not. The mechanics involved in making lenses is often more challenging than the optics. One possibility is to go for a reusable, interchangeable-parts approach.
HTS 203A0 10x 21mm Chrome Triplet Jeweler's Loupe with Leather Case
Running it will generate three part files, one for each lens. Based on our research, we have found these excellent products to be well worth the money and should be able to meet your needs. It's important to do your research before buying any new product.
Ive looked into it hezz, $2k for the tooling on each lens for custom lenses, that price quote was from edmunds, and i dont see it much cheaper then that anywhere else. To anyone who has downloaded the drawing files there is something you need to be aware of. It has to do with the sign conventions for numbers that the optical design software uses.
A good brand will always produce quality products, so a product with an established name should be good enough for your needs. Please enable JavaScript to view the comments powered by Disqus. Mark Parrish is a consummate designer and a prolific producer of DIY astronomy products. You may eventually want to get a small altaz or equatorial telescope mount for your telescope. The easiest method is to make a simple wooden stand for the lens and another with a sheet of white card fixed vertically to it. The first stage of the build requires you to measure the focal length of your lens.
Comfort– Comfort is the other primary factor we took into consideration when evaluating triplet lenses. After all, the more comfortable a triplet lenses is, the less likely you will dislike it. To overcome this, modern telescopes have ‘doublet’ lenses that use two different glass elements to bring most of the colours to focus at the same point.
This cancellation is not perfect either, so, Cooke Triplets are usually restricted to applications requiring only moderate speed and field coverage . My last camera was build with 2 box of cardboard and only one meniscus lens and seem like work so fine but this project i can't move the body for focus. For remedy this problem i'd like to project a lens like Cooke Triplet or other simple schema to focus more easy and adapt this lens to different kind of body that i'll build.
We are not yet diffraction limited and there are certainly more steps one can take but we stop here. Any significant improvement would most likely involve lens splitting, glass choice, and/or aspheres. As one can see in the design, using only spherical elements with relative common glass choice, it performs well on- and off-axis.
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This shows that astigmatism is actually the most dominant aberration with 87.3 waves of wavefront error shown by the \(W_\) term. Coma is the second most dominant with -38.9 waves of error as shown by the \(W_\) term. Remember this is just a listing of the third-order aberrations. While specific aberrations are difficult to quantify from the spot diagram, Zemax calculates specific Siedel coefficients and converts them in terms of wavefront error with units of waves. Also, I can't avoid the small apertures and diffraction.
Because the curvature is so small it may appear as a straight or negative surface on a drawing. There won't really be much work to do, unless he is grinding extra-large glass lenses for you. Stock lens blanks should just be sitting on somebody's shelf already made up and polished. If you are lucky enough to have access to bellows, you have an ideal focuser for homemade lenses. The last step is to generate the three lenses needed for the triplet using the values from the patent along with the focal length. Swing out loupe design protects the loupes lens when it is carried and acts as a handle when you use the loupe.
Here is a zip file of a solidworks e-drawing of the lens solid model. The glass ones are expensive - $16.56US each, but the acrylic ones starting on page four of the positive meniscus lens section are made of acrylic and cost only $8.79US each. There, you’ll be able to see many more examples of homemade lenses and the images they produce. Once again, spherical aberration resulted in soft, “glowing” images.
Could also be a bit of effort in getting the glass types required, although you have more flexibility then you would think as you do not specifically need FPL-51 or FPL-53. I'd look into using an old camera lens (eg. nikon f mount) in reverse. Posting something on this thread to get it out of the arcives for a time as someone has found possible builder of the lens. Rather than having custom lenses made you could even use piece together a lens system with used eyeglasses for nothing. There is also the possibility of having the lenses mounted in a water tight lens housing and using index matching liquids between the lenses. Done properly this can work as good or better than AR coatings on the lens.
This lens uses a 191 mm achromat ($9 from SurplusShed). The image on the left was shot with the imperfect optics of a homemade lens. Exploring the soft, dreamy world of DIY camera lenses in surprisingly easy.
The way I figure it the average dot size for a high resolution CRT monitor is around .24 mm. This dot consists of three color pixels so lets say that for a lens system to accurately focus on these small objects it must be able to focus each subpixel. So we need a lens that can focus a spot size of .08 mm to be able to accurately focus the image.
Align the front plane of lens3 14.14mm from the back plane of lens2. Also this lens requires certain glass types to work properly and they would not be available in eyeglass lens blanks. Typically off the shelf lenes are only available in sizes up to 80 mm in diameter and that is smaller than the smallest lens in this system. Also, getting the exact prescriptions would not likely be possible with off the shelf lenses.
I'm not going to anything with them and they would only get lost or broken in due course.Peter Drew May 19, 2017 I nearly did as well, it was a steal at the price. Create a new assembly and add the three lenses in the order lens1, lens2 and lens3. Align the front plane of lens2 7.89mm from the back plane of lens1.
Designing a Cooke Triplet
Is the common generic design of triplet lens, like Rodenstock's Geronar, among others. I'm personally tempted to try a long focus Crown and flint achromat as my next project, I've seen a book on the subject and figure if I read it enough times I might just stand a chance! First off, I am in the process of making my own projector and trying to figure out what projection lens to use has brought me to this thread. So what this comes down to is that we need a lens system that can accurately focus an image as small as .08 mm or 80 microns.
The good thing about building a small refractor telescope is that they’re light and portable, making them idea for taking to dark-sky sites. We create a merit function using the Zemax Optimization Wizard with attempts to minimize the root-mean-squared spot size radius calculated from the centroid, with 3 rings and 6 arms. We also insert an optimization operand, EFFL, to control the effective focal length of 50 mm. The 2D Layout shown below shows significant coma aberration in the caustic of the off-axis fields.
Is it possible to build a triplet apochromatic refractor?
When a lens designer starts a design, he has a set of goals. Telescope objective designers don't care how their lens performs with light entering at a 20 degree angle, because it will be mounted in a long tube with a tiny eyepiece at the other end. Rays coming in at more than 1 degree will never make it to the eyepiece. A particular telescope objective might work okay with a 20 degree off-axis ray, but it might not. The mechanics involved in making lenses is often more challenging than the optics. One possibility is to go for a reusable, interchangeable-parts approach.
I think you need to stick to the low end of that range, since you need a field fresnel that is a bit longer than the LCD to lens distance. Lumenlab has 790 mm fl fresnels that would work with a lens near the low end, in a split fresnel design. Due to the constraints of the room I'm building for, my projector needs to be around 16 feet away from the screen.
Are you looking for the best triplet lenses but don't know where to start? We have done a lot of research and analysis to present the best triplet lenses available. There are various triplet lenses options on the market, and you can get surprising advantages from these products.
The equation is placed into a function called ‘GetBackRadius’ which calculates the value when given a set of parameters, such as the thickness of the lens, refractive index of the material, etc. We can call the function repeatedly for different parameters. The patent completely describes the three lenses but we are going to make it a bit more interesting by calculating the radius of the back of the lens from the focal length. To do that we need to use the lensmaker’s equation. The loupe frame and lens barrel are all flat matte black to prevent interference from reflected light. Measuring the distance between the glass of the lens and the card gives you an approximate value for its focal length, which will help you design the rest of the telescope.
Adjustable Focus
I have compared it to a four element optimized glass tessar lens and the tessar is slightly better giving a 32 micron spot for the paraxial axis. For most application the slight improvement of the tessar over the cooke triplet does not justify the cost and added complexity. For us it shouldn't matter too much as the cooke has twice the on-axis resolution that we need. When a lens is used to focus parallel rays of light, the focal length is the distance from the lens to the point of focus. This means that for a single element camera lens, the focal length determines the distance the lens needs to be from the film or sensor.
A telescope’s focuser allows small adjustments to be made to the distance between the eyepiece and objective lens to accommodate different sizes of eyepiece and the standard of your eyesight. Next to the thickness for surface 5 there is a “M”. I know there are other companies who would do it for less but it still would not be cheap. I think my eventual design goal will be to make this lens into a tessar with some plastic lenses and then make the lenses by hand. The highest precision lenses have historically been made by hand until just in the last five years where advance CNC machines have taken over a lot of the production. However, most of the machines are designed to do smaller lenses of say less than 100 mm.
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You might be able to make it work by adjusting the lamp-to-condensor-fresnel distance to make the rays going to the field fresnel into a slightly diverging cone. This increases the distance from the field fresnel to the focussed image of the lamp arc. Depending on how we address the mechanics of the lens, focal lengths in the range of 60 – 200 mm are good candidates for DIY camera lenses. The general approach we will take is to draw a 2D profile of half of the lens on the XY plane and then create a revolve boss around the X axis. The X axis is the optical axis (i.e. the center of rotation for the lens).
The mold pucks will then be hand ground using conventional hand lens grinding techniques to get the mold cavities to a high standard. First the lenses will be compression molded in a small metal press with machined inserts. If you have a way to communicate with me your lens configuration I will model it and we will see how good it is.
Starting Simple
This is the focal length of the lens, or close to it. Ideally, the light source should be an infinite distance away, but I find that a light across the room gives me a pretty good approximation. The #1 model won this place with its consistent performance, ease of use, and quality build. At this stage it’s a good idea to make a temporary stand for your eyepiece and replace the card with it to confirm that the optical arrangement works effectively. You may even have a pair of broken binoculars with one salvageable objective lens. Thankfully, lenses are relatively easy to come by and can be surprisingly cheap at around £20 for a 60mm lens.
There are so many variables that triplet design was really an art form until computers became available. Early designers had to spend weeks doing the math to model how the lens would perform, changing each parameter a tiny bit each time through the calculations to see if it helped or hurt. Another approach is to use two tubes with slightly different diameters to build a sliding focuser. Cardboard mailing tubes or PVC pipes are possible sources for the sliding tubes. Sticky-back felt, from your local arts and crafts store, can be used to create a nice friction fit between the two tubes.
