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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.
Loupe 10x Oval Hasting Triplet 18mm Black Quality Metallic, Focal 1" Clarity
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.
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.
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.
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