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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.
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.
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