If you're looking for something that's not just a toy but a real optical tool, this is definitely the one for you. Overall, I think this is a really cool and high-quality spyglass that is well worth the price. But if you can brace it on a branch or trekking pole, it's not a problem. However, I do have to admit that using a spyglass does require some patience and a steady hand since it is longer and therefore exerts more leverage over you. It does take a little practice to get the focus right, but once you get the hang of it, the glass is crystal clear and the magnification is amazing, better than what you can get from most binoculars at this price point. The matte metal finish looks great and the fact that it comes with a leather carrying case makes it easy to take with me on any outdoor adventure. The telescope itself is made of high-quality materials and has a nice weight to it, giving it a really solid feel. If you put the object at the focal point then the rays refracted by the lens end up parallel and thus never converge and no image is formed.I just got my hands on this awesome spyglass and it's everything I was hoping for. The reason the light rays all converge to a point and you do get an image is a result of the special geometry of the lens. Another way of looking at it is that at each point on the screen you are getting rays from a little area on the object rather than a single point. What is happening is that rays from each point in the object arrive at the screen spread out. If you put a screen there you get a blurry, out of focus, image. Near, but not at, the image these rays will all pass through a small area but not exactly the same point. Your diagram shows only the three easiest rays to trace but we could draw any number of rays all originating from the top of the object and passing through the image. There is only one place where this happens. This point is the image of the top of the object. To have something that looks like the top of the object you would have to have all these rays of light coming from another single point. If the intensity distributions of the patches are known, it is possible to use computer image processing techniques to retrieve the sharp image from the blurry picture.Īn image looks like an object because rays of light come from the some point in space (where the image is) in the same way that they come from the object.Ĭonsider a single point on the object, say the top of the object as shown in the diagram, rays will spread out all originating from that point. In the displaced receiving plane we have therefore lost the ability to detect small detail, namely that there are really two close points instead of one, and we would feel that the image in the displaced receiving plane is blurry. We may therefore think that there is only one object point instead of two close points. If the two points are very close to each other, the patches will overlap almost completely, and may seem to be one patch instead of two. The overlap of the patches is given by the distance between the two points in the object. At the places where these patches overlap, the resulting illumination is the sum of the illumination due to each patch. If we consider two points close to each other, we now see two circular patches in the displaced receiving plane, each patch contributing its own illumination. If a receiving plane is displaced a little from the sharp image point, all the infinitely many paraxial rays go on, spreading out from the image point, filling a cone of light, making a circular or elliptical patch of illumination in the displaced receiving plane.Īn extended object consists of infintely many object points. In real life we may see images at other places, but this can only be studied using the model of wave-optics. To make the image itself, we need to have a crossing of all the infinitely many paraxial rays from the object point. Two paraxial rays are enough to find the position of the image point, but they are not enough to make an image. Since all paraxial rays from the object point cross at this point, we can find the position of the image point by choosing only two arbitrary rays out of all the infinitely many rays and compute where these two rays cross. We can find the position of the image point by computing where the rays cross. This is the definition of the image point in the world of paraxial optics. In the paraxial model of geometrical optics a lens can make all the infinitely many rays from an object point hitting the lens converge to a single infinitely small geometrical point.
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