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The simplest eyepiece , beyond a single lens, is the Ramsden, with two singlets, as shown in Fig. The color correction is limited to the choice of the two glasses.
Naturally the performance is poor, and the example is included only as an introduction to eyepieces. Realistically, this type of eyepiece would rarely be used at these apertures. Remember that in these drawings the eye position is to the left of the drawing, and the intermediate image is on the right. This can often cause confusion! Click to enlarge.
Note that the eye relief 12 mm is about half the focal length, which is reasonable but not as good as more complex eyepieces to be described later in these notes.
Transverse ray aberrations for this design are shown in Fig. With two single lenses, spherical aberration and axial color are not correctable. And with this configuration, lateral color evident in the separation of the tangential curves at the origin for 10 and 15 deg is not correctable. Also, as we have noted in the previous chapter, the Petzval sum is not correctable in any type of simple eyepiece with two positive lenses. Sign In View Cart 0 Help.
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The simplest eyepiece , beyond a single lens, is the Ramsden, with two singlets, as shown in Fig. The color correction is limited to the choice of the two glasses. Naturally the performance is poor, and the example is included only as an introduction to eyepieces. Realistically, this type of eyepiece would rarely be used at these apertures. Remember that in these drawings the eye position is to the left of the drawing, and the intermediate image is on the right. This can often cause confusion!
The Ramsden eyepiece
An eyepiece , or ocular lens , is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device. The objective lens or mirror collects light and brings it to focus creating an image. The eyepiece is placed near the focal point of the objective to magnify this image.
The eyepiece for many optical instruments is a simple magnifier. Because of aberrations , a single lens is not adequate for the eyepiece of a high quality optical instrument, and many lens combinations have been developed to minimize the aberrations. A sample is shown here. In the Ramsden eyepiece, the two lenses are made of the same kind of glass, e. The lenses are of equal focal length and their separation is equal to the focal length. The field lens coincides with the first principal plane , which is convenient for the placing of crosshairs or reticules, but inconvenient in that it highlights any dust on the lens. This eyepiece is effective in reducing chromatic aberration , doing a better job with longitudional achromatism than with lateral.