![]() The less expensive 1.25” resin-bodied types are perfectly good for this type of astronomy. I have used both 1.25” and 2” Amici prisms for several years, primarily for rich field with short tube refractors and lunar observing with catadioptric and refractor telescopes. There is no visible diffraction spike while lunar observing and most rich field or deep sky objects lack sufficient brightness.Ībove: 1.25" Baader Zeiss specification with T2 'CLICKLOCK' and helical eyepiece holders. Although this can be perfectly adequate for rich field and lunar viewing. The 2” Long Perng Amici variants perform no better than their 1.25” equivalents. The Baader is slightly heavier as well as being more expensive. Oddly, the APM nosepiece has no filter thread. In use its overall optical performance compares favourably with the 2” Baader BBHS which has a 44mm clear aperture. The APM features a 46mm clear aperture as well as the ‘Q-Lock’ quick clamp eyepiece holder. The Long Perng and Baader Zeiss specification eyepiece holders both feature compression rings, unlike the APM which deploys internal ferrules to lock the eyepiece in place.ĪPM eyepiece holder showing internal ferrules. The APM and Baader both possess a form of twistlock. The Long Perng has a brazed eyepiece holder. A diagonal manufactured by Long Perng, often marketed under other brand names, an APM and a Baader ‘Zeiss specification’. Although I should imagine that it would take a great deal of force to achieve this.Īs far as I know there are only three variations of 90° two inch Amici diagonals on the market. A feasible problem with the resin-bodied housings is that heavy eyepieces may cause either the holder or nose to pull out of the resin body itself. In my experience only the Baader Zeiss specification Amici prisms have a larger aperture. ![]() Only the WO has a compression ring.Īnother feature of these diagonals, regardless of their specific manufacturing origin, is that they only have around 22mm of clear aperture. They all feature resin bodies except for the WO. Left to right: GSO, Orion, Antares and WO erecting diagonals. They are actually compatible with each other. Interestingly the nosepiece and eyepiece holder threads of virtually all of the Asian manufactured Amici diagonals are the same size. However, some of the metal diagonals feature brazed eyepiece holders. The nosepieces and eyepiece holders of both sorts are usually metal and threaded into their respective housings. ![]() They tend to fall into two categories: resin-bodied and metal-bodied. Most of the one and a quarter inch 90° Amici diagonals on the market are probably intended for occasional daylight viewing with astronomical telescopes. I am not sure why the design was changed but it may have been to rectify a problem with the prism occasionally becoming unseated in its housing. Old and new style William Optics Amici diagonals featuring a helical focusing eyepiece holder. Although these effects can be ameliorated somewhat with modern phase coatings. Another purported effect of using an Amici, particularly at high magnifications, is phase interference and light scattering. Otherwise a noticeable diffraction spike may be revealed when used to view bright or highly contrasted nocturnal objects. The roof section where the two faces meet needs to be manufactured to very high tolerances. Roof prisms are fine for diurnal viewing but have an inherent flaw for general use in astronomy. ![]() The Amici prism not only deviates the light path and inverts the image, it concomitantly reverts the perceived image by flipping the reflection back to a natural view. However, the now upright image is mirror-reversed. The prism effectively uprights this image. The view through a telescope directly (without a prism) actually produces an upside-down image. These diagonals are most likely made by Kunming United Optics. A conventional right-angled prism, as utilised in a star diagonal, will deviate the light path by 90° and simultaneously invert the image.Ībove: William Optics Amici diagonal body displaying the roof prism in its housing. Reflection from these faces produces an image that is laterally flipped. Roof prisms contain a section where two of the roof faces meet at a 90° angle. The right-angled Amici roof prism, also referred to as a direct vision or erecting prism, was invented by the Italian astronomer Giovanni Amici (1786-1863). ![]()
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