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KASAI & BinoTechno
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The innovative erecting diagonal prism jointly developed by Kasai and BinoTechno, yielding perfectly right-side-up erecting images without sharpness deterioration by reflecting the light path twice on the right and left flat roof surfaces of a large amich prism. Especially suitable for high magnification observations of the moon, planets and double stars. Thanks to the total reflection of the prism, the reflectivity is almost 100% - very suitable for faint deep-sky observations, too. The 27.5mm dia. large clear aperture ensures no field vignetting even with ultra-wide angle eyepieces. The 109mm light path length enables many telescopes to reach the focus to infinity. This one-and-only unique prism is widely recommended to many telescope users who feel uncomfortable with the mirror-reversed images with normal diagonal mirrors or prisms, or who are dissatisfied with the image degradation with conventional erecting prisms at high magnifications.
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šEZP Light Path š

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<Product Concept>
An ordinary diagonal mirror or prism yields mirror-reversed images - quite inconvenient for directional identification and/or sketching of the objects. While, an ordinary erecting prism yields right-side-up erecting images, but due to the ridgeline in the center of the prism, the image sharpness is more or less deterirated even with a very high precision one, which causes inconvenience in high magnification observations. A pentaprism can avoind this sharpness deterioration together with no mirror-reversed images, but it cannot be used for terrestrial use because of the upside-down inverted images, and it is also inconvenient for those observers who prefer right-side-up erecting images even for astronomical observations. The only way to obtain perfectly right-side-up erecting images without sharpness deterioration was to use a 2-mirror erect-image device (like EMS or EZM), but the light path length is usually too long to reach the focus with not a few telescopes, and expensive high-reflectivity dielectric coated or silver coated mirrors must be used to prevent light loss due to double-surface reflection. Besides, the exposed reflective surfaces require minimal maintenance.

We wondered if it's possible to produce a perfect 90-degree erecting viewing device that "does not deterorate sharpness even at high magnifications", "maintains almost 100% reflectivity", "can be focused with most telescopes", and "completely maintenance free"..... The only solution is to use an oversized large amici prism with a width twice the required light path diameter, with an eccentric aperture avoiding the central ridgeline of the prism, and reflecting twice only on the left and right flat surfaces of the prism's roof. In addition, the nature of the glass prism enables the light path length to be shorter than that of a normal two-mirror erect-iamge device, making it easier to reach the focus with more telescopes. Besides, since all the reflective surfaces are inside the prism, there is no need for cleaning - completely maintenance free.

Kasai collaborated with BinoTechno, well-known for their 2-mirror erect-image device "EZM" and various binocular telescopes, to realize and commercialize this ideal right-angle viewing device, and the resulted product is "Erecting Zenith Prism (EZP)".
<Oversized Amici Prism>
A high precision (with the angular error of less than 5") oversized 55mm width large amici prism is used. All the surfaces are boradband multi-coated. Thanks to the total reflection of the prism, it ensures almost 100% reflectivity. The flatness of the reflective surfaces is also extremely precise, so there is no deterioration in sharpness even under high magnification observations. The light path length is kept to 109mm, which is even shorter than that of a standard 2" diagonal mirror (approx. 120mm), so it can reach the focus with every telescope that can reach the focus with most 2" diagonal mirrors.
<Housing>
All the mechanical parts are made of black anodized hard aluminum alloy. The main housing is covered with durable hexagonal frames to withstand heavy loads like binoviewers. The 1.25" eyepiece holder is a compression ring type. And, the eyepiece fixing screw can be switched in three directions at 120-degree intervals. The 1.25" nosepiece is tapered to prevent slippage, and the inner surface is fully threaded with anti-reflection mat-black finish to prevent internal reflection. Of course M28.5 filter threads are equipped. The 27.5mm dia. large clear aperture yields no field vignetting even with ultra-wide long focus eyepieces.
<Addendum> As an additional function, the positions of the nosepiece and the eyepiece adapter can be switched left to right / right to left easily, making a reversed version. See below.
<Low-Power (Deep-Sky & Terrestrial) Observations>
EZP is an ideal 90-degree viewing device for low-power observations of faint deep-sky objects, as it does not vignette the field of view even with ultra-wide and long focus eyepieces, and provides nearly 100% reflectivity. Of course it can be used comfortably for terrestrial viewings, too, as it provides perfectly right-side-up erecting images.
<High Power (Lunar, Planetary and Double Stars) Observations>
High magnification observations are where the true potential of EZP can be best demonstrated. With no deterioration in sharpness due to the two reflections on the high-precision flat surfaces, it can maintain very crisp images of the moon, planets, and double stars thru the highest magnifications. In addition, since perfectly right-side-up erecting images can be obtained, it is widely recommended to many telescope users who feel uncomfortable with the mirror-reversed images with a diagonal mirror or prism, or who are dissatisfied with the image deterioration with a conventional erecting prism.
<Overall Suitability>
Among many diagonal viewing devices, EZP is quite unique and really one-of-a-kind. This innovative prism, which has solved almost all the problems of existing diagonal mirrors and prisms at once, will give many telescope users a fresh surprise. It is a revolutionary product to be recommended for all the telescope owners as a universal diagonal prism that can fully cover various observing situations, from deep-sky observations at low magnifications to lunar and planetary observations at high magnifications, and even terrestrial viewings with right-side-up erecting images.
Optical Light Path Length 109mm
Clear Aperture 27.5mm dia.
Nosepiece 1.25" (M28.5 Filter Threads equipped)
Eyepiece Adapter 1.25"
Dimension 145mm x 90mm x 75mm
Weight 660gr.
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The positions of the nosepiece and the eyepiece adapter are switched left to right / right to left. Please choose this if this version is more suitable for your observing condition.
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With the use of 2 EZP's (one is normal and the other is reversed) + 2 small refractors, you can complete a set of erect-image binocular telescopes instantly as shown in the right photo. A pair of L & R EZP's are offered at a special price for those who plan to produce such binocular telescopes.
Kasai Trading Co., Ltd.
1-3-16, Naka-Cho, Meguro-Ku, Tokyo 153-0065, JAPAN

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