I’d appreciate your input about field of view with the acf and if it can be used with my old binoviewer.
The focal length of the telescope will ve reduced approximately by factor 5.9.
Please note that the focal length of a Schmidt-Cassegrain changes, if you place accerories farther away, e.g. with a 2" star diagonal. That's why we recommend a smaller T-2-star-diagonal. We do not have data on how much the focal length of a Meade ACF changes with a 2" star diagonal exactly, but it shouldn't be too much.
Unfortunately, we have never measured the change in back-focus, as this is hard to do with an SC/EdgeHD with its moving main mirror.
The 7.5m T-2 extension #2 mentioned on the left side of the PDF is included in the scope of delivery of the UAG, so you can screw the UAG between any binoviewer with T-2-thread like the MaxBright II or the old MaxBright and any of our T-2 star diagonals.
If you have a standard 1.25" star diagonal without T-thread, this will not work to your satisfaction, as these star diagonals do have a longer optical length and no thread for attaching the binoviewer. We recommend a T-2 prism diagonal (they have the shortest optical length) plus the BTA-adapter for Schmidt-Cassegrains # 2408160, which can be screwed onto the back of your telescope, or a 2"/T-2 nose piece #2408150, if you have a 2" eyepiece holder on the back of your telescope.
Universal Alan Gee II - Telecompressor (UAG II)
The Universal Alan Gee II is the only telecompressor/reducer on the market which works fine with a binoviewer.
The standard Alan Gee Telecompressor Mark II was designed by Roland Christen (the producer of AstroPhysics apochromatic telescopes) as a reducer for Schmidt-Cassegrains which also delivers a flat field. The Universal Alan Gee II (UAG II) puts the optical elements of the Alan Gee in a regular 2" nose piece with an additional T-2-thread on the telescope side. The UAG II can be used for visual observations with Celestron EdgeHD telescopes. too.
The combination: Mark V Giant Bino / Baader 35mm ED-eyepieces / Universal Alan Gee II (UAG II) / Baader T2 Prism delivers a field of view of ca. 1,2° when used with a C8 – that's 72 minutes of arc, as much as a 2" 40mm eyepiece will show you! So, instead of waiting for an (unaffordable) 2" binoviewer, you can achieve the same effect on most SC-telescopes with the UAG II – be it monocular with a star diagonal or binocular with a binoviewer!
Please note that the reducing factor of the UAG II only depends on the distance between UAG II and eyepiece. It is designed for a working distance of 121mm then you get a reduction factor of 0.59. But if you focus to a focus plane farther away than the designed back focus of a Schmidt-Cassegrains or EdgeHD telescope, the focal length of the telescope itself becomes longer, and you get a different reducing factor than that which is calculated only from the distance between reducer ad eyepiece. The result depends on the individual adaptation and the telescope, we can't give a universal value for the reducing factor – but you will clearly notice the much larger field of view.
Use with a binoviewer
The UAG II can be attached directly to all Baader T-2 star diagonals with the included Baader T-2 / 7.5 mm Extension Tube (T-2 part #25C) (#1508155, € 16,58) . Although a binoviewer could mechanically also be attached to a 2" star diagonal, we recommend for a Schmidt-Cassegrain the short adaptation with a T-2-prism and the Baader T Adapter (BTA) for SC and MAK Telescopes (T-2 part #21) (#2408160, € 54,59) , so that the ideal focus point (and the focal length of the telescope in front of the UAG II) don't change too much from the original design. A binoviewer with T-2 thread like the MaxBright® II or the Mark V Großfeld (Giant)-Binocular (#2456410, € 1242,86) can be attached directly to the UAG II. The distance to the eyepieces is then about 120 mm.
Monocular use with a star diagonal
The UAG II can also be installed in front of a T-2 star diagonal. In addition, you need a T-2 eyepiece clamp and – depending on the desired distance/reduction factor – a T-2-extension. The UAG should be as close to the telescope as possible, so we recommend the optional Baader T Adapter (BTA) for SC and MAK Telescopes (T-2 part #21) (#2408160, € 54,59) to attach it to the telescope's SC-thread. If your telescope is equipped with a 2" ClickLock eyepiece clamp (#2956220 for C8/C925 or #2956233 for C11 and C14), you can also use this with the 2" nose piece of the UAG.
Baader 2" star diagonals with removable 2" nosepiece, you can also use the Baader Expansion Ring 2"a/T-2i with 1mm optical path length (T-2 part #28) (#2958242, € 22,42) to install the UAG in front of the star diagonal. It replaces the 2" nose piece. The distance between eyepiece and reducer is then equal to the optical length of the star diagonal. To place the UAG closer to the telescope, you can use the optional Baader T Adapter (BTA) for SC and MAK Telescopes (T-2 part #21) (#2408160, € 54,59) genutzt werden.
The UAG II may also be used with a camera (up to APS-C sensor size); the distance between UAG II and camera should be 121mm. The Alan Gee II was originally designed to be placed inside of the baffle of a Schmidt-Cassegrain, so for photography we still recommend the classic Alan Gee Telecompressor Mark II (T-2 part #20) (#2454400, € 238,82) in a configuration as described in its manual.
|Optical length (mm)||< 50|
|Usage||MaxBright II Binocular|
|Optical Design||Field Flattener, Telecompressor|