Dramatically widens the field of view of Schmidt-Cassegrain telescopes Engineered to produce a sharp, flat field for visual observation Creates a significantly faster focal ratio for brighter images Specifically designed for close-coupling with select binoviewers Requires precise spacing for optimal optical correction Description FAQ Specifications In the Box Downloads Warranty Baader Alan Gee Telecompressor Mark II The Baader Alan Gee Telecompressor Mark II is a specialized optical corrector designed to solve the primary limitation of Schmidt-Cassegrain telescopes: their narrow, long-focus field of view. This telecompressor significantly reduces the effective focal length of your SCT, delivering a wider, flatter, and brighter image. It is engineered specifically for visual observers using binoviewers, transforming the observing experience on large deep-sky objects. Widen Your SCT's Field for Rich-Field Views Standard SCTs excel at high-power planetary views but struggle to frame large objects like the Andromeda Galaxy (M31) or the Pleiades (M45). The Alan Gee Telecompressor Mark II corrects this by shortening the telescope's light cone, expanding your true field of view to encompass these expansive targets. The result is a sharp, flat field that turns your SCT into a capable rich-field instrument. Optimized for Baader, Zeiss, and Celestron Binoviewers Unlike generic focal reducers, the Alan Gee Mark II is a purpose-built solution for binoviewing. Its design requires critical "close coupling" — a very specific and short distance between the compressor and the binoviewer prisms. This precise spacing is essential to achieve a fully illuminated and corrected field, limiting its use to specific Baader, Zeiss, and Celestron binoviewer models that can physically achieve this connection. Alan Gee Mark II vs. Standard f/6.3 Reducers While a standard f/6.3 reducer/corrector offers a moderate increase in field of view, the Alan Gee Telecompressor is a more aggressive and specialized design. It provides a greater degree of focal reduction, but this comes with a critical trade-off. Standard f/6.3 Reducer: Offers more forgiving back-focus, making it compatible with a wide range of cameras and accessories. It's a general-purpose solution for both imaging and visual use. Baader Alan Gee Mark II: Provides a wider, flatter field specifically for visual use with binoviewers. Its strict spacing requirements make it unsuitable for general imaging, but for its intended purpose, it delivers superior edge-of-field correction and a more immersive wide-field experience. Why won't the Baader Alan Gee Mark II work with my Denkmeier or Tele Vue binoviewer? The Alan Gee Mark II's optical design requires extremely close spacing to the binoviewer's prisms to function correctly. Most binoviewers have a long optical path (e.g., through a power-switch diagonal) that makes this physically impossible. It is specifically designed for direct, close-coupled attachment to certain Baader, Zeiss, and Celestron models. Can I use the Alan Gee Mark II for astrophotography? This telecompressor is not recommended for general astrophotography. It is optimized for visual use and creating a flat field for the human eye within a binoviewer. Achieving the correct spacing with a camera sensor, filter wheel, and off-axis guider is typically not feasible and will result in poor optical correction. How does the Alan Gee Mark II affect the image brightness in my Celestron 11" SCT? By reducing the telescope's effective focal ratio, the telecompressor concentrates the same amount of light into a smaller area. This creates a brighter image surface, which is especially beneficial for observing faint, extended objects like the Veil Nebula (NGC 6960). The background sky will appear brighter, but the nebula's contrast against it will increase. What is the "close coupling" mentioned for the Alan Gee Mark II? "Close coupling" refers to the minimal physical distance required between the last lens of the telecompressor and the focal plane (or in this case, the prisms of the binoviewer). The optical corrections of the Alan Gee design are only valid at this specific, short distance. Increasing this distance will introduce significant aberrations like coma and field curvature. Do I need to modify my SCT to use the Baader Alan Gee Mark II? No permanent modification is needed, but you will need the correct adapters to thread the telecompressor directly to your binoviewer and then attach the entire assembly to your telescope's visual back. It replaces the standard diagonal in your optical train. Will this telecompressor help me fit the entire Orion Nebula (M42) in the view of my 8" SCT with a binoviewer? Yes, this is precisely the kind of application the Alan Gee Mark II is designed for. A standard 8" SCT with a binoviewer often cannot frame the full extent of M42's nebulosity. This telecompressor widens the field sufficiently to capture the entire object, from the Trapezium core to the fainter outer loops, in a single immersive view. Net weight (kg) 0.09 AR-Coating Multi-Coated (MC) Optical Design Field Flattener, Telecompressor Compatible telescopes Schmidt-Cassegrain Optical length (mm) < 50 Baader Planetarium Alan Gee II Telecompressor Manual Baader Planetarium Warranty
