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?
Yes. Baader supplies it for photographic use on Schmidt-Cassegrains with DSLR and CCD cameras. It is recommended for sensors up to APS-C (its fully illuminated image circle is 18 mm; remaining vignetting is easily removed in processing, full-frame shows more) and works best at 121 mm from its rear lens to the sensor, so filter wheels and off-axis guiders must be fitted into that distance. It cannot be used for photography on EdgeHD telescopes.
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" means mounting the telecompressor lens directly in front of the binoviewer, which is the only way to reach focus with a binoviewer on an SCT. The ideal working distance is 121 mm between the rear lens and the focal plane; a longer distance gives a faster f-ratio (about f/3.5 at 193 mm) but a smaller field of view.
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. For binoviewing it sits directly in front of the binoviewer, behind the star diagonal or T-2 prism; for photography or a 1.25in diagonal it is inserted into the telescope's baffle tube.
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.
