You will need to add the proper length back focus spacer extension when purchasing the QUADTCC in order to achieve the required 80.8mm spacing. Please reference the chart below.
| Telescope | Part # | Length of Extension | Spacing w/ 3.27" Extension | Spacing w/o Extension |
| AP 130 GTX | EXT327-22.1 | 22.1 mm | 80.8 mm | 102.9 mm |
| TEC 140 | EXT327-18.3 | 18.3 mm | 80.8 mm | 99.1 mm |
| TEC 160 | EXT327-17.0 | 17.0 mm | 80.8 mm | 97.8 mm |
| TEC 180 | EXT327-16.0 | 16.0 mm | 80.8 mm | 96.8 mm |
| ???? | EXT327-34.1 (new in May 2021) | 34.1 mm | 80.8 mm | 114.9 mm |
If you have a TEC telescope, you will also need to order a Drawtube Endcap (S35RFAA) for the focuser. This only applies to the TEC focusers and is integral to the Astro-Physics 3.5" focusers, but is not needed as a separate purchase. The S35RFAA screws directly onto the drawtube's 4.1" x 24 thread (same as Starlight Instrument's 3.5" focuser endcap thread).
If you own more than one telescope that can use the QUADTCC, just substitute the required back focus spacer extension for each instrument. All other components in your imaging train can remain the same, since you will have achieved the correct back focus spacing.
Available Diagrams from Astro-Physics
- Extension for the QUADTCC to achieve optimal back focus (see chart below for proper extension size for your telescope)
- 16.1 mm of back focus to be used with the TEC 180
- 16.1 mm Back Focus Spacer Extension
