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

• Field Flatteners, TCCs, and QUADTCC Imaging Train Options
• Optimizing your Field Flattener, Lens, Camera Combination
• Schematic showing Back Focus Spacer and Adapter Spacing

• 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