3.27" Backfocus Spacer Extensions for Astro-Physics Focusers and Accessories (EXT327-)

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In Stock, unless indicated

When purchasing the QUADTCC, 110TCC or other other accessories you may need to add the proper length backfocus spacer extension according to the chart below in order to achieve the required 80.8mm spacing. 

If you have a TEC scope, you will also need to order a Drawtube Endcap (S35RFAA) for the focuser. This only applies to the TEC focusers. This part is integral to the Astro-Physics 3.5" focusers and is not needed as a separate purchase. The S35RFAA screws onto the drawtube's 4.100" x 24 thread (same as Starlight Instrument's 3.5" focuser endcap thread).

Scope Part # Length of Extension Spacing with 3.27" Extension Spacing without Extension
AP 175EDF for field flattener (175FF) EXT327-34.1  (formerly A2681)  34.1 mm 80.0 mm  114.9mm
AP 130 GTX EXT327-22.1  (formerly A5020) 22.1 mm 80.8 mm 102.9 mm
TEC 140 EXT327-18.3  (formerly A2680) 18.3 mm 80.8 mm 99.1 mm
TEC 160 EXT327-17.0  (formerly A5022) 17.0 mm 80.8 mm 97.8 mm
TEC 180 EXT327-16.0  (formerly A5023) 16.0 mm 80.8 mm 96.8 mm
AP 110GTX EXT327-14.7 14.7 mm 80.8mm 95.5mm

If you own more than one scope that can use the QUADTCC, simply substitute the required backfocus spacer extension for each instrument. All other components in your imaging train can remain the same since you will have achieved the correct backfocus spacing. 


In late May 2021, part numbers were revised as stated above.