40 mm extension tube for ESATTO 3" (PrimaLuceLab, SKU: PL3600317 ) increases the working distance (back-focus) of the ESATTO 3" focuser by exactly 40 mm. The tube has an external M81 × 1 thread on one side and an internal M81 × 1 thread on the other, so you can screw any accessory (ARCO 3 rotator, corrector, camera) between the focuser without losing axiality and mechanical stiffness.

Key Features

• precise optical length of 40 mm – easy setting of the required back-focus
• Threads: M81 × 1 male (extractor side) / M81 × 1 female (accessory side)
• full 76mm internal diameter – no vignetting for full frame sensors
• CNC milled body made of 6061-T6 aluminum, hard anodized - lightweight and corrosion resistant
• blackened and grooved interior – effective reduction of reflections, better contrast

Set components

• spacer sleeve 40 mm M81 × 1

Technical parameters

• input thread: M81 × 1 (female)
• output thread: M81 × 1 (male)
• optical length: 40 mm
• Inner diameter: 76 mm
• material: aluminum 6061-T6, anodized
• Compatibility: ESATTO 3" extractor and accessories with M81 × 1 thread
• EAN: 8059020774271
• manufacturer: PrimaLuceLab – Italy

PL3600317 is a fast and precise solution when you need additional back-focus in astrophotography setups with ESATTO 3" focuser, while maintaining full aperture and stability of mechanical connection.