Optec Inc. Optec-DSI 3.5x24tpi Extension Tube Set, 5-Piece

Innovative Collaboration: Developed jointly by Rich Simons of Deep Sky Instruments and Optec, targeting large aperture telescopes.
Enhanced Diameter Standard: A new spacer set extending the Astro-Physics 2.7-inch standard to accommodate larger diameter requirements.
Improved Light Transmission: Designed to overcome the 2.5" clear aperture limits of AP2.7 spacers, reducing edge ray clipping for better light passage.
Diverse Length Options: The set includes five different lengths: 1/2", 3/4", 1", 1-1/2", and 3", for versatile spacing needs.
Stackable Design: Features female and male threading for easy stacking and versatile combinations. Knurled bases enhance attachment and detachment ease.
High-Quality Construction: Made from durable 6061 aluminum alloy with a black anodized finish to reduce reflection and ensure longevity.
Advanced Optical Performance: Incorporates anti-reflection threading and internal baffles, especially in the largest tube, to minimize internal reflections.
Versatile Spacer Combinations: Provides extensions from 0.5" to 6.25" in 1/4-inch increments, plus a 6.75" option using all spacers combined.
Ultra-Flat Black Internal Coating: Ensures a non-reflective interior for optimal optical efficiency.
Optimized Spacer Configurations: Includes a reference table for ideal spacer combinations, catering to various telescope configurations.

Specifications