This precision-machined 15 mm M48 Extension Tube is designed to provide an exact increase in optical path length for fine-tuning backfocus in astrophotography systems. Featuring M48x0.75 male threads on one end and M48x0.75 female threads on the other, this spacer integrates seamlessly with any accessory, camera, or reducer/flattener that uses the standard 2" filter-thread format.
Constructed from high-grade anodized aluminum, the tube offers excellent rigidity, smooth threading, and long-term durability even under frequent configuration changes. Its internal surface is fully blackened to minimize reflections, enhancing image contrast and reducing unwanted stray light in fast optical systems.
Use this extension when dialing in backfocus for reducers, flatteners, or correctors, or when achieving the ideal spacing between filters, tilt adjusters, off-axis guiders, and imaging sensors. At a true 15 mm optical length, it provides reliable and repeatable spacing with no added optical elements—just clean, simple mechanical extension.
Specification |
|
|---|---|
| Thread Size | M48 × 0.75 (male to female) |
| Optical Length | 15 mm |
| Mechanical Length | 15 mm (excluding threads) |
| Clear Aperture | 45 mm depending on step-in geometry |
| Material | CNC-machined aluminum |
| Finish | Hard anodized, matte black |
| Internal Treatment | Black-matte, anti-reflection internal surface |
| Use Case | Backfocus spacing, threaded extension, imaging train optimization |
| Compatibility | Any accessories using M48 × 0.75 threads (filter drawers, correctors, OAGs, cameras, etc.) |
