ASToptics M48 0.3mm Aluminum Spacer Ring

ASToptics 0.3mm M48 Aluminium Spacer Ring

Every tenth of a millimetre matters when you build an imaging train. Extension tubes handle the large distances, but when you need to shift a sensor or filter by just a fraction of a millimetre, precision spacer rings take over. The ASToptics aluminium spacer ring for M48x0.75 thread, at only 0.3mm thick, is exactly that kind of tool - simple, yet indispensable in practice. It is made from aluminium, so it is sturdy and light at the same time, adding no unnecessary weight to your setup.

Universal M48 thread - fits almost everywhere

The M48x0.75 thread, also known as the 2″ filter thread, is one of the most widely used standards in astronomical optics. You find it on camera adapters, filter drawers, reducers, and filters themselves. This means you can insert this M48 spacer ring almost anywhere in the imaging train without needing additional adapters. Simply thread it between two components and the distance is set precisely.

Why backfocus precision matters in astrophotography

In astrophotography, the exact distance between the sensor and the rear of the lens or reducer directly affects image quality - particularly field flatness and the amount of vignetting in the corners of the frame. By combining several rings of different thicknesses, you can reach the exact distance you need without any compromise. Precise backfocus adjustment is one of the key factors that determines whether stars in the corners of your image appear sharp or stretched.

Key specifications

When to use this spacer ring

• Fine-tuning sensor position behind a focal reducer or field flattener
• Adjusting backfocus distance without modifying other components
• Combining multiple rings to reach a precise total distance
• Eliminating star elongation in image corners caused by incorrect backfocus