The Dark Clear Skies M54M to M42M Fine Back-Focus Spacer (1.5 mm) is a precision-machined spacer designed for fine adjustment of back-focus distance in astrophotography imaging trains.

Purpose & Use

Many telescope reducers and field flatteners require a precise back-focus distance to deliver optimal star shapes and edge correction. Small spacing errors of even 1–2 mm can noticeably affect image quality, particularly with fast optical systems and larger sensors.

This spacer provides an accurate mechanical thickness of 1.5 mm and is intended for fine back-focus correction once the main spacing has already been established.

Key Features

• Fixed 1.5 mm mechanical spacing for fine back-focus adjustment
• M54 × 0.75 male thread on telescope side
• M42 × 0.75 (T2) male thread on camera side
• CNC-machined aluminium construction
• Matte black internal finish to minimise reflections
• Rigid, low-profile design for imaging trains

Important Usage Note

This spacer is intended for fine back-focus adjustment only. It is not suitable for building primary spacing distances and should be used in conjunction with existing spacers or adapters where small spacing corrections are required.

Compatibility

This spacer is designed for astrophotography imaging trains requiring an M54 to M42 (T2) thread transition. It is compatible with many reducers, flatteners, filter wheels, cameras, and adapters that use standard M54 and M42 thread interfaces.

Typical Applications

• Fine tuning reducer or flattener back-focus spacing
• Correcting edge star distortion caused by spacing errors
• Adjusting imaging trains after adding filters or accessories
• Astrophotography and EAA camera setups

Technical Specifications

If you are unsure whether a 1.5 mm spacer is required for your optical system, feel free to contact us for guidance before purchase.