Details
Achieve Precision Back-Focus with Ease!
This comprehensive 11-piece shim and spacer ring set is an essential toolkit for any astrophotographer looking to fine-tune the spacing between their imaging train components. Made from durable 304 stainless steel, each ring features a standard M42 thread-compatible diameter (42 mm inner / 52 mm outer) and comes in a carefully selected range of thicknesses: 0.02 mm, 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, and 1.0 mm. By combining multiple rings, you can dial in virtually any spacing increment you need—down to hundredths of a millimetre.
Correct back-focus distance is one of the most critical—and often overlooked—factors in producing sharp, well-corrected astrophotographs. Field flatteners, coma correctors, and reducers all require a specific sensor-to-optic spacing to perform as designed. Even a fraction of a millimetre off can introduce star elongation, tilt, or field curvature at the edges of your frame. These spacer rings let you make micro-adjustments with confidence, slotting neatly between adapters, filter drawers, off-axis guiders, and camera bodies in your M42 imaging train.
The stainless steel construction ensures each shim remains flat, rigid, and corrosion-resistant over years of use, unlike plastic alternatives that may compress or deform under load. The set is equally useful whether you're working with a dedicated astronomy camera, a DSLR/mirrorless adapter, or a CCD setup. Common use cases include:
- Dialling in the precise 55 mm back-focus distance required by many popular field flatteners and reducers
- Compensating for spacing differences introduced by filter wheels, electronic focusers, or tilt adjusters
- Fine-tuning sensor distance when switching between cameras with different flange depths
- Eliminating edge-of-field star distortion caused by even minor spacing errors
Additional Information
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