Complete reference guide for identifying and selecting optical filter mounting systems
A quick cheatsheet for optical filter thread types, sizes, and mounting standards used in labs, cameras, and industry.
Thread Specification indicates the diameter and pitch of the thread. For example, M12×0.5 means 12 mm diameter with 0.5 mm thread pitch (distance between threads), while 1.035"-40 means 1.035 inch diameter with 40 threads per inch (TPI).
| Mount Type | Thread Specification | Suitable Optics Size | Features & Notes | Typical Applications |
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| Mount Type | Thread Specification | Suitable Optics Size | Features & Notes | Typical Applications |
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| Mount Type | Specification | Suitable Optics Size | Features & Notes | Typical Applications |
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Yes! SM1 external threads (1.035"-40) are designed to screw into SM1 internal threads. This allows SM1 threaded components like lens tubes, adapters, and mounts to connect together seamlessly. The same principle applies to all threaded mount systems - external threads mate with internal threads of the same specification.
No, C-Mount and M25 are different! C-Mount uses 1"-32 TPI (25.4mm diameter, 32 threads per inch), while M25 uses M25×0.75 (25mm diameter, 0.75mm thread pitch). Though similar in diameter, they have different thread pitches and are not interchangeable. C-Mount has coarser threads (32 TPI ≈ 0.79mm pitch) compared to M25's finer 0.75mm pitch.
Yes, optics can be slightly smaller than the mount's clear aperture - typically up to 0.2mm smaller. For example, a 24.8mm diameter filter can fit in a 25mm mount. However, ensure there's enough material around the optical element for the retaining ring to secure it properly.
Optics are typically secured using a retaining ring that threads into the mount. The optical element (filter, lens, etc.) sits in a groove or shoulder inside the mount, and the retaining ring threads in from the front to hold it in place. This provides secure mounting while allowing for easy removal when needed.
Metric threads (like M25×0.75) specify diameter in millimeters and pitch in millimeters between threads. Imperial threads (like 1.035"-40) specify diameter in inches and threads per inch (TPI). Imperial systems are common in North American lab equipment (especially Thorlabs), while metric is standard in European and Asian optics.
Yes! Adapter rings are available to convert between different mount types. For example, you can get SM1-to-C-Mount adapters, or M25-to-M52 step-up rings. These adapters allow you to use filters and optics with different thread types in your optical system.