For most screws, crests and roots do not terminate at a sharp point, so crest and root truncation values are included in the definitions of major and minor diameter. The major diameter is taken from the crests of a thread while the minor diameter is taken from the roots. Each feature is shown in the diagram to the right. Unless otherwise stated, threads have a flank angle of 30°, resulting in a total angle between flanks of 60°. The flank angle is defined as the angle the flank makes with a perpendicular ray drawn from the screw axis. The distance between corresponding points on adjacent threads is known as the pitch of the thread. Except in special cases, threads have symmetrical sides inclined at equal angles when a vertical line is drawn through the center of a crest or root. For more details regarding specifications and dimensions, please consult the Machinery's Handbook, available for purchase at many bookstores.Ī thread consists of three repeating features: a crest, flank, and root (see drawing to the right). The following is a general overview of screw threading. Object Distance and Magnification for Lens and Spacer CombinationsĬlick to Enlarge Threading Specifications Please refer to the Object Distances tab for more details. The modification of the specified object distance with extension tubes and spacer rings may reduce the ability of these lenses to eliminate aberrations. When used to image objects within the range of specified object distances, Thorlabs' camera lenses are designed to correct for optical aberrations. We also offer extension tube and spacer ring kits, which contain a variety of thicknesses/lengths to allow for fine/coarse adjustment of the image distance without having to search for a single piece to provide the right distance. For the construction of optical systems, Thorlabs offers lens tubes that accept Ø1/2", Ø1", Ø30 mm, Ø2", or Ø3" optics, each of which is equipped with an SM thread standard that depends on the tube diameter. Non-standard optics with diameters between 0.87" (22.0 mm) and 0.97" (24.6 mm) can be secured inside the tubes with C-Mount retaining rings. However, the 0.97" (24.6 mm) inner diameter of the C-Mount tubes is too small to accept Ø1" (Ø25.4 mm) or Ø25 mm (Ø0.98") optics. The 1.20" (30.5 mm) outer diameter of the C-Mount extension tubes is the same as that of Thorlabs' Ø1" lens tubes, so the C-Mount tubes are compatible with all clamps and slip rings for Ø1" lens tubes. These rings fit between two C-Mount components and provide fine spacing adjustments. In addition, brass spacer rings that fit over external C-Mount threads are available in thicknesses from 0.25 mm (0.01") to 2.00 mm (0.08").
We also offer adjustable extension tubes for continuous adjustment up to 0.81" (20.6 mm). We offer C-Mount extension tubes in lengths from 5 mm to 100 mm for coarse adjustments of an optical system's length.
The decreased object distance increases the magnification of the image on the camera sensor while decreasing the depth of field. These extension tubes or spacers increase the image distance between the lens and the camera sensor. This allows the lens to focus on objects at shorter distances than would be possible without a spacer. The C-Mount extension tubes and spacer rings sold here are designed to be used as spacers with C-Mount and CS-Mount instruments such as Thorlabs' CCD/CMOS cameras and camera lenses. Extension Tubes and Spacers Compatible with C-Mount Lenses and Cameras.
Increase the Magnification of C-Mount (1.00"-32) Camera Lenses.The introduction of an extension tube or spacer ring between a camera and a lens decreases the object distance and increases the image distance.
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