C-Mount Extension Tubes and Spacer Rings

CML05

CS- to C-Mount Adapter

CMRR

C-Mount Retaining Ring

Extension Tubes and Spacer Rings for C-Mount (1.00"-32) Components
Reduce the Object Distance of Camera Lenses
Introduce Distances from 0.25 mm (0.01") to 100.0 mm (3.94")

Application Idea

CML25 Extension Tube Between a Machine Vision Lens and a Scientific CCD Camera

CMSP150

1.50 mm Spacer Ring

CMSP100 Spacer Ring Between CML100 and CML15 Extension Tubes

Please Wait

Overview
Object Distances
Threading Specs
Feedback

Ray Diagram Demonstrating the effect of a C-Mount Extension Tube

Click to Enlarge
The introduction of an extension tube or spacer ring between a camera and a lens decreases the object distance and increases the image distance.

Features

Increase the Magnification of C-Mount (1.00"-32) Camera Lenses
Extension Tubes and Spacers Compatible with C-Mount Lenses and Cameras
Also Compatible with CS-Mount
Also Available in Kits (See Below)

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. 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 decreased object distance increases the magnification of the image on the camera sensor while decreasing the depth of field.

We offer C-Mount extension tubes in lengths from 5 mm to 100 mm for coarse adjustments of an optical system's length. We also offer adjustable extension tubes for continuous adjustment up to 0.81" (20.6 mm). 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"). These rings fit between two C-Mount components and provide fine spacing adjustments.

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. 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. 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. 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.

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.

When used to image objects within the range of specified object distances, Thorlabs' camera lenses are designed to correct for optical aberrations. The modification of the specified object distance with extension tubes and spacer rings may reduce the ability of these lenses to eliminate aberrations. Please refer to the Object Distances tab for more details.

C-Mount Compatible Products
CCD/CMOS Cameras	Camera Lenses	Zoom Lenses	Thread Adapters	Terminated Fiber Adapters

Thorlabs' Camera Lenses for Machine Vision each have a characteristic range of object distances. Objects placed within this range can be brought to a sharp focus on the sensor of the C-Mount camera. As seen in the image sequence below, the addition of an extension tube between the camera and the lens changes this range of object distances and allows the system to focus on objects closer to the lens. This increases the magnification of the image on the camera while decreasing the depth of field. The following table lists the range of possible object distances for various combinations of Thorlabs' C-Mount extension tubes and machine vision lenses.

Note that Thorlabs' camera lenses are designed to correct for optical aberrations witin a specified range of object distances. The modification of the specified minimum object distance with an extension tube may reduce the ability of these lenses to eliminate aberrations.

14" (356 mm) Object Distance
No Spacer

Click to Enlarge
Click Here for Raw (2048 x 2048) Image

4" (102 mm) Object Distance
No Spacer

Click to Enlarge
Click Here for Raw (2048 x 2048) Image

4" (102 mm) Object Distance
5 mm Spacer

Click to Enlarge
Click Here for Raw (2048 x 2048) Image

5/8" (16 mm) Object Distance
20 mm (15 mm + 5 mm) Spacer

Click to Enlarge
Click Here for Raw (2048 x 2048) Image

RSP1X15 rotation mount imaged using a previous-generation scientific camera (Item # 4070M-GE) and MVL25M43 Lens at different object distances. A 20 mm spacer was created by using CML05 and CML15 spacers together.

Object Distance and Magnification for Lens and Spacer Combinations
Camera Lens	Focal Length	Design Format	No Spacer		1 mm Spacer		5 mm Spacer		10 mm Spacer		20 mm Spacer
Camera Lens	Focal Length	Design Format	Minimum Object Distance	Magnification	Minimum Object Distance	Magnification	Minimum Object Distance	Magnification	Minimum Object Distance	Magnification	Minimum Object Distance	Magnification
MVL8M23	8 mm	2/3"	120 mm	0.07	30 mm	0.2	-	-	-	-	-	-
MVL12M23	12 mm	2/3"	150 mm	0.08	70 mm	0.16	-	-	-	-	-	-
MVL12M1	12 mm	1"	300 mm	0.04	93 mm	0.12	-	-	-	-	-	-
MVL12M43	12 mm	4/3"	100 mm	0.1	48 mm	0.19	-	-	-	-	-	-
MVL16M23	16 mm	2/3"	200 mm	0.08	110 mm	0.14	-	-	-	-	-	-
MVL16M1	16 mm	1"	300 mm	0.05	134 mm	0.11	-	-	-	-	-	-
MVL25M23	25 mm	2/3"	200 mm	0.12	150 mm	0.16	73 mm	0.31	-	-	-	-
MVL25TM23	25 mm	2/3"	100 mm	0.24	79 mm	0.28	46 mm	0.44	29 mm	0.63	-	-
MVL25M1	25 mm	1"	300 mm	0.08	200 mm	0.12	83 mm	0.28	-	-	-	-
MVL25M43	25 mm	4/3"	150 mm	0.15	115 mm	0.19	56 mm	0.35	31 mm	0.55	12 mm	0.96
MVL35M23	35 mm	2/3"	200 mm	0.18	175 mm	0.21	115 mm	0.32	81 mm	0.46	51 mm	0.73
MVL35M1	35 mm	1"	300 mm	0.12	243 mm	0.15	138 mm	0.26	91 mm	0.4	-	-
MVL50M23	50 mm	2/3"	200 mm	0.3	190 mm	0.32	160 mm	0.39	135 mm	0.48	105 mm	0.65
MVL50TM23	50 mm	2/3"	100 mm	0.46	91 mm	0.48	76 mm	0.58	64 mm	0.7	49 mm	0.94
MVL50M1	50 mm	1"	500 mm	0.11	424 mm	0.13	269 mm	0.2	189 mm	0.3	124 mm	0.5
MVL75M1	75 mm	1"	1000 mm	0.078	858 mm	0.091	553 mm	0.14	389 mm	0.21	251 mm	0.34
MVL75M23	75 mm	2/3"	1200 mm	0.07	1010 mm	0.08	630 mm	0.13	440 mm	0.2	285 mm	0.34
MVL100M23	100 mm	2/3"	2000 mm	0.05	1700 mm	0.06	1060 mm	0.1	740 mm	0.15	480 mm	0.25

Click to Enlarge

Threading Specifications

The following is a general overview of screw threading. For more details regarding specifications and dimensions, please consult the Machinery's Handbook, available for purchase at many bookstores.

Features of a Thread
A thread consists of three repeating features: a crest, flank, and root (see drawing to the right). 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. The distance between corresponding points on adjacent threads is known as the pitch of the thread. The flank angle is defined as the angle the flank makes with a perpendicular ray drawn from the screw axis. Unless otherwise stated, threads have a flank angle of 30°, resulting in a total angle between flanks of 60°. Each feature is shown in the diagram to the right.

The major diameter is taken from the crests of a thread while the minor diameter is taken from the roots. 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 pitch diameter is approximately halfway between the major and minor diameters.

Thread Form
A thread form is a set of rules that define the features' scale relative to one another. Common thread forms include the Unified Screw Thread Form, used in the United States of America and measured in imperial units, and the ISO Metric Screw Thread Form, used in many parts of the world and measured with the International System of Units. There are many thread forms in the Unified screw thread standard designated by either UN, which defines a flat root contour, or UNR, which defines a round root contour. These can be further described by appending more letters. For example, an extremely fine thread with a flat root contour is designated UNEF. Those forms which are not standardized by the Unified screw thread system are designated UNS.

Thread Series
Most screws are identified by their thread series. Thread series are denoted by the major diameter and density of threads. Unified threads specify density in threads per inch, while Metric threads specify the thread pitch. For example, in the Unified nomenclature, a 1/4"-20 cap screw has a 1/4" diameter barrel and the pitch is 20 threads per inch (TPI). In metric nomenclature, an M4 x 0.7 cap screw has a 4 mm barrel and the pitch is 1 thread per 0.7 mm. The term M4 x 0.7 is often shortened to just M4.

Unified Thread Class Tolerancing
Location	Loose	Optimal	Strict
Internal	1B	2B	3B
External	1A	2A	3A

Metric Thread Tolerance Positions
Location	Loose	Optimal	Strict
Internal	-	G	H
External	e or f	g	h

Metric Thread Tolerance Grades
Dimension	Location	Tolerance Grades^a
Minor Diameter	Internal	4, 5, 6, 7, 8
Major Diameter	External	4, 6, 8
Pitch Diameter	Internal	4, 5, 6, 7, 8
Pitch Diameter	External	3, 4, 5, 6, 7, 8, 9

The tolerance becomes looser as the grade increases. The underlined grades are used with normal lengths of thread engagement.

Thread Class
The tolerances and allowances on a thread series are given by a thread class. Unified thread classes are alphanumeric identifiers starting with a number from 1 through 3, where 1 is the loosest tolerance and 3 is the tightest, and either A for external threading or B for internal threading.

Metric threads have a slightly more complex tolerancing method that uses tolerancing grades, designated by a number 3 through 9; and tolerancing positions, which use letters e through h. Grades provide a measure of the tolerance itself: the smaller the number, the tighter the tolerance. Positions denote the distance of the tolerance from the pitch diameter. Uppercase positioning letters indicate internal threads while lowercase positioning letters indicate external threads.

Quoting from the Machinery's Handbook, 29th Edition, p. 1885: "To designate the tolerance class, the grade and position of the pitch diameter is shown first followed by that for the major diameter in the case of the external thread or that for the minor diameter in the case of the internal thread, thus 4g6g for an external thread and 5H6H for an internal thread. If the two grades and positions are identical, it is not necessary to repeat the symbols, thus 4g, alone, stands for 4g4g and 5H, alone, stands for 5H5H."

Thorlabs' SM Series Threads
Threading specifications for our SM threads, utilized in our lens tube and cage system components, are given below so that you can machine mating components to suit your application. Most SM series threads utilize a non-standard Unified thread form, indicated by the letters UNS, with a 30° flank angle and a thread class of 2A and 2B. The exception is our SM30 series thread, which is a Metric thread form with a 30° flank angle and a tolerance of 6H/6g. We also offer products with C-Mount and RMS threads, and the specifications for these threads are given below for reference. Please note that other manufacturers may have different tolerances for C-Mount and RMS threads. For other thread specifications that are not listed here, please contact Tech Support.

SM05 Threading: Ø1/2" Lens Tubes, 16 mm Cage Systems
External Thread, 0.535"-40.0 UNS-2A		Internal Thread, 0.535"-40.0 UNS-2B
Max Major Diameter	0.5340"	Min Major Diameter	0.5350"
Min Major Diameter	0.5289"	Min Pitch Diameter	0.5188"
Max Pitch Diameter	0.5178"	Max Pitch Diameter	0.5230"
Min Pitch Diameter	0.5146"	Min Minor Diameter (and 83.3% of Thread)	0.508"
Max Minor Diameter	0.5069"	Max Minor Diameter (and 64.9% of Thread)	0.514"

RMS Threading: Objective, Scan, and Tube Lenses
External Thread, 0.800"-36.0 UNS-2A		Internal Thread, 0.800"-36.0 UNS-2B
Max Major Diameter	0.7989"	Min Major Diameter	0.8000"
Min Major Diameter	0.7934"	Min Pitch Diameter	0.7820"
Max Pitch Diameter	0.7809"	Max Pitch Diameter	0.7866"
Min Pitch Diameter	0.7774"	Min Minor Diameter (and 83.3% of Thread)	0.770"
Max Minor Diameter	0.7688"	Max Minor Diameter (and 64.9% of Thread)	0.777"

C-Mount Threading: Machine Vision Lenses, CCD/CMOS Cameras
External Thread, 1.000"-32.0 UN-2A		Internal Thread, 1.000"-32.0 UN-2B
Max Major Diameter	0.9989"	Min Major Diameter	1.0000"
Min Major Diameter	0.9929"	Min Pitch Diameter	0.9797"
Max Pitch Diameter	0.9786"	Max Pitch Diameter	0.9846"
Min Pitch Diameter	0.9748"	Min Minor Diameter (and 83.3% of Thread)	0.966"
Max Minor Diameter	0.9651"	Max Minor Diameter (and 64.9% of Thread)	0.974"

SM1 Threading: Ø1" Lens Tubes, 30 mm Cage Systems
External Thread, 1.035"-40.0 UNS-2A		Internal Thread, 1.035"-40.0 UNS-2B
Max Major Diameter	1.0339"	Min Major Diameter	1.0350"
Min Major Diameter	1.0288"	Min Pitch Diameter	1.0188"
Max Pitch Diameter	1.0177"	Max Pitch Diameter	1.0234"
Min Pitch Diameter	1.0142"	Min Minor Diameter (and 83.3% of Thread)	1.008"
Max Minor Diameter	1.0068"	Max Minor Diameter (and 64.9% of Thread)	1.014"

SM30 Threading: Ø30 mm Lens Tubes
External Thread, M30.5 x 0.5 – 6H/6g		Internal Thread, M30.5 x 0.5 – 6H/6g
Max Major Diameter	30.480 mm	Min Major Diameter	30.500 mm
Min Major Diameter	30.371 mm	Min Pitch Diameter	30.175 mm
Max Pitch Diameter	30.155 mm	Max Pitch Diameter	30.302 mm
Min Pitch Diameter	30.059 mm	Min Minor Diameter (and 83.3% of Thread)	29.959 mm
Max Minor Diameter	29.938 mm	Max Minor Diameter (and 64.9% of Thread)	30.094 mm

SM1.5 Threading: Ø1.5" Lens Tubes
External Thread, 1.535"-40 UNS-2A		Internal Thread, 1.535"-40 UNS-2B
Max Major Diameter	1.5339"	Min Major Diameter	1.535"
Min Major Diameter	1.5288"	Min Pitch Diameter	1.5188"
Max Pitch Diameter	1.5177"	Max Pitch Diameter	1.5236"
Min Pitch Diameter	1.5140"	Min Minor Diameter (and 83.3% of Thread)	1.508"
Max Minor Diameter	1.5068"	Max Minor Diameter (and 64.9% of Thread)	1.514"

SM2 Threading: Ø2" Lens Tubes, 60 mm Cage Systems
External Thread, 2.035"-40.0 UNS-2A		Internal Thread, 2.035"-40.0 UNS-2B
Max Major Diameter	2.0338"	Min Major Diameter	2.0350"
Min Major Diameter	2.0287"	Min Pitch Diameter	2.0188"
Max Pitch Diameter	2.0176"	Max Pitch Diameter	2.0239"
Min Pitch Diameter	2.0137"	Min Minor Diameter (and 83.3% of Thread)	2.008"
Max Minor Diameter	2.0067"	Max Minor Diameter (and 64.9% of Thread)	2.014"

SM3 Threading: Ø3" Lens Tubes
External Thread, 3.035"-40.0 UNS-2A		Internal Thread, 3.035"-40.0 UNS-2B
Max Major Diameter	3.0337"	Min Major Diameter	3.0350"
Min Major Diameter	3.0286"	Min Pitch Diameter	3.0188"
Max Pitch Diameter	3.0175"	Max Pitch Diameter	3.0242"
Min Pitch Diameter	3.0133"	Min Minor Diameter (and 83.3% of Thread)	3.008"
Max Minor Diameter	3.0066"	Max Minor Diameter (and 64.9% of Thread)	3.014"

SM4 Threading: Ø4" Lens Tubes
External Thread, 4.035"-40 UNS-2A		Internal Thread, 4.035"-40.0 UNS-2B
Max Major Diameter	4.0337"	Min Major Diameter	4.0350"
Min Major Diameter	4.0286"	Min Pitch Diameter	4.0188"
Max Pitch Diameter	4.0175"	Max Pitch Diameter	4.0245"
Min Pitch Diameter	4.0131"	Min Minor Diameter (and 83.3% of Thread)	4.008"
Max Minor Diameter	4.0066"	Max Minor Diameter (and 64.9% of Thread)	4.014"

Posted Comments:

Leszek Lisowski (posted 2022-03-14 04:13:31.437)

Is It possible to order the C-Mount Extension Tubes in raw aluminum. We would like to use our coloration?

jdelia (posted 2022-03-14 04:31:31.0)

Thank you for contacting Thorlabs. We will reach out to you directly to discuss quoting these tubes without the anodization.

jdelorme (posted 2016-12-16 02:48:58.713)

There is a mistake in the table of the section : C-Mount Extension Tubes. CML05 -- 5.0 mm (0.39") -- 4.2 mm (0.17") --> 5.0 mm ≠ 0.39''

tfrisch (posted 2016-12-16 10:40:30.0)

Thank you for bringing this to our attention.

C-Mount Extension Tubes

Zoom

Stackable Design
Internally C-Mount Threaded (1.00"-32)
Directly Compatible With Our Clamps and Slip Rings for Ø1" Lens Tubes
Extension Tube Kit is Also Available (See Below)

These C-Mount extension tubes introduce a fixed spacing between C-Mount components, such as Thorlabs' CCD/CMOS cameras and camera lenses. They have a stackable design and C-Mount (1.00"-32) threads for direct compatibility with any C-Mount components. The CML05 CS-Mount to C-Mount Extension Adapter is sized to increase the flange-to-sensor distance of a CS-Mount camera by 5 mm (0.39") to match the C-Mount standard distance.

These extension tubes have a 0.97" (24.6 mm) inner diameter that is too small to accept Ø1" (Ø25.4 mm) or Ø25 mm (Ø0.98") optics. Optics with diameters between 0.87" (22.0 mm) and 0.97" (24.6 mm) can be secured inside these tubes with C-Mount retaining rings. These extension tubes do not include C-Mount retaining rings, which can be purchased below.

Item #	L	Thread Depth
CML05	5.0 mm (0.20")	4.2 mm (0.17")
CML10	10.0 mm (0.39")	9.2 mm (0.36")
CML15	15.0 mm (0.59")	14.2 mm (0.56")
CML25	25.0 mm (0.98")	24.2 mm (0.95")
CML40	40.0 mm (1.58")	39.2 mm (1.55")
CML50	50.0 mm (1.97")	49.2 mm (1.94")
CML100	100.0 mm (3.94")	99.2 mm (3.91")

Alternatives	Ø1/2", Ø1", Ø30 mm, Ø2", and Ø3" Stackable Lens Tubes for Optical System Construction

C-Mount Spacer Rings

Zoom

Click to Enlarge
CMSP100 Spacer Ring Between CML100 and CML15 Extension Tubes

Introduce a Fixed Spacing Between Two C-Mount Components
Fit Over External C-Mount (1.00"-32) Threads
Brass Construction
0.25 mm (0.01") to 2.00 mm (0.08") Thickness
Spacer Ring Kit is Also Available (See Below)

These C-Mount Spacer Rings fit between two C-Mount (1.00"-32) components, such as Thorlabs' C-Mount extension tubes, camera lenses, and CCD/CMOS cameras. Much like the extension tubes sold above, the rings add length to an optical system. As shown to the right, these spacer rings fit over external C-Mount threads and allow for much finer adjustments of the spacing between components. The rings must be introduced between two other C-Mount components. They are constructed from brass and laser engraved with a part number.

C-Mount Retaining Ring

Zoom

Standard Retaining Ring with C-Mount (1.00"-32) Threads
Compatible with CMR Lens Mount, C-Mount Extension Tubes, and C-Mount Cameras

Our C-Mount-threaded (1.00"-32) retaining ring is ideal for securing components into our C-Mount extension tubes, CMR lens mount, and C- or CS-Mount compatible CCD and CMOS cameras. As shown in the photo to the left, these retaining rings are engraved with both the part number and "C-Mount" to distinguish it from our SM-threaded retaining rings. Each retaining ring is machined with two slots for compatibility with our SPW801 adjustable spanner wrench, which is sold below. Note that Thorlabs' C-Mount extension tubes cannot accept Ø1" (25.4 mm) or Ø25 mm (0.98") optics.

C-Mount Extension Tube and Spacer Ring Kits

Zoom

CMSP-KIT Contains Spacers with Thickness from 0.25 mm to 5 mm
CML-KIT Contains Extension Tubes with Lengths from 5 mm to 100 mm
Compatible with C-Mount and CS-Mount Lenses and Cameras
Extension Tubes Compatible with Clamps and Slip Rings for Ø1" Lens Tubes

These kits 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. Both kits contain a CS- to C-Mount extension adapter to allow compatibility with both types of lenses and cameras. In addition, the CML-KIT comes with two CMRR C-Mount retaining rings.

CMSP-KIT C-Mount Brass Spacer Kit
Component Description (Item #)	Qty.
0.25 mm Thick Spacer (CMSP025)	2
0.50 mm Thick Spacer (CMSP050)	2
1.00 mm Thick Spacer (CMSP100)	2
1.25 mm Thick Spacer (CMSP125)	2
1.50 mm Thick Spacer (CMSP150)	2
2.00 mm Thick Spacer (CMSP200)	2
CS- to C-Mount Extension Adapter (CML05)	1

CML-KIT C-Mount Extension Tube Kit
Component Description (Item #)	Qty.
CS- to C-Mount Extension Adapter (CML05)	1
10 mm Long Extension Tube (CML10)	1
15 mm Long Extension Tube (CML15)	1
25 mm Long Extension Tube (CML25)	1
40 mm Long Extension Tube (CML40)	1
50 mm Long Extension Tube (CML50)	1
100 mm Long Extension Tube (CML100)	1
C-Mount Retaining Ring (CMRR)	2

Click to Enlarge
Contents of CML-KIT

Adjustable Spanner Wrench

Zoom

Diameter Range from 0.12" to 2.89" (3.0 mm to 73.4 mm)
Self-Centering, One-Handed Diameter Adjustment Mechanism
Replaceable Stainless Steel Blades

Thorlabs' Adjustable Spanner Wrench features a spanning range that is continuously adjustable from 0.12" to 2.89" (3.0 mm to 73.4 mm). It is capable of providing an exact fit for retaining rings as large as the SM3RR for Ø3" Lens Tubes and Mounts. The diameter spanned by the blades remains centered while the knurled knob is adjusted.

The reversible blades have a flat tip on one end intended for use with retaining rings, and an edge-offset fine point on the opposing end for adapters with holes. The blades extend 1.6" (40.7 mm) from the body of the wrench. Hence, compared to our cylindrical spanner wrenches sold above, the SPW801 is ideal for securing lenses with a high radius of curvature because the guide flanges on the cylindrical spanner wrenches may come into contact with the lens. To reverse the blades, a 0.050" (1.3 mm) balldriver or hex key is needed. Replacement blade pairs are available separately.

The SPW801 wrench withstands a maximum torque of 80 inch-pounds (9 N·m).