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Extension Tubes with C-Mount and SM1 Threading


  • External C-Mount Threading, Internal SM1 Threading
  • Increase Magnification of Ø1" Lens Systems for C-Mount Cameras
  • House Fixed-Focus Lenses for C-Mount Cameras

CM1L03

0.33" Extension

CM1L05

0.53" Extension

CM1L10

1.03" Extension

CM1L20

2.03" Extension

CM1L30

3.03" Extension

Application Idea

An extension tube increases image magnification of an SM1 lens system on a C-Mount camera. See the Application tab for more information.

Related Items


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

The simplified drawing above shows how the introduction of an extension tube between a camera and a lens decreases the object distance and increases the image distance.
Adapters Button

Features

  • External C-Mount Threading for Camera Mounting
  • Internal SM1 (1.035"-40) Threading for Ø1" Optics
    • Increase Magnification of Attached Lens Systems
    • House Custom, Fixed-Focus Lens Systems
  • Five Extension Lengths Available Between 0.33" and 3.03"
  • One SM1RR Retaining Ring Included with Each Extension Tube

The external threading of these extension tubes allows for direct connection to C-Mount cameras, while the internal thread is Thorlabs' standard SM1 threading for mounting Ø1" optics or connecting optomechanical components. Each tube can be used to increase magnification and decrease minimum focus distance of a user-built optical assembly in an SM1 lens tube. These can also be used to house fixed-focus systems that can mount directly to C-Mount and CS-Mount cameras, such as our scientific CCD cameras. These tubes are available in five extension lengths: 0.33", 0.53", 1.03", 2.03", and 3.03". To order other lengths of these extension tubes, contact Tech Support.

An extension tube increases magnification of an attached SM1 lens system by increasing the distance between the image and the sensor, as shown in the diagram to the right. This increase in image distance also decreases the object distance, reducing the minimum focus distance of the lens system. The internal SM1 threading is also designed to mount Ø1" optical elements. Elements can be locked in place with retaining rings and separated with plastic or brass spacers. To easily differentiate the two thread standards of these extension tubes, there are two grooves along the circumference of the tube near the side with the external C-Mount threading. The item # of each tube is engraved on its end face.

Our large selection of stock optical elements and optomechanical components can be used to build an imaging solution from the ground up. To see a lens assembly built with Thorlabs components and how extension tubes can be used to enhance magnification, see the Application tab. We also offer lens tubes with internal and external C-Mount threading for connecting two C-Mount components, as well as a variety of lens tubes with internal and external SM1 threading

Custom Thorlabs Camera Lens Images Target
Click to Enlarge
View Imperial Product List
Item #QtyDescription
Lens Assembly
SM1A91Adapter with External C-Mount Threads and Internal SM1 Threads
CM1L101Extension Tube, Internal SM1 Threading of 1" Depth, External C-Mount Threading, One Retaining Ring Included
SM1NR11SM1 Zoom Housing for Ø1" Optics, Non-Rotating, 2" (50.8 mm) Travel
SM1L20C1SM1 Slotted Lens Tube, 2" Thread Depth, 2 Retaining Rings Included
LB1811-A1N-BK7 Bi-Convex Lens, Ø1", f = 35.0 mm, ARC: 350-700nm
SM1S6M1Ø1" Brass Optic Spacer, 6 mm in Length
LC2679-A1Ø1", N-SF11 Plano-Concave Lens, f = -30.0 mm, ARC: 350-700 nm
SM1S10M1Ø1" Brass Optic Spacer, 10 mm in Length
LC1582-A1N-BK7 Plano-Concave Lens, Ø1", f = -75.0 mm, AR Coating: 350-700 nm
SM1S10M1Ø1" Brass Optic Spacer, 10 mm in Length
LBF254-050-A1N-BK7 Best Form Lens, Ø1", f = 50 mm, ARC: 350-700 nm
SM1T21SM1 (1.035"-40) Coupler, External Threads, 0.5" Long
SM1D251SM1 Lever-Actuated Iris Diaphragm (Ø0.8 - Ø25 mm)
SM1L101SM1 Lens Tube, 1.00" Thread Depth, One Retaining Ring Included
Camera and Table Mounting
8051C-USB18 Megapixel Color Scientific CCD Camera, Standard Package, USB 3.0 Interface
TR21Ø1/2" Optical Post, SS, 8-32 Setscrew, 1/4"-20 Tap, L = 2"
UPH21Ø1/2" Universal Post Holder, Spring Loaded Locking Thumbscrew, L = 2"
Target and Rail
R2L2S1N1Negative NBS 1963A Resolution Target, 2" x 2", 1 to 18 cycles/mm
XYF11XY Mount for 1/2" - 3" Rectangular Optics, 8-32 Taps
TR21Ø1/2" Optical Post, SS, 8-32 Setscrew, 1/4"-20 Tap, L = 2"
PH21Ø1/2" Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L = 2"
RC11Dovetail Rail Carrier, 1.00" x 1.00" (25.4 mm x 25.4 mm), 1/4" (M6) Counterbore
RLA18001Dovetail Optical Rail, 18", Imperial
View Metric Product List
Item #QtyDescription
Lens Assembly
SM1A91Adapter with External C-Mount Threads and Internal SM1 Threads
CM1L101Extension Tube, Internal SM1 Threading of 1" Depth, External C-Mount Threading, One Retaining Ring Included
SM1NR11SM1 Zoom Housing for Ø1" Optics, Non-Rotating, 2" (50.8 mm) Travel
SM1L20C1SM1 Slotted Lens Tube, 2" Thread Depth, 2 Retaining Rings Included
LB1811-A1N-BK7 Bi-Convex Lens, Ø1", f = 35.0 mm, ARC: 350-700nm
SM1S6M1Ø1" Brass Optic Spacer, 6 mm in Length
LC2679-A1Ø1", N-SF11 Plano-Concave Lens, f = -30.0 mm, ARC: 350-700 nm
SM1S10M1Ø1" Brass Optic Spacer, 10 mm in Length
LC1582-A1N-BK7 Plano-Concave Lens, Ø1", f = -75.0 mm, AR Coating: 350-700 nm
SM1S10M1Ø1" Brass Optic Spacer, 10 mm in Length
LBF254-050-A1N-BK7 Best Form Lens, Ø1", f = 50 mm, ARC: 350-700 nm
SM1T21SM1 (1.035"-40) Coupler, External Threads, 0.5" Long
SM1D251SM1 Lever-Actuated Iris Diaphragm (Ø0.8 - Ø25 mm)
SM1L101SM1 Lens Tube, 1.00" Thread Depth, One Retaining Ring Included
Camera and Table Mounting
8051C-USB18 Megapixel Color Scientific CCD Camera, Standard Package, USB 3.0 Interface
AP25E6M1Adapter with External 1/4"-20 Threads and External M6 x 1.0 Threads
TR50/M1Ø12.7 mm Optical Post, SS, M4 Setscrew, M6 Tap, L = 50 mm
UPH50/M1Ø12.7 mm Universal Post Holder, Spring-Loaded Locking Thumbscrew, L = 50 mm
Target and Rail
R2L2S1N1Negative NBS 1963A Resolution Target, 2" x 2", 1 to 18 cycles/mm
XYF1/M1XY Mount for 1/2" - 3" Rectangular Optics, M4 Taps
TR50/M1Ø12.7 mm Optical Post, SS, M4 Setscrew, M6 Tap, L = 50 mm
PH50/M1Ø12.7 mm Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L=50 mm
RC11Dovetail Rail Carrier, 1.00" x 1.00" (25.4 mm x 25.4 mm), 1/4" (M6) Counterbore
RLA450/M1Dovetail Optical Rail, 450 mm, Metric
Figure 1: A Cooke Triplet Lens Installed on a CCD Camera with an Extension Tube to Increase Magnification.

Increasing Image Magnification Using Extension Tubes

Thorlabs manufactures a wide variety of photonics equipment, providing a platform to create custom assemblies from scratch. We designed a simple four-element lens to demonstrate how using an extension tube increased the system's magnification.

We designed a simple 100 mm focal length lens assembly in Zemax; the .zar file for the assembly be downloaded by clicking here. The design was constrained to use only Ø1", stock Thorlabs spherical lenses and separate them with only brass spacers. The assembly is a variation on a Cooke Triplet housed in a 2" long lens tube. To enable manual focusing, the tube was inserted into an SM1NR1 non-rotating zoom housing. The 8051C-USB scientific CCD camera has C-Mount threading, like many industry cameras. In order to adapt our lens to the camera, we used an SM1A9 thread adapter, which allowed our lens to focus to infinity when fully retracted. An SM1D25 iris was added at the front of the lens with an SM1T2 coupler to allow adjustment of light incident on our sensor. An empty SM1L10 1" long lens tube was added at the front to act as a lens hood, which prevented lens flair and bloom by limiting light from outside the lens's field of view. The complete setup can be seen in Figure 1 with the extension tube added. 

We used an R2L2S1N negative NBS 1963A resolution target as our subject. The lens was stopped down to f/16. Without an extension tube, the minimum focus distance was found to be approximately 300 mm from the lens hood (Figure 2). At this magnification, the lens can conservatively resolve down to 4 lp/mm; at higher line pair densities, the chromatic aberrations cause the lines to blur into each other (Figure 3). By removing our SM1A9 thread adapter and adding a CM1L10 1" extension tube between our SM1 zoom housing and our C-Mount camera, we were able to reduce the minimum focus distance to approximately 200 mm (Figure 4). The resulting magnification allowed us to resolve up to 11 lp/mm before chromatic aberrations blurred the line pairs (Figure 5).

This design is limited, but it serves to illustrate how extension tubes like this can be used to increase image magnification and decrease minimum focus distance. This is useful in multiple applications where a lens system needs to operate close to a subject, e.g. quality control inspection equipment for small components or macrophotography. The extension tubes on this page make it easy to quickly build assemblies of Ø1" optics and attach them to a C-Mount camera.

Custom Camera without Extension Tube
Click to Enlarge
Figure 2: Without an extension tube, the minimum focus distance for the system is approximately 300 mm and the system can be focused to infinity.
Target Imaged with Extension Tube on Custom Camera
Click for Details
Figure 3: Image Taken without an Extension Tube
Custom Camera Lens with Extension Tube
Click to Enlarge
Figure 4: With an extension tube added, the minimum focus distance is reduced to approximately 200 mm; this increases the magnification, but the system can no longer focus to infinity.
Target Imaged with Extension Tube on Custom Camera
Click for Details
Figure 5: Image Taken with a 1" Long Extension Tube

Thorlabs' Threading Specifications

Thorlabs' lens tubes utilize a series of non-standard threadings. Threading specifications are given below for our SM threadings utilized in our lens tube and cage system components so that you can machine mating components to suit your application. We also offer products with C-Mount and RMS threadings, and the specifications for these threadings are also given below. Please note that other manufacturers may have different tolerances for these 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 LensesCCD/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, M30.5x0.5 Internal Thread, M30.5x0.5
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"

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Extension Tubes with External C-Mount Threading and Internal SM1 Threading

These extension tubes introduce a fixed spacing between an SM1-threaded system and a C-Mount threaded component, like a CCD camera. This length is listed in the table below as L2. The internal diameter of 1.035" allows Ø1" optics to be mounted; one SM1RR retaining ring is included with each extension tube, and additional retaining rings can be purchased below. The C-Mount thread depth is 0.16" for all extension tubes. These extension tubes cannot be stacked with each other, but they can be lengthened by adding SM1 stackable lens tubes. For custom extension tube lengths, contact Tech Support

Item # L1 L2 SM1 Thread Depth
CM1L03 0.49" (12.4 mm) 0.33" (8.4 mm) 0.30" (7.6 mm)
CM1L05 0.69" (17.5 mm) 0.53" (13.5 mm) 0.50" (12.7 mm)
CM1L10 1.19" (30.2 mm) 1.03" (26.2 mm) 1.00" (25.4 mm)
CM1L20 2.19" (55.6 mm) 2.03" (51.6 mm) 2.00" (50.8 mm)
CM1L30 3.19" (81.0 mm) 3.03" (77.0 mm) 3.00" (76.2 mm)
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
CM1L03 Support Documentation
CM1L03Customer Inspired! Extension Tube, Internal SM1 Threading of 0.30" Depth, External C-Mount Threading, One Retaining Ring Included
$18.03
Today
CM1L05 Support Documentation
CM1L05Customer Inspired! Extension Tube, Internal SM1 Threading of 0.50" Depth, External C-Mount Threading, One Retaining Ring Included
$18.85
Today
CM1L10 Support Documentation
CM1L10Customer Inspired! Extension Tube, Internal SM1 Threading of 1" Depth, External C-Mount Threading, One Retaining Ring Included
$20.19
Today
CM1L20 Support Documentation
CM1L20Customer Inspired! Extension Tube, Internal SM1 Threading of 2" Depth, External C-Mount Threading, One Retaining Ring Included
$23.07
Today
CM1L30 Support Documentation
CM1L30Customer Inspired! Extension Tube, Internal SM1 Threading of 3" Depth, External C-Mount Threading, One Retaining Ring Included
$29.25
Today

Ø1" Retaining Rings and Spanner Wrenches

Retaining Ring Specs
Item # Feature Thickness Inner
Diameter
SM1RR Aluminum 0.08"
(2.0 mm)
0.90"
(22.9 mm)
SM1LTRR Aluminum with Rubber O-Ring
for Stress-Free Mounting
0.16"
(3.9 mm)
0.82"
(20.7 mm)
SM1RRC Aluminum, 5 mm Thick for
High-Curvature Lenses
0.20"
(5.0 mm)
0.90"
(22.9 mm)
SM1PRR Non-Marring Plastic 0.11"
(2.8 mm)
0.80"
(20.3 mm)
POLARIS-SM1RR Stainless Steel 0.08"
(2.0 mm)
0.90"
(22.9 mm)
Spanner Wrench Application
Click to Assemble

Spanner Wrench Usage
  • Five Types of Retaining Rings for Securing Ø1" Optics
  • Spanner Wrenches Provide One-Handed Adjustment of Retaining Rings
  • SPW801 Adjustable Spanner Wrench can Accommodate Diameters from 0.12" (3.0 mm) to 2.89" (73.4 mm)

Thorlabs offers five different kinds of SM1 (1.035"-40) retaining rings. The SM1RR is our standard aluminum retaining ring that ships with our Ø1" lens tubes as well as many other Thorlabs components, and is available individually and in packs of 10.

Additionally, SM1RR Retaining Rings can be swapped out for one of the SM1-threaded retaining rings listed in the table to the right. Please keep in mind that due to the increased thickness of some retaining rings, the maximum optic thickness that can be housed inside our standard SM1-compatible mounts will be diminished in some cases.

Thorlabs also offers several spanner wrench choices. The 1" long SPW606 and the 3.87" long SPW602 can be used with the SM1RR and SM1LTRR retaining rings, while the adjustable SPW801 can be used with all three types of SM1 retaining rings. These spanner wrenches can be inserted into the lens tube, as shown to the right, and are hollow to prevent obstruction of the beam path. We also offer the SPB1 Spanner Bit, which can be used with a standard 1/4" hex driver (sold separately). The SPB1 is included as part of the SPB600 Spanner Wrench Bit Kit.

Alternatives Ø1/2", Ø2", and Ø3" Fixed Diameter Spanner Wrenches Ø1/2", Ø2", and Ø3" Retaining Rings
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
SM1RR Support Documentation
SM1RRSM1 Retaining Ring for Ø1" Lens Tubes and Mounts
$4.50
Today
SM1RR-P10 Support Documentation
SM1RR-P10SM1 Retaining Ring for Ø1" Lens Tubes and Mounts, 10 Pack
$40.50
Today
SM1LTRR Support Documentation
SM1LTRRSM1 (1.035"-40) Stress-Free Retaining Ring
$23.01
Today
SM1RRC Support Documentation
SM1RRCExtra-Thick SM1 (1.035"-40) Threaded Retaining Ring
$10.83
Today
SM1PRR Support Documentation
SM1PRRCustomer Inspired! SM1 (1.035"-40) Plastic Retaining Ring for Ø1" Lens Tubes and Mounts
$5.73
Today
POLARIS-SM1RR Support Documentation
POLARIS-SM1RRCustomer Inspired! Stainless Steel SM1 (1.035"-40) Threaded Retaining Ring
$11.64
Today
SPW606 Support Documentation
SPW606Customer Inspired! Spanner Wrench for SM1-Threaded Retaining Rings, Length = 1.00"
$27.55
Today
SPW602 Support Documentation
SPW602Spanner Wrench for SM1-Threaded Retaining Rings, Graduated Scale with 0.1"
(2.5 mm) Increments, Length = 3.88"
$27.55
Today
SPW801 Support Documentation
SPW801Adjustable Spanner Wrench
$100.94
Today
SPW102 Support Documentation
SPW102Adjustable Spanner Wrench, Replacement Blade Set
$29.36
Today
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