Adjustable Mechanical Slits

  • 1-to-1 Micrometer to Slit Width Adjustment
  • 0" to 0.24" (0 to 6 mm) Slit Size
  • SM05-Threaded Aperture


Mechanical Slit

Back View Opened

Front View Nearly Closed

Back View Closed


Mechanical Slit for
30 mm Cage System

Related Items

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Variable slit and shutter
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View Imperial Product List
Item #QtyDescription
CFH2130 mm Cage Plate with Removable Filter Holder for Ø1" Optics, 8-32 Tap
CFH2-V1Variable Attenuator Insert for use with CFH2(/M) and Fiber Optic Filter Mounts
ER2-P41Cage Assembly Rod, 2" Long, Ø6 mm, 4 Pack
TR31Ø1/2" Optical Post, SS, 8-32 Setscrew, 1/4"-20 Tap, L = 3"
PH21Ø1/2" Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L = 2"
VA100C130 mm Cage System Adjustable Slit, 8-32 Tap, Imperial Micrometer
View Metric Product List
Item #QtyDescription
CFH2/M130 mm Cage Plate with Removable Filter Holder for Ø1" Optics, M4 Tap
CFH2-V1Variable Attenuator Insert for use with CFH2(/M) and Fiber Optic Filter Mounts
ER2-P41Cage Assembly Rod, 2" Long, Ø6 mm, 4 Pack
TR75/M1Ø12.7 mm Optical Post, SS, M4 Setscrew, M6 Tap, L = 75 mm
PH50/M1Ø12.7 mm Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L=50 mm
VA100C/M130 mm Cage System Adjustable Slit, M4 Tap, Metric Micrometer
The VA100C Variable Slit and the CFH2-V Variable Shutter in a 30 mm Cage System
Item # VA100 VA100C VA100/M VA100C/M
Slit Width (Maximum) 0.24" 6 mm
Micrometer Graduation 0.001" per Division 10 µm per Division
Slit Width Adjustment per Rev 0.025" 0.5 mm
Slit Width Repeatability 0.001" 20 µm
Slit Centering Tolerance ±0.003" ±0.08 mm
Post Mounting Tap 8-32 Tap M4 Tap


  • Fine Micrometer Adjustment of Slit Width
  • Slit Width: 0 to 0.24" (0 to 6 mm)
  • Internal SM05 (0.535"-40) Threads for Integrating Lens Tubes

The VA100(/M) Mechanical Slit and VA100C(/M) Mechanical Slit for our 30 mm Cage System provide precise adjustment of two A2 tool steel blades centered equally about an SM05-threaded through hole. Each blade is black to reduce unwanted reflections. The VA100C(/M) slit is mounted in a housing with four Ø6 mm through holes for 30 mm cage system rods; each rod can be locked in place with setscrews using a 0.05" (1.3 mm) hex key or balldriver. When mounted within a cage system, these through holes allow the slit to be oriented either vertically or horizontally. The unique design of both the VA100(/M) and VA100C(/M) mounts provides a 1-to-1 correlation between the adjustment of the precision micrometer drive and the subsequent change in slit width to within 0.001" (20 µm for the metric micrometer). The actual slit width ranges from fully closed to 0.24" (6 mm) wide with 0.025" (0.5 mm for the metric micrometer) of adjustment per revolution.  

In the fully closed position, the two blades are touching. However, imperfections in the blades and the degree to which the blades are parallel can cause gaps as large as 0.001" (25 µm) in width. The slit opening remains centered on the SM05-threaded (0.535"-40) aperture as the slit width is varied. The slim profile of the mounts makes them ideal for use with compact optical assemblies. On each mount there is a bottom-located 8-32 or M4 mounting hole that is compatible with our standard Ø1/2" posts. Each mount also has a through hole that is SM05 threaded on both sides. The back side threads are 0.24" (6.2 mm) deep on every mount, while the front side threads are 0.09" (2.4 mm) deep on the VA100(/M) and 0.09" (2.2 mm) deep on the VA100C(/M). This SM05 threading allows for compatibility with a variety of Thorlabs' products, including mounted optics and Ø1/2" lens tubes

Posted Comments:
Valle Pedro J.  (posted 2021-03-26 06:11:17.073)
When the slit is closed the micrometer is about 0.25 mm bellow the zero mark. It is possible readjust the micrometer perhaps with the lateral screws? Thank you very much in advance.
YLohia  (posted 2021-04-08 04:14:18.0)
Thank you for contacting Thorlabs. This could be a case of overdriving the micrometer and losing calibration. Due to our manufacturing/assembly tolerances, the micrometer is permitted to be +/-2 tick marks from “0” when the blades are fully closed. This is something that can be resolved by the end-user directly. With the blades in a fully closed position, slightly loosen the cap screw that holds the micrometer using a 2mm (5/64”) hex key, then reset the micrometer to “0”, and realign the micrometer witness line to face the front of the housing.  Please note that the micrometer is under spring pressure, so you have to maintain pressure on it by squeezing/pinching the micrometer into the main housing the entire time. 
victormanuel  (posted 2018-09-24 10:10:39.853)
Hello. I am using your VA100 mechanical slit. It works very well! however, I would like to get feedback from you: Does the screw lecture equal to the slit width?. I performed a diffraction experiment (the diffraction of a single slit into the Fraunhofer approx) to get the width of the slit and my experiment shows that actually, the slit separation is a half of the screw lecture. Am I right?. Best regards! P.D.: I agree with the comments below. It would be very useful to have furthermore a rectangular 2D slit mechanism.
nbayconich  (posted 2018-11-16 09:42:14.0)
Thank you for contacting Thorlabs. The VA100 mounts provide a 1-to-1 correlation between the adjustment of the precision micrometer drive and the subsequent change in slit width, so that the translation for one blade of the slit is half the translation of the micrometer.
kuchermatteo  (posted 2017-11-29 17:31:57.28)
I would like to know if you also sell a motorized version of the adjustable slit. Or if it is possible to buy it without the micrometerhead and install an acctuator myself.
nbayconich  (posted 2018-01-04 02:06:07.0)
Thank you for your feedback. At the moment we do not have a motorized actuator that is compatible with the VA100 or a motorized variable slit. I will forward your request for future consideration.
psciortino  (posted 2015-06-16 10:48:28.573)
I have two of your variable slits #VA100. They work well but I am burning the SS slits with my 230mw laser. I have to reset the position of the slit after about 30 minutes of exposure with the laser or an average of 2-3 days. While in use the beam changes fringes as it burns the edge of the slit. Can you make the slit parts in Molybdenum so they don't melt and also make the edge thinner then the present 100um, say around 10um.The whole slit blade can be made thinner. The Moly has a melting point of 2610 degrees C. SS melts at about 1440 degrees C. Thanks for your help in this product improvement. Paul Sciortino Senior Engineer Polarization Solutions, LLC
besembeson  (posted 2015-09-21 11:19:44.0)
Response from Bweh at Thorlabs USA: I will followup with you by email to discuss this further.
pfsciortino  (posted 2015-03-10 17:04:12.15)
I would like to know if you are going to make an adjustable slit made out of thinner harder material such as moly. I have a DUV laser and I am using your product VA100. The problem is that the SS slit is too thick and also melts very easily after the beam has passed through the slit for about 30 minutes(accumulated time). Thanks for any help in regard to this matter.
cdaly  (posted 2015-03-25 03:12:36.0)
Response from Chris at Thorlabs: No I'm afraid we would not be able to offer a custom version of the mechanical shutter VA100(/M) with a different blade material.
amartya  (posted 2014-10-14 00:40:53.077)
Can I have a slit having movements both in the vertical and horizontal direction?
jlow  (posted 2014-10-22 04:24:40.0)
Response from Jeremy at Thorlabs: This is not something we have at the moment. We would have to design this from scratch. I will contact you directly to discuss more about this.
ole.hitzemann  (posted 2014-07-03 17:00:50.05)
Would it be possible to change the design of the mechanical slot so that it could be opened all the way to have a 0.5" (12.7 mm) free aperture? Or is it possible to change the micrometer screw to open the slit further? A slit that can be opened up to 10 or 12 mm would be very useful for us!
cdaly  (posted 2014-08-07 03:02:53.0)
Response from Chris at Thorlabs: Unfortunately, We would not be able to change the mount to have a 12.7 mm aperture. There is not enough room in the current package to accommodate the additional size of the components required and a complete redesign would be required. Perhaps we can offer a larger version with a bigger aperture in the future though. We will discuss the idea internally. Thank you for your suggestion.
tcohen  (posted 2012-07-12 11:41:00.0)
Response from Tim at Thorlabs: Thank you for your feedback! I agree this would be a very useful feature. Right now, our design engineers are working on a lot of new ideas, many of them which have been customer feedback. One of our most exciting projects is a new integrated optomech family and one of the new design ideas is a calibrated slit. We certainly hear your feedback for a cage mountable system and we appreciate you sharing your feedback so that we can incorporate them into our upcoming designs.
burnette.21  (posted 2012-07-05 13:08:43.0)
Make cage system compatible.
tcohen  (posted 2012-06-14 14:13:00.0)
Response from Tim at Thorlabs: Thank you for your interest in our VA100! Reviewing the design, there is no reason for any performance difference when mounting vertically or horizontally.
gregory.a.garrett.civ  (posted 2012-06-13 17:30:16.0)
How stable is this design if I mount the slits horizontally? Will there be much creep over time?
apalmentieri  (posted 2010-03-24 11:42:32.0)
A response from Adam at Thorlabs: Due to the current design of the VA100, it is not possible to add stepper motors to this product. The main body is only 0.380" thick so the hole cannot be opened up to 0.375" to accommodate the 3/8" barrel of the ZST6B. I believe that this is a good new product idea and will suggest this to our opto-mechanical engineering team as a customer-inspired idea.
user  (posted 2010-03-23 19:57:51.0)
is it possible to have this motorized using one of your 1/4-80 stepper motors?
technicalmarketing  (posted 2008-01-29 13:19:36.0)
According to an estimate made by Thorlabs Technical Support Staff, the distance between the sets of slits would be ~4.36 mm. Thank-you for the interest in our product and please contact us if you have any further questions.
sclarke  (posted 2008-01-28 19:10:57.0)
Hello, How far from the face are the blades in the VS100? I need two adjustable slits - one x and one y - as close to the same plane as possible. If the removable plate from two VS100 were removed and the two parts placed right against each other, how close would the two sets of blades be? Thanks Steve Clarke Los Alamos National Lab
acable  (posted 2007-10-15 20:37:35.0)
Tried to find this page by searching on adjustable slit, then variable slit, then i used slit but then had to guess that mechanical slit was the right choice in the large number of options given in response to the last query. The reason why i wanted to find the product page was to understand the minimum slit width, the presentation says fully closed, could you clarify what you mean by this less than precise term.
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