Visible Air-Spaced Achromatic Doublets, AR Coated: 350 - 700 nm

  • Minimal Focal Shift Over the Design Wavelength Range
  • Superior Performance When Compared to Cemented Doublets
  • 1" Outer Diameter Aluminum Housing



Each mount includes an engraved arrow
indicating the direction of light propagation
required to collimate a point source.

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General Specifications
Coating Rangea 350 - 700 nm
Design Wavelengths 486.1, 587.6, 656.3 nm
Surface Quality 20-10 Scratch-Dig
(to Prevent Scattering from
High-Power Sources)
Clear Aperture  Ø20 mm
Irregularity per Surface <λ/4 at 633 nm
Focal Length Tolerance ±1% at 587.6 nm
Reflectance Ravg < 0.5% (350-700 nm)
Housing  Ø1" 6061-T6 Aluminum Barrel
  • The AR coating is designed for 350 - 700 nm, but the glass used to construct these doublets provides poor transmission in the UV. See the transmission plots below for more details.
Air-Spaced Doublet in a Lens Tube
Click to Enlarge

Air-Spaced Achromatic Doublet in an SM1L30C Slotted Lens Tube with Two SM1RR Retaining Rings


  • Air-Spaced Doublet Design Provides Superior Aberration Performance than Singlet Lenses
  • Ø20 mm Clear Aperture
  • 1" Outer Diameter for Mounting Inside a Ø1" Lens Tube
  • AR Coating for the 350 - 700 nm Range

Thorlabs' Air-Spaced Achromatic Doublets are designed to provide superior spherical and chromatic aberration correction. Air-Spaced Doublets have two more degrees of freedom than cemented doublets because the interior lens surfaces do not need to have the same curvature. These extra variables allow the performance of these air-spaced doublets to exceed the performance of equivalent cemented doublets in some cases. For details, please see the Lens Comparison tab. The air-spaced design is also highly resistant to laser damage, since no cement is utilized in the fabrication process. Although these lenses have an AR coating for the 350 - 700 nm range deposited on both surfaces, the glass they are fabricated from displays limited or no transmission in the UV (<400 nm). Hence, please refer to the table below for exact specifications and transmission plots for each air-spaced doublet.

The doublets are pre-mounted in an aluminum barrel with tight tolerances on lens and barrel diameter to minimize the effects of lens decentering. Each mount includes an engraving with the part number, AR coating wavelength, focal length, and the direction of light propagation required to collimate a point source. The mount has a 1" outer diameter for mounting inside a Ø1" lens tube (as shown in the photo to the right).

Note: We do not recommend disassembly of these lenses, as this may affect performance.

Optic Cleaning Tutorial
Optical Coatings and Substrates

The table below contains links to pop-ups with plots containing a comparison of the theoretical performance of an air-spaced achromatic doublet and a cemented achromatic doublet with the same focal length. Comparisons are made for the transmitted wavefront error and spot radius. Raw data from each graph below can be downloaded by clicking here.

350 - 700 nm Lenses

Cemented Item #a Air-Spaced Item #a Wavefront Error Plots Spot Diameter Plots
AC254-030-A ACA254-030-A 30 mm WFE 30 mm Spot Radius
AC254-050-A ACA254-050-A 50 mm WFE 50 mm Spot Radius
AC254-060-A ACA254-060-A 60 mm WFE 60 mm Spot Radius
AC254-075-A ACA254-075-A 75 mm WFE 75 mm Spot Radius
AC254-100-A ACA254-100-A 100 mm WFE 100 mm Spot Radius
AC254-150-A ACA254-150-A 150 mm WFE 150 mm Spot Radius
AC254-200-A ACA254-200-A 200 mm WFE 200 mm Spot Radius
  • For the f = 30 mm lenses, the wavefront error was calculated with a Ø7 mm aperture and the f=50 mm lenses with a Ø15 mm aperture. All other lenses are calculated over the clear aperture.
Plot Key
Cemented Doublets Air Spaced
Air-Spaced Doublets Cemented Key
Diffraction Limit
Airy Disk

Posted Comments:
Christian Goerke  (posted 2023-03-28 16:47:27.99)
I am missing a download option for the transmission data in the table. Can you provide one?
ksosnowski  (posted 2023-05-01 03:37:33.0)
Thanks for reaching out to Thorlabs. We have contacted you directly to share a data table format for these plots.
user  (posted 2021-08-26 23:46:56.397)
Missing axial color plot, I need for ACA254-200-A
cdolbashian  (posted 2021-08-31 03:47:34.0)
Thank you for contacting us here at Thorlabs. I have contacted you directly with this data.
ludoangot  (posted 2016-01-29 14:47:39.4)
From the plots comparing the cemented and air-spaced doublets it appears that for f=150 and 200mm, there is no clear advantage (from an optical performance perspective) to using an air-spaced doublet over a cemented one. Is there any advantage for these 2 focal lengths in using an air-spaced doublet over a cemented one for imaging application?
besembeson  (posted 2016-02-03 04:41:27.0)
Response from Bweh at Thorlabs USA: For general imaging applications, performance will be very similar for these two doublets. However, if you have a high power level application, the air-spaced doublets will be better suitable.
scottie730318  (posted 2014-04-30 16:51:32.23)
The transmission Plot of ACA254-100-A shows that high transmission cover the wavelength from 300 nm to 700 nm. Can the transmittance at wavelength between 300 nm t0 350 nm be believed?
jlow  (posted 2014-05-01 08:44:01.0)
Response from Jeremy at Thorlabs: It seems that we made a mistake on these graphs. We will be updating the transmission curves on this page shortly. Thanks for bringing this to our attention.
user  (posted 2013-10-01 09:39:19.1)
Could you check the spot radius plots? The plots seem to show larger spot sizes at shorter focal lengths, with sub micron spot sizes available from 150mm and 200mm focal length lenses.
tcohen  (posted 2013-10-01 21:06:00.0)
Response from Tim at Thorlabs: These plots were calculated to show the quality of the design using RMS spot radius with respect to the centroid. The performance of the actual lenses will still be limited by diffraction. Some lenses that are theoretically borderline on the diffraction limit can end up being not diffraction limited depending on manufacturing tolerancing. Plotting the theoretical values such as this allow us to see the design and the margin below the diffraction limit. Although the diffraction limit will increase with increasing focal length and with decreasing beam diameters, these lenses will typically have theoretical rms spot sizes that decrease with increasing focal lengths and decreasing beam diameters. In terms of the RMS spot size shown in these plots, yes, we should expect to see smaller spot sizes for longer focal length lenses. However, I believe you were noting the point that if they are diffraction limited, in reality the actual diffraction limited spot size will be larger for longer focal lengths, which is correct. We are discussing how to make these plots more understandable. Thanks for your feedback!
curtis.volin  (posted 2013-02-20 13:02:50.053)
Can you publish zmx files for these lenses? The ZAR files published for some of them are useless in other versions of zemax than were used to create them. My attempts to create my own ZMX files from the data in the table are failing. The specs for ACA254-050-A give a lens with 30mm EFL. I could assume the table is shifted and this is the prescription for ACA254-030-A, but I don't trust the glass table, either.
tcohen  (posted 2013-02-21 14:58:00.0)
Response from Tim at Thorlabs: Thank you for your feedback! You are correct. There was a clerical error in the table and we are updating this right now. Supplying both .zar and .zmx is an active project. In the meantime, we can supply these files on request to I will contact you directly to provide the .zmx versions.
tcohen  (posted 2012-11-13 10:23:00.0)
Response from Tim at Thorlabs: Thank you for contacting us. We will update our presentation with these files. In the meantime, I will send you them directly.
dbarker2  (posted 2012-11-09 14:49:54.147)
Is it possible to get Zemax files for the -A coated doublets?
sharrell  (posted 2012-08-01 12:12:00.0)
Response from Sean at Thorlabs: Thank you for your feedback. You are correct that the focal shift units should be mm. We are in the process of updating those graphs. The link that is present in your feedback is for our -A coated achromats, while these air-spaced doublets feature our -B (650-1050 nm) coating. There is a curve for our -B cemented doublets here: that agrees with the curve on this page. If you are interested in air-spaced doublets with our -A coating (400-700 nm), we will be adding these lenses to our product line within the next two months.
user  (posted 2012-08-01 10:35:58.0)
The focal shift data presented here seems inconsistent with the data published elsewhere ( Should the focal shift units be mm? Besides the units, there also appears to be a discrepancy in the values.
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Air-Spaced Achromatic Doublets, 350 - 700 nm AR Coating

Item # f
Air Gapc
ACA254-030-A 30 19.98 -27.32 -20.49 -40.68 7.76 5.00 1.23 15.2 21.3 Air-Spaced Doublet Drawing
ACA254-050-A 50 32.53 -32.53 -28.45 -78.02 6.82 3.23 1.25 13.3 41.4
ACA254-060-A 60 39.43 -39.43 -35.34 -97.49 6.83 3.16 1.16 13.3 51.5
ACA254-075-A 75 50.67 -50.67 -46.30 -122.59 4.68 4.63 1.10 13.1 67.5
ACA254-100-A 100 41.39 -41.39 -40.63 -361.30 5.39 4.94 1.02 14.1 88.8
ACA254-150-A 150 96.25 -46.58 -45.88 -312.80 4.00 4.00 1.02 12.5 141.3
ACA254-200-A 200 211.55 -34.81 -33.69 -199.82 4.00 4.00 1.05 12.7 191.5

a. Left Lens Center Thickness in the Reference Drawing b. Right Lens Center Thickness in the Reference Drawing c. Center Air Spacing Between the Lenses.

Item # Transmission Plota, b Left Lens Materialc Right Lens Materialc Image Space NA Design RMS Wavefront Error
ACA254-030-A Plot N-SSK2 N-SF57 0.331 <3.5λ
ACA254-050-A Plot N-SSK2 N-SF57 0.198 <λ/5
ACA254-060-A Plot N-SSK2 N-SF57 0.166 <λ/5
ACA254-075-A Plot N-SSK2 N-SF57 0.133 <λ/8
ACA254-100-A Plot N-K5 N-KZFS8 0.101 <λ/10
ACA254-150-A Plot N-SSK2 N-KZFS8 0.060 <λ/20
ACA254-200-A Plot N-SSK2 N-KZFS5 0.045 <λ/20
  • The shaded region represents the specified coating range of the lenses.
  • The AR coating is designed for 350 - 700 nm, but the glass used to construct these doublets provides poor transmission in the UV (click the transmission plot links for more details on each item).
  • "Left" and "Right" refer to the orientations of the lenses in the Reference Drawing found by clicking on the info icon above.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ACA254-030-A Support Documentation
ACA254-030-AAir-Spaced Achromatic Doublet, AR Coating: 350-700 nm, f=30 mm
ACA254-050-A Support Documentation
ACA254-050-AAir-Spaced Achromatic Doublet, AR Coating: 350-700 nm, f=50 mm
ACA254-060-A Support Documentation
ACA254-060-AAir-Spaced Achromatic Doublet, AR Coating: 350-700 nm, f=60 mm
ACA254-075-A Support Documentation
ACA254-075-AAir-Spaced Achromatic Doublet, AR Coating: 350-700 nm, f=75 mm
ACA254-100-A Support Documentation
ACA254-100-AAir-Spaced Achromatic Doublet, AR Coating: 350-700 nm, f=100 mm
ACA254-150-A Support Documentation
ACA254-150-AAir-Spaced Achromatic Doublet, AR Coating: 350-700 nm, f=150 mm
ACA254-200-A Support Documentation
ACA254-200-AAir-Spaced Achromatic Doublet, AR Coating: 350-700 nm, f=200 mm
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