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Mounted N-BK7 Bi-Convex Lenses (Uncoated)


  • Positive Focal Length for Use at Finite Conjugates
  • Uncoated Wavelength Range: 350 - 2000 nm
  • SM05-Threaded or SM1-Threaded Mounts

LB1869-ML

(Ø1")

LB1187-ML

(Ø1/2")

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N-BK7 Bi-Convex Spherical Singlets
Lens Shape Convex/Convex
Material N-BK7 (Grade A)
Wavelength Rangea 350 nm - 2.0 μm (Uncoated)
Design Wavelength 633 nm 
Index of Refraction 1.515 (@ 633 nm)
Surface Quality 40-20 Scratch-Dig
Surface Irregularity λ/4
Spherical Surface Power 3λ/2
Abbe Number vd=64.17
Centration ≤3 arcmin
Clear Aperture Ø1/2" lenses: >Ø11.04 mm
Ø1" lenses: >Ø22.86 mm
Diameter Tolerance +0.00 mm / -0.10 mm
Focal Length Tolerance ±1%
  • Also available with a -A coating for the 350 - 700 nm range, a -B coating for the 650 - 1050 nm range, or a -C coating for the 1050 - 1700 nm range.

Features

  • Material: N-BK7
  • Wavelength Range: 350 - 2000 nm (Uncoated)
  • Available Sizes:  Ø1/2" and Ø1"
  • Focal Lengths Available from 15.0 mm to 1.0 m
  • Well Suited for Many Finite Imaging Applications
  • Offers Excellent Transmittance Throughout the Visible and Near Infrared
  • Mounted in SM-Compatible Lens Cells

Thorlabs' Mounted Uncoated N-BK7 Bi-Convex Lenses are popular for many finite imaging applications. This type of lens is best suited for use in situations where the object and image are on opposite sides of the lens and the ratio of the image and object distances (conjugate ratio) is between 0.2 and 5. 

N-BK7 is probably the most common optical glass used for high-quality optical components. It is typically chosen whenever the additional benefits of UV fused silica (i.e., good transmission further into the UV and a lower coefficient of thermal expansion) are not necessary. These Ø1/2" and Ø1" lenses are mounted in SM05- (0.535"-40) and SM1- (1.035"-40) compatible mounts, respectively.

Although this page features our uncoated bi-convex lenses, these lenses are also available with one of three antireflection coatings (-A, -B, or -C) deposited on both sides to reduce the amount of light reflected from each surface. Links to each of these pages can be found in the table to the right. Please see the Graphs tab for coating details.

Lens kits are available. Please click here for information.

Zemax Files
Click on the red Document icon next to the item numbers below to access the Zemax file download. Our entire Zemax Catalog is also available.
Optic Cleaning Tutorial
Optical Coatings and Substrates
Quick Links to Other Spherical Singlets
Plano-Convex Bi-Convex Best Form Plano-Concave Bi-Concave Positive Meniscus Negative Meniscus

Below is the transmission curve for N-BK7, a RoHS-compliant form of BK7. Total Transmission is shown for a 10 mm thick, uncoated sample and includes surface reflections. Each N-BK7 bi-convex lens can be ordered uncoated or with one of the following broadband AR coatings: 350 - 700 nm (designated as -A), 650 - 1050 nm (designated as -B), or 1050 - 1700 nm (designated as -C).

Our high-performance multilayer AR coatings have an average reflectance of less than 0.5% (per surface) across the specified wavelength ranges and provide good performance for angles of incidence (AOI) between 0° and 30° (0.5 NA). For optics intended to be used at large incident angles, consider using a custom coating optimized at a 45° angle of incidence; this custom coating is effective from 25° to 52°. The plot shown below indicates the performance of the standard coatings in this family as a function of wavelength. Broadband coatings have a typical absorption of 0.25%, which is not shown in the reflectance plots.

N-BK7 Transmittance
Click to Enlarge

Click Here for Raw Data


Thorlabs' Standard Broadband Antireflection Coatings

N-BK7 Index of Refraction
Click here for detailed substrate data.
In the thick lens equation, use the index of refraction for N-BK7 at the wavelength of interest to approximate the wavelength-dependent focal length of any of the bi-convex lenses.

The focal length of a thick spherical lens can be calculated using the thick lens equation below. In this expression, nl is the index of refraction of the lens, R1 and R2 are the radii of curvature for surfaces 1 and 2, respectively, and d is the center thickness of the lens.

thick lens equation

For bi-convex lenses, where the front and back radii of curvature are equal in magnitude and opposite in sign, R1 = -R2 = R, we have

Lens Equation Final Biconvex

The focal length of the lens calculated using the simplified thick lens equation directly above is the distance between the second (back) principle plane (H") and the position at which a collimated beam incident on the curved surface of the bi-convex is focused. The same analysis can be performed using a point source and the first (front) principle plane (H'). The principle plane positions of a thick lens can be calculated with the following equations:

principal plane equation one and Principal plane equation two

Again, for the same bi-convex lens, R1 = -R2 = R, we can solve for H' and H' :

Principle Plane Final


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Ø1/2" Mounted N-BK7 Bi-Convex Lenses (Uncoated)

Item #DiameterFocal LengthaDiopterbRadius of CurvatureCenter ThicknessEdge ThicknessBack Focal LengthaWorking DistanceaHousingReference
Drawing
LB1092-ML 1/2" 15.0 mm +66.7 14.6 mm 4.7 mm 1.8 mm 13.4 mm 11.8 mm SM05-Threaded
Mount
Bi-Convex Lens Drawing
LB1450-ML 1/2" 20.0 mm +50.0 19.9 mm 3.9 mm 1.8 mm 18.7 mm 16.7 mm
LB1014-ML 1/2" 25.0 mm +40.0 25.2 mm 3.4 mm 1.8 mm 23.8 mm 21.7 mm
LB1258-ML 1/2" 30.0 mm +33.3 30.4 mm 3.1 mm 1.8 mm 28.9 mm 26.6 mm
LB1378-ML 1/2" 40.0 mm +25.0 40.7 mm 2.8 mm 1.8 mm 39.1 mm 36.7 mm
LB1844-ML 1/2" 50.0 mm +20.0 51.1 mm 2.6 mm 1.8 mm 49.1 mm 46.6 mm
LB1187-ML 1/2" 100.0 mm +10.0 102.6 mm 2.2 mm 1.8 mm 99.3 mm 96.7 mm
  • The focal length tolerance is ±1%. The back focal length and working distance values here are referenced to the design focal length.
  • Reciprocal of the Focal Length in Meters
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
LB1092-ML Support Documentation
LB1092-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1/2", f = 15.0 mm, Uncoated
$38.76
Today
LB1450-ML Support Documentation
LB1450-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1/2", f = 20.0 mm, Uncoated
$38.51
Today
LB1014-ML Support Documentation
LB1014-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1/2", f = 25.0 mm, Uncoated
$36.72
Today
LB1258-ML Support Documentation
LB1258-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1/2", f = 30.0 mm, Uncoated
$36.47
Today
LB1378-ML Support Documentation
LB1378-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1/2", f = 40.0 mm, Uncoated
$35.96
Today
LB1844-ML Support Documentation
LB1844-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1/2", f = 50.0 mm, Uncoated
$38.25
Today
LB1187-ML Support Documentation
LB1187-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1/2", f = 100.0 mm, Uncoated
$35.96
Today

Ø1" Mounted N-BK7 Bi-Convex Lenses (Uncoated)

Item #DiameterFocal LengthaDiopterbRadius of CurvatureCenter ThicknessEdge ThicknessBack Focal LengthaWorking DistanceaHousingReference
Drawing
LB1761-ML 1" 25.4 mm +39.8 24.5 mm 9.0 mm 1.9 mm 22.2 mm 21.5 mm SM1-Threaded
Mount
Bi-Convex Lens Drawing
LB1811-ML 1" 35.0 mm +28.6 34.9 mm  6.8 mm 2.0 mm 32.7 mm 31.0 mm
LB1471-ML 1" 50.0 mm +20.3 50.6 mm  5.2 mm 2.0 mm 48.2 mm 44.7 mm
LB1901-ML 1" 75.0 mm +13.3 76.6 mm  4.1 mm 2.0 mm 73.6 mm 70.7 mm
LB1676-ML 1" 100.0 mm +10.1 102.4 mm 3.6 mm 2.0 mm 98.8 mm 95.7 mm
LB1904-ML 1" 125.0 mm +8.1 128.2 mm 3.3 mm 2.0 mm 123.9 mm 120.7 mm
LB1437-ML 1" 150.0 mm +6.7 154.0 mm 3.1 mm 2.0 mm 149.0 mm 145.7 mm
LB1945-ML 1" 200.0 mm +5.0 205.6 mm 2.8 mm 2.0 mm 199.1 mm 195.6 mm
LB1056-ML 1" 250.0 mm +4.0 257.1 mm 2.6 mm 2.0 mm 249.1 mm 245.6 mm
LB1779-ML 1" 300.0 mm +3.3 308.6 mm 2.5 mm 2.0 mm 299.2 mm 295.6 mm
LB1391-ML 1" 400.0 mm +2.5 411.7 mm 2.4 mm 2.0 mm 399.2 mm 395.6 mm
LB1869-ML 1" 500.0 mm +2.0 514.7 mm 2.3 mm 2.0 mm 499.2 mm 495.5 mm
LB1475-ML 1" 750.0 mm +1.3 772.2 mm 2.2 mm 2.0 mm 749.3 mm 745.6 mm
LB1409-ML 1" 1000.0 mm +1.0 1029.8 mm 2.2 mm 2.0 mm 999.3 mm 995.6 mm
  • The focal length tolerance is ±1%. The back focal length and working distance values here are referenced to the design focal length.
  • Reciprocal of the Focal Length in Meters
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
LB1761-ML Support Documentation
LB1761-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 25.4 mm, Uncoated
$40.29
Today
LB1811-ML Support Documentation
LB1811-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 35.0 mm, Uncoated
$34.94
Today
LB1471-ML Support Documentation
LB1471-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 50.0 mm, Uncoated
$37.23
Today
LB1901-ML Support Documentation
LB1901-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 75.0 mm, Uncoated
$36.72
Today
LB1676-ML Support Documentation
LB1676-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 100.0 mm, Uncoated
$36.21
Today
LB1904-ML Support Documentation
LB1904-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 125.0 mm, Uncoated
$36.21
Today
LB1437-ML Support Documentation
LB1437-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 150.0 mm, Uncoated
$35.45
Today
LB1945-ML Support Documentation
LB1945-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 200.0 mm, Uncoated
$35.19
Today
LB1056-ML Support Documentation
LB1056-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 250.0 mm, Uncoated
$34.94
Today
LB1779-ML Support Documentation
LB1779-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 300.0 mm, Uncoated
$34.94
Today
LB1391-ML Support Documentation
LB1391-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 400.0 mm, Uncoated
$34.94
Today
LB1869-ML Support Documentation
LB1869-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 500.0 mm, Uncoated
$34.94
Today
LB1475-ML Support Documentation
LB1475-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 750.0 mm, Uncoated
$34.94
Today
LB1409-ML Support Documentation
LB1409-MLCustomer Inspired! Mounted N-BK7 Bi-Convex Lens, Ø1", f = 1000.0 mm, Uncoated
$34.43
Today
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