N-BK7 and N-SF11 Bi-Concave Lenses, Uncoated

Overview
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Mounting Options
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N-BK7 and N-SF11 Bi-Concave Lenses
Lens Shape	Concave/Concave
Material	N-BK7 or N-SF11^a
Wavelength Range	N-BK7: 350 nm - 2.0 μm N-SF11: 420 nm - 2.3 μm
Design Wavelength	587.6 nm
Index of Refraction (at Design Wavelength)	N-BK7: 1.515, N-SF11: 1.778
Surface Quality	40-20 Scratch-Dig
Spherical Surface Power^b	3λ/2
Surface Irregularity (Peak to Valley)	λ/4
Diameter Tolerance	+0.0/-0.1 mm
Thickness Tolerance	±0.1 mm
Centration	≤3 arcmin
Clear Aperture	≥90% of Diameter
Focal Length Tolerance	±1%

Click Link for Detailed Specifications on the Substrate
Much like surface flatness for flat optics, spherical surface power is a measure of the deviation between the surface of the curved optic and a calibrated reference gauge, typically for a 633 nm source, unless otherwise stated. This specification is also commonly referred to as surface fit.

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.

Features

Material: N-BK7 or N-SF11
N-BK7 Wavelength Range: 350 nm - 2.0 μm
N-SF11 Wavelength Range: 420 nm - 2.3 μm
Focal Lengths from -6.0 mm to -100.0 mm Available
Spherical Surface Irregularity: λ/4

Thorlabs offers Bi-Concave lenses fabricated from either an N-BK7 or an N-SF11 substrate. These lenses are available uncoated or with one of our three popular broadband antireflection coatings deposited on both sides to reduce the amount of light reflected from each surface of the lens. the lenses on this page are uncoated and have broad wavelength ranges. Please see the Graphs tab for detailed coating curve information.

Bi-concave lenses have a negative focal length and are best used to diverge a converging beam. Similar to a plano-concave lens, a bi-concave lens can diverge a collimated beam to a virtual focus like in a Galilean-type beam expander. Since the Abbe Number of N-SF11 (25.76) is lower than that for N-BK7 (64.17), lenses fabricated from N-SF11 will exhibit higher dispersion than those fabricated from N-BK7.

Lens kits with bi-concave lenses made from N-BK7 are available.

N-BK7 and N-SF11 Bi-Concave Lens Selection Guide
Unmounted Lenses	Mounted Lenses
Uncoated	Uncoated
A Coating (350 - 700 nm)	A Coating (350 - 700 nm)
B Coating (650 - 1050 nm)	B Coating (650 - 1050 nm)
C Coating (1050 - 1700 nm)	C Coating (1050 - 1700 nm)

Quick Links to Other Spherical Singlets
Plano-Convex	Bi-Convex	Best Form	Plano-Concave	Bi-Concave	Positive Meniscus	Negative Meniscus

Click to Enlarge
Click Here for Raw Data
Above 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.

Click to Enlarge
Click Here for Raw Data
Above is the transmission curve for N-SF11. Total Transmission is shown for a 10 mm thick, uncoated sample and includes surface reflections.

N-BK7 and N-SF11 Bi-Concave Lens Selection Guide
Unmounted Lenses	Mounted Lenses
Uncoated	Uncoated
A Coating (350 - 700 nm)	A Coating (350 - 700 nm)
B Coating (650 - 1050 nm)	B Coating (650 - 1050 nm)
C Coating (1050 - 1700 nm)	C Coating (1050 - 1700 nm)

The lenses sold on this page are also available with broadband antireflective coatings, the reflectance traces of which are shown in the graph below.

These 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). 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.

Thorlabs' Standard Broadband Antireflection Coatings

Click to Enlarge
CXY1 Translation Mount and
SM1 Lens Tube Mounted in a
30 mm Cage System

Click to Enlarge
Ø1" Optic Mounted in a
ST1XY-S XY Translator

Click to Enlarge
LMR1 Fixed Mount with Ø1" Lens

Click to Enlarge
LM2XY Translating Mount with Ø2" Lens

Recommended Mounting Options for Thorlabs Lenses
Item #		Mounts for Ø2 mm to Ø10 mm Optics
Imperial	Metric	Mounts for Ø2 mm to Ø10 mm Optics
(Various)		Fixed Lens Mounts and Mini-Series Fixed Lens Mounts for Small Optics, Ø5 mm to Ø10 mm
(Various)		Small Optic Adapters for Use with Standard Fixed Lens Mounts, Ø2 mm to Ø10 mm
Item #		Mounts for Ø1/2" (Ø12.7 mm) Optics
Imperial	Metric	Mounts for Ø1/2" (Ø12.7 mm) Optics
LMR05	LMR05/M	Fixed Lens Mount for Ø1/2" Optics
MLH05	MLH05/M	Mini-Series Fixed Lens Mount for Ø1/2" Optics
LM05XY	LM05XY/M	Translating Lens Mount for Ø1/2" Optics
SCP05		16 mm Cage System, XY Translation Mount for Ø1/2" Optics
(Various)		Ø1/2" Lens Tubes, Optional SM05RRC Retaining Ring for High-Curvature Lenses (See Below)
Item #		Mounts for Ø1" (Ø25.4 mm) Optics
Imperial	Metric	Mounts for Ø1" (Ø25.4 mm) Optics
LMR1	LMR1/M	Fixed Lens Mount for Ø1" Optics
LM1XY	LM1XY/M	Translating Lens Mount for Ø1" Optics
ST1XY-S	ST1XY-S/M	Translating Lens Mount with Micrometer Drives (Other Drives Available)
CXY1		30 mm Cage System, XY Translation Mount for Ø1" Optics
(Various)		Ø1" Lens Tubes, Optional SM1RRC Retaining Ring for High-Curvature Lenses (See Below)
Item #		Mount for Ø1.5" Optics
Imperial	Metric	Mount for Ø1.5" Optics
LMR1.5	LMR1.5/M	Fixed Lens Mount for Ø1.5" Optics
(Various)		Ø1.5" Lens Tubes, Optional SM1.5RR Retaining Ring for Ø1.5" Lens Tubes and Mounts
Item #		Mounts for Ø2" (Ø50.8 mm) Optics
Imperial	Metric	Mounts for Ø2" (Ø50.8 mm) Optics
LMR2	LMR2/M	Fixed Lens Mount for Ø2" Optics
LM2XY	LM2XY/M	Translating Lens Mount for Ø2" Optics
CXY2		60 mm Cage System, XY Translation Mount for Ø2" Optics
(Various)		Ø2" Lens Tubes, Optional SM2RRC Retaining Ring for High-Curvature Lenses (See Below)
Item #		Adjustable Optic Mounts
Imperial	Metric	Adjustable Optic Mounts
LH1	LH1/M	Adjustable Mount for Ø0.28" (Ø7.1 mm) to Ø1.80" (Ø45.7 mm) Optics
LH2	LH2/M	Adjustable Mount for Ø0.77" (Ø19.6 mm) to Ø2.28" (Ø57.9 mm) Optics
VG100	VG100/M	Adjustable Clamp for Ø0.5" (Ø13 mm) to Ø3.5" (Ø89 mm) Optics
SCL03	SCL03/M	Self-Centering Mount for Ø0.15" (Ø3.8 mm) to Ø1.77" (Ø45.0 mm) Optics
SCL04	SCL04/M	Self-Centering Mount for Ø0.15" (Ø3.8 mm) to Ø3.00" (Ø76.2 mm) Optics
LH160C	LH160C/M	Adjustable Mount for 60 mm Cage Systems, Ø0.50" (Ø13 mm) to Ø2.00" (Ø50.8 mm) Optics
SCL60C	SCL60C/M	Self-Centering Mount for 60 mm Cage Systems, Ø0.15" (Ø3.8 mm) to Ø1.77" (Ø45.0 mm) Optics

Mounting High-Curvature Optics

Thorlabs' retaining rings are used to secure unmounted optics within lens tubes or optic mounts. These rings are secured in position using a compatible spanner wrench. For flat or low-curvature optics, standard retaining rings manufactured from anodized aluminum are available from Ø5 mm to Ø4". For high-curvature optics, extra-thick retaining rings are available in Ø1/2", Ø1", and Ø2" sizes.

Extra-thick retaining rings offer several features that aid in mounting high-curvature optics such as aspheric lenses, short-focal-length plano-convex lenses, and condenser lenses. As shown in the animation to the right, the guide flange of the spanner wrench will collide with the surface of high-curvature lenses when using a standard retaining ring, potentially scratching the optic. This contact also creates a gap between the spanner wrench and retaining ring, preventing the ring from tightening correctly. Extra-thick retaining rings provide the necessary clearance for the spanner wrench to secure the lens without coming into contact with the optic surface.

Posted Comments:

rob.roberts (posted 2015-10-08 10:26:16.703)

Please check the focal length of the LD2060. Given the radius of curvature and center thickness, it seems that the focal length would be approximately -23mm rather than -15mm. Thank you.

besembeson (posted 2015-10-08 04:56:31.0)

Response from Bweh at Thorlabs USA: The focal length is correct. If you have used Zemax software for lens design, you will notice that you have flexibility in adjusting lens parameters to meet your design constraints.

max.schiller (posted 2014-09-18 11:32:19.52)

Hello. Is there an actual ZEMAX Lens Katalog of all Thorlabs lenses for download available? Max

sharrell (posted 2014-09-25 10:26:04.0)

A response from Sean at Thorlabs: Thank you for your feedback. Currently we do not have the Zemax catalog available for download as a single file. We are looking into ways to add the Zemax catalog to our site and ensure that it remains reasonably up to date as we add new products. In the meantime our catalog is available within Zemax--and if you need a particular optic that is not available within the catalog in Zemax it can often be found by clicking on the red "Docs" icon next to each item number below.

mohomed (posted 2009-07-01 13:11:55.0)

Great Product! alert(XSS)

Ø6 mm Bi-Concave Lenses

Item #	Diameter	Focal Length	Diopter^a	Radius of Curvature	Center Thickness	Edge Thickness^b	Back Focal Length^c	Reference Drawing
LD2746	6.0 mm	-6.0 mm	-166.7	-9.7 mm	1.5 mm	2.5 mm	-6.4 mm

Suggested Fixed Lens Mounts: LMR6(/M)

Reciprocal of the Focal Length in Meters
Edge Thickness Given Before 0.2 mm at 45° Typical Chamfer
Measured at the Design Wavelength, 587.6 nm

Ø9 mm Bi-Concave Lenses

Item #	Diameter	Focal Length	Diopter^a	Radius of Curvature	Center Thickness	Edge Thickness^b	Back Focal Length^c	Reference Drawing
LD2568	9.0 mm	-9.0 mm	-111.1	-14.4 mm	2.0 mm	3.4 mm	-9.5 mm

Suggested Fixed Lens Mounts: LMR9(/M)

Reciprocal of the Focal Length in Meters
Edge Thickness Given Before 0.2 mm at 45° Typical Chamfer
Measured at the Design Wavelength, 587.6 nm

Ø1/2" (Ø12.7 mm) Bi-Concave Lenses

Item #	Diameter	Focal Length	Diopter^a	Radius of Curvature	Center Thickness	Edge Thickness^b	Back Focal Length^c	Reference Drawing
LD2060	1/2"	-15.0 mm	-66.6	-24.0 mm	3.0 mm	4.7 mm	-15.7 mm
LD1357	1/2"	-50.0 mm	-20.0	-52.1 mm	3.5 mm	4.3 mm	-51.0 mm

Suggested Fixed Lens Mount: LMR05(/M)

Reciprocal of the Focal Length in Meters
Edge Thickness Given Before 0.2 mm at 45° Typical Chamfer
Measured at the Design Wavelength, 587.6 nm

Ø1" (Ø25.4 mm) Bi-Concave Lenses

Item #	Diameter	Focal Length	Diopter^a	Radius of Curvature	Center Thickness	Edge Thickness^b	Back Focal Length^c
LD2297	1"	-25.0 mm	-40.0	-39.6 mm	3.0 mm	7.2 mm	-25.6 mm
LD1464	1"	-50.0 mm	-20.0	-52.0 mm	3.0 mm	6.1 mm	-50.8 mm
LD1170	1"	-75.0 mm	-13.3	-77.9 mm	3.5 mm	5.6 mm	-75.9 mm
LD1613	1"	-100.0 mm	-10.0	-103.7 mm	4.0 mm	5.6 mm	-101.0 mm

Suggested Fixed Lens Mounts: LMR1(/M) & SM1L05

Reciprocal of the Focal Length in Meters
Edge Thickness Given Before 0.2 mm at 45° Typical Chamfer
Measured at the Design Wavelength, 587.6 nm

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