Features

• Material: N-BK7
• AR-Coated for the 350 - 700 nm Range
• Choose from Ø1/2" or Ø1" Optics
• Mounted in SM-Compatible Lens Cells

These Plano-Convex Lenses are fabricated from N-BK7, a RoHS-compliant version of BK7 glass, and feature an antireflection coating for the 350 to 700 nm range. 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.

These lenses are popular for many applications. They have a positive focal length and near-best-form shape for infinite and finite conjugate applications. Plano-convex lenses focus a collimated beam to the back focus and collimate light from a point source.

To minimize the introduction of spherical aberration, a collimated light source should be incident on the curved surface of the lens when being focused and a point light source should be incident on the planar surface when being collimated. The focal length of each lens can be calculated using a simplified thick lens equation:

f= R/(n-1).

Here n is the index of refraction and R is the radius of curvature of the lens surface.

Our mounted N-BK7 Plano-Convex lenses are available uncoated or with one of three Antireflection Coatings (-A, -B, or -C), which can reduce the amount of light reflected from each surface of the lens. The lenses with a -A coating, which is designed for the 350-700 nm range, are highlighted on this page. Lenses with a -B (650 - 1050 nm range) or -C (1050 - 1620 nm range) antireflection coating are featured elsewhere. Links to these pages are provided in the selection guide table below. Please see the Graphs tab for coating information.

N-BK7 lens kits are also available. Please click here for information.

Below is the transmission curve for N-BK7. Total Transmission is shown for a 10 mm thick, uncoated sample and includes surface reflections. Each N-BK7 plano-convex lenses can be ordered uncoated (unmounted or mounted) or with one of the following broadband AR coatings: 350 - 700 nm (unmounted or mounted) (Designated with -A), 650 - 1050 nm (unmounted or mounted) (Designated as -B), or 1050 - 1620 nm (unmounted or mounted) (Designated as -C).

These high-performance multilayer AR coatings have an average reflectance of less than 0.5% (per surface) across the specified wavelength ranges. These coatings are designed for angles of incidence between 0 and 30 degrees (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; these coatings are 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 reflectivity plots.

Click Here for Raw Data
Click to Enlarge

Click on the image to download the raw 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 plano-convex lenses.

The focal length of a thick spherical lens can be calculated using the thick lens equation below. In this expression, n_l 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.

.

When using the thick lens equation to calculate the focal length of a plano-convex lens, R₁=∞ and R₂=-R. Note that the minus sign in front of R is due to the sign convention used when deriving the thick lens equations and values of R are reported in the Specs tab as well as on the mechanical drawing for each lens. Therefore, via substitution, the thick lens equation becomes

.

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 plano-convex is focused. The principle plane positions of a thick lens can be calculated with the following equations:

and .

However, as with the thick lens equation, H' simplifies to zero and H" simplifies to

when used to calculate the principle plane locations of plano-convex lenses. f_b is the back focal length of the lens, which is often referred to as the working distance of the lens.