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Multi-element lenses

Singlet lens performance is limited by its aberrations. To achieve better optical performance,  multi-element lens designs are required.  A multi-element lens uses a combination of various singlet elements to minimize the overall aberrations. This is possible because some of the singlet element may have positive aberrations while others may have negative aberrations.  By choosing the element combination judiciously, the overall aberrations can be minimized to an acceptable level. The lens elements can be made of different materials, and are of different shapes,  and different surface curvatures.  The process of determining the optimal lens element configuration is performed by a lens designer with the aid of appropriate computer software. The following is a list of well-known lens configurations that provide greatly improved performance for the chosen applications.

Achromatic doublets
An achromatic doublet is made of two singlet lens elements, often cemented together as one unit.  This configuration can eliminate the spherical and longitudinal aberration completely. In fact,  diffraction limited performance can be achieved in many cases.  We provide a range of diffraction-limited doublet lenses that were optimized for the visible spectrum.  You can also use our lens design wizard to design custom doublet lenses. Their major limitations are: (1) Off-axis performance of achromatic doublets deteriorates rapidly with the field of view, and (2) The f/# of achromatic doublet lenses are limited to about f/3 or higher.
Achromatic doublet with matching aplanatic meniscus lens

By adding a properly designed meniscus lens,  it is possible to extend the relative aperture o of a doublet by the index of refraction of the meniscus lens.  A meniscus lens can be designed to reduce the overall focal length without introducing additional spherical aberration. Such a meniscus lens is known as aplanatic form. We provide a list of standard aplanatic meniscus lenses. You can also use our lens design wizard to create custom aplanatic meniscus lenses. Because the meniscus lens is not achromatized,  the overall system will have longitudinal chromatic aberration.


















Symmetric lens pairs
For finite conjugate applications where both the object and the image are at finite distance, 
a pair of identical lenses may be considered. This configuration is provides nearly perfect performance if the object distance and image distance are approximately equal. The following diagram illustrates the performance advantages of lens pair vs a bi-convex lens.
Cooke triplet lenses
All above lens configurations provide improved performance on-axis only.  To achieve good performance both on- and off-axis,  more complex lens forms are required.  Cooke triplet is a well-know lens form that provides good imaging performance over a field of view of +/- 20-25 degrees.  Many consumer grade film cameras use lenses of this type.
 
Double Gaussian lens
To achieve higher image quality and to increase the relative aperture (i.e, lowering the f/#) over a Cooke triplet,  a lens form known as "Double Gaussian" is used.  The double Gaussian design uses two cemented doublets and two companion singlets.  This lens form offers excellent performance over a significant field of view, and the relative aperture can be as low as F/1.2.  Double Gaussian lenses are used in many SLR lenses, and C-mount lenses for electronic cameras.

Reverse telephoto lens

To provide more field of view coverage,  a reverse telephoto lens type is often used.  The front lens group has negative power which reduces the input field of view.  The second group is positive and it does the focus.  With this configuration,  the field of view can be increased to +/-35 degrees.  The other advantage of this configuration is that the system back focal length can be longer than the effective focal length.  This property makes this design form very attractive to short focal length lenses commonly seen on digital cameras.
Wide-angle "fisheye" lenses
Wide-angle "fisheye" lenses are sometimes required for security and surveillance applications.  These lenses require significant number of components. It is also worth noting that the distortion of such lenses can be very significant.

Custom lenses
There is no universal lens design for all applications.  To achieve the best performance/cost trade-offs, many applications will require custom lens designs.  The goal of a custom lens design is to reach an acceptable performance level for the intended application while minimizing the cost.  Modern lens design software can provide a great deal of computation power that allows many design configurations to be evaluated within a short period of time.  However,  computer software does not substitute for experience, judgment and intuition. Manufacturability is often the key determinant of the success of any optical design.   Custom optical solutions.


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