1998 International Optical Design Conference
Lens Design Problem
--------------------------------------------------------------------------------
CORRECTION: February 9, 1998 - Image diameter (paraxial) changed to Detector size (non-paraxial)
--------------------------------------------------------------------------------
CLARIFICATION: April 24, 1998 - Relative Illumination defined; Mass and Edge Thickness parameter clarified; RMS spot ’size’ changed to ’radius’
--------------------------------------------------------------------------------
Introduction:
With the exception of some very successful solid catadioptric systems, the all-cemented objective has been neglected as a genre since the arrival of anti-reflection coatings. There are reasons for this: we depend heavily on the large refractive index differences between glass and air! This task promises to reveal just how important this dependence is to us. On the other hand, the air-glass interface only too easily leads to total internal reflection. In a sense, this task has a family relationship with the monochromatic quartet problem of the 1990 OSA Lens Design conference, in that for the latter problem it was clear that one was restricted to 8 air-glass interfaces - here you are restricted to 2. You will notice that in this task there is no restriction to refracting surfaces and it is anticipated that some of the solutions might be catadioptric.
- Jon Maxwell/Imperial College, London
Design Parameters:
Configuration solid (all-cemented) lens
no airspaces (except last lens surface to image)
in-line refractive or solid catadioptric
no plastic elements, no diffractives, no GRIN
F/number
(on-axis)
(paraxial) in-line refractive: F/1.8
obscured systems MUST have an unobscured
aperture AREA equivalent to an F/1.8 lens
any unobscured system with beamsplitter: F/1.3
Detector size
(non-paraxial) 50 mm circular
Focal length unspecified - set by mass constraint
Spectral band white light (C d F)
Spectral weights 656.2nm:1 586.7nm:1 486.1nm:1
Mass less than 1 Kg; Mass is to be calculated based on the size of the defined apertures on each surface. This may require that the lens edges be a series of tapered cones, connected by the different surface diameters. The entrant should have defined diameters for each surface, these are the same apertures used to calculate vignetting and edge thickness.
Relative Illumination greater than 70% at full field; RI defined as: (Number of rays successfully traced at max field integrated over the projected solid angle of the exit pupil at max field) divided by (Number of rays successfully traced on-axis integrated over the projected solid angle of the exit pupil on-axis)
Image surface flat (plane) (and in air)
Object at infinity (and in air)
Merit function M = on-axis geometric polychromatic RMS spot radius
+ 0.7 field geometric polychromatic RMS spot radius
+ 0.8 field geometric polychromatic RMS spot radius
+ 1/2(full field geometric polychromatic RMS spot radius)
Surface shapes spherical only
Materials catalog glasses only (e.g. Schott, Ohara, Hoya, …)
no plastics, no crystalline (e.g. MgFl etc.)
Edge thicknesses 0 mm at maximum aperture consistent with vignetting and mass calculation.
Evaluation:
The merit function, M, will be evaluated based on polychromatic, geometric RMS spot size for the specified F/number (or T/number), spectral weighting, image size, and vignetting (relative illumination). Systems that exceed the mass requirement (computed using the supplied optical clear apertures or the minimum clear apertures required to meet the relative illumination requirement) will be penalized in the merit function by the CUBE of the computed weight divided by 1Kg. There is no competitive advantage to producing a system lighter than 1 Kg (unless of course it produces a better merit function). Lenses that do not meet the effective F/number, image size, or relative illumination requirements (within ~2%, as evaluated by the independent team described below) will not be considered in the competition.
Catadioptric solutions:
If there is a large discontinuity between in-line refractive and catadioptric designs, two separate categories may be created. The effective collecting area after accounting for obscuration must equal or exceed that of the equivalent unobscured system. Catadioptric solutions with beamsplitters will not be considered in the competition.
Noncompliant Designs:
Designs with noncompliant features such as diffractive surfaces, gradient index materials, nonspherical surfaces, liquid lenses, or materials that are not in the catalogs (any vintage) of a mainstream visible glass supplier will not be included in the competition, but at the discretion of the moderator/committee, may receive an honorable mention. The committee reserves the right to remove a lens from the competitive list that is more creative than we can currently anticipate.
Noncompliant designs - Diffractive surfaces:
There is already enough interest in diffractive solutions that they are likely to be an honorable mention category, so the following guidelines are provided. Diffractives should be placed on the external surfaces. The F/number of a design should be faster due to transmission of 90% per diffractive. Relative illumination should be higher, due to falloff of throughput with wavelength. The minimum line spacing should be greater than 5 microns.
Honorable Mention:
Some criteria for honorable mention might include, best design with the smallest number of glasses, best design with the largest number of glasses, design with the longest focal length, design with the highest, or lowest variation in focus with a 10 degree C temperature change.
Other Comments:
The stop can be anywhere in the lens system.
The focal length is not specified, it is controlled by the weight requirement
The image plane clearance need only be greater than 0
Distortion does not have a requirement
Glass transmission will be assumed to be 1.0
Lens units of mm is preferred
Submission of Solutions:
If at all possible, please submit your solutions in electronic format (by e-mail or disk) to the software vendor whose software was used to perform the design AND also send a copy to: gardner@ods-inc.com (Leo Gardner)
Vendors will be asked to independently verify each solution submitted electronically in their software format and provide a common data package. If your software vendor does not have the resources to support this endeavor, please contact Leo Gardner to see what can be arranged. The results will be compiled and presented by Brian Caldwell and Leo Gardner of Optical Data Solutions.
If you cannot provide an electronic lens file, mail (do not fax) your entry to Leo Gardner, Optical Data Solutions (Mass. Office), 151 Nehoiden Street, Needham, MA, 02192 USA
Deadline:
To allow time to compile all the results, please submit solutions before May 4, 1998. We cannot guarantee that solutions submitted after that date will be included in the presentation. We also cannot guarantee that a complex solution that cannot be submitted electronically will be included in the competition, regardless of when it is submitted.
Presentation of Results:
The results will be compiled and presented at a special session, as at past conferences. The lens design problem session is scheduled for Wednesday evening, June 10, at 8pm. You do not have to attend the conference to be included in the competition. You may request that your solution be anonymous. The committee has decided that the software package used for a design will not be reported at the presentation session.
Last Minute Rule Changes or Additions:
If there are any last minute changes to these instructions, they will be posted on various web pages including OSA and SPIE and most of the software vendors listed above.