Optics Software for Layout and Optimization
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`Optics Reference
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`Version 6.1
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`Lambda Research Corporation
`80 Taylor Street
`P.O. Box 1400
`Littleton, MA 01460
`
`Tel: 978-486-0766
`Fax: 978-486-0755
`
`support@lambdares.com
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`COPYRIGHT
`The OSLO software and Optics Reference are Copyright © 2001 by Lambda
`Research Corporation. All rights reserved.
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`TRADEMARKS
`Oslo® is a registered trademark of Lambda Research Corporation.
`TracePro® is a registered trademark of Lambda Research Corporation.
`GENII® is a registered trademark of Sinclair Optics, Inc.
`UltraEdit® is a registered trademark of IDM Computer Solutions, Inc.
`Adobe® and Acrobat® are registered trademarks of Adobe Systems, Inc.
`Pentium® is a registered trademark of Intel, Inc.
`Windows® 95, Windows® 98, Windows NT®, Windows® 2000 and Microsoft® are
`either registered trademarks or trademarks of Microsoft Corporation in the United
`States and/or other countries
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`247
`Standard lenses
`Lenses like the above Cooke triplet are typically designed for film cameras. The above lens has a
`50mm focal length, which suits the 24x36mm format used for 35mm cameras. The lens is not
`optimum for a typical digital camera, which has a smaller image size, because the focal length is
`too long. In this example we consider the use of the GENII error function to redesign the lens to
`have a focal length of 10mm, more suited to contemporary digital cameras. In addition, we will
`make the lens faster by 3dB, so that the paraxial specifications become 50mm efl, f/2.8, 20 degrees
`field angle.
`The steps are the following:
`• Open the demotrip lens, open the surface data spreadsheet, and right-click in the
`spreadsheet to pop-up the edit menu. Scale the lens to a focal length of 10mm. Then, set
`the entrance beam radius to 1.78571mm. Note that this makes the speed f/2.8 (use Pxc in
`the text window).
`• Change the apertures of all the surfaces to 1.8 mm so the larger beam can get through.
`With the scaled lens, the elements are too thin to support an aperture of 1.8. Increase the
`thickness of the front and back elements to 0.7mm, and the thickness of the center
`element to 0.3mm. Now the on-axis beam can get through, but the focal length is no
`longer 10mm because the thicknesses have been changed.
`• To fix the focal length, put an axial ray angle solve on the last refracting surface (6),
`setting the angle to -0.178571. This will adjust the curvature so the focal length is exactly
`10mm again. As soon as you have adjusted the curvature, remove the solve by clicking
`the button in the radius cell and selecting Direct Specification. The curvature will not be
`changed, but the constraint will be removed, and the curvature can then be used as a
`variable in optimization.
`The GENII error function is designed to hold the paraxial properties of the system at the values
`that exist at the start of optimization. It is essential that you have the right paraxial properties
`(focal length, aperture, and field) prior to beginning to optimize. Fortunately, you have just set up
`the system so that it has the correct propertures - efl = 10, fnb = 2.8, ang = 20.
`• Click on the Variables button in the surface data spreadsheet and make all the curvatures
`variable. Also make the air spaces variable. Close the variables spreadsheet but not the
`surface data spreadsheet. You will see "V's" on the appropriate buttons.
`• Use Optimize>>Generate Error Function>>GENII Ray Aberration to enter the error
`function. Accept all the defaults in the dialog box without change.
`• Change the Lens ID to something more descriptive of the current system, and save the
`lens in your private directory under a new name. The final solution in the public demo
`library is called digitrip.len, so pick a related but different name. Then close the Surface
`data spreadsheet using the Green check and immediately re-open it. This allows you to
`cancel unfortunate changes that might be made during optimization by canceling using
`the Red X button. After you have re-opened the spreadsheet (turn on Autodraw so you
`can see what is happening to your lens), you are ready to optimize it.
`• Use the Ite button in the Text window to iterate the design until it doesn't improve
`anymore. This should produce an error function of about 0.64.
`• Change the center element from F4 to a model glass, leaving the index and v-number
`unchanged, by clicking the button in the Glass column and selecting Model. Then click
`the button again and make it a special variable (RN only). In the variable spreadsheet, set
`boundaries of 1.5 to 1.8 for the RN variable. Close the variables spreadsheet.
`• Change the glass in the front and back elements to LAK33.
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` Ex. 1009
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`HP,
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