A zoom lens design method, july 3, 2013

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My method for designing zoom lenses, explained step by step

Text of A zoom lens design method, july 3, 2013

  • 1.A Zoom Lens Design Method Dave Shafer 1) Start with the simplest possible monochromatic design, using low-order aspherics and appropriate vignetting 2) Optimize until pretty good performance is reached3) Replace aspheric lenses, one at a time, with spherical doublets 4) Achromatize moving groups, then achromatize fixed lenses 5) Complete optimization

2. Focal length range)8 mm 30 mm (minimumSensor2/3 HDF-number 2.8, constant over the zoom rangeMechanical constraintsoverall length < 160 mm back focal distance > 20 mm number of zoom movements: 2WavelengthZoom design example specsVISDistortion75% on-axis Relative illumination @ 5.5 mm >35% Focus Range groupInfinity to 250 mm with separate focusingLets look at some relevant designs 3. Compact Zoom Example 3: n p n pDesigned by Zeiss Dodoc, Toward the global optimum in zoom lens design, SPIE 8488 Disadvantage: Very large variator group (green), 3 movements 4. 4mmRetrofocusDesigned by Zeiss10mm20mm40mmAlexander Epple SPIE contestwinning design for shortest 20X zoom with 4 aspheric lenses. This is a PNNP design. But it is f/10 and might not work well for our f/2.8 design requirements.60mm80mmCarl Zeiss SMT AG, Alexander Epple, LIT-TSDTelephotoPage 4 5. New designs for this talk PNNP30 mm f.l. PNNP was tried, with 4 aspherics. Very short only 80 mm long. But performance was not too good and it has some strong aspheres.8 mm f.l. 6. NNPP was also tried but it has bad vignetting problems. OSLOs ASA program was used to find PNNP, NNPP, and PNPP paraxial zoom solutions. PNPP has the best vignetting situation, Petzval sum, and zoom motions. Other system specs might give different preferred zoom type, like NPNP. 7. PNPP design 30 mm f.l. 21 degree field Design with 4 aspheric lenses meets the monochromatic performance goals over field and zoom range. Length = 105 mm. Spec is

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