SCHOTT AGAs this illustration indicates, the lens employs a full seven elements of extra low dispersion glass, including three of large diameter at the front for maximum aberration control. This optical formula provides superior image quality that will be obvious particularly at the edges of images made with a full-frame DSLR.ED GlassColor correction in optical systemsor why optical design needs fluoro-phosphate glassesDr. Ralf Jedamzik, Application Manager, SCHOTT Advanced Optics Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 http://www.photocrati.com/nikon-70-200mm-f2-8g-af-s-ed-vr-ii-lens-review-field-test-report/SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGOptical glasses are mainly categorized according to their refractive index and Abbe number2Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 SCHOTT Advanced Optics Color correction in optical systems SCHOTT AG3Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 n = 1.487air n1glassn212) sin() sin(nn=|on = 2.02The world of optical glassThe refractive index n is a measure for the deflection of light in transition to a different mediumo|SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGThe Abbe number is a measure for the change of refractive index with the wavelength (dispersion)4Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 C Fddn nn=1vThe higher the Abbe number the lower the dispersionC Fn n dnwavelength in mRefractive index1.531.491.510.3 0.4 0.5 0.6 0.7 0.8SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGRefraction of different glasses as seen with a prism5Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 Flint glasses: high refractive index + high dispersionCrown glasses:low refractive index +low dispersionN-FK58 XLDSCHOTT Advanced Optics Color correction in optical systems SCHOTT AGChromatic aberration: color fringes in high resolution lens systems (example tele zoom lens)6Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 Chromatic aberrationshow stopper forhigh resolution opticsSCHOTT Advanced Optics Color correction in optical systems SCHOTT AGChromatic aberration of a single lens: blue refraction (B) is stronger than red refraction (R)7Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 GRBSCHOTT Advanced Optics Color correction in optical systems SCHOTT AGThe size of the chromatic aberration of a single lens is the quotient of the focal length and the Abbe number8Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 = R B = :: = nd 1nP nCD= 1] = n 1 1R1 1R2The longitudinal chromatic aberration error is proportional to the focal length and decreases with increasing Abbe number.Large Abbe number => low chromatic aberration! SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGCorrection of chromatic aberration with two lenses:9Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 Focal length of two lenses with short distance:Achromatic condition (R= B):v = Abbe numberAbbe number is always > 0,1or 2< 0 The achromat11 + 12 = 111 :1 +12 :2 = uclassical: Fraunhofer BK7 and F2crown glass flint glasswhite lightachromat achromat imageSCHOTT Advanced Optics Color correction in optical systems SCHOTT AGPositive lens: crown glass Negative lens: flint glassAt fixed focal length of the system (example 100 mm), the focal length of each single lens is larger if the Abbe number difference is large.Large focal length of single lenses = less lens bending = less monochromatic image aberrationsAchromat: large Abbe number difference between crown and flint glass needed!10Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 -200-150-100-5005010010 20 30 40 5018.1833.3346.1557.1466.67 22.22 50.00 85.71133.33 200.00Abbe # Difference crown-flintFocallength, crown, flintf (crown)f (flint) SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGThe achromat is corrected for two wavelengths: but an error remains, the secondary spectrum!Color error diagramExample: Achromat with 100 mm focal length (SCHOTT N-BK7, F2)has an color error of 0.5 mmThe single SCHOTT N-BK7lens has a color error of 15.8 mm11Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 AchromatSecondaryspectrumSingle lensPos.e.g. VIS21ASCHOTT Advanced Optics Color correction in optical systems SCHOTT AGThe reason for the secondary spectrum is the different bending of the dispersion curves of crown and flint glasses12Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 The secondary spectrum is small if the bending of the dispersion curve of the crown and flint glass is the same: glasses with anomalous partial dispersionCalculated from datasheet Sellmeier coefficients.SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGF gn n C Fn n C FF gF gn nn nP=,The partial dispersion is a measure for the bendingof the dispersion curve13Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 Principle dispersionRelative Deflection of Rays in 1 m Distance [mm]SF66 Dispersion Angle of Incidence 65 degr-LineC-Lined-Linee-LineF-Lineg-LineRelative partial dispersionPartial dispersionN-SF66SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGIn the diagram relative partial dispersion versus Abbe number, many glasses are located on a line called normal line14Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 The line is given by the glasses K7 and F2 (be careful, other glass vendors have different definitions)) 001682 , 0 6438 , 0 (, dC FF gF gn nn nP v = A Abbe number vdNormal lineSCHOTT Advanced Optics Color correction in optical systems SCHOTT AGThe slope of the normal line is directly proportional to the secondary color error!15Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 An achromat built with two glasses only on the normal line has always the same secondary color error. The longer the focal length of the lens the more critical the color error!Glasses with anomalous partial dispersion are located away from the normal line!SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGThe smaller the slope of the two partners in the PgF diagram, the smaller the secondary spectrum and the better the color correction! Without PK/FK glasses no color correction possible!16Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 PK/ FK glasses and short flint glasses (KZFS glasses) have a very pronounced anomalous partial dispersionLow slopes are possible with this combinationSCHOTT Advanced Optics Color correction in optical systems SCHOTT AGIdeal: position of CaF2, but expensive and sensitive pro-cessing. Alternative: Fluoro-phosphate glasses on CaF2 position17Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 CaF2SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGOn the way to CaF2! Extremely low dispersion glasses (XLD) Target: better processability!XLD glass N-FK58 successful production run! 18Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 optical position:= 1.45600,= 90.80 extremely low dispersion excellent processing properties offers outstanding apochromatic correction capabilities in combination with SCHOTT KZFS glasses (e.g. N-KZFS4/5/8/11) supplements the low dispersion glass portfolio of N-PK52A and N-FK51A CaF2N-FK58dvdnSCHOTT Advanced Optics Color correction in optical systems SCHOTT AG19Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 SCHOTT has improved its melting capabilities for the production of low dispersion glasses. During a recent melting campaign for N-PK52A and N-FK51A, development of a new extremely low dispersion (XLD) glass N-FK58 was accomplished by a successful production runWe are not selling glass, we are selling properties!Most anomalous dispersion glasses are available in step 0.5!Highly accurate and economic metrology is an important prerequisite for the success!SCHOTT Advanced Optics Color correction in optical systems SCHOTT AG nd= 1.45600, vd= 90.80 extremely low dispersion excellent processing properties outstanding apochromatic correction capabilities in combination with SCHOTT KZFS glasses (e.g. N-KZFS4/5/8/11) supplements the low dispersion glass portfolio of N-PK52A and N-FK51A The datasheet of XLD glass N-FK58 is currently generated and will be available soon.N-FK58 XLD: A new extremely low dispersion glass with excellent processing properties20Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGN-FK58 XLD: A new extremely low dispersion (XLD) glass with excellent processing properties21N-FK58Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGN-FK58 XLD: A new extremely low dispersion (XLD) glass with high internal transmittance! 22200 300 400 500 600 7000,20,30,40,50,60,70,80,91,0internal transmittancewavelength [nm]N-FK58, 25 mm competitor 1 competitor 2 competitor 3 competitor 4Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGSupporting glasses: SCHOTTs N-KZFS4 shows the largest deviation from the normal line compared to the competition23Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 -0,012-0,01-0,008-0,006-0,004-0,0020N-KZFS4 N-KZFS5 N-KZFS8APgFSCHOTTcompetitor 1competitor 2competitor 3SCHOTT Advanced Optics Color correction in optical systems SCHOTT AGSCHOTTs N-PK52A: High transmission up to 4 m24Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 1.0Wavelength (nm)Spectraltransmittance0.80.70.60.50.40.30.20.10.00.92500 3000 3500 4000 4500 5000 5500 600041-201400156-05 N-PK52A 24.09.2013 16:50 1.99 mm 41-201400156-06 N-PK52A 25.09.2013 23:00 1.99 mm 41-201400156-07 N-PK52A 29.09.2013 02:35 1.99 mmSCHOTT Advanced Optics Color correction in optical systems SCHOTT AGHigh end applications need glasses with anomalous partial dispersion25Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 Fluoro-phosphate glassesare used as LD, ED, ELD or SLD lenses in many applications. SCHOTT offers all glasses that are neededfor high quality designs!As this illustration indicates, the lens employs a full seven elements of extra low dispersion glass, including three of large diameter at the front for maximum aberration control. This optical formula provides superior image quality that will be obvious particularly at the edges of images made with a full-frame DSLR.ED Glasshttp://www.photocrati.com/nikon-70-200mm-f2-8g-af-s-ed-vr-ii-lens-review-field-test-report/