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Equation of mirrors : zi = (1/2Ri)r2 + A2,i r4 + A^r6. Axial separations: ASi. * Conic constant from third order: K = 8R3A4 i - 1 and K = -1 for a paraboloid.

Equation of mirrors : zi = (1/2Ri)r2 + A2,i r4 + A^r6. Axial separations: ASi. * Conic constant from third order: K = 8R3A4 i - 1 and K = -1 for a paraboloid.

Fig. 6.25 Left: Trss telescope optical design from Table 6.14. Entrance pupil at M2. Right: Residual spherochromatism blur images for 20 and 10-mm thickness plates as equivalent thickness of the filter and cryostat window. The corresponding blur rms diameters are 0.20 and 0.10arcsec, respectively

Z3,Sphe = 0.464455 10—4 r2 + 0.100192 10—12 r4 + 0.0043 10—19 r6 + 0.233 10—29 r8 Z3,Flex = 0.003016 10—4 r2 - 0.953149 10—12 r4 + 0.1022 10—19 r6 - 0.233 10—29 r8 Z3,Rota = 0.006014 10-4 r2

z3,Opt = 0.473485 10-4 r2 - 0.852957 10-12 r4 + 0.1065 10-19 r6 + 0.000 10+00 r8

The final geometry of the double vase shell is derived from the thickness distributions in the two latter tables. The normal thickness of the M1-M3 intermediate ring - which links the mirrors in the region r3,max < r < r1min - must be set such as the flexural sag of M1 at r = r3,max remains unchanged when passing from the single vase to the double vase (Table 6.17 and Fig. 6.26).

• Case of a wide-field space telescope - Stress figuring: As stated in Sect. 6.6.1 from the active optics co-addition law, the above double vase shell geometry for obtaining M1 and M3 hyperboloid mirrors is valid whatever the aspherization process, either in situ stressing or stress figuring.

For a wide-field space telescope, the conditions in space entail that the aspheriza-tion of M1 and M3 must be carried out by elastic relaxation after spherical figuring

Fig. 6.25 Left: Trss telescope optical design from Table 6.14. Entrance pupil at M2. Right: Residual spherochromatism blur images for 20 and 10-mm thickness plates as equivalent thickness of the filter and cryostat window. The corresponding blur rms diameters are 0.20 and 0.10arcsec, respectively

Table 6.15 Normal thickness distribution {tn} for the hyperbolization of Trss telescope vase shell M1 mirror. Mirror clear aperture 2,200mm. Substrate dext =2,320mm. Load q = —50kPa. rN = 1,100mm, tx = 70mm. Ropt = 10,620mm, Rsphe = 10,765.3mm, RFlex = 786,760mm, <R>=11,362. [Units: mm]

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