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Radial distortion

The standard coordinates are then corrected for the effects of radial field distortion:

ξ' = ξD(ρ)

η' = ηD(ρ)

ρ= (ξ2 + η2)1/2

These effects should be negligible for the JKT f/15, INT f/15 and WHT f/11 foci, but corrections are required for WHT and INT Prime and JKT f/8. In particular, WHT Prime requires precise location of guide stars, since the autoguider field is small. The formula:

D(ρ) = 1 + aρ+ bρ2 + cρ3 + dρ4

is appropriate, with coefficients as given in Table 1.


Configuration a b c d
WHT Prime 1.2797 27.458 24320.0 0.0
INT Prime
JKT f/8 0.0 13.32 0.0 0.0
Table 1: Radial distortion coefficients for corrected foci. 

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Mon Mar 1 17:52:09 GMT 1999