EUROPEAN SOUTHERN OBSERVATORY La Silla Science Operations: NTT
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The SofI detector is linear up to about 5000 A.D.U. at level of 0.1%. For higher illumination the non-linearity hits in and it reaches about 1% at 13000-14000 A.D.U.
Nota Bene: We strongly urge the users to avoid having raw count levels above 10000 A.D.U. (including the sky level). The correction described here has been tested only partially.
The plot bellow shows the deviation from linearity. To correct for this deviation one has to multiply the raw count level (designated with CL) by the linearity correction factor (designated as LCF) defined by the polynomial given there. The coefficients are intentionally not rounded up to minimize round up errors. This correction was derived from data obtained on May 14, 2007 (available here).

LCF = 0.9999308 (+/-5.491569E-04) + 9.842033E-09 (+/-3.976830E-07) x CL - 1.240610E-11 (+/-7.976254E-11) x CL^2 + 6.953866E-15 (+/-5.842071E-15) x CL^3 - 1.908840E-19 (+/-1.403206E-19) x CL^4

Send comments to ls-sofi[@]eso.org This page created: May 14, 2007, by Valentin D. Ivanov. Last Update: May 14, 2007, by Valentin D. Ivanov