Lens monitoring was performed from 1996 February to 1999 July, using the CCD camera of the 82 cm IAC-80 Telescope, sited at the Instituto de Astrofísica de Canarias' Teide Observatory (Tenerife, Canary Islands, Spain). A Thomson 1024 x 1024 chip was used, offering a field of nearly 7.5 arcminutes. Standard B,V,R,I broad band filters were used.

An alternative method to obtain multi-band CCD photometry was developed. Accurate photometry was obtained by sumultaneously fitting a stellar two-dimensional profile on each QSO component (A and B) with two field stars (D and H) as reference stars. The photometric data in B, V, R, and I were presented in ApJ.

The observations of the gravitational lens system 0957+561 A,B have given us fairly continuous light curves in B, V, R, and I for both components. An analysis of the observations performed by groups from three different institutions-Princeton Univeristy, Harvard-Smithsonian Center for Astrophysics, and Instituto de Astrofísica de Canarias-covering the period 1984-99 leaded to a time delay of 422.6 days, with an uncertainty of 0.6 days.

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