SITELLE filters show slight changes in their bandpass with the (x,y) position. This changes is generally a shift of the filter curve but, especially in the corners, the filter curve cannot be modeled any more with only a wavelength shift. The best way to model the filter would be to measure the filter curve everywhere in the field of view and get a 3d filter curve. Up to now we only have a few measures in the center and the corners and the filter model is thus not behaving very well in the corners of the field. If you experience such a problem, a good workaround is to set the option ‘nofilter=True’ in the fitting function. The drawback is that you won’t be able to fit emission lines on the border of the filter.