By making use of advanced methods for the calculation of electron trajectories in the presence of space charge fields we have designed and built a novel electron energy-loss spectrometer for the purpose of measuring spin flip excitations at surfaces. The measurement of the spin asymmetry requires a deflection angle between the photocathode and the sample position which amounts to 90^° in total. That deflection angle is not provided by standard electron deflectors, or by a combination of those. We show that a 90^° deflection angle can be realized by a combination of two novel deflectors with 90^° and 180^° deflection angles each. The performance of the new spectrometer matches the performance of the best electron spectrometers developed for surface vibration spectroscopy.