The QTM Restoration Method is not a Non Linear Iterative Method, but an Inverse Filtering method, and is intended for very special circumstances only. It can produce much noise amplification because it is not optimized to deal with Poisson noise, for example. This amplification is caused by the reconstruction by the inverse filter of the high frequencies in the Fourier spectrum of the image. Not only are these frequencies dominated by noise, but the OTF has low intensities at these frequencies as well. Therefore the inverse filter divides noise-dominated frequencies by low transfer values which result in a strong amplification of the noise in the restoration result. Therefore, it is an option only for very low-noise images. For an iterative and more stable alternative the Iterative Constrained Tikhonov Miller (ITCM) is recommended, and in general all the new algorithms implemented in Huygens as the Classic Maximum Likelihood Estimation.
For a general overview of all algorithms in Huygens see Restoration Methods.