Brightfield illumination has been one of the most widely used observation modes in optical microscopy for the past 300 years. The technique is best suited for utilization with fixed, stained specimens or other kinds of samples that naturally absorb significant amounts of visible light. Images produced with brightfield illumination appear dark and/or highly colored against a bright, often light gray or white, background. (Molecular Expressions Microscopy Primer)
Brightfield microscopes are not Linear Systems.
That's no longer the case as Dr. Marcel Oberlaender et al. from the MPI of Neurobiology in Martinsried now proved the validity of the Huygens deconvolution for brightfield data using the protocol as described here. (Journal of Microscopy Vol. 233, Pt 2, 2009 pp 275-289).
The linear Tikhonov Miller algorithm (present in Huygens Professional) proves ideal for various reasons. The most important among them the fact that it handles the background correctly.
Blind deconvolution with its iterative character and lack of parameter checking (therefore also not present in any of the Huygens software packages) should not be applied at all. The MLE algorithms (present in all Huygens software packages) should also not be applied on brightfield data despite the fact that it's highly validated for all other types of light microscopic data.
For more details on deconvolving this type of images see Process Brightfield Images.