Erm... what??If you attach film lens in to digital camera , glass infrared window will decrease the mtf %20 and increase the spherical aberration.
More likely (only as a possibility) it is chromatic aberration, not spherical. But infrared?? I don't think so.
No, I don't believe the "decrease in MTF of 20%". How is this qualified, and in what specific circumstances?
Articles like this are very generalised, vague and wordy. This should be better researched, published, subject to peer review, analysis and proof, and then cited. Some of us are not easily taken in by bald statements. And is it important? If proven, it might be. For what it's worth, all of my analogue lenses are totally functional on digital bodies (old and newest) without problem because they are from the manufacturer, not a third party — and that is where many lenses do give problems with bodies, especially digital (the marques do not licence metering and AF algorithms to third parties). And no, I don't have a digital to take those lenses because I do not use digital for my production (and never will).