Reliability of MTF?

Can one rely mainly on MTF charts to compare different lenses or are there other hidden factors; internal to the lens, that dont show up in the graphs.

MTF shows the fidelity of reproduction of a lens in mathematical terms, and is used in lens design, so it does give a measure of a lens's quality. However, a lens is a work of art as well as science and has all sorts of qualities that MTF alone does not reveal.

Some lenses have high resolution at the expense of contrast, some have high contrast and look snappier but actually resolve less. Some have wonderful bokeh, which describes how the out of focus areas look, others less so. Some have a warm colour balance, some neutral, some cold. Portrait lenses might be relatively soft at wider apertures, which your subjects might be glad of, but sharpen up when stopped down. Macro lenses have a flat field, zooms probably do not...

And so on. I like the design parameters of Pentax lenses, but you might prefer something else.

A book on lenses might be a good start to whet your appetite. How about "The Lens Book" by Roger Hicks and Frances Shultz (David & Charles, ISBN 0 7153 0149 7)

John