Thanks folks...I'd borrowed it to try a catch a couple of Lapwings that are nesting in the field in front of the castle (Pitfichie, Monymusk), but they didn't show.
When viewed at 100% on Lightroom, it just seems to lack any clarity or sharpness which I get from my 135 mm primes, and it didn't seem to cope with the contrasty light of the scene...