This is a standard quality zoom lens; star testing shows that a fairly
decent behaviour can be obtained with two stopping down. Testing was
made on a clear and cold night of
December 2010, with automatic tracking of my Kenko NES mount. Exposures
and ISO were selected to maintain a constant nominal exposure, except
the two higher apertures.
The results show that a decent star shape is obtained at f/5.6, even if
a residual radial elongation is still present.
Thanks to Alessandro Gambaro for testing together his objective.
Aperture testing with Canon EOS 5D (full
Click on the image for the full-res
version (200% of original resolution)