This is a great zoom lens and star testing shows that a good behaviour
can be obtained with a small 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 good star shape is obtained at f/5.6.
Thanks to Alessandro Gambaro for testing together his objective.
Aperture testing at 200 mm and 135 mm,
with Canon EOS 5D (full
Click on the image for the full-res
version (200% of original resolution)