Ståle Sannerud wrote:


Compare this to an IS lens, which de facto lets the image circle chase the
wobbling image so that it stays in the same place relative to the sensor.

In fact the displacement in IS lenses does cause loss of illumination
(asymmetrical vignetting) as well as localised aberrations. One of the
main arguments against using IS lenses is that at the best (IS turned
off) they may not entirely match the performance of similar non-IS
designs, and at the worst (moving element or group at maximum
displacement) optical performance will be visibly compromised.

One slightly ironic point is that so far all the sensor-stabilised
cameras have been 1.5X APS factor. In practice, even lenses like the
11-18mm and 10-20mm wide angles provide 2mm or more coverage beyond this
at their shortest setting - the Tamron 11-18mm will cover full frame at
13-14mm. Yet Canon uses 1.6X sensors, which would be even better (more
room to move round!) with sensor-based IS than the 1.5X format.

The only lens I know which causes problems with sensor-based IS on the
KM/Sony 1.5X bodies is the Sigma 30mm f1.4 - it was, I think, really
designed to work on Canon 1.6X or Sigma 1.7X sensors, and it's already
pushing its coverage on 1.5X when wide open.

David