About OSS degrading image quality

Started Apr 29, 2013 | Questions thread
Bart Hickman
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Re: About OSS degrading image quality
In reply to OpticsEngineer, Apr 30, 2013

OpticsEngineer wrote:

"Decentering of any element reduces IQ. You often see lens tests where they criticize a lens for being decentered (manufacturing error). If I understand OIS correctly, it works by deliberately decentering one or more elements."

That is correct, but still only 50% of the answer.

The other half is closely related.   When a lens is designed, it has an optimal set of lens curvatures thickness and indices of refraction.  Any deviation from that optimal design, including decenters, reduces lens performance.   It is possible to design a lens that gives fantastic performance when everything is perfect.  But with even slight deviations from that optimum, the peformance plummets.    Another lens design may not give that fantastic performance at optimum, but it maintains very good peformance with small variations of curvatures, thicknesses, indices and decenters.

The process of coming up with a design that still works well when things are not exactly perfect is called tolerancing. It usually involves evaluating random variations by Monte Carlo analysis.  It is not easy and most engineers say it comprises about half of time spent on a lens design.

The design that tolerates small imperfections is called "less peaky"  and it is much perferrred.  It can manufactured much more cost effectively.

A lens that is designed to allow optical stablization elements in it has to be designed to be less peaky and more tolerant to decenters.  But that also means it has to give up some of the peakiness that allows for the best performance.

Very informative.  Thanks.

Are these tradeoffs different for telephoto zoom versus wider zoom lenses or prime lenses?  It seems like a telephoto lens would tend to require a more "heavy-duty" stabilization system, but then such a lens has more empty space anyway where you can fit the extra mechanism, so maybe it balances out in the end.

Could it just be that Zeiss' preferred flavor of lenses (mid to wide angle and large aperture) tend to be more difficult to optimize with stabilization?

Bart

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