04-12-2014, 03:28 PM
(This post was last modified: 04-13-2014, 08:45 AM by Rainer.)
If you imagine a very simple optical system, that just uses 2 lenses, and if you
also assume, the first lens of the two lenses would be in the "correct position"
(whatever that actually means), then you will find several ways, in which the
seconds lens can be out of its "correct position".
Typically, to be correct, the lenses have to be "coplanar" and "coaxial" ...
this means the two planes in which the lenses are have to be parallel and
the lenses shall be in the same optical axis. If the planes are not parallel,
the resulting image defect is different from that when the lenses are not in
the same axis.
The cause? Whichever you want! It might already be a defect that has its
origin in the assembly process. The lens might have been faling down or
it took a hit when it was used. Note, however, that no lens is the world is
absolutely perfectly centered.
Just my 2cts ... Rainer
Quote:Hello
What is an off coplanar projection defect ?
I read in the Zone of photozone that it was a form of centering defect.
What is the symptom and what is the cause of such defect ?
Do all decentered lens suffer from off-coplanar projection ?
There is a test that mention such defect but there is no image sample showing the issue:
http://www.opticallimits.com/Reviews/276...ew?start=1
Best regards
Emmanuel
RTFAQ:
http://www.opticallimits.com/lens-test-faq
Q: What is a <i>centering</i> defect ?
<p style="margin-left:40px;">A: A centering defect originates in a misaligned lens element or lens group. The result is a blurry corner, an off-coplanar projection (symmetrical blur) or object edge shadows. A centering defect is normal to some degree - there's simply no perfect lens out there, not even a Leica. Generally centering problems are more obvious with large aperture lenses and they're more frequent with budget (third-party) lenses.
/Dave
http://dave9t5.zenfolio.com
