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
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