Re: Aberrations of lines (scratches) in mirror

On Apr 17, 6:24 pm, wsnel...@xxxxxxxxxxx wrote:
On Apr 17, 1:59 am, Chris L Peterson <c...@xxxxxxxxxxxxxxxxxx> wrote:

On Thu, 16 Apr 2009 18:47:59 -0700 (PDT), wsnel...@xxxxxxxxxxx wrote:
On axis, the central portion of the secondary is not being hit by any
light from the sky, because the secondary itself casting a shadow over
the central portion of the primary.  Just as light can be reflected,
so can a shadow.

Okay. I somehow had the impression from your comment that you were
seeing the image as the reflection of the secondary in the primary
(which is how these images usually look- people don't usually image
their cats from the inside).

Even so, this scope doesn't seem to have all that large an obstruction.
Mapping the aperture to obstruction ratio onto the secondary still puts
most of the scratches into the illuminated annulus.

I think the OP removed the corrector assembly from scope and that
looks like a baffle glued to the second surface of the corrector.  The
obstruction looks to be about 30 percent or more, and from what I can
see most of those, that are seen in the photo, seem to be concentrated
in the center.  There may very well be many more scratches, located
all over the secondary but not visible in the photo, which I hinted at
earlier.

Perhaps the OP could return the unit for a full refund and try a
different vendor if he is that concerned about the situation.

But the problem is that the manufacturer salesman in Russia
won't believe that such scratches could occur. He thought
I did the scratches myself or customs people did it. How
can I convince him that manufacturing can produce it?
Do you or anyone know exactly where in the fabrication
stage can the scratching occurs? Note the glass is not
scratched, only the aluminized spots at the back of
the corrector. I have to convince him it can occur in
manufacturing.. but where exactly? Have to write him
message to be forwarded to technical department
explaining them how scratches could be possible
in the fabrication stage. After the aluminum coating
is applied at back of corrector. Is it a procedure
to wipe it with clothe? Why wipe it when there is
no dusts.. perhaps some chemical residue??
Another, an unrelated question.. in the figuring of
mirrors and spherical aberrations... does the
primary and secondary have equal weight in
contributing to spherical aberrations. Or is it
only the primary that is the main factor.. meaning if
the primary is say 1/8 wave and the secondary
is 1 wave or bad surface accuracy, would the
final image be close to 1 wave or 1/8 wave?

Mk
.

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