Re: Aberrations of lines (scratches) in mirror

On Apr 18, 7:53 pm, wsnel...@xxxxxxxxxxx wrote:
On Apr 18, 2:41 am, Mark Franzels <markfranz...@xxxxxxxxx> wrote:







Another, is the purpose of the secondary mirror
only to reflect the image with the primary and
corrector doing ALL the aberrations corrections?
If the secondary mirror doesn't do any aberrations
control, then I can really just plug in a separate
secondary molded to the same shape and
curvature as the corrector.. or I can turn it into
a MAK-NEWTONIAN by using flat mirror in place
of the curved secondary just like newtonian with
eyepiece at the sides. Well. There is such thing
called ATM (Amateur Telescope Making) and
I can turn my frustrations into creative pursuits
if the supplier won't replace the corrector, etc.
(which I doubt now).

As I said before: "I would leave the optics alone and use them as is."

If you want to try ATM either start from scratch  ;-) with a mirror-
grinding kit or else buy finished optics and build the rest of a new
scope yourself.



If the aluminized spot can be clearly seen through the front surface
of the corrector, you might try pointing the scope at a 100-watt bulb
and looking up through the empty focuser to see how much light is
making its way through the aluminized spot.- Hide quoted text -

Well. I tried to look at the rear of the mak at the bright sky,
I can see the center of the black secondary lightening up
a bit so it is a bit transparent.. but I wonder why only in
the middle center of the secondary and not the entire
secondary since it is just aluminized spot of the corrector.

Now try the same test with a bright bulb located a dozen centimeters
away, but cover the front of the scope with a cardboard mask having a
central hole only large enough to allow light the reach the diagonal
spot.  Try to post some photos of the front end of the scope with and
without the mask, and photos through the focuser of the aluminized
spot with the mask in place so that one can see what it looks like
with a bright light bulb shining though all of the holes and
scratches.  Do NOT point the scope anywhere near the Sun !!- Hide quoted text -

- Show quoted text -

After looking at it from all sides. I noticed that the
brightening at the very center of the secondary
is not because the corrector is transparent but
because of off-axis light from objective lens
as well as reflections from rear field flattener
going back to the secondary. The purpose
why you asked me to use mask is to prevent
off-axis light from reaching the corrector
causing brightening of the secondary center,
isn't it.

After looking at the rear or empty focuser
looking at the view in front of the corrector.
I noticed that 75% of the scratches are
indeed convered by the secondary. That
leaves 25%. Well. One can say to leave
the optics alone. Ok. But I need to know some
theoretical principles to understand optics which
i've been interested from time to time. .

If the scratches are seen from the sides, they are
more solid than directly looking at them. Why?
Mr. Peterson mentioned that thin scratches can
cause diffraction effect only and not scattering,
I wonder how far from the airy discs can these
scattering caused by thin scratches reach. Any
idea? I'm calculating what mid magnication to
use so that these diffraction effect can't be noticed
by the human eyes both daytime and nightime
imaging. Also he said wide scratches
can cause scattering where the light can reach
far from the airy discs like 10mm off center. Now
how do I distinguish between thin and wide scratches??
Can it be noticed by looking from the bare eyes alone.
Well, the fact that my scratches are more solid looking
if seen from the sides could perhaps give a clue whether
it is thin or wide?? Or based on my first pictures, is the
scratch thin or wide? This is just for theoretical exploration
and understanding and not for practical purposes where
one can simply say "Shut Up and Observe" much like
the physicists "Shut Up and Calculate" when inquired
further (like the foundations of quantum mechanics
whether Copenhagen or Many world interpretation is
correct).
Thanks

Mk
.

Relevant Pages

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    (sci.astro.amateur)
  • Re: Aberrations of lines (scratches) in mirror
    ... But if I look at the secondary mirror holding it towards my ... noticed the scratches. ... viewing with an ordinary bright light or daylight then they will not ... If I'd just return the corrector to the manufacturer. ...
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