Often people say "a scope is such and such wave". I have become familiar with the inta outer star test, and downloaded the abberator program to fool around, but I haven't figured out how someone says "its 1/4 wave". Is there a thread, web page, or book that explains this simply?
Questions about waves
Started by Peter Glus, 11/30/2007 01:54AM
Posted 11/30/2007 01:54AM
Opening Post
Posted 11/30/2007 06:31AM
| Edited 11/30/2007 06:31AM
#1
The book by Dick Suiter explains it well. Highly
recommended:
http://www.willbell.com/tm/tm5.htm
But there really is not much to it. If you run
aberrator with the spherical (LSA), astigmatism, coma,
pinch, and tube zeroed-out, set the [de-]focus to
5 waves, and click on "star" you will see a pattern of rings.
Maybe you will need to set some parameters to get nice
patterns:
Resolution (pix/arcsec)=5
FFT space=512
Aperture(mm)=100
Focal ratio=10
If you set the focus to -5 instead
you get the same pattern. That implies perfect
optics.
Now if you put in say 1/4 wave of
spherical (3rd LSA = 0.25), you will now see
very different patterns at focus of 5 and -5.
The problem, of course, is that imperfect optics
give poorer resolution and contrast. You can
explore this by setting the focus back to
zero, and clicking "star" again to see that the
in-focus star looks like. As you put in more spherical
error (LSA) you will see the star pattern getting fatter and
more light going into the rings (instead of the central
spike).
recommended:
http://www.willbell.com/tm/tm5.htm
But there really is not much to it. If you run
aberrator with the spherical (LSA), astigmatism, coma,
pinch, and tube zeroed-out, set the [de-]focus to
5 waves, and click on "star" you will see a pattern of rings.
Maybe you will need to set some parameters to get nice
patterns:
Resolution (pix/arcsec)=5
FFT space=512
Aperture(mm)=100
Focal ratio=10
If you set the focus to -5 instead
you get the same pattern. That implies perfect
optics.
Now if you put in say 1/4 wave of
spherical (3rd LSA = 0.25), you will now see
very different patterns at focus of 5 and -5.
The problem, of course, is that imperfect optics
give poorer resolution and contrast. You can
explore this by setting the focus back to
zero, and clicking "star" again to see that the
in-focus star looks like. As you put in more spherical
error (LSA) you will see the star pattern getting fatter and
more light going into the rings (instead of the central
spike).
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