Re: Star Testing using large disc

On Nov 11, 10:36 pm, AM <sctu...@xxxxxxxxxxx> wrote:
Tenifer wrote:
Do you know where I can get a tested Celestron C9.25" with
at least 1/8 wave optics? I read that you can push a Celestron
C9.25" to 450X with a 1/8 wave optics while you can only reach
250X with a 1/4 wave optics and only 150X with a 1/2 wave
optics
Teni

No.....

You can order from Co 7, and get one that
will pass an optical alignment test, and
they star tested my C 11, but NO ONE (!!!)
sells a guaranteed 1/8 SCT anywhere.
Sorry, but you are not that special.
(unless you got BIG $$$ to spend...)

For the user cost of an SCT, we are getting
a deal. A well corrected, and *perfect* 8"
SCT would cost $5000.00 US minimum IMHO at least.
The kind of perfection you seek, is not what
one usually gets with a mass produced SCT.

Sounds like you need to buy a TMB, TEC, or AP
apo retractor... (if you want that quality...)

My 1980 C8 star tests out extremely well,
I've been able to push 500x on Jupiter,
and the Moon a few times. My C 11, isn't
quite as good, but once or twice a year
I can push 400x + Sky conditions make more
of a difference here. 450x is a LOT to ask
from ANY scope. An awful lot.......

Using a light pole/reflector several miles
away tells me about as much as shining a
flashlight down the tube and seeing how bad
the mirror is..... (total waste of time IMHO)

Nothing but an actual star test will tell
ya the truth !

Personally, I think you are worrying about
the numbers WAY too much... (seriously)
Seeing conditions are what you should be
worrying about....

Go out and USE the darn thing !!!!
I assume you did buy this to look at REAL
DSO's, and stars ?? (didn't you??)

--

AM

Once I owned a 8" SCT. After using it for year.
I still could't see more than two bandings in jupiter
even under clear seeing and using all kinds of EP
from pentax smc orthos 7mm to televue radians.
I couldn't see any other details. So if that particular
scope is just 1/3 wave. It would explain it. This means
had I got a 1/7 wave 8" SCT. I should have seen
more than two bandings.

About testing scopes using not the airy disc method
by extended object. You know what. I'm wondering
that spherical aberrations is an aberration in focus.
Therefore even when focusing extended object such
as big star or street lamp miles away. When you
defocus it, the in and out (left and right focusing
changes) patterns should reflect the spherical
aberrations because SA is all about focusing. One
can use the airy disc diffraction patterns when
detecting resolution changes and contrast and say
that 10%+ energy in the center is pumped to the
patterns. But when detecting mere spherical
aberration, one can use extended source such as
point of light, why not??! (since it's just about focusing).
Suiters is just human and not God where everything
he said must be obeyed to the book.

Teni

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