How good is good enough?

I recently got an Orion 127 mm Mak-Cas telescope, and although the images
seem to be pretty good, I was wondering are there any tests for determining
if a given telescope is performing as well as it should? How sharp a point
should a star focus to? It seems to depend on the brightness of the star
too. At high (150X) magnification, I do see little rings around some stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

Albert

At high (150X) magnification, I do see little rings around some stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

Hi:

Yes. As for how to tell "how good"? The star test is one way. Unfortunately, it
can be hard for novices to interpret and may be amgiguous when used with a
scope that moves the primary mirror to focus. How else? Home much detail does
the cooled and collimated scope show on planets? Again, it may be difficult for
a novice to evaluate. Best bet, if you're concerned, grab a member of the local
club who knows what to look for.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

At high (150X) magnification, I do see little rings around some stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

Hi:

Yes. As for how to tell "how good"? The star test is one way. Unfortunately, it
can be hard for novices to interpret and may be amgiguous when used with a
scope that moves the primary mirror to focus. How else? Home much detail does
the cooled and collimated scope show on planets? Again, it may be difficult for
a novice to evaluate. Best bet, if you're concerned, grab a member of the local
club who knows what to look for.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Albert,

When everything is right, stars should appear as pinpoints...crisp and
sharp. If you bought your scope from Orion recently, you should telephone
them for assistance. You will find that these people are very helpful and
not afraid to take a faulty item back to keep the customer satisfied.

On a Cas telescope, what you describe could be the fault of proper
collimation. While I'm not familiar with a Mak-Cas, I do believe that there
are means of collimating this scope. I could be wrong, so check your owners
manual to see if collimation is doable on your scope and for instructions on
how to do it. Either that or call Orion.

Al


wrote in message ...
I recently got an Orion 127 mm Mak-Cas telescope, and although the images
seem to be pretty good, I was wondering are there any tests for
determining
if a given telescope is performing as well as it should? How sharp a point
should a star focus to? It seems to depend on the brightness of the star
too. At high (150X) magnification, I do see little rings around some
stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

Albert

Albert,

When everything is right, stars should appear as pinpoints...crisp and
sharp. If you bought your scope from Orion recently, you should telephone
them for assistance. You will find that these people are very helpful and
not afraid to take a faulty item back to keep the customer satisfied.

On a Cas telescope, what you describe could be the fault of proper
collimation. While I'm not familiar with a Mak-Cas, I do believe that there
are means of collimating this scope. I could be wrong, so check your owners
manual to see if collimation is doable on your scope and for instructions on
how to do it. Either that or call Orion.

Al


wrote in message ...
I recently got an Orion 127 mm Mak-Cas telescope, and although the images
seem to be pretty good, I was wondering are there any tests for
determining
if a given telescope is performing as well as it should? How sharp a point
should a star focus to? It seems to depend on the brightness of the star
too. At high (150X) magnification, I do see little rings around some
stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

Albert

Albert,

When everything is right, stars should appear as pinpoints...crisp and
sharp. If you bought your scope from Orion recently, you should telephone
them for assistance....

On a Cas telescope, what you describe could be the fault of proper
collimation.....

Sounds to me like the scope is in good collimation:

From the Original Post:

"At high (150X) magnification, I do see little rings around some stars:are
these the Airy circles? "

Rather than being a sign that the scope is out of collimation, those rings
around the stars are nice diffraction rings and a sign that the scope is indeed
in pretty good collimation....

jon

Albert,

When everything is right, stars should appear as pinpoints...crisp and
sharp. If you bought your scope from Orion recently, you should telephone
them for assistance....

On a Cas telescope, what you describe could be the fault of proper
collimation.....

Sounds to me like the scope is in good collimation:

From the Original Post:

"At high (150X) magnification, I do see little rings around some stars:are
these the Airy circles? "

Rather than being a sign that the scope is out of collimation, those rings
around the stars are nice diffraction rings and a sign that the scope is indeed
in pretty good collimation....

jon

Albert posted:

I recently got an Orion 127 mm Mak-Cas telescope, and although the images
seem to be pretty good, I was wondering are there any tests for determining
if a given telescope is performing as well as it should? How sharp a point
should a star focus to? It seems to depend on the brightness of the star
too. At high (150X) magnification, I do see little rings around some stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

The rings are known as "diffraction rings" and surround the tiny disk of light
which is known as the "Airy Disk". These features are caused by the
interference of light that is being gathered and focused by the telescope, and
are quite normal, generally becoming easily visible at magnifications of 30x
per inch of aperture and above (150x in the case of the 127mm Mak-Cass). I
have used a 127mm Orion Mak-Cass, and generally, it is a pretty good
instrument overall. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Albert posted:

I recently got an Orion 127 mm Mak-Cas telescope, and although the images
seem to be pretty good, I was wondering are there any tests for determining
if a given telescope is performing as well as it should? How sharp a point
should a star focus to? It seems to depend on the brightness of the star
too. At high (150X) magnification, I do see little rings around some stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

The rings are known as "diffraction rings" and surround the tiny disk of light
which is known as the "Airy Disk". These features are caused by the
interference of light that is being gathered and focused by the telescope, and
are quite normal, generally becoming easily visible at magnifications of 30x
per inch of aperture and above (150x in the case of the 127mm Mak-Cass). I
have used a 127mm Orion Mak-Cass, and generally, it is a pretty good
instrument overall. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

@hpl.hp.com () wrote in message ...
I recently got an Orion 127 mm Mak-Cas telescope, and although the images
seem to be pretty good, I was wondering are there any tests for determining
if a given telescope is performing as well as it should? How sharp a point
should a star focus to? It seems to depend on the brightness of the star
too. At high (150X) magnification, I do see little rings around some stars:
are these the Airy circles? I'm new at this so any pointers would be
appreciated.

Don't laugh, but daytime testing can reveal glaring deficiencies in a scope.

One of my "tricks" after reassembling a scope is to attempt to read the label
and serial number of a microwave dish about 1/4 mile away from my back yard.
You could do the same for gear mounted on distant power or telephone poles.

I recently did this with my Orion Apex 90 after I flocked its baffle tube and
did a rough indoors collimation and, by golly, the digits in the serial number
were crystal clear and I only needed to perform a minor additional tweak later
that day (actually night :-) with a star test.

Another test is examining leaves on a distant tree and see if you can detect
the veins in the leaves and, hopefully, the absence of any blue/purple color
fringing around the leaf's edges; this is also a good test for refractors.

FWIW, the Apex/StarMax 127 (I have one, too) is overall a very good performer
and there are some exquisite astrophotos taken using them that people have
posted to the "OSAO" Yahoo group.