How high-end refractors "retain" their collimation ?

Hi,

Speaking on my website about ST-80 scopes that hit the market after the
release of the first Orion ST-80 and more recently the 2d generation of
ST-80 ED, I wonder how such small scopes "retain" their collimation or the
alignment of their doublet ?

Usually a low-end scope like a 100 mm f/6 achromat comes with a collimation
eyepiece to fix the problem if it occurs. The cell has screws that the
amateur has to adjust until all is aligned.

But we all know also that high-ends apochromats (and surely oil-spaced
triplet) have not to be realigned, hence the beleiving that refractors have
not to be collimated (like MCT).
But if this must occur by a bad luck, most of us will return their scope to
the manufacturer for servicing. One each 10-15 years is not too much ;-)

Question:
I suspect Astro-Physics, Tele Vue or Takashashi scopes to be collimated or
there must be very few samples returning to the manufacturer fo that purpose
(statistics should be welcome)
What do AP? TV or Tak designers to prevent such problem to happen ?
Do they use special cells or is theere, by design, a "tricks" to prevent
this problem ? (probably not)
Who knows...

Thanks in advance

Thierry
http://www.astrosurf.com/lombry

Collimation of a refractor is completely different than a reflective scope.
The lenses are held in a good alignment with each other and that is set at
the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the actual
angle at which the lenses are relative to the optical axis is relatively
insensitive so you end up not having to worry so much about collimation.
Many smaller telescopes don't even have the ability to collimate as they are
basically so insensitive to the problem that the need just isn't there.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

Collimation of a refractor is completely different than a reflective scope.
The lenses are held in a good alignment with each other and that is set at
the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the actual
angle at which the lenses are relative to the optical axis is relatively
insensitive so you end up not having to worry so much about collimation.
Many smaller telescopes don't even have the ability to collimate as they are
basically so insensitive to the problem that the need just isn't there.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

"Bob May" wrote in message
...
Collimation of a refractor is completely different than a reflective
scope.
The lenses are held in a good alignment with each other and that is set at
the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the
actual
angle at which the lenses are relative to the optical axis is relatively
insensitive so you end up not having to worry so much about collimation.

Agree, but some are however equipped with screws on the cell and a
collimation eyepiece to made the adjustment (Orion 100 f/6)

But my question is first addressed to AP, TV and Tak. How do they do to not
be as sensitive to a bad alignment as their smaller sister achromatic
According some users it is know that some Orion small refractors are
delivered with a bad collimation....

Thierry


Many smaller telescopes don't even have the ability to collimate as they
are
basically so insensitive to the problem that the need just isn't there.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink
less.
Works every time it is tried!

"Bob May" wrote in message
...
Collimation of a refractor is completely different than a reflective
scope.
The lenses are held in a good alignment with each other and that is set at
the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the
actual
angle at which the lenses are relative to the optical axis is relatively
insensitive so you end up not having to worry so much about collimation.

Agree, but some are however equipped with screws on the cell and a
collimation eyepiece to made the adjustment (Orion 100 f/6)

But my question is first addressed to AP, TV and Tak. How do they do to not
be as sensitive to a bad alignment as their smaller sister achromatic
According some users it is know that some Orion small refractors are
delivered with a bad collimation....

Thierry


Many smaller telescopes don't even have the ability to collimate as they
are
basically so insensitive to the problem that the need just isn't there.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink
less.
Works every time it is tried!

"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm wrote
in message ...

"Bob May" wrote in message
...
Collimation of a refractor is completely different than a reflective
scope.
The lenses are held in a good alignment with each other and that is set
at
the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the
actual angle at which the lenses are relative to the optical axis is
relatively
insensitive so you end up not having to worry so much about collimation.

Agree, but some are however equipped with screws on the cell and a
collimation eyepiece to made the adjustment (Orion 100 f/6)

But my question is first addressed to AP, TV and Tak. How do they do to
not
be as sensitive to a bad alignment as their smaller sister achromatic
According some users it is know that some Orion small refractors are
delivered with a bad collimation....

Those are high end refractors, built to a lot tighter tolerance than those
Orion refractors. We're talking about the difference between a Mazda 323
(Orion) and a Mercedes Benz here (the high enders). This not only includes
the manufacturing phase but also the quality inspection is higher. And once
a refractor is built is shouldn't need collimation unless you drop it on a
concrete floor, in which
--
Sincerely,
--- Dave

----------------------------------------------------------------------
A man is a god in ruins.
--- Duke Ellington
----------------------------------------------------------------------



Thierry


Many smaller telescopes don't even have the ability to collimate as they
are
basically so insensitive to the problem that the need just isn't there.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink
less.
Works every time it is tried!

"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm wrote
in message ...

"Bob May" wrote in message
...
Collimation of a refractor is completely different than a reflective
scope.
The lenses are held in a good alignment with each other and that is set
at
the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the
actual angle at which the lenses are relative to the optical axis is
relatively
insensitive so you end up not having to worry so much about collimation.

Agree, but some are however equipped with screws on the cell and a
collimation eyepiece to made the adjustment (Orion 100 f/6)

But my question is first addressed to AP, TV and Tak. How do they do to
not
be as sensitive to a bad alignment as their smaller sister achromatic
According some users it is know that some Orion small refractors are
delivered with a bad collimation....

Those are high end refractors, built to a lot tighter tolerance than those
Orion refractors. We're talking about the difference between a Mazda 323
(Orion) and a Mercedes Benz here (the high enders). This not only includes
the manufacturing phase but also the quality inspection is higher. And once
a refractor is built is shouldn't need collimation unless you drop it on a
concrete floor, in which
--
Sincerely,
--- Dave

----------------------------------------------------------------------
A man is a god in ruins.
--- Duke Ellington
----------------------------------------------------------------------



Thierry


Many smaller telescopes don't even have the ability to collimate as they
are
basically so insensitive to the problem that the need just isn't there.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink
less.
Works every time it is tried!

David Nakamoto wrote:
"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm wrote
in message ...

"Bob May" wrote in message
...

Collimation of a refractor is completely different than a reflective
scope.
The lenses are held in a good alignment with each other and that is set

at

the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the
actual angle at which the lenses are relative to the optical axis is

relatively

insensitive so you end up not having to worry so much about collimation.

Agree, but some are however equipped with screws on the cell and a
collimation eyepiece to made the adjustment (Orion 100 f/6)

But my question is first addressed to AP, TV and Tak. How do they do to

not

be as sensitive to a bad alignment as their smaller sister achromatic
According some users it is know that some Orion small refractors are
delivered with a bad collimation....


Those are high end refractors, built to a lot tighter tolerance than those
Orion refractors. We're talking about the difference between a Mazda 323
(Orion) and a Mercedes Benz here (the high enders)

Likely a bad analogy these days. The Mazda is probably much more
reliable :-)

David Nakamoto wrote:
"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm wrote
in message ...

"Bob May" wrote in message
...

Collimation of a refractor is completely different than a reflective
scope.
The lenses are held in a good alignment with each other and that is set

at

the factory by the construction of the lenses themselves, not by any
alignment later.
Since lenses have less of the problems like coma and astigmatism, the
actual angle at which the lenses are relative to the optical axis is

relatively

insensitive so you end up not having to worry so much about collimation.

Agree, but some are however equipped with screws on the cell and a
collimation eyepiece to made the adjustment (Orion 100 f/6)

But my question is first addressed to AP, TV and Tak. How do they do to

not

be as sensitive to a bad alignment as their smaller sister achromatic
According some users it is know that some Orion small refractors are
delivered with a bad collimation....


Those are high end refractors, built to a lot tighter tolerance than those
Orion refractors. We're talking about the difference between a Mazda 323
(Orion) and a Mercedes Benz here (the high enders)

Likely a bad analogy these days. The Mazda is probably much more
reliable :-)

Some of the Tele Vue refractors, the Genesis SDF in particular, are of a
very poor mechanical design that is easily knocked out of collimation. This
requires shipping the telescope back to Tele Vue along with about $200 to
set it right. Unfortunately, that only lasts until the next time it gets
knocked out of collimation. All it takes is for the case to be dropped on
its end by airport luggage handlers, or even by UPS when it is shipped back
from Tele Vue!. I speak from a very dissappointing experience. It will be
reflectors for me from now on.

Del Johnson



"Thierry" Answer direct via http://www.astrosurf.com/lombry/post.htm wrote
in message ...

Question:
I suspect Astro-Physics, Tele Vue or Takashashi scopes to be collimated or
there must be very few samples returning to the manufacturer fo that
purpose
(statistics should be welcome)
What do AP? TV or Tak designers to prevent such problem to happen ?
Do they use special cells or is theere, by design, a "tricks" to prevent
this problem ? (probably not)
Who knows...

Thanks in advance

Thierry
http://www.astrosurf.com/lombry