LX200R

I would still like to hear from those who have acquired a Meade LX200R
Ritchey-Chretien telescope. A few of them are now in amateur hands. (I saw
one yesterday in a local telescope store.)

I want to know whether the LX200R optics are truly apo-like, as some
speculate, or at least whether the LX200R optics are better than SCT optics.

Thank you.

Simon W.

Simon W. wrote:
I would still like to hear from those who have acquired a Meade LX200R
Ritchey-Chretien telescope. A few of them are now in amateur hands. (I saw
one yesterday in a local telescope store.)

I want to know whether the LX200R optics are truly apo-like, as some
speculate, or at least whether the LX200R optics are better than SCT optics.

Thank you.

Simon W.


Uses mirrors, so no color if that's what you asking, APO-like.
It has a large central obstruction, (over 35%) like any other compound
telescopes, so star images will be bloated, from diffraction rings.
RC scopes advantages over standard SCT is flat field, no mirror flop,
because the stationary primary.
JS

Protagonist wrote:

Uses mirrors, so no color if that's what you asking, APO-like.
It has a large central obstruction, (over 35%) like any other compound
telescopes, so star images will be bloated, from diffraction rings.
RC scopes advantages over standard SCT is flat field, no mirror flop,
because the stationary primary.
JS

Hi:

Well...I believe he's asking about the R not the RCX...two different
animals ;-).

This scope is nearly identical to the LX200GPS. Same focal ratio, same
secondary diameter, same OTA, same mount. It's not an RC, either, maybe
"optimized SCT" would be a better label. Finally, it focuses by moving
the primary mirror, just like the LX200GPS that it is (apparently)
replacing.

Optical quality? I have not used one yet, but I will GUESS that
edge-of-field performance will be superior to that of the "standard"
SCT. ;-)

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
and _The Urban Astronomer's Guide_

Like SCTs and MCTs?
Join the SCT User Mailing List.
http://www.groups.yahoo.com/group/sct-user

See my home page at
http://skywatch.brainiac.com/astroland/index.htm
for further info

For Uncle Rod's Astro Blog See:
http://journals.aol.com/rmollise/UncleRodsAstroBlog/

On Sun, 05 Mar 2006 23:27:21 GMT, "Simon W." wrote:

I have it on good authority that the RCX400, from which the LX200R was
derived, does not have "bloated" star images, so I'm hoping the LX200R
doesn't have them, either.

Well, you'd hope the optics of the R scope would be at least as good as
an SCT, and since they don't have "bloated" images, I don't imagine this
modified SCT design will, either.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Sun, 05 Mar 2006 23:27:21 GMT, "Simon W." wrote:

I have it on good authority that the RCX400, from which the LX200R was
derived, does not have "bloated" star images, so I'm hoping the LX200R
doesn't have them, either.

Simon

You don't understand. The star images have diffraction rings around
them. A scope with a large central obstruction pours more light into
the diffraction rings. At a magnification just low enough to prevent
visual resolution of the diffraction disc, you see the star as
"bloated" because your eye is fusing the first (and second?)
diffraction ring into a continiuous circle. However, once you get to
the point where you can resolve the diffraction disc, you will see it
is in fact smaller than that of a small refactor which doesn't "show"
bloated star images.
-Rich

Simon W. wrote:
I have it on good authority that the RCX400, from which the LX200R was
derived, does not have "bloated" star images, so I'm hoping the LX200R
doesn't have them, either.

Simon

Right! Try to split the double-double, than come back.
Low power, wide field you don't see the diffraction rings, but once you
kick up the power, they will dance around your stars, like gypsies
around the camp fire.
JS



"Protagonist" wrote in message
...
Simon W. wrote:
I would still like to hear from those who have acquired a Meade LX200R
Ritchey-Chretien telescope. A few of them are now in amateur hands. (I
saw one yesterday in a local telescope store.)

I want to know whether the LX200R optics are truly apo-like, as some
speculate, or at least whether the LX200R optics are better than SCT
optics.

Thank you.

Simon W.
Uses mirrors, so no color if that's what you asking, APO-like.
It has a large central obstruction, (over 35%) like any other compound
telescopes, so star images will be bloated, from diffraction rings.
RC scopes advantages over standard SCT is flat field, no mirror flop,
because the stationary primary.
JS

"Protagonist" wrote in message
...
Simon W. wrote:
I would still like to hear from those who have acquired a Meade LX200R
Ritchey-Chretien telescope. A few of them are now in amateur hands.
(I saw one yesterday in a local telescope store.)

I want to know whether the LX200R optics are truly apo-like, as some
speculate, or at least whether the LX200R optics are better than SCT
optics.

Thank you.

Simon W.
Uses mirrors, so no color if that's what you asking, APO-like.
No. Has a corrector, with different shapes on the two surfaces, so will
show a small amount of chromatic aberration. However in general not
noticeable.

It has a large central obstruction, (over 35%) like any other compound
telescopes, so star images will be bloated, from diffraction rings.
RC scopes advantages over standard SCT is flat field, no mirror flop,
because the stationary primary.
JS
RC, does not have a 'flat field'. The field curvature is dependant on the
focal length of the primary, and the secondary. Hence RC's with large
secondaries, and relatively long focal length primaries, have a _flatter_
field than a traditional SCT, but still have a very curved field. The
'point' about the RC, is that it has the largest _coma free_ field of most
scope designs. Hence though the stars get larger towards the edges of the
field because of the field curvature, they remain round. This also then
means you can use a field flattener, and have a flat field with coma free
images. The 'R', will have more field curvature than the RCX, because of
it's faster primary.
Think of the design as an 'SCT-GT', rather than as a RC.
Now the energy being moved from the centre of the Airy disk, will mean
that the star images are larger than an equivalent APO. However the amount
will be slightly less on the R, than the RCX (smaller secondary), and the
old 'rule of thumb', of aperture-obstruction, gives a good approximation
of how well an obstructed scope performs in the worst case part of the
mtf. The best case resolution, will be that of it's aperture, but for the
8" scope (say), a good comparison, would be with a 5" APO. The extra
aperture will allow you to see 'deeper' than this will manage.
Historically, the commercial SCT, has been a slightly 'bodged' version of
the design (with near spherical optics, rather than the ellipsoid
secondary that should be used), and the RCX, produces centre field images,
that are closer to the traditional SCT, but without the coma further out
in the field, that this design displays.

Best Wishes

On or about Mon, 06 Mar 2006 00:30:51 -0500 did Rich
dribble thusly:

On Sun, 05 Mar 2006 23:27:21 GMT, "Simon W." wrote:

I have it on good authority that the RCX400, from which the LX200R was
derived, does not have "bloated" star images, so I'm hoping the LX200R
doesn't have them, either.

Simon

You don't understand. The star images have diffraction rings around
them. A scope with a large central obstruction pours more light into
the diffraction rings. At a magnification just low enough to prevent
visual resolution of the diffraction disc, you see the star as
"bloated" because your eye is fusing the first (and second?)
diffraction ring into a continiuous circle. However, once you get to
the point where you can resolve the diffraction disc, you will see it
is in fact smaller than that of a small refactor which doesn't "show"
bloated star images.

Well, that last bit is key. The Airy disc in a 4" refractor will be
more than twice the angular size as that in a 10" LX200 or RCX400.

Putting more light into the rings might make it look more "bloated"
than in a 10" unobstructed scope, but certainly not compared to a tiny
refractor.
--
- Mike

Ignore the Python in me to send e-mail.

On 6 Mar 2006 09:23:52 -0800, wrote:

There are a few things that would prevent APO-like images--the central
obstruction is a big one, but another on is the extremem care in
construction the optics. Both AP and TMB boast of 96% Strehl for the
'system' or somehwat better than 1/10 wave. A scope with the CO of a
SCT cannot have a 'system' strehl of better than 82%-odd. SCTs win by
giving the user portability, and large aperture at low-ish costs.


SCTs work on brute force aperture. Which is why (since resolution is
determined by aperture) some of the best planet shots come from big
SCTs and when it comes to large images of individual deepsky objects,
you cannot beat a long focal length instrument with large aperture.
-Rich

Rich wrote:
On 6 Mar 2006 09:23:52 -0800, wrote:


There are a few things that would prevent APO-like images--the central
obstruction is a big one, but another on is the extremem care in
construction the optics. Both AP and TMB boast of 96% Strehl for the
'system' or somehwat better than 1/10 wave. A scope with the CO of a
SCT cannot have a 'system' strehl of better than 82%-odd. SCTs win by
giving the user portability, and large aperture at low-ish costs.



SCTs work on brute force aperture.

Well, I do think that is a bit oversimplified