Equipment review: Meade 127 ED refractor (long)
Ian Turner
In article <freeman-not-h...@netcom.com>,
freeman-...@netcom.com (Jay Reynolds Freeman) wrote:
Prompted by discussion on sci.astro.amateur, and further seduced
by the fact that no one in my local observing group had one, I
recently bought a used optical tube assembly (OTA) for a Meade 127 mm
(five-inch) f/9 "ED" refractor. After preliminary tests and
evaluation, I report the following:
Thanks Jay
That was one of the best reviews I have ever read...........
Ian Turner
--
_____________________________________________________________________
Ian Turner
email: skysh...@mindspring.com.NOSPAM
For Astrophoto and CCD Imaging Tips & Photos:
http://www.mindspring.com/~skyshooter/
_____________________________________________________________________
Jay Reynolds Freeman
Prompted by discussion on sci.astro.amateur, and further seduced
by the fact that no one in my local observing group had one, I
recently bought a used optical tube assembly (OTA) for a Meade 127 mm
(five-inch) f/9 "ED" refractor. After preliminary tests and
evaluation, I report the following:
1) The Meade 127 ED I bought has a quite good achromatic
objective, though by no means a perfect one.
2) Mechanical quality of the OTA is good to excellent.
3) At present new and used prices -- I paid $1200 for a bare-bones
OTA with simple tube rings and with finder bracket (but no
finder) -- I consider the unit a good value.
4) The Meade 127 ED is not as well color-corrected as Vixen and
Takahashi fluorite doublet refractors, or Astro-Physics triplets.
5) The Meade 127 ED is not an apochromat, in either the technical
or the colloquial sense of the word. Meade calls it
"apochromatic"; Meade is lying.
Truth is in the details, however, so here they are.
According to the seller, I am the third owner of this particular
127 ED, and the consensus of the two previous was that this unit is
one of the better ones Meade has turned out. Reading those words made
me a little nervous, however, not just because they might be false,
but also because they might be bad news even if true. Meade's optical
quality control has been a matter of much debate recently. Three of
the four Meade objectives I have previously owned have had good to
excellent optics, and the fourth was cheerfully replaced by the
factory under warranty, but even so, the buyer of a used telescope,
with no warranty protection, does not sleep easily.
The unit showed up in due course, well packed by the seller in a
special home-built shipping unit -- he observed that I was acquiring
not only a fine telescope, but also a handsome piece of student
furniture. I opened it eagerly, hauled out the OTA, sat it on the
counter like a small beached whale, then pulled the dust cap and found
-- hoorah! -- that the optics had escaped intact from the clutches of
UPS. I took it home, cleaned it off, and set about figuring how to
set it up. I won't tell you what I used for a mount -- suffice it to
say that the Society for Prevention of Cruelty to Great Polarises has
a warrant out for my arrest. Seriously, I was surprised to find that
the GP does in fact handle a telescope of this size, though I expect
that even a little wind will render it unusable. But that was the
biggest mount I had, and a recently-purchased half-pier brought the
eyepiece up to more comfortable levels, and the OTA proved lighter
than expected, so I was indeed in business.
Though light, the OTA seems solid. The cell has push-pull
adjustments. The dew cap is held on with a setscrew. The huge rack
and pinion focuser moves smoothly, with little play, and with
adjustable tension. There are at least four internal baffles.
The finder bracket arrived late, in a separate package, but that
didn't stop me, and the notorious curse of foul weather for months
after acquiring a new telescope held off. I was able to perform a
cursory test within a few days.
As a rule of thumb, a doublet using extra-low dispersion glass
("ED" glass) as one of its components, will produce only about thirty
percent as much longitudinal chromatic aberration as one made with
good glass of more conventional types. Five-inch refractors made with
conventional-glass doublets are starting to show embarrassing amounts
of color, at focal lengths as long as f/15, so I was eager to see
whether the designer of this faster instrument had asked too much of
the fancier optical material. The quick answer was that the tradeoff
was well made -- for at 190x, the Meade showed only the barest hint of
a violet fringe on a vertically-running portion of the edge of the
Moon's disc -- less than I see in my 80 mm f/11.4 Vixen conventional
doublet. (It is important to pick a vertically-running part of the
edge of the Moon for this test, for portions inclined more toward the
horizontal might show color from atmospheric refraction alone.)
Bright stars, even Vega, showed only a faint violet haze, again much
less than similar conventional doublets. The 127 ED certainly showed
a lot less color than an old-style five-inch f/15.
By the time the instrument had settled down thermally, I was ready
for a star test. I chose one of the stars at the corners of the Great
Square. Racking the eyepiece inside focus until four or five
diffraction rings were visible gave a pleasingly regular pattern --
just like the ones in Suiter's book for a good, unobstructed system --
embedded in only a trace of violet glow. Racking the same distance
outside focus produced a puzzle: The pattern was not clean at all --
there was a broad greenish haze with a smaller set of purplish blue
features superimposed, the most prominent of which was a single blue
ring, of diameter about seventy percent of the diameter of the largest
diffraction ring seen at the corresponding inside-focus position. I
suspected a combination of spherochromatism and perhaps a zonal
aberration -- I wish I knew more about the star test -- and decided to
pursue the matter on another night. I did notice, however, that as I
was beginning to rack the eyepiece outside of focus, for the first
tiny movement the central disc of the diffraction pattern stayed quite
sharp and turned purple: Thus red and blue light were both coming to
focus longwards of green, so that the instrument was an achromat, not
an apochromat, at least, not in the strict technical sense of the
word. (See the appendix on "What's an `Apochromat'?")
I also looked at Saturn. The seeing was not perfect -- my star
test had the in-focus Airy disc always visible, but the rings always
in motion. Nevertheless, Saturn looked very fine in those occasional
instants when the seeing was best -- at 190x, I could see the Cassini
division as a feature of noticeable width, not just a line. I could
see the crepe ring and the prominent dark band in the southern
hemisphere of the planet. It was a promising view.
Later in the week, I went out earlier in the evening, for a longer
test run. I had dug out an old set of Wratten eyepiece filters, to
investigate the star test at various wavelengths. While waiting for
telescope and atmosphere to settle down, I took a look at Jupiter, at
190x. Despite unsteady conditions, the Galilean satellites all showed
distinctly non-stellar discs, of different sizes. Jupiter went behind
a tree shortly, but later on I enjoyed views of Saturn and of the Moon
similar to those of the previous evening.
For star testing, I chose Vega -- a demanding target. With no
filters, 190x revealed the same patterns as before. I repeated the
tests with red (Wratten #25A), green (#58) and violet (#47) filters in
alternation. The outside-focus ring was still present with each of
the filters, though it was diminished in intensity with the green or
red filter, compared to the violet filter and to no filter at all.
Furthermore, the distribution of intensity in the inside-focus pattern
was different for the three filters. Compared to the edge, the
relative brightness of the center was about the same with the green
filter as for no filter at all, but the center was relatively brighter
with the red filter, and relatively dimmer with the violet one. This
change in intensity is spherochromatism, also known as chromatic
variation of spherical aberration -- the system's figure is different
in different wavelengths. Spherical aberration of opposite signs in
red and violet is another hallmark of the plain achromat, and another
indication that the design is not an apochromat in the technical sense
of the word. The Wratten filters were very useful for these tests,
though they are far from perfect. Wrattens have very broad bandpasses
which are not sharply delineated: A good set of narrow-band filters
would have been much more illuminating.
These star tests were performed with a 6 mm Vixen Lanthanum
eyepiece. I repeated enough of them with another eyepiece -- an 8 mm
Brandon -- and with another star -- Polaris -- to be confident that
the results were not peculiar to just Vega or to just that eyepiece.
I attribute the less-than-perfect star test to a combination of
longitudinal color, spherochromatism, and possibly a minor zonal
error. All the text and pictures I have seen, that aid in
interpretation of star tests, are for monochromatic images. I know
very little about how to unravel test results in which different
colors of light do different things.
Polaris was of course split wide open, so for a lark I tried a
much more demanding multiple star, gamma Andromeda. The wide pair of
this system was well separated, again "of course", but I was delighted
to see at 456x just the barest hint of elongation of gamma-two
Andromeda in what, on checking, turned out to be the right position
angle. I only logged the elongation as "suspected", but even that is
quite an achievement for five inches of aperture.
My third night out with the 127 ED was for the occultation of
Aldebaran by the Moon, on October 18-19, 1997. I went to Fremont
Peak, near Salinas, California. Seeing was better than on the first
two nights, and the telescope had a long cool-down riding in the back
of my car. Jupiter at 228x showed much rich detail, and the steadier
view of Saturn confirmed all the features I had glimpsed fleetingly on
the preceding evenings. I had not brought my Wratten filters, but I
demonstrated the by now familiar star test results to several other
observers, using Altair and 228x. We also repeated those tests with
yet another eyepiece -- a 6 mm Zeiss Abbe orthoscopic, with no
significant difference except that the Zeiss orthoscopic showed less
intrinsic glare than the Vixen Lanthanum -- as had the 8 mm Brandon.
The other observers present all seemed impressed with the telescope,
and promised not to tell the SPCGP where I was.
I did a little Messier hunting -- no surprises there -- then moved
on to the Moon. Plato was several days away from the terminator, so
much that there were no shadows in or near it, but even so, I could
see at 228x three or four white spots on the floor of the crater,
three of which were at positions of some of the craterlets shown in
Rukl's atlas. Nearer the terminator, in an area of contrasty shadows,
I could see the well-developed rille system on the floor of Atlas.
The 127 ED was showing all the detail depicted in Rukl.
Not too many telescopes were present, but I got to do one neat
comparison test. Someone had an Intes 6-inch f/12 Maksutov. I was
curious to compare it to the 127 ED, because I own an Intes 6-inch
f/10, yet cannot do side-by-side comparisons with my own telescope
since I have only one mount large enough for the 127 ED or for the
Intes. The Meade seemed to be giving a slightly more contrasty view
of Saturn than did the Intes; that's about what I would have expected,
from comparing my own Intes with other five-inch refractors.
Other comparisons I can do from memory: The Meade 127 ED does not
give quite as good images as late-model Astro-Physics 130 mm
refractors, or as Takahashi 5-inch fluorites. Indeed, the Meade 127
ED shows more in-focus chromatic aberration than either Vixen and
Takahashi fluorite doublets (which are almost color-free, but will
show a trace of violet haze if you know where to look for it), or
Roland Christen's late-model Astro-Physics triplets. These latter
telescopes appear to show no chromatic aberration whatsoever, on any
object, and are the only refractors which I have ever seen that
warrant the adjective "apochromatic" in the colloquial sense (see
appendix). (Note that I do not know for sure whether the Christen
designs are in fact apochromats in the technical sense.)
(The 127 ED is a great telescope for comparison with Astro-Physics
130s. What the Meade does better, it does by its own superior virtue;
what the 130s do better is because they have 3 more mm of aperture...)
Thus although the Meade 127 ED has a fine objective -- at least,
mine does -- it is not quite the telescope for purists that the modern
fluorite doublets or the Astro-Physics triplets are; anyone who buys a
Meade ED will sooner or later see a Vixen or Takahashi fluorite, or a
Christen triplet, and be disappointed, for it is these telescopes that
create that rabid fanaticism which causes enthusiasts to swear, "You
can have my refractor when you pry it from my cold, dead hands."
When disappointment arises, perhaps the unhappy owner will say to
Meade, "What you sold is not what you advertised -- an apochromat; I
want my money back." I will be curious what Meade does in such cases,
because their advertising is manifestly absolutely false -- they
wouldn't have a leg to stand on, to justify the label "apochromatic",
if it came to a court case. You can tell the judge I said so. I am
not certain the error is deliberate -- folks who prepare ad copy often
don't know the first thing about what they are selling -- but as a
corporation, Meade is lying: There is surely enough optical expertise
within their walls to know the ED doublet they sell is not an
apochromat in the technical sense, and is not sufficiently color-free
to warrant the colloquial meaning of "apochromat".
Yet there is no reason to allow the reputation of a nice achromat
to be besmirched by the shoddy business practices and dishonest
advertising of its manufacturers. My Meade 127 ED optical tube
assembly is a fine telescope, and at $1200 (used) was an excellent
value. I expect to keep it for a long time to come.
################ Appendix -- What's an `Apochromat' ################
"Apochromat" is one of those words that has a precise technical
meaning, but has entered popular usage with a colloquial meaning that
is somewhat different. Here is an overview of what the term means.
If you plot focal length of a given telescope vertically, versus
wavelength of light horizontally, what you are hoping to see is a
straight, horizontal line -- all wavelengths of light come to focus at
the same point. Any telescope which uses only reflecting optics to
form its image will meet that goal -- Newtonians do it regularly.
Yet, put lenses in the system, and the nice straight line disappears.
One task of the optical designer is to make the graph nearly enough
straight, over the wavelengths of visible light, so that no error of
color is apparent. Just how straight it has to be depends on the
aperture and focal ratio of the telescope.
In a common-sized refractor whose objective is a simple lens, the
curve of focal length versus wavelength is an inclined line -- blue
focuses shorter than red -- of such steepness that only a small
portion of the visible spectrum is in focus at once. Simple-lens
refractors indeed show enormous color fringes about their images.
Add a second piece of the right glass, and the graph is a broad,
flattish curve, concave up. The designs used generally have the low
point of the curve at green wavelengths -- green focuses shorter than
any other wavelength -- and red and blue approximately equally out of
focus. This is the conventional achromat, in the technical sense.
With common glass types, it is hard to make the curve flat enough to
result in an image that appears color-free -- it takes small lenses
and long focal ratios to do so. ED glass makes the task easier -- the
curve is squashed by about a factor of four compared to regular types
of glass. Fluorite flattens the curve by another factor of two or
more. Thus ED achromats are better than conventional ones, and
fluorite achromats better still, as far as color correction goes.
A third piece of glass, of a type well chosen, can make the actual
graph fit the straight line even better. The curve now resembles a
very stretched-out horizontal "S". It comes up from below the
straight line at one end of the spectrum, crosses the line, flattens
out, dips back below the line, and rises, crossing one more time, and
continuing to rise, at the other end of the spectrum. This
"three-crossings" property is one of the features which define an
apochromat in the technical sense. Such a lens is sometimes said to
"bring three colors to the same focus". I will get to the other
property later. With good choices of glass, an apochromat can offer
better color correction than a conventional achromat. Not all
apochromats do that -- some early ones used the extra design freedom
to make a lens that would be in focus simultaneously for visual light
and for blue and near-ultraviolet light, so that one could focus
visually and use early, blue/ultraviolet sensitive photographic
emulsions to take a well-focused picture.
We are almost done. The second property that has to do with the
technical definition of an apochromat is how well it corrects
spherical aberration at various wavelengths. A conventional achromat
has zero spherical aberration at only one wavelength -- typically,
green. In telescope-maker's terms, the figure is good at only one
wavelength. In a classic three-lens apochromat, there are two
wavelengths at which spherical aberration is zero, and if the design
is well done, the instrument will be better corrected for spherical
aberration at other wavelengths, than an achromat.
Thus an apochromat, in the technical sense:
1) Has an "s-curve" graph of focal length versus wavelength,
so it "brings three colors to the same focus", and
2) Has zero spherical aberration at two different wavelengths.
So much for the technical definition. If you've made it this far
the rest is easy -- the colloquial definition of an apochromat is
simply an instrument which shows no false color in its images. As I
said before, there are vast numbers of instruments out there which are
superb apochromats in the colloquial sense -- any Newtonian will do
(except those few that use prism diagonals instead of mirror
diagonals). (Newtonians of course have other aberrations, such as
coma and the distortion of the diffraction pattern created by diagonal
and spider, but they are indeed color-free.)
--
Jay Reynolds Freeman -- freeman at netcom dot com -- I speak only for myself.
Clive Gibbons
In article <freeman-not-h...@netcom.com>,
Jay Reynolds Freeman <freeman-...@netcom.com> wrote:
> Prompted by discussion on sci.astro.amateur, and further seduced
>by the fact that no one in my local observing group had one, I
>recently bought a used optical tube assembly (OTA) for a Meade 127 mm
>(five-inch) f/9 "ED" refractor. After preliminary tests and
>evaluation, I report the following:
Super report, Jay!
Your additional comments about what's an "Apochromat" are especially
compelling, IMHO. Meade should take them to heart.
If memory serves, S&T did a review of the 127 a few years ago and the
optics they tested sound like a near-clone of what you have, right down to
the mild zonal error. Perhaps most of the 127s have this slight problem
with their optical figure, due to the polishing/figuring technique Meade
uses.
It's amazing to me that Meade labels their 6" and 7" scopes as
"Apochromatic", when it's obvious that they aren't any such thing. When
does a company cross the line between "creative marketing" and
"consumer fraud"??
(a rhetorical question... no need to reply, folks! <g>)
Anyways, FWIW, I'd buy a 127, too (if the price and optics were right)...
Cheers,
--
Clive Gibbons
Technician, McMaster University,
School of Geography and Geology.
Robert Preston
I stopped at a random garage sale yesterday and chanced upon a 14"-long,
5.5" diameter stove pipe with a tarnished concave mirror at one end, plus
the remains of a focusser tube and three holes in the stovepipe where
the spider for a Newtonian secondary had been attached. The primary mirror
cell and the focusser support were custom-machined parts.
It turned out that the 70+ year-old gentleman sitting in a lawn chair outside
the garage had ground the mirror about 45 years ago: a 4.5 inch, f3.3 RFT.
He hadn't gone as far as mounting it, and the secondary and focusser had been
lost along the way. He said he used to hand-hold it for rich-field viewing
(it gives 12x with a 26mm, so I guess he had steadier hands back then ;-)
He had also ground a 12" Newtonian mirror, but that 'scope was donated to a
college in New York somewhere, long ago.
"Things are different now," he reported. "They make 16" mirrors half-an-inch
thick, now, instead of 3 inches thick, and you can buy telescopes for cheap
that show just about anything you'd want to see. You can even get a
computer
telescope that aims itself."
"I know," I said. "I have one of those."
We traded stories for a while, and then I asked him how the figure was on the
4.5" and he said it was pretty decent, for rich-field viewing, at least. Then
he said I could have it free, if I'd like to fix it up. I said I'd take it.
But I said he'd better take at least a symbolic payment, to avoid any potential
problem with the garage management (his wife). It cost me $5. I guess it'll
be another $30 to realuminize it. I took it home and used the secondary and
focusser from my ancient 6" f8 Newt to get it operational for star testing.
The view was just horrible at first sight, but after the tube currents
disappeared it was like he said - great for low power viewing (well, it will be
great after recoating it and the secondary - right now it has about 25% total
reflectance, comparing the image with that in a 10x70 monocular that has
half the
area). It's even pretty acceptable for "high" power (with a 6.4mm plossl the
"high" power is only 50x!). The 50x view of Saturn was reminiscent of the
images
I saw 40 years ago (through a toy 3" Newtonian) that originally hooked me on the
night sky and telescopes.
Has anyone else found any telescope deals (or busts!) at a garage sale?
RP
Pittsburgh PA
Todd Gross
regarding the Vixen 90mm...
> 105 mm is bigger than 90 mm, and aperture wins. However, as far as
>optical quality goes, my mid-1980s-vintage 90 mm Vixen fluorite,
>originally sold under the Celestron label, gives up nothing to nobody.
>With it I have seen six stars in the Trapezium, and clouds and snow in
>the vicinity of Olympus Mons on Mars (last opposition).
you've got to be kidding
> I have no way
>to know whether they are all that good (except hearsay, which says
>they are), but if you get one like mine I suspect you will be well
>pleased, and will find the instrument to have high resale value in any
>case. My 90 mm is the only refractor I have that I would not for a
>moment consider selling. The original owner moved out of the Bay Area
>shortly after he sold it to me, and I did not see him again for some
>eight years. When we encountered one another the next time, I shook
>his hand delightedly and said, "Hi ____! You can't have your
>telescope back!"
Jay.. thanks for that encouragement, I believe it is the 1980s model, yes.
Well, that explains a few things. I actually dis-believed the seller when he
claimed to have seen the Cassini division during 1996.. since I could barely
make it out in a 7" meade mak
Appreciate the info.
Thanks! - Todd
_________________________________
BOSTON TV METEOROLOGIST TODD GROSS
Weather/Astronomy Home Page: http://www.weatherman.com
Administrator, Meade Advanced Product User Group: ma...@shore.net
Administrator, New England Weather Observer Mail List: wxob...@shore.net
IRC Channel Operator: #Weather (Undernet)
Originator of the NE.WEATHER newsgroup
_________________________________
Email: to...@weatherman.com Work Phone# (617)725-0777
Borcard Daniel
On Mon, 20 Oct 1997, Jay Reynolds Freeman wrote:
> Prompted by discussion on sci.astro.amateur, and further seduced
> by the fact that no one in my local observing group had one, I
> recently bought a used optical tube assembly (OTA) for a Meade 127 mm
> (five-inch) f/9 "ED" refractor. After preliminary tests and
> evaluation, I report the following:
>
> Polaris was of course split wide open, so for a lark I tried a
> much more demanding multiple star, gamma Andromeda. The wide pair of
> this system was well separated, again "of course", but I was delighted
> to see at 456x just the barest hint of elongation of gamma-two
> Andromeda in what, on checking, turned out to be the right position
> angle. I only logged the elongation as "suspected", but even that is
> quite an achievement for five inches of aperture.
<GASP!> Last year I got the same results when testing my 6 inch Aries
refractor, and even Markus Ludes (who sells these beasts) told me that he
would first have a look at it before believing me! After all, the two
components are only 0.5 arc seconds apart... Compliments!
Daniel
Jay Reynolds Freeman
> I seem to remember a series of recent posts on splitting gamma
> Andromedae with an AP Traveler as well. Is this binary really the
> extreme test of optics that we're making it out to be? (admittedly I
> have not yet been able to split it in my C5 but that's not saying much)
Gamma Andromeda is a very easy double -- ten arc seconds or so, comparable
magnitudes. One of those two components, however, is itself an 0.5 or 0.6
second double, whose components differ in brightness by enough to matter.
I have seen it elongated in five and six inches aperture. I myself have
split it in no aperture smaller than eleven inches (might be doable, though);
I doubt any five- or six-inch telescope will split gamma-two Andromeda at
its present separation, much less any four-inch
Steve
Jay Reynolds Freeman wrote:
<snip>
> Gamma Andromeda is a very easy double -- ten arc seconds or so, comparable
> magnitudes. One of those two components, however, is itself an 0.5 or 0.6
> second double, whose components differ in brightness by enough to matter.
> I have seen it elongated in five and six inches aperture. I myself have
> split it in no aperture smaller than eleven inches (might be doable, though);
> I doubt any five- or six-inch telescope will split gamma-two Andromeda at
> its present separation, much less any four-inch
>
Jay,
I realize that you are discussing the "second" close double but I wrote
inaccurately. "Split" was not the correct word to use because, if I
remember the Traveler posts correctly, the dimmer star was sitting in in
the first diffraction ring of its brighter companion. Elongation is
more accurate and I stand corrected. Thanks
Good seeing
Steve
Steve
Todd Gross wrote:
>
<snip>
> Read Jay's other post to you, he's talking about further splitting one of the
> stars.. (only a .5 arc second separation)
Todd,
Thanks for pointing out Jay's reply - I've already posted back that I
wrote "split" but should have written "elongated". I know there's a big
difference between the two but wasn't thinking critically at the time.
I also have to apologize to everyone for the multiple reply posts -
server problems.
>The ultimate test, which I have not
> yet had skies steady enough to beat.
<snip>
Can you used defocusing to beat moderately unsteady skies? Would the
dimmer companion's diffraction rings be visible as they cut across the
diffraction minima from the brighter star? I suppose a purist might
consider this cheating but if you needed to know whether there was a dim
member of a binary, this might give you the answer.
Good seeing,
Steve
Steve
Jay Reynolds Freeman
> > Gamma Andromeda is a very easy double -- ten arc seconds or so,
> > comparable magnitudes. One of those two components, however, is
> > itself an 0.5 or 0.6 second double, whose components differ in
> > brightness by enough to matter. I have seen it elongated in five
> > and six inches aperture. I myself have split it in no aperture
> > smaller than eleven inches (might be doable, though); I doubt any
> > five- or six-inch telescope will split gamma-two Andromeda at its
> > present separation, much less any four-inch
>
> I realize that you are discussing the "second" close double but I wrote
> inaccurately. "Split" was not the correct word to use because, if I
> remember the Traveler posts correctly, the dimmer star was sitting in in
> the first diffraction ring of its brighter companion. Elongation is
> more accurate and I stand corrected. Thanks
Um, the radius from the center of the Airy disc to the middle of the first
*bright* ring, in a theoretically perfect diffraction pattern at 105 mm
aperture, is rather more than two arc seconds. Radius to the first minimum
is something like 1.3 arc seconds. I missed that thread, sounds as if it
was interesting. It is still not clear from what you said, where the presumed
star was located.
Todd Gross
> I seem to remember a series of recent posts on splitting gamma
>Andromedae with an AP Traveler as well. Is this binary really the
>extreme test of optics that we're making it out to be? (admittedly I
>have not yet been able to split it in my C5 but that's not saying much)
Read Jay's other post to you, he's talking about further splitting one of the
stars.. (only a .5 arc second separation) The ultimate test, which I have not
yet had skies steady enough to beat.
Thanks! - Todd
Steve
Jay Reynolds Freeman wrote:
<snip>
>
> *bright* ring, in a theoretically perfect diffraction pattern at 105 mm
> aperture, is rather more than two arc seconds. Radius to the first minimum
> is something like 1.3 arc seconds. I missed that thread, sounds as if it
> was interesting. It is still not clear from what you said, where the presumed
> star was located.
Jay,
It's a tough job being an idiot and I guess I've volunteered. I did a
DejaNews search and it turns out that the star in question was Delta
Cygni not Gamma Andromedae. My sincere and humble apologies to all who
wasted their time reading my erroneous posts.
For those who are interested here is the original post from Phil Blanda:
Subject: Delta Cygnus experience
From: bla...@aol.com (Blandp1)
Date: 1997/09/12
Message-ID: <19970912122...@ladder02.news.aol.com>
Newsgroups: sci.astro.amateur
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I was clued in that Delta Cygnus would be a challenging test for a 4"
telescope (Or most any kind, read on). While at 1st glance the
seperation,
1.8", doesn't seem like a big deal, the primary is mag 2.87 and the
comes
is approx. mag. 6.5. What makes this even harder is that 1.8"
seperation
puts the comes in the 1st diffraction ring of the primary.
Being a new, enthusiastic Traveler owner (105mm f/5.8 APO) and a budding
double star observer, I thought I'd give it a go.
At 135X (TV 2X Barlow and Nagler 9mm) I could barely make out the comes.
It was detectable, just not real obvious. At 203X (TV 2X Barlow and 6mm
Pentax SMC Ortho) it was obvious. It appeared to be a faint bluish star
right on or near the diffraction ring, depending on how the atmosphere
was
dancing. It is a neat looking double with the blueness of the comes,
the
brightness of the primary and the diffraction rings all coming into
play.
It didn't seem that the Travler was challenged too much by this double.
Anyone else try this star?
-Philip J. Blanda III
Now you'll have to excuse me while I go crawl under a rock and hide.
Steve
Jay Reynolds Freeman
> It's a tough job being an idiot and I guess I've volunteered.
Cheer up, it gets lots easier with practice. I should know...
Clifford Rourke
freeman-...@netcom.com (Jay Reynolds Freeman) wrote:
> Prompted by discussion on sci.astro.amateur, and further seduced
>by the fact that no one in my local observing group had one, I
>recently bought a used optical tube assembly (OTA) for a Meade 127 mm
>(five-inch) f/9 "ED" refractor. After preliminary tests and
>evaluation, I report the following:
Thank you very much for taking to time to write this interesting and
educational review.
I have a few questions after reading it:
- How did you find the used scope?
- How did you work the deal with the seller?
Good Seeing!.
Clifford Rourke
Antelope Valley Astronomy Club
Remove the spam block to email.
Steve
Jay Reynolds Freeman wrote:
>
> > It's a tough job being an idiot and I guess I've volunteered.
>
> Cheer up, it gets lots easier with practice. I should know...
>
> --
>
Jay,
Thanks for the sentiment. I'm going to try not to practice too hard
:-)
Good seeing,
Steve
Jay Reynolds Freeman
>freeman-...@netcom.com (Jay Reynolds Freeman) wrote:
> > Prompted by discussion on sci.astro.amateur, and further seduced
> > by the fact that no one in my local observing group had one, I
> > recently bought a used optical tube assembly (OTA) for a Meade 127 mm
> > (five-inch) f/9 "ED" refractor. After preliminary tests and
> > evaluation, I report the following:
>
> Thank you very much for taking to time to write this interesting and
> educational review.
>
> I have a few questions after reading it:
>
> - How did you find the used scope?
It came up in the ads on AstroMart (http://www.astromart.com)
> - How did you work the deal with the seller?
I mailed the seller a check at approximately the same time the
seller shipped the OTA. We were each trusting the other, to some
degree. Other means of dealing with large purchases include
UPS COD or USPS COD, and I believe there are brokers who will
take delivery of the shipped item and the check, and not forward
either till both are in hand -- though then, of course, you
both have to trust the broker.
Paul F. Gustafson, D.V.M.
Jay,
Just curious--the Meade catalog is very specific in stating that the
_front_ element of the air-spaced doublet is multicoated. Since they are
not shy about describing the qualities of their equipment, I would assume
their being so specific about the coated front element and not mentioning
the rear element when talking about coatings means the rear element is not.
This would mean half of the four air/glass surfaces are uncoated, and this
should impact the light transmission and contrast noticeably. Meade's own
binocular ads claim that each uncoated surface reduces light transmission
ten percent. From what I've read, that is probably an overstatement on
Meade's part. Are you able to tell if the rear element is coated or not?
Regards,
Paul
Jay Reynolds Freeman <freeman-...@netcom.com> wrote in article
<freeman-not-h...@netcom.com>...
> Prompted by discussion on sci.astro.amateur, and further seduced
> by the fact that no one in my local observing group had one, I
> recently bought a used optical tube assembly (OTA) for a Meade 127 mm
> (five-inch) f/9 "ED" refractor. After preliminary tests and
> evaluation, I report the following:
(snip)
AndersonRM
In article <01bce33e$3a9ee2a0$6153...@drgus.erols.com>, "Paul F.
Gustafson, D.V.M." <dr...@erols.com> writes:
> Meade's own
>binocular ads claim that each uncoated surface reduces light transmission
>ten percent. From what I've read, that is probably an overstatement on
>Meade's part. Are you able to tell if the rear element is coated or not?
>
>
Uncoated surfaces reflect 4% of the light. Hard coated, single layer, mag
fluoride is 97.5-98.5% and multicoatings take it to about 99%.
Look at the reflections of a point source or a light in the front of the
lenses. You will see multiple reflections of the light at each surface.
Reflections from the coated surfaces will be coloured blue or green,
uncoated will be naturally coloured.
-Rich
Clive Gibbons
In article <01bce33e$3a9ee2a0$6153...@drgus.erols.com>,
Paul F. Gustafson, D.V.M. <dr...@erols.com> wrote:
>This would mean half of the four air/glass surfaces are uncoated, and this
>binocular ads claim that each uncoated surface reduces light transmission
>ten percent. From what I've read, that is probably an overstatement on
>Meade's part. Are you able to tell if the rear element is coated or not?
I'm sure Jay will confirm this; Yes the rear element is uncoated.
However, it's no big deal, since the each uncoated surface reflects about
4.5%, compared to about 1% for the coated surfaces. This results in a loss
of about 7% in total, which I seriously doubt anyone could visually
detect. The effect on the scope's level of contrast would be even less
apparent. If there were 2 or three more uncoated surfaces in the system,
the difference might be apparent.
If Meade actually claims that each uncoated surface reduces transmission
by 10%, that statement is blatantly false.
Geoff Gaherty
I joined this group just after your original message had scrolled off my
news server, but finally went to the archives and captured. Very
informative. I only wish that you'd been able to evaluate the other
half of the scope: the mounting.
Has anyone else here had firsthand experience with the mountings on
Meade's so-called apochromats?
Geoff Gaherty
Toronto, Canada
AndersonRM
In article <34565A...@logicbbs.org>, Geoff Gaherty
<Geoff....@logicbbs.org> writes:
>Has anyone else here had firsthand experience with the mountings on
>Meade's so-called apochromats?
Yes. The are all quite stable, but in this order, best to worst:
Meade 6-inch and mount.
Meade 7-inch and mount.
Meade 4-inch and mount.
Meade 5-inch and mount.
I've used them all and found the LX drives to work very well.
The 7-inch on it's mount is theoretically the least stable, but
in real use, it's mass damps out high-frequency vibration and
it settles down quite fast after having been touched.
All the scopes can be set-up in about 5 minutes.
My record was three minutes with the 7-inch over a concrete
driveway! Scary when you're dealing with a lens the size of
a small dinner plate!
-Rich
Paul F. Gustafson, D.V.M.
Your figures are what I have seen elsewhere. For fun, pick up any birding
magazine, go to the 2-page Meade ad--they not only say an uncoated surface
reflects 10 % of the light, they even have a little picture of the 10%
bouncing away. :-)
Regards,
Paul
Clive Gibbons <gibb...@mcmail.cis.McMaster.CA> wrote
>>snip<<
>each uncoated surface reflects about 4.5%
>>snip<<
> If Meade actually claims that each uncoated surface reduces transmission
> by 10%, that statement is blatantly false.
> Cheers,
Ernest M. Sheckolyan
10% - average lose if light passes through glass with
two uncoated surfaces (10%=5%+5%).
Ernest.
Paul F. Gustafson, D.V.M. <dr...@erols.com> wrote in article
<01bce602$f027e240$5a53...@drgus.erols.com>...
Paul F. Gustafson, D.V.M.
I understand. However, Meade shows the 10% loss from the single front
surface in the ad, not both surfaces.
Regards,
Paul
Ernest M. Sheckolyan <Ern...@msoft.ru> wrote in article
<01bce61a$4fe0c500$a5cd...@ernest.MSoft>...
David Boll
From: dwb...@gr.hp.com (David Boll)
Paul F. Gustafson, D.V.M. (dr...@erols.com) wrote:
: I understand. However, Meade shows the 10% loss from the single front
: surface in the ad, not both surfaces.
We better inform them of their mistake, I'm sure they wouldn't want
to mislead anyone.
--
Dave Boll
http://www.omn.com/dboll
Discreet
In article <34529...@mournblade.ptw.com>,
crourk...@ptw.com (Clifford Rourke) wrote:
>freeman-...@netcom.com (Jay Reynolds Freeman) wrote:
>
>> Prompted by discussion on sci.astro.amateur, and further seduced
>>by the fact that no one in my local observing group had one, I
>>recently bought a used optical tube assembly (OTA) for a Meade 127 mm
>>(five-inch) f/9 "ED" refractor. After preliminary tests and
>>evaluation, I report the following:
>
>Thank you very much for taking to time to write this interesting and
>educational review.
>I have a few questions after reading it:
>- How did you find the used scope?
>- How did you work the deal with the seller?
>
>
>Good Seeing!.
>Clifford Rourke
>Antelope Valley Astronomy Club
>Remove the spam block to email.
>
I have always heard that a "Florite" coating is the best refractor, is Mead's
"ED" better?
Clive Gibbons
In article <01bce61a$4fe0c500$a5cd...@ernest.msoft>,
Ernest M. Sheckolyan <Ern...@msoft.ru> wrote:
>10% - average lose if light passes through glass with
>two uncoated surfaces (10%=5%+5%).
>
>Ernest.
Uhh, by that method, if there were 20 uncoated surfaces, the
transmission would be zero... ;)
Actually to derive the transmission (assuming 5% loss per surface), it's
0.95 x 0.95 x 100 = % transmitted, which is 90.25% in this case.
Cheers,
--
Clive Gibbons
Ander...@mizar.ursa.fi
From: ander...@aol.com (AndersonRM)
In article <63e6ru$h...@sjx-ixn8.ix.netcom.com>, Discreet
<disc...@ix.netcom.com> writes:
> I have always heard that a "Florite" coating is the best refractor, is
>Mead's
>"ED" better?
And you professionally use telescopes for astrophotography?
You don't know anything about telescopes do you?
Fluorite is a crystalline material used in the construction of
apochromatic refractor objectives and some microscope objectives.
Magnesium FluoriDe is a material used to coat glass lenses
to decrease surface reflectivity.
ED can be any number of different glasses with abnormal
dispersive properties.
-Rich
AndersonRM
In article <c9860b...@mizar.ursa.fi>, David Boll
<David...@mizar.ursa.fi> writes:
>: I understand. However, Meade shows the 10% loss from the single front
>: surface in the ad, not both surfaces.
>
>We better inform them of their mistake, I'm sure they wouldn't want
>to mislead anyone.
The exaggeration by Meade and other companies isn't suprising.
People seem to think that the extra light transmission is the most
important thing for coatings to do. The true importance of
enhanced coatings and multicoatings is to increase image
contrast thereby making details more easily visible.
-Rich
Paul F. Gustafson, D.V.M.
:-)
David Boll <dwb...@gr.hp.com> wrote in article
> We better inform them of their mistake, I'm sure they wouldn't want
> to mislead anyone.
> Dave Boll
Clive Gibbons
In article <63d9km$n7...@hpbs1500.boi.hp.com>,
>: surface in the ad, not both surfaces.
>
>to mislead anyone.
ROTFL!!
Good one, Dave! :)
Clive Gibbons
In article <19971102112...@ladder02.news.aol.com>,
AndersonRM <ander...@aol.com> wrote:
>The exaggeration by Meade and other companies isn't suprising.
>People seem to think that the extra light transmission is the most
>important thing for coatings to do. The true importance of
>enhanced coatings and multicoatings is to increase image
>contrast thereby making details more easily visible.
>-Rich
This raises an interesting point, though.
Enhanced coatings, multicoatings, even plain ol' aluminum or MgF2 coatings
actually increase scattering, when compared to uncoated optics. Therefore,
they are not entirely beneficial to image contrast. For a rather extreme
example, consider the coronagraph (an instrument used to observe the solar
corona without the aid of a total solar eclipse). All lens surfaces in
such instruments are uncoated, since any coating would decrease contrast
to the point that the Sun's corona wouldn't be visible.
Multi-coated optics scatter more light than single coated optics, which
scatter more light than uncoated optics.
Personally, it's my belief that adverting claims of "enhanced
coatings", etc. *noticably* increasing visual contrast in typical
telescope systems, is so much hype. Yes, they can noticably increase the
brightness of the image, but in a well-baffled system, image contrast
won't be improved by any perceptible margin.
Nils Olof Carlin
Clive wrote:
> This raises an interesting point, though.
> Enhanced coatings, multicoatings, even plain ol' aluminum or MgF2
coatings
> actually increase scattering, when compared to uncoated optics.
Therefore,
> they are not entirely beneficial to image contrast.
My impression is that coatings improve contrast by reducing the non-focused
reflected light reaching the focal plane (where it is spread more or less
evenly).
Nils Olof
Jeff Medkeff
On 2 Nov 1997 20:30:24 -0500, gibb...@mcmail.cis.McMaster.CA
(Clive Gibbons) is suspected to have said:
>Enhanced coatings, multicoatings, even plain ol' aluminum or MgF2 coatings
>actually increase scattering, when compared to uncoated optics.
>Personally, it's my belief that adverting claims of "enhanced
>coatings", etc. *noticably* increasing visual contrast in typical
>telescope systems, is so much hype.
Interesting posting, Clive.
I have an eyepiece here ($3 swap table special, guy forced me to
take it with what I was really buying), it is a three-element
design, two of the lenses are cemented together. Apparently there
is no coating on any surface. Reflections are horrible in this
eyepiece (I kept it thinking I would make a Cheshire with it),
and contrast is very damaged for that reason.
Is the problem here that the eyepiece has no coatings and thus
reflects a lot of light around internally, or is the eyepiece a
piece of junk no matter what the coatings are?
I realize that your comments were in the context of a thread
about objectives, and this is changing the subject a bit.
--
Jeff Medkeff | If a little knowledge is a dangerous
An Amateur Astronomer | thing, where is the man who has so
in Sierra Vista, AZ | much as to be out of danger?
| (Thomas Henry Huxley)
AndersonRM
In article <63j9fg$r...@mcmail.CIS.McMaster.CA>,
gibb...@mcmail.cis.McMaster.CA (Clive Gibbons) writes:
>Enhanced coatings, multicoatings, even plain ol' aluminum or MgF2 coatings
>actually increase scattering, when compared to uncoated optics.
Only if the optics suffer from noticeable surface roughness.
If the optics are smooth (or low power like a camera lens)
they are improved by coating them.
-Rich
tri...@nospam.earthlink.net
Clive Gibbons wrote:
>
>Multi-coated optics scatter more light than single coated optics,
>which scatter more light than uncoated optics.
Huh??
Transmission = Incident-Reflection-Absorbtion
Clive, if a surface reflects or absorbs more light, how can transmission
be higher? Perhaps I'm naive, but I always thought that coatings
increased transmission by reducing absorbtion and reflection.
James McSheehy
<to reply, make the necessary changes in my e-mail address>
Clive Gibbons
In article <63l83d$p...@mcmail.cis.mcmaster.ca>,
Clive Gibbons <gibb...@mcmail.cis.McMaster.CA> wrote:
>In article <19971103101...@ladder01.news.aol.com>,
>AndersonRM <ander...@aol.com> wrote:
>>Only if the optics suffer from noticeable surface roughness.
>>If the optics are smooth (or low power like a camera lens)
>>they are improved by coating them.
>>-Rich
>
>optics, to show the contrary.
D'OH!!
My apologies for following up my own post and further apologies to Rich
for my mistake in saying that an Al coating will increase light
scattering, compared to bare glass. This is untrue. Texereau shows that an
evaporated Al surface has essentially the same scattering characteristic
as the bare glass reflecting surface.
However, I stand by my previous statements that anti-reflection coatings
do increase light scattering, compared to bare glass and the more layers
the coating has, the greater the amount of scatter.
Over and out...