80 mm Messier hunting from Palo Alto, California
Jay Reynolds Freeman
Anxious to take advantage of a break in a long run of wet weather,
I hauled an 80 mm f/11.3 Celestron refractor into my yard in Palo
Alto, California, on the evening of Sunday, 23 November, 1997, for a
round of Messier hunting. The rain-washed sky was quite transparent,
hence the lights of suburbia were less bother than usual. At 32x, I
started ambitiously with M74, perhaps the most difficult Messier
galaxy, on grounds of low surface brightness and small size. It took
averted vision to hold it, but it was there. M77, not far away, was
much easier, and M76 -- faint but of higher surface brightness --
showed its well-known two-lobed shape.
M33 was much easier than M74 had been. Still at 32x, I could hold
it with direct vision, though it was tenuous. M1 was not difficult,
and hinted of asymmetric shape. The clusters M34, M35, M36, M37 and
M38 were all easily resolved, as were the Pleiades. I saw no hint of
nebulosity in the latter. Dropping to Lepus, I found the fuzzy spot
of globular M79, well down in the haze. M78, in Orion, showed two
stars embedded in a stubby comet-shaped patch of nebulosity, and
M42/43 were gloriously detailed, but revealed no color to my eye with
this aperture on this evening.
My 80 mm Celestron is one of the older models, made by Vixen in
Japan, It has very nice optics, which are well baffled. The mounting
is the kind of altazimuth that both Celestron and Meade have sold with
refractors of similar sizes; it takes a lot of fiddling with wrenches
and screwdrivers to keep the slop to manageable proportions, but it is
a light, inexpensive altazimuth mounting that does work -- the whole
telescope, together with a small pouch of eyepieces, is a one-hand
carry out to my yard.
How nice to be reminded that amateur astronomy which is
interesting, and perhaps even subtle, can be done with small aperture
from a suburban location. The rewards are particularly pleasant when
the weather conspires against better-planned trips to darker sites,
as they have been for almost a month. And tonight, it is pouring
again....
--
Jay Reynolds Freeman -- freeman at netcom dot com -- I speak only for myself.
Len
In article <freeman-not-h...@netcom.com>,
freeman-...@netcom.com (Jay Reynolds Freeman) wrote:
> How nice to be reminded that amateur astronomy which is
> interesting, and perhaps even subtle, can be done with small aperture
> from a suburban location. The rewards are particularly pleasant when
> the weather conspires against better-planned trips to darker sites,
> as they have been for almost a month. And tonight, it is pouring
> again....
>
> --
>
> Jay Reynolds Freeman -- freeman at netcom dot com -- I speak only for myself.
Hey Jay. I really enjoy my Celestron 80mm 11.3 as well for the same
resons. It's one of the new Chinese ones but seems to have ok optics.
Jupiter and Saturn are very good up to 150x (18mm Univ. Ortho and Meade
#126 barlow placed in front of a University 90 degree diagonal). Cassini's
is seen under good seeing and I've had no trouble seeing many tiny belts
in Jupiter's N and S hemispheres as well as hints of detail in the EQ
regions. Satellite phenomena are very nice, although I can't be sure I've
seen a transit of anything but the moons' shadows. Perhaps I haven't had
the right seeing at the proper time yet.
The moon is spectacular and chromatic abberation is not too objectionable
even at 150x. The double cluster looks great even under light polluted
skies. Globulars and Ring Nebula look like smudges and so does Andromeda.
I have no trouble seeing its brighter companion M110 as a distinct very
small smudge in the field. Currently I use the Celestron 26mm as low power
but am getting a Meade Super Plossl 40mm for X-mas. The extra exit pupil
should give better detail in faint nebulosity.
One question: the star test is fine inside focus, and images form nice
pinpoints, but outside focus I can't get a diffraction pattern, just a
bunch of "noise", i.e. tiny swirling areas where the diffraction pattern
should be. I've split the double double with no problem on many occasions.
I've tried the star test on many different nights on many different stars
after adequate cooling and with different mag/eyepiece combos and get the
same result. What gives?
Thanks,
-Len
--
In summing up the moral seems a little bit obscure...
-Phish
Phil Sullivan
On Tue, 25 Nov 1997 05:00:47 GMT, freeman-...@netcom.com (Jay
Reynolds Freeman) wrote:
snip, snip
> How nice to be reminded that amateur astronomy which is
>interesting, and perhaps even subtle, can be done with small aperture
>from a suburban location. The rewards are particularly pleasant when
>the weather conspires against better-planned trips to darker sites,
>as they have been for almost a month. And tonight, it is pouring
>again....
Jay,
I've often thought that telescopes are similar to boats. The amount
of use one gets from them is inversely proportional to their size I
love my little Celestron 80mm flourite refractor on an old Polaris
mount. I use it frequently despite have a C14 in an observatory
nearby.
Phil Sullivan
William Hamblen
On Wed, 26 Nov 1997 04:20:48 -0600, rai...@usa.net (Len) wrote:
>One question: the star test is fine inside focus, and images form nice
>pinpoints, but outside focus I can't get a diffraction pattern, just a
>bunch of "noise", i.e. tiny swirling areas where the diffraction pattern
>should be. I've split the double double with no problem on many occasions.
>I've tried the star test on many different nights on many different stars
>after adequate cooling and with different mag/eyepiece combos and get the
>same result.
Try putting a deep yellow filter on the eyepiece. Chromatic
aberration messes up the star test on ordinary refractors and a yellow
filter will block the out of focus color. Use highest possible
magnification and don't throw the star much out of focus - just enough
to see 5 or 6 diffraction rings either way.
Len
In article <3484cbd0...@news.nashville.com>,
William...@nashville.com wrote:
> Try putting a deep yellow filter on the eyepiece. Chromatic
> aberration messes up the star test on ordinary refractors and a yellow
> filter will block the out of focus color. Use highest possible
> magnification and don't throw the star much out of focus - just enough
> to see 5 or 6 diffraction rings either way.
Thanks!
Jay Reynolds Freeman
> [Report on one of the "new", Chinese-manufactured Celestron 80 mm
> refractors]
> One question: the star test is fine inside focus, and images form nice
> pinpoints, but outside focus I can't get a diffraction pattern, just a
> bunch of "noise", i.e. tiny swirling areas where the diffraction pattern
> should be. I've split the double double with no problem on many occasions.
> I've tried the star test on many different nights on many different stars
> after adequate cooling and with different mag/eyepiece combos and get the
> same result. What gives?
Two things may be going on. First, whey you rack outside of focus,
you are actually focusing the telescope for distances less than
infinity. If seeing is poor, you may find that you are focused
precisely on one of the turbulent layers of the atmosphere that cause
it; you will then in effect be looking a sharp image of atmospheric
burbles illuminated by starlight. If your image outside of focus is
at all in motion, this phenomenon is likely to be present, and you
must wait for better seeing to continue the test.
But even in good seeing, there is still an effect which is actually
related to the objective, which may cause the difficulty. In a
conventional achromat, the focal position for green light is closest
to the objective; all other wavelengths of visible light are focused
to various slightly greater distances. Thus when you rack a bit
outside of focus, you are looking at a mixture of out-of-focus green,
with other colors of light that are in better focus. This jumble can
be quite confusing. The reason why the effect is less inside of focus
is that inside of focus, all the other colors of light are even more
out of focus than green is, and are so much blurred out that the only
details you see are from the green light.
That is, the star test, as conventionally described, is for light of
a single color only -- when different colors of light behave
differently -- as they do in a conventional refractor -- things can
get quite confusing. If you had a very narrow-band green filter, you
might get better results outside of focus -- you'd need a quite
specialized one, though; just a piece of green glass or a
photographer's green filter won't do it well enough. But I do not
think you should buy one unless you are really curious; if your
telescope gives the textbook pattern inside focus, and gives good
images otherwise, it's probably fine -- or at any rate, is doing as
well as you'd expect a conventional doublet to do.
Todd gross
>photographer's green filter won't do it well enough. But I do not
>think you should buy one unless you are really curious; if your
>telescope gives the textbook pattern inside focus, and gives good
>images otherwise, it's probably fine -- or at any rate, is doing as
>well as you'd expect a conventional doublet to do.
>--
> Jay Reynolds Freeman -- freeman at netcom dot com -- I speak only for myself.
Jay, excellent post. However, this has been frustrating me on non apos lately.
I think it clouds the issue of Spherical Aberration, and your suggestion above
would lead the newbie star tester to overlook SA... if he just assumes that he
should just check the inside of focus pattern for concentric rings, crispness,
etc.. the outside could be horrible, because of strong SA, no??
Also..by definition.. do APOs all have no color on either side of focus.. or
just in-focus. The best scopes I have tried are colorless both ways, but other
supposedly APO scopes have showed some color on eithe rside of focus.
don
Jay Reynolds Freeman wrote in message ...
>>Two things may be going on. First, whey you rack outside of focus, you
are actually focusing the telescope for distances less than infinity. If
seeing is poor, you may find that you are focused precisely on one of the
turbulent layers of the atmosphere that cause it; you will then in effect be
looking a sharp image of atmospheric burbles illuminated by starlight. If
your image outside of focus is at all in motion, this phenomenon is likely
to be present, and you must wait for better seeing to continue the test.<<
Not having previously given this a lot of thought, it seems to me that if we
move the focuser to the rear (what I have traditionally thought as moving
"outside of focus") aren't we actually focusing closer? If so, wouldn't
this really be moving "inside of focus?"
Believe it or not this is a legitimate question for me.
Best, Don
Jay Reynolds Freeman
> > photographer's green filter won't do it well enough. But I do not
> > think you should buy one unless you are really curious; if your
> > telescope gives the textbook pattern inside focus, and gives good
> > images otherwise, it's probably fine -- or at any rate, is doing as
> > well as you'd expect a conventional doublet to do.
>
> Jay, excellent post. However, this has been frustrating me on non apos
> lately. I think it clouds the issue of Spherical Aberration, and your
> suggestion above would lead the newbie star tester to overlook
> SA... if he just assumes that he should just check the inside of focus
> pattern for concentric rings, crispness, etc.. the outside could be
> horrible, because of strong SA, no??
My understanding of the star test is that when done with monochromatic
light, the images inside and outside of focus are duals, in the sense
that any aberration visible in one position will show up in some other
way in the other position. There are specific aberrations which are
easier to detect in one location than the other, but I think my advice
was reasonable.
> Also..by definition.. do APOs all have no color on either side of
> focus.. or just in-focus. The best scopes I have tried are colorless
> both ways, but other supposedly APO scopes have showed some color on
> either side of focus.
By strict definition, in the technical sense of the word, an
apochromat is not guaranteed to be color-free even in focus, though
most of those on the market are pretty much so. There are also
non-apochromats (again using the word in its technical sense) which
have little or no detectable color in focus -- such as the fluorite
refractors by Vixen and Takahashi.
Jay Reynolds Freeman
> >Two things may be going on. First, whey you rack outside of focus, you
>
> move the focuser to the rear (what I have traditionally thought as moving
> "outside of focus") aren't we actually focusing closer? If so, wouldn't
> this really be moving "inside of focus?"
I'd say you are moving the focuser outside of focus, because you are
moving the eyepiece further away from the rest of the telescope. But you
may certainly use whatever convention you wish...
don
Jay Reynolds Freeman
>> I'd say you are moving the focuser outside of focus, because you are
moving the eyepiece further away from the rest of the telescope. But you
may certainly use whatever convention you wish...<<
Jay,
This has always been my understanding too I was just thinking out loud about
what might be inside or out side of focus based on what you said about
moving the focuser so the eyepiece moves away from the objective is actually
moving the focus to the inside of infinity. Then again, that's what happens
when I think too often. The mind is a terrible thing. :-)
don
Scott G. Ainsworth
Since the focal length of the primary objective is fixed, I thought the
focal point was also fixed. So, moving outside of focus is moving farther
away from the primary and moving inside of focus is getting closer. (Then
again, I am just getting back into this and may be confused.)
don wrote in message <65uf23$2he$1...@news01.micron.net>...
Herm Perez
Hey Jay, this sounds like an OIII filter (g)..
Herm
On Sat, 29 Nov 1997 20:26:36 GMT, freeman-...@netcom.com (Jay
Reynolds Freeman) wrote:
>
> That is, the star test, as conventionally described, is for light of
>a single color only -- when different colors of light behave
>differently -- as they do in a conventional refractor -- things can
>get quite confusing. If you had a very narrow-band green filter, you
>might get better results outside of focus -- you'd need a quite
>specialized one, though; just a piece of green glass or a
Herm Perez
Hi Don, on a related subject..when focusing an SCT, rotating the knob
clockwise is "outside" or "inside"???...this makes it hard to do a
star test if you don't know the direction of focus.
Herm
On Mon, 1 Dec 1997 05:38:02 -0800, "don" <bo...@compuserve.com-spam>
wrote:
>
>Jay Reynolds Freeman
>
>>> I'd say you are moving the focuser outside of focus, because you are
>moving the eyepiece further away from the rest of the telescope. But you
>may certainly use whatever convention you wish...<<
>
>Jay,
>
>This has always been my understanding too I was just thinking out loud about
>what might be inside or out side of focus based on what you said about
>moving the focuser so the eyepiece moves away from the objective is actually
>moving the focus to the inside of infinity. Then again, that's what happens
>when I think too often. The mind is a terrible thing. :-)
>
>don
>
Bill Greer
Sounds like an interesting possibility Herm. If the OIII filter
doesn't do the job alone, one could try adding a #58 green filter to
cut the blue. Though one would need a fairly bright test star. I
just tested these filters on my monitor. Blue letters could be seen
through either filter, but using both filters together completely
erased the blue, leaving only the black print visible on the light
background.
Bill Greer
>Hi Don, on a related subject..when focusing an SCT, rotating the knob
>clockwise is "outside" or "inside"???...this makes it hard to do a
>star test if you don't know the direction of focus.
That's an easy one Herm. Focus the scope in the daytime on a distant
object, then point the scope at a nearby object. Which direction do
you need to turn the knob to refocus? That's the same direction you
would need for moving 'outside' (moving the eyepiece further from the
focal plane -- away from the objective).
Steve
If you focus on a star and then slide the eyepiece further out of the
focuser without moving the focuser, aren't you then "outside" of focus?
Similarly, if you then refocus the star by moving the focuser and slide
the eypiece back into the focuser, aren't you then inside focus? Makes
sense to me but that might not be saying much.
Good seeing,
Steve
Bob Luffel
An additional factor to consider when testing a refractor (besides color
focus error) is spherochromatism. Refractors will exhibit different
levels of spherical correction at different wavelengths. Different
lens designs will exhibit different variations in correction vs wavelength.
This is another good reason to test in the green (where I would expect most
if not all visually optimized lenses would be designed for). In good
triplets (at least the couple I have seen data for), the visual ranges
have correction levels theoretically above 95% strehl (1/8 wave p-v).
Doublets would likely have less than this level at some wavelength(s).
Tom Back would likely know the levels of various designs.
Bob
Lance Olkovick
>herm...@worldnet.att.net (Herm Perez) wrote:
>>Hi Don, on a related subject..when focusing an SCT, rotating the knob
>>clockwise is "outside" or "inside"???...this makes it hard to do a
>>star test if you don't know the direction of focus.
1) Focus the SCT on a star.
2) Turn the focusing knob clockwise to defocus the star.
3) Slowly draw the eyepiece out of the draw tube while observing what
happens to the star: if the star keeps expanding, you were outside
of focus (clockwise turn put you outside focus); if the star
contracts to a point, you were inside of focus (clockwise turn put
you inside focus).
--
Lance
Todd Gross
In article <662783$gv...@hpbs1500.boi.hp.com> blu...@gr.hp.com (Bob Luffel) writes:
>From: blu...@gr.hp.com (Bob Luffel)
>Subject: Re: 80 mm Messier hunting from Palo Alto, California
>Date: 2 Dec 1997 23:56:51 GMT
>An additional factor to consider when testing a refractor (besides color
>focus error) is spherochromatism. Refractors will exhibit different
>levels of spherical correction at different wavelengths. Different
>lens designs will exhibit different variations in correction vs wavelength.
>This is another good reason to test in the green
so, use a green filter?
Thanks! - Todd
_________________________________
BOSTON TV METEOROLOGIST TODD GROSS
Weather/Astronomy Home Page: http://www.weatherman.com
Administrator, Meade Advanced Product User Group: ma...@shore.net
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_________________________________
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Michael Richmann
>> Perez) wrote:
>>
>> >Hi Don, on a related subject..when focusing an SCT, rotating the knob
>> >clockwise is "outside" or "inside"???...this makes it hard to do a
>> >star test if you don't know the direction of focus.
>>
>> object, then point the scope at a nearby object. Which direction do
>> you need to turn the knob to refocus? That's the same direction you
>> would need for moving 'outside' (moving the eyepiece further from the
>> focal plane -- away from the objective).
>
> If you focus on a star and then slide the eyepiece further out of the
>focuser without moving the focuser, aren't you then "outside" of focus?
Correct.
>Similarly, if you then refocus the star by moving the focuser and slide
>the eypiece back into the focuser, aren't you then inside focus? Makes
>sense to me but that might not be saying much.
You're on the money.
--
Mike
My opinions, not Argonne's...