1. ## Eyepiece Question

I bought a Meade ETX telescope last year for my kids and myself. A few
weeks ago, I purchased a 9.7mm Super Plossl eyepiece on e-bay to
replace the 26mm one supplied with the ETX. Basically, I just wanted a
better view of the planets.

I received it a few days ago, and while certain things are certainly
larger, such as the moon, I find that some objects, such as Saturn and
Mercury, are distinctly fuzzy and grainy. So I'm trying to figure out
why I can't get the same clarity as I get with the 26mm eyepiece. Is
the 9.7mm eyepiece too much for the ETX? Are atmospheric conditions
the problem? Or is there a chance that the eyepiece is defective?

2. ## Eyepiece Question

vinylanach@aol.com wrote:

There are several reasons why these objects are fuzzy and grainy.

First, let's review some math.

Maximum magnification
The maximum magnification you can expect from a telescope equals
(aperture in inches) X 60. Some folks use (aperture in inches) X 50.
Whatever.

You don't tell us which ETX you have so I'm just guessing. The ETX-80
has an aperture of 3.15 inches; ETX-90 is 3.5 inches and ETX-125 is 5
inches. Applying the factor of 60 would yield the following maximum
magnification figures:
ETX-80: 3.15 x 60 = 180X
ETX-90 = 210X
ETX-125 = 300X

Eyepiece magnification
The magnification provided by an eyepiece equals (telescope focal
length) divided by (eyepiece focal length). The focal lengths for the
ETX scopes are: ETX-80, 400MM; ETX-90, 1250MM. With a 9.7 mm
ETX-80: 400mm divided by 9.7mm = 41X
ETX-90: 1250mm divided by 9.7mm = 129X
ETX-125: 1500mm divided by 9.7mm = 196X

Now, what does this tell us? If the eyepiece is yielding a
magnification that is close to or more than your scope's maximum
magnification, that could cause fuzzy seeing because you are pushing
the scope to its optical limits. HOWEVER -- we see that this is not
the situation here -- for example, the ETX-90 has a maximum mag of 210X
while the 9.7mm eyepiece gives a 129X magnification, well within the
scope's capabilities.

So, your problem is not caused by too much magnification. Here are
some possiblities.

1. Not focused correctly. I suspect when you put the eyepiece into
the scope you insert the eyepiece barrel all the way into the eyepiece
holder. It could be that the eyepiece needs to be pulled slightly out
of the holder because the travel of the focuser is not quite enough to
focus with that eyepiece. So -- insert the eyepiece into the scope so
that about 1/3 of the silver barrel is sticking out of the eyepiece
holder and try to focus the scope.

In this same vein, are you certain you are focussing the scope? The
ETX scopes use that tiny little silver knob that's impossible to grip
and you may not be focussing the scope -- can you focus other objects
such as stars, or, can you focus on terristreal objects -- that is,
point the scope at a hilltop several miles away and make certain you
can focus.

As a former ETX-90 owner, I recommend you replace the stock focussing
knob with a Flexi-Focus -- several dealers sell them -- do a google
search for "ETX flexi-focus" or "ETX accessories." Here is an example:
http://www.shutan.com/Merchant2/merc...ategory_Code=a

2. Seeing conditions. Atmospheric conditions control what you see.
The sky may appear to the naked eye to be clear when, in fact, it's
anything but. It doesn't take much in the way of haze, light
pollution, or humidity to cause objects to look fuzzy.

If you are focussing correctly, try viewing over a period of several
nights. Wait for a cold front to move through and clear out the air.

3. You may have a bad eyepiece. Can you focus on other objects, both
celestial and terrestrial?

3. ## Eyepiece Question

Kickin' Ass and Takin' Names wrote:

This is something I've tried to find out on my own. The box, the
owner's manual and the telescope itself say nothing other than ETX. I
finally dug up the receipt just now, and it says ETX-90.

I just tried this, and it didn't make a difference. In either
position, the eyepiece is able to focus on the moon. It's when I tried
to look at Mercury and Saturn last night that it just wouldn't focus
well enough. My 26mm did just fine. Mercury and Saturn, of course,
were closer to the horizon, which makes me think that it is an issue
with the atmosphere. I do live in LA, which probably explains
everything.

Like I said, I could focus on the moon just as well with the 26mm
eyepiece. Most of the brighter stars I focused on were just more
indistinct and fuzzier no matter where they were in the sky.

Since I've finally figured out that it is indeed an ETX-90, this sounds
like a great idea. I've always been a little disappointed with the
stock knob.

I think this is it.

I'll try this, too.

Yes and yes.

Thanks for the very thorough answer to my question!

4. ## Eyepiece Question

Viewing planets at high magnification is always a crapshoot. I looked
at Saturn two nights ago with my 10 inch SCT, but the seeing was poor
and I could not split the Cassini Division.

There are many considerations when viewing planets with a telescope.
They are best seen when nearest the zenith, where you are observing
then through a smaller column of air.
They are also best seen when at opposition, when they are closest to
the Earth.

Fred W. Price, Cambridge press. ISBN 0 521 78981 8 paperback. There is
an explanation about seeing conditions and how they effect planetary
observing.

Matthew Ota

vinylanach@aol.com wrote:

5. ## Eyepiece Question

vinylanach wrote:

There's a chance, but it's unlikely. The subjective impression is often
that the view through the longer focal length (and therefore lower
magnification) eyepiece is sharper. One thing you might try next time
is to see if there's actually a detail you can see at 50x (with the
26 mm eyepiece) that you can't see at 130x (with the 9.7 mm eyepiece).
If there isn't, you can likely rule out eyepiece defect, though a defect
is still not necessarily indicated even if there is such a detail. Your
eye/brain is better able to see details at certain sizes.

It may be useful to keep in mind that an eyepiece is really just a well
corrected magnifying glass. The rest of the telescope forms an image in
your focuser tube that's like a miniature of whatever it is you're
looking at. The eyepiece simply serves to make that miniature more
easily visible to your eye. So although a shorter focal length eyepiece
makes the object look bigger, it also makes the blurriness from seeing
(that is, atmospheric turbulence) look bigger, too.

My guess is that your symptoms are rooted in atmospheric turbulence.
This is especially the case with Mercury, which (unless you exhibited a
certain degree of intrepidity) you probably observed while it was close
to the horizon. Close to the horizon is just where turbulence is worst,
because it is in exactly those cases that you are looking through the
most atmosphere. Mercury is so small that the extent of the seeing is
probably a good fraction of Mercury's apparent size. If it looks as if
Mercury is bobbing, weaving, and bubbling, that's seeing.

Saturn can be seen high in the sky these days, but you have to stay up
kind of late--it is highest in the sky at around three in the morning.
It rises around eight in the evening, so my guess is that you saw that
while it was close to the horizon, too. Saturn isn't quite as low
contrast as Mercury, but the details that one wants to see on Saturn,
such as subtle shading in the cloud bands and the ring divisions, have
the disadvantage that they are comparatively small and are therefore
highly susceptible to atmospheric turbulence. You may have heard that
the larger the telescope's objective (90 mm in your case), the finer the
detail that can be seen through it. Well, the Cassini division in the
rings of Saturn (the widest division) can be made out in a 60 mm scope
under excellent conditions, but when Saturn is low to the horizon under
poor conditions, it can be difficult to make out in a 10-inch (250 mm)
scope. Atmospheric turbulence is the great equalizer: It doesn't quite
bring a 10-inch telescope to its two-inch knees, but it makes things a
heck of a lot closer than they would be otherwise.

In short, I wouldn't worry too much about the eyepiece. It's probably
just fine. You picked an extremely challenging target to begin with in
Mercury--observers much more experienced than you have made scores of
incorrect observations on it. Saturn is easier, but you might want to
wait either later in the night or later in the year for it to get higher
up in the sky. If you can stand to do it, try it at five in the morning
these days. It will still be reasonably high in the sky, and seeing is
often the best just before dawn.

--
Brian Tung <brian@isi.edu>
The Astronomy Corner at http://astro.isi.edu/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html

6. ## Eyepiece Question

Hi,

The planets are not a good choice for evaluating a new eyepiece when
you are first starting out. They are a little fuzzy to begin with and
if viewed when they are low in the sky it is hard to tell what is in
the eyepiece and what is a problem with the viewing conditions. After
you get to know your scope better you can try using planets to judge
optics.

I'd start with the moon when it is high in the sky. Try looking at the
terminator (the imaginary line dividing the sunlit part from the part
that is dark). The shadows there are sharp and full of contrast and
will be easier to judge.

You can also look at the Clear Sky Clock site to find a clock for your
area
http://cleardarksky.com/csk/index.html#clock_list You can look there
to get a prediction on how good the seeing is going to be for your
area. There is also a section that describes how to judge seeing
conditions. If the seeing is bad, no eyepiece in the world can make
everything look sharp.

Let us know how it goes!

Chuck Taylor
Do you observe the moon?
Try http://groups.yahoo.com/group/lunar-observing/
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On Dec 31 2006, 8:05 pm, "Matthew Ota" <otake...@bigvalley.net> wrote: