What am I doing wrong?

I recently bought a Skywatcher Explorer 130P. This is a 5.1inch reflector
with focal ration F5.

I have two eye pieces - 10mm and 25mm and a x3 barlow.

I was observing jupiter last night on maximum mag (10mm and barlow - about
x195 I think) it looked big but I was unable to achieve a good focus. Using
different combinations I could achieve a sharper focus but without the
magnification to see better! Viewing conditions weren't ideal but I was
wondering - is this lack of focus down to the barlow?

What would be a better set-up with the equipment I've got or what new eye
pieces would anyone recommend. I have seen posts in other forums from people
with the same scope and they seem to be doing much better!

Thanks for any help you can give

Steve

"ELIZABETH KEARNEY" wrote in message
.uk...
I recently bought a Skywatcher Explorer 130P. This is a 5.1inch reflector
with focal ration F5.

I have two eye pieces - 10mm and 25mm and a x3 barlow.

I was observing jupiter last night on maximum mag (10mm and barlow - about
x195 I think) it looked big but I was unable to achieve a good focus.
Using
different combinations I could achieve a sharper focus but without the
magnification to see better! Viewing conditions weren't ideal but I was
wondering - is this lack of focus down to the barlow?

What would be a better set-up with the equipment I've got or what new eye
pieces would anyone recommend. I have seen posts in other forums from
people
with the same scope and they seem to be doing much better!

Thanks for any help you can give

Steve



Your scope has a focal length of 900mm. Your 10mm eyepiece will give you
90X (900mm / 10mm = 90X). Add the 3X Barlow and you get 90X x 3 = 270X.

I Googled your scope and find it listed with 260X as the highest potential
magnification. Thus, with the 10mm eyepiece and the 3X Barlow, you were at
or above max mag for this scope.

Rule of thumb is to multiply 50 times the aperture in inches for max mag.
Thus, your 5 inch scope would yield a maximum magnification of 250X -- which
is about what the manufacturer states.

I have a XT-12 -- 12-inch dob, 1500mm focal length -- 12 inches x 50 ==
600X max mag. I have eyepieces that will get me up to 450X but my best
viewing of the planets is always around 175X - 250X. Anything more and
atmospheric conditions -- seeing conditions -- degrade the view. Also -- at
300X or more, objects move across the field of view pretty quickly.

Your 25mm and 10mm eyepieces are now giving you 36X and 90X, respectively.
With the 3X Barlow you get 108X and 270X -- and as we see, the 270X is not
usable.

A 2X Barlow would be a good investment. With the 10mm and 25mm eyepeices
and the 2X and 3X Barlows, you would have the following magnifications:
-- With the 25mm eyepiece: 36X, 72X, and 108X
-- With the 10mm eyepiece: 90X, 180X, 270X (not usable at 270X)

The 10mm with a 2X Barlow at 180X will give you excellent views of the
planets.

Like Joe said, you're pushing the magnification of that scope to it's
limits. Occasionally, one can get away with that on something like
splitting double stars, but only on the best nights.
Also, those nights when the air is so still that you can use your
highest powers are RARE. Even though the image will be tiny, you're
usually best off starting with lower powers and then working your way
up. (This is especially true on dimmer deep sky objects.) Try to get
comfortable and look at your target for a considerable amount of time,
waiting for the moments of best seeing. As time goes by, your eye and
brain will learn to pick up more fine detail. Hang in there.
Marty

In addition to a possible problem with too much magnification, there are
other potential problems:
Seeing might be bad, and/or there may be internal air currents in your
scope. Point to a bright object and set the EP out of focus so that there
is a large bright image.
Ripples across the image mean that the external seeing is bad (turbulent
atmosphere). Ripples which seem to circle around in the image mean that
there is turbulent air in your scope. For the internal problem, you need to
let your scope reach the same temperature as the surrounding air.
For the external problem, you might try moving the scope so that it does not
point over some source of rising heat, such as roofs, A/C outside units,
etc.

Bill.
"ELIZABETH KEARNEY" wrote in message
.uk...
I recently bought a Skywatcher Explorer 130P. This is a 5.1inch reflector
with focal ration F5.

I have two eye pieces - 10mm and 25mm and a x3 barlow.

I was observing jupiter last night on maximum mag (10mm and barlow - about
x195 I think) it looked big but I was unable to achieve a good focus.
Using
different combinations I could achieve a sharper focus but without the
magnification to see better! Viewing conditions weren't ideal but I was
wondering - is this lack of focus down to the barlow?

What would be a better set-up with the equipment I've got or what new eye
pieces would anyone recommend. I have seen posts in other forums from
people
with the same scope and they seem to be doing much better!

Thanks for any help you can give

Steve

I recently bought a Skywatcher Explorer 130P. This is a 5.1inch reflector
with focal ration F5.

I have two eye pieces - 10mm and 25mm and a x3 barlow.

I was observing jupiter last night on maximum mag (10mm and barlow - about
x195 I think) it looked big but I was unable to achieve a good focus.
Using
different combinations I could achieve a sharper focus but without the
magnification to see better! Viewing conditions weren't ideal but I was
wondering - is this lack of focus down to the barlow?

What would be a better set-up with the equipment I've got or what new eye
pieces would anyone recommend. I have seen posts in other forums from
people
with the same scope and they seem to be doing much better!

Thanks for any help you can give

Steve

Do not rush out and buy expensive eyepieces, as they will not correct for
your inability to achieve a "sharp" focus at high powers. Instead, make
sure your scope is working as well as it should with the eyepieces you have.
Unless your scope is collimated and cooled down you will not get decent
high-powered views. The cool down is relatively easy - give it an hour or
two outside. Collimation takes some understanding of what needs to line up
with what. Google "newtonian collimation" and you will find lots of info.
Finally, join your local astro club and observe with others who have more
experience. They will help you to understand your scope and get the most
out of it.

Dennis

One other thing occurs to me. I have seen inexperienced telescope
users mistake the bright circle you see both inside and outside of
focus for the image itself and wonder why they see no detail. Be sure
to adjust the eyepiece so that the circle of light you see is as small
as possible. The correct focus will be near that point. Seems simple,
but focusing an eyepiece can be confusing for first time telescope
users.
Clif
Ashcraft

ELIZABETH KEARNEY wrote:
I recently bought a Skywatcher Explorer 130P. This is a 5.1inch reflector
with focal ration F5.

I have two eye pieces - 10mm and 25mm and a x3 barlow.

I was observing jupiter last night on maximum mag (10mm and barlow - about
x195 I think) it looked big but I was unable to achieve a good focus. Using
different combinations I could achieve a sharper focus but without the
magnification to see better! Viewing conditions weren't ideal but I was
wondering - is this lack of focus down to the barlow?

What would be a better set-up with the equipment I've got or what new eye
pieces would anyone recommend. I have seen posts in other forums from people
with the same scope and they seem to be doing much better!

Thanks for any help you can give

Steve

You're going to get a wide variety of opinions here. Here are my two
cents ---

(1) Too much magnification. The rule of thumb is 20x to 30x per inch of
aperture is as much magnification as you can carry on most telescopes on
most nights. At 208x (125mm * 5 / 3mm) you're way above this.

Any telescope is limited in useful magnification by its aperture,
quality of optics, quality of the seeing (atmospheric blurring), and
other factors. The rule I gave is a good first order measure of what
you can achieve.

On rare nights of rock steady seeing, you might be able to push the
magnification higher, but the top limit seems to be around 80x to 90x.
In decades of observing, I've been able to push it this high only on
three or four nights, as memory serves. The rest of the time, 20x to
30x was the limit.

(2) Telescope manufacturers don't necessarily package their goods with
any logic or reason. Just because they pack a 10mm eyepiece with a 3x
Barlow to give you a 3.33mm eyepiece, doesn't mean you can use that much
magnification every night, or through every scope.

(3) Since you have a reflector, you can help your cause by keeping your
telescope in collimation, meaning the optics are lined up accurately and
correctly. There are websites that show you how to do this, and I'll
leave it to others to point these out.

(4) You can further help your cause by observing under the right
conditions. Avoid concrete and asphalt surface since they emit a lot of
heat as they cool at night, causing atmospheric distortions. Grass
tends to be better, dirt being a second choice. Let the telescope cool
down, or better yet don't let it get warm in the first place; heat
currents in the tube can cause problems. Don't look over buildings;
they generate a lot of heat also at night.

(5) Observe the planets, or any object for that matter, then it's
halfway up from the horizon or higher. You're looking through less
atmosphere, getting away from rising air currents from objects around
you, and looking through less haze and other things.

(6) When observing at high magnifications, do whatever you can to reduce
or eliminate shaking of the telescope. Some weight their mount bases
down using beanbags or other things. Avoid the wind at all costs; it
shakes the telescope and can blur the view.

Sincerely,
--- Dave Nakamoto
========================================
Miller's Daughter --- There, I was visited by a bizarre, strange imp
of a man.
Sam Shovel --- Pee Wee Herman?
Miller's Daughter --- Not THAT strange.

If you're looking to see Jupiter with tack sharp edges like some photos are,
you aren't going to be getting there with a small scope. You're guestimate
of 195 power is about right and this still generally leaves a rather small
image of Jupiter for you.
The problems are that the scope angular resolution makes the edges soft as
well as the "seeing" conditions which make the image dance about. Seeing
problems are due to the air in the path of the light not having all the same
temp and getting blown about by the winds. This causes refraction of the
light due to the changine temps and thus the objects in the sky dance about.
You will notice that the clarity of Jupiter changes over time and this is
the path sometimes happening to be all stable. The scope itself can also
make for seeing conditions being bad if the scope isn't stabilized to the
night air. A hot mirror and tube in a scope will make for heat waves in the
tube which will affect the seeing of the sky.

--
Why do penguins walk so far to get to their nesting grounds?

On Sat, 06 May 2006 05:17:01 -0500, ELIZABETH KEARNEY
wrote:

I recently bought a Skywatcher Explorer 130P. This is a 5.1inch reflector
with focal ration F5.

I have two eye pieces - 10mm and 25mm and a x3 barlow.

I was observing jupiter last night on maximum mag (10mm and barlow -
about
x195 I think) it looked big but I was unable to achieve a good focus.
Using
different combinations I could achieve a sharper focus but without the
magnification to see better! Viewing conditions weren't ideal but I was
wondering - is this lack of focus down to the barlow?

What would be a better set-up with the equipment I've got or what new eye
pieces would anyone recommend. I have seen posts in other forums from
people
with the same scope and they seem to be doing much better!

Thanks for any help you can give

Steve

There is a review for a similar model telescope at:
http://www.skywatchertelescope.com/13065Review.html

It is worth noting that while the two eyepieces were of Plossl
design (usually very good), the Barlow is the traditional
(next to useless) plastic model which accompanies so many beginner
scopes. This alone could account for the poor images at high power.

However, other conditions, such as tube currents and miscollimation,
are factors which should be checked.
There are many good web pages for collimation instructions.
My own is at:
http://larryg54.home.texas.net/collimat/notools2.html

If this checks OK, and you still have fuzzy images after letting
the scope optics reach ambient temperature, then the optics are
suspect, starting with the Barlow.

Hope this helps.
Larry G.




--
Calling Austin HOME since 1982!

If you're looking to see Jupiter with tack sharp edges like some photos are,
you aren't going to be getting there with a small scope.

5.1 inch reflector with good optics is EASILY capable of "tack sharp
edges"
on Jupiter at powers of 195x-250x if the seeing is good. And loaded
with
more detail than most amateurs could draw to boot. Turbulence,
optical quality, and or tube components not cooled down to ambient
are the three biggest culprits for soft images at high power.

Dan Chaffee