planetary eyepiece for skyquest xt 4.5

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Date: 11 Dec 2006 19:09:12
From:
Subject: planetary eyepiece for skyquest xt 4.5

Hi everyone,
What is the maximum useful magnification for the skyquest(dobsonian)
4.5 inch telescope, for viewing planets and the moon?
What is a good quality eyepiece you would recommend?
[Would it be useful to buy a wide field eye piece with focal length in
the range - 4 to 6 mm?]
Thanks,
Marvin

Date: 11 Dec 2006 21:31:39
From: Starlord
Subject: Re: planetary eyepiece for skyquest xt 4.5

I've used everything from a 4.8mm to a 17mm on my Stargazer Steve 4.25inch
F9 Dob.

--
There are those who believe that life here, began out there, far across the
universe, with tribes of humans, who may have been the forefathers of the
Egyptians, or the Toltechs, or the Mayans. Some believe that they may yet be
brothers of man, who even now fight to survive, somewhere beyond the
heavens.

The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html

<smetalman2006@yahoo.com > wrote in message
news:1165892952.860952.239250@16g2000cwy.googlegroups.com...
> Hi everyone,
> What is the maximum useful magnification for the skyquest(dobsonian)
> 4.5 inch telescope, for viewing planets and the moon?
> What is a good quality eyepiece you would recommend?
> [Would it be useful to buy a wide field eye piece with focal length in
> the range - 4 to 6 mm?]
> Thanks,
> Marvin
>

Date: 12 Dec 2006 10:48:07
From: W. H. Greer
Subject: Re: planetary eyepiece for skyquest xt 4.5

On 11 Dec 2006 19:09:12 -0800, smetalman2006@yahoo.com wrote:

>Hi everyone,
>What is the maximum useful magnification for the skyquest(dobsonian)
>4.5 inch telescope, for viewing planets and the moon?
>What is a good quality eyepiece you would recommend?

Hi Marvin,
It's easier to use wide-field eyepieces for high magnifications with a
Dobsonian. The wider field makes it easier to keep the object in the
field of view, even if (as is likely) the image quality deteriorates
as the object approaches the field edge.

The maximum useful magnification depends on the quality of the optics,
the accuracy of the scope's collimation, and the seeing conditions
(among other things). Some 4.5 inch scopes can handle 250x. Others
might top off at 100x or even less!

*If* the telescope provides sharp, crisp planetary images with the
highest power (10mm) eyepiece it's supplied with, then I would suggest
getting a 6mm wide-field eyepiece (about 150x for the 4.5 inch
Skyquest). You could later go up a bit higher *if* the image remains
sharp and crisp. On the other hand, if planetary images are "fuzzy"
with the 10mm eyepiece, then there's little point in purchasing a
shorter focal length eyepiece.

In a "best case" scenerio, when *everything* is perfect, a high
quality 4.5 inch scope would be able to handle a maximum magnification
in the neighborhood of 270x. Would *any* 4.5 inch Skyquest qualify at
such a magnification? I don't know!

In addition to the factors mentioned above, different individuals have
different tolerances and preferences concerning maximum useful
magnification. There's also the mount to consider. Your maximum
useful magnification will not be the same for all objects, nor for the
same object on different nights. In the end, it's your job and duty
to find the right magnification for each task. In some aspects (such
as selecting the right magnification) amateur astronomy is an
experimental science.

Experiment, Observe, and Enjoy!
--
Bill
Celestial Journeys
http://cejour.blogspot.com

Date: 12 Dec 2006 07:12:57
From: John Carruthers
Subject: Re: planetary eyepiece for skyquest xt 4.5

smetalman2006@yahoo.com wrote:

> Hi everyone,
> What is the maximum useful magnification for the skyquest(dobsonian)
> 4.5 inch telescope, for viewing planets and the moon?
> What is a good quality eyepiece you would recommend?
> [Would it be useful to buy a wide field eye piece with focal length in
> the range - 4 to 6 mm?]
> Thanks,
> Marvin

Value for money; a 5 or 6mm orthoscopic, not a huge field but sharp.
Maybe a Burgess/TMB planetary, wider field,I use a 6mm.
Cash no object ? a 5mm monocentric, I want one :-)
jc

Date: 12 Dec 2006 09:24:10
From: Joe S.
Subject: Re: planetary eyepiece for skyquest xt 4.5

Date: 12 Dec 2006 09:08:11
From: Joe S.
Subject: Re: planetary eyepiece for skyquest xt 4.5

Date: 12 Dec 2006 08:05:57
From: Joe S.
Subject: Re: planetary eyepiece for skyquest xt 4.5

<smetalman2006@yahoo.com > wrote in message
news:1165892952.860952.239250@16g2000cwy.googlegroups.com...
> Hi everyone,
> What is the maximum useful magnification for the skyquest(dobsonian)
> 4.5 inch telescope, for viewing planets and the moon?
> What is a good quality eyepiece you would recommend?
> [Would it be useful to buy a wide field eye piece with focal length in
> the range - 4 to 6 mm?]
> Thanks,
> Marvin
>

Rule of thumb for maximum magnification is 50 multiplied by the aperture in
inches. So, in the case of the 4.5, the result is 4.5 x 50 = 225X --
maximum magnification is 225X.

XT-4.5 focal length is 910mm. Magnification is focal length of the scope
divided by focal length of the eyepiece. Thus, a 4mm eyepiece would yield:
910 mm divided by 4mm = 227X. A 4mm eyepiece will get you to maximum
magnification for this scope.

Then there is the consideration for exit pupil size and eye relief, none of
which I understand but I'm certain there are lots of wise people here who
will tell you about those two aspects.

Practically speaking, you are not likely to be happy running the scope up to
max magnification because the max mag you can use is really limited by
seeing conditions -- atmospheric conditions, light pollution, and the like.
A 5mm eyepiece will give you 182X, which will show you a lot of planetary
detail while staying below max mag.

I have an XT-12, 1500mm focal length, theoretical max mag is 600X. For
planets, I use a 7mm Nagler (214X), a 10mm Radian (150X), and a 5mm
University Optics orthoscopic (300X). Most nights, the 7mm at 214X is the
best I can do what with light pollution and atmospherics. Occasionally I
can use a 3.7mm Orion ED eypiece at 405X, but those nights are rare.

Another factor is movement and field of view. As mag goes up, FOV becomes
smaller. At 300X in my scope, a planet (or any other object for that
matter) moves across the FOV rather quickly and I find myself spending more
time moving the scope than observing.

A lot of folks prefer orthoscopic eyepieces for planetery work because they
have fewer glass elements to interfere with the light path, thereby
supposedly revealing more planetary detail. You might look at University
Optics orthos -- good eyepieces, modest prices -- but orthos have very
little eye relief.

Here is a discussion of eyepieces that uses only TeleVue eyepieces:
http://www.analyticalsci.com/Astronomy/Telescopes/imagestv/selecting_an_eyepiece_set.htm

Another option is to get yourself a good 2X Barlow. I see in the Orion
catalog that the XT-4.5 came with two eyepieces that yield 36X and 91X.
With a 2X Barlow, you'll now have 36X, 72X, 91X, and 182X. Try that, see
what 182X does for you -- then, you would have an idea of what higher mags
look like and you can decide if you want another eyepiece or just stick with
the existing eyepieces and the Barlow.

Date: 12 Dec 2006 17:09:45
From: Dennis Woos
Subject: Re: planetary eyepiece for skyquest xt 4.5