Best Eyepiece for 5" Scope to View Saturn

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Date: 25 May 2007 12:35:45
From: Lauren the Ravishing
Subject: Best Eyepiece for 5" Scope to View Saturn

Looking in the Orion catalog I can spend anywhere from $25 to $700 on
an eyepiece. I'd like to spend about $75, but only if I can get
something that will work reasonably well to view Saturn. I suppose I
want the most magnification I can for my 5" reflection scope.

Right now I have what came with my Celestron: a crappy 3x Barlow, a
4cm and a usable 20cm.

Can anyone help me figure out what's the best thing to get? I'm
thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
first I want to focus (ha ha) on the eyepiece.

~ L

Date: 26 May 2007 15:59:01
From:
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

Hello,

You may be very disappointed with the performance of you scope at
extreme power. Atmospheric conditions don't usually allow the highest
power, for instance. Also, the image isw dimmer and the field of view
generally smaller at high power

That being said, good orthoscopic eyepieces are exceptional on the
planets and they sell for well under $100. The downside on them is
that the apparent field of view is generally only around 48 degrees.

University Optics sells very good orthos. I have a set and they are my
favorites on the planets and doubles.

Btw, you didn't say which type of 5" scope you own. A 5" Newtonian,
Cat, or refractor makes quite a difference in choosing eyepieces as
does the focal ratio.

Clear skies.

Tom B.

Date: 26 May 2007 07:51:51
From: Joe S.
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

"Lauren the Ravishing" <lauren_the_ravishing@yahoo.com > wrote in message
news:1180121745.171868.67070@k79g2000hse.googlegroups.com...
> Looking in the Orion catalog I can spend anywhere from $25 to $700 on
> an eyepiece. I'd like to spend about $75, but only if I can get
> something that will work reasonably well to view Saturn. I suppose I
> want the most magnification I can for my 5" reflection scope.
>
> Right now I have what came with my Celestron: a crappy 3x Barlow, a
> 4cm and a usable 20cm.
>
> Can anyone help me figure out what's the best thing to get? I'm
> thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
> first I want to focus (ha ha) on the eyepiece.
>
> ~ L
>

First, let's cover a few basic matters.

Your scope has two important specifications, both of which you should be
able to find on a data plate on in the paperwork that accompanied the scope:
-- FOCAL LENGTH (abbreviated fl, f/l, FL, or F/L); expressed in
millimeters -- such as FL: 1,000mm
-- APERTURE. You already know this -- it's 5 inches

Now, let's cover other considerations.

-- Maximum magnification. Every scope has a magnification limit. Exceed
that limit, and image quality is degraded. In fact, as you approach the mag
limit, image quality suffers. You really don't want to push a scope up to
its max mag. Rule of thumb is that the maximum mag for a scope equals 40 x
aperture. Some folks say the rule of thumb is 50 x aperture, or, 60 x
aperture. Whatever. With a 5-inch scope, your maximum magnification is: 40
x 5 = 200X; or, 50 x 5 = 250X; or, 60 x 5 = 300X. Thus, you don't want an
eyepiece, or an eyepiece-Barlow combination that gives you more than 250X
(250 power, 250 magnification). Furthermore, you are best advised to stay
away from such high mag because rarely will seeing conditions allow you to
use your scope's theoretical maximum magnifications.

-- Seeing conditions. Unless your scope is a real piece of trash -- in
which the scope itself limits what you can see -- the seeing conditions
impose serious limitations on what you can see and how well you see it.
"Seeing conditions" include: humidity; clouds; haze; light pollution (from
street lights, parking lot lights, security lights, etc.); bright moon;
rising or setting sun. Even the very best scope and the very best eyepiece
(whatever that means) can't see diddly if the atmosphere is cloudy, hazy, or
filled with smoke -- or -- if the moon is bright -- etc.

-- Eyepiece magnification. To calculate the magnification (power) of an
eyepiece, divide the scope's focal length by the eyepiece focal length. For
example, if your scope's FL is 1,000mm and you have a 10mm eyepiece, then
the magnification of that eyepiece is 1,000 divided by 10 = 100X (or, 100
power). A 2X Barlow combined with a 10mm eyepiece on a scope with a FL of
1,000mm will yield 200X ( that is: 1,000mm FL divided by 10mm eyepiece =
100X multiplied two times by the Barlow = 200X).

-- Movement of objects in the sky. Remember, the Earth is rotating as you
are observing. That's why, when you look at something through your scope,
the object appears to move across the field of view. Of course, if you have
a motorized scope that tracks objects, that's why the scope is motorized --
to follow the object as it appears to move across the sky. As magnification
goes up, the field of view - that is, the slice of the sky you are
viewing -- gets smaller. At higher magnifications, objects tend to move
quickly across the field of view -- or a motorized scope must move faster to
keep up with the object.

So -- you need to figure out your scope's maximum theoretical
magnification -- that's probably around 250X (250 power).

Then -- for viewing Saturn, something around 150X is perfectly fine. At
higher magnification, the object you are viewing will zip across the field
of view and you will be constantly moving the scope to find the object.
150X combined with good seeing conditions will show the Cassini division,
bands on the planet, and the rings with striking clarity. You need to
determine your scope's focal length and from that determine the focal length
of the eyepiece you need. Again, assume a scope FL of 1,000mm. To achieve
150X, you would need a 7mm eyepiece (1,000mm divided by 7mm = 143X (close
enough to 150X)).

Finally -- decide how much you want to spend and how you want to spend it.
If you need a 7mm eyepiece to achieve 150X, you could by a 7mm eyepiece, or,
you could buy a 14mm eyepiece (or something around that -- 12mm, 13mm, 14mm,
15mm) and a 2X Barlow and have the equivalent of two eyepieces -- and the
Barlow can be used with every eyepiece. As to which eyepiece and Barlow to
purchase -- you are welcome to ask that question but be prepared to hear as
many opinions as there are people offering opinions.

You mentioned that you have an Orion catalog and want to spend around
$75.00. I have a couple of the Orion Epic ED eyepieces and am really happy
with them. They come in several focal lengths and you should be able to
find something there that will yield around 150X for planetary viewing.

Date: 26 May 2007 20:27:01
From: Andrew Smallshaw
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

On 2007-05-26, Joe S. <noname@nosuch.net > wrote:
>
> -- Movement of objects in the sky. Remember, the Earth is rotating as you
> are observing. That's why, when you look at something through your scope,
> the object appears to move across the field of view. Of course, if you have
> a motorized scope that tracks objects, that's why the scope is motorized --
> to follow the object as it appears to move across the sky. As magnification
> goes up, the field of view - that is, the slice of the sky you are
> viewing -- gets smaller. At higher magnifications, objects tend to move
> quickly across the field of view -- or a motorized scope must move faster to
> keep up with the object.

The magnification of the scope is irrelevant to how fast it has to
track - after all it has to point in the right direction which
doesn't change when you change EPs. An EQ mount will rotate once
per sidereal day, regardless of where it is pointing or what is in
the eyepiece holder.

--
Andrew Smallshaw
andrews@sdf.lonestar.org

Date: 25 May 2007 20:55:18
From: Ed B.
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

On May 25, 2:35 pm, Lauren the Ravishing
<lauren_the_ravish...@yahoo.com > wrote:
> Looking in the Orion catalog I can spend anywhere from $25 to $700 on
> an eyepiece. I'd like to spend about $75, but only if I can get
> something that will work reasonably well to view Saturn. I suppose I
> want the most magnification I can for my 5" reflection scope.
>

Hi,

I'm partial to the Orion Ultrascopic/Antares Ultima/Celestron Ultima
line of eyepieces. I started with a used 15 mm Ultrascopic eyepiece
and it quickly became my favorite. I currently have the 5, 7.5, 10,
15, 20, and 30 mm sizes. The 5 mm is best suited to my short focal
length scopes (Starblast and Short Tube 80). For Saturn, I usually
have the best views with the 10 mm (120x), if the skies are good (rare
in South Jersey), I can use the 7.5 mm (167x) in my 6" F8 Dobsonian.
I have found 20x to 30x per inch to be a reasonable expection for
magnification. These eyepiecs work well in my 80 mm refractor and
4.25" F4, 6" F8, and 10" F6 reflectors.

Ed

Date: 25 May 2007 21:03:26
From: Andrew Smallshaw
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

On 2007-05-25, Lauren the Ravishing <lauren_the_ravishing@yahoo.com > wrote:
> Looking in the Orion catalog I can spend anywhere from $25 to $700 on
> an eyepiece. I'd like to spend about $75, but only if I can get
> something that will work reasonably well to view Saturn. I suppose I
> want the most magnification I can for my 5" reflection scope.
>
> Right now I have what came with my Celestron: a crappy 3x Barlow, a
> 4cm and a usable 20cm.
>
> Can anyone help me figure out what's the best thing to get? I'm
> thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
> first I want to focus (ha ha) on the eyepiece.

Others have already mentioned the 50x per inch of aperture rule,
but I got the impression that we talking about a low-end scope so
I did a little digging for some background. I see you're using a
Powerseeker 127 EQ, which looking at it is pretty much on a par
with my Bresser Messier N130. Neither are high-end scopes so it
does pay to be a little more conservative.

My scope came with 25mm, 15mm and 10mm EPS plus a 2x barlow, none
of which were particularly good. I found I got the best views of
Saturn with the 10mm (100x) or 15mm+barlow (133x). Going up to
200x wasn't worth it as the image got blurry. I've since invested
in some Meade 4000si. While they do come in for some stick from
some quarters they are a quantum leap above the supplied EPs.

I now find I get the best images with a 6.4mm for 156x. Going up
to 206x with a 9.7mm EP and my existing barlow doesn't really gain
anything. I'd be interested to see what I got with a 4mm-ish
eyepiece but didn't get one that size given my earlier exerience
with higher powers.

In addition, I find a Meade no 11 filter nice for viewing Saturn.
While observing the Cassini division is a challenge on these scopes
that makes it perfectly doable, and its relatively high transmission
makes it ideal for smaller scopes.

--
Andrew Smallshaw
andrews@sdf.lonestar.org

Date: 25 May 2007 18:56:46
From: Dennis Woos
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

> Others have already mentioned the 50x per inch of aperture rule,
> but I got the impression that we talking about a low-end scope so
> I did a little digging for some background. I see you're using a
> Powerseeker 127 EQ, which looking at it is pretty much on a par
> with my Bresser Messier N130. Neither are high-end scopes so it
> does pay to be a little more conservative.
>
> My scope came with 25mm, 15mm and 10mm EPS plus a 2x barlow, none
> of which were particularly good. I found I got the best views of
> Saturn with the 10mm (100x) or 15mm+barlow (133x). Going up to
> 200x wasn't worth it as the image got blurry. I've since invested
> in some Meade 4000si. While they do come in for some stick from
> some quarters they are a quantum leap above the supplied EPs.
>

The 50x "rule" is pretty useless for most scopes, most of the time. I like
a 30x target much better, and appreciate the times when the optics and
seeing allow for more. Sure, I have gotten 50x and even better on occasion,
but not often and usually in the hour or two before sunrise. Furthermore, I
know that my optics, collimation, cooldown, etc are on the money.

So far as eyepieces go, I have a Burgess Planetary 6mm that is a great
performer, including good eye relief and wide field. A barlowed longer
focal length plossl, ortho, etc is also a good way to go, so long as the
barlow is high quality. Everyone (including me) seems to like the Orion
Shorty Plus, or the Celestron version. Of course, there are others such as
the Televue, Klee and Dakin.

Dennis

Date: 25 May 2007 15:06:35
From: Dave
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

Date: 26 May 2007 14:39:33
From: Mik3
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

Dave wrote:

> "Lauren the Ravishing" <lauren_the_ravishing@yahoo.com> wrote in message
> news:1180121745.171868.67070@k79g2000hse.googlegroups.com...
> > Looking in the Orion catalog I can spend anywhere from $25 to $700 on
> > an eyepiece. I'd like to spend about $75, but only if I can get
> > something that will work reasonably well to view Saturn. I suppose I
> > want the most magnification I can for my 5" reflection scope.
> >
> > Right now I have what came with my Celestron: a crappy 3x Barlow, a
> > 4cm and a usable 20cm.
> >
> > Can anyone help me figure out what's the best thing to get? I'm
> > thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
> > first I want to focus (ha ha) on the eyepiece.
> >
> > ~ L
> >
>
> Lauren,
> A good rule of thumb is that your maximum magnification is equal to 50 times
> the diameter of your primary which equals 250X in your case.

Think about this! That only applies IFF the optics of the scope
support it. Otherwise you are magnifying bad optics and the traits
of bad optics. This "5" reflection Celstron" is no Takahashi !

> Now since
> you're thinking of getting a decent barlow say 3x, you take a third of the
> 250 "81X" and use that to determine your highest power eyepiece. your
> telescope fl in mm divided by the 81X gives you the correct eyepiece fl you
> need for your max power with the barlow. when buying more eyepieces remember
> that each one represents 2 magnifications with and without the barlow. that
> way you don't wind up having as many eyepieces to cover the full range.
> at the moment I don't remember the rule for minimum magnification -
> hopefully someone else will provide that for the other end of the range for
> your scope.
> Dave

Date: 25 May 2007 20:06:12
From: M
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

I got a 130mm Newtonian (just over 5") and try to work to the guide that
ideal max mag is 2x aperture (in mm).....therefore my max mag is 260x

With a focal length of my scope being 650mm this max mag works out as
650/260 = 2.5mm ep.

( Personally I use a 4mm ep with a 2x barlow to give me a mag of 325x and a
6mm ep with 2x barlow for 216x for viewing Saturn)

--
M
------
"Any society that would give up a little liberty to gain a little security
will deserve neither and lose both."
[Benjamin Franklin]

"War is delightful to those who have had no experience of it."
[Erasmus]

"A collision at sea can ruin your entire day."
[Thucydides]

"Lauren the Ravishing" <lauren_the_ravishing@yahoo.com > wrote in message
news:1180121745.171868.67070@k79g2000hse.googlegroups.com...
> Looking in the Orion catalog I can spend anywhere from $25 to $700 on
> an eyepiece. I'd like to spend about $75, but only if I can get
> something that will work reasonably well to view Saturn. I suppose I
> want the most magnification I can for my 5" reflection scope.
>
> Right now I have what came with my Celestron: a crappy 3x Barlow, a
> 4cm and a usable 20cm.
>
> Can anyone help me figure out what's the best thing to get? I'm
> thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
> first I want to focus (ha ha) on the eyepiece.
>
> ~ L
>

Date: 25 May 2007 15:54:46
From: Dennis Woos
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

> Looking in the Orion catalog I can spend anywhere from $25 to $700 on
> an eyepiece. I'd like to spend about $75, but only if I can get
> something that will work reasonably well to view Saturn. I suppose I
> want the most magnification I can for my 5" reflection scope.
>
> Right now I have what came with my Celestron: a crappy 3x Barlow, a
> 4cm and a usable 20cm.
>
> Can anyone help me figure out what's the best thing to get? I'm
> thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
> first I want to focus (ha ha) on the eyepiece.
>
> ~ L
>

I would go for 150x to 200x magnification, with the lower range probably
your best bet. The magnification of an eyepiece in your scope is computed
by dividing the focal length of your scope by the focal length of the
eyepiece. So, for instance, if the focal length of your scope is 1000mm (I
am not saying it is - you need to check what it is for your scope) then a
5mm eyepiece will provide a magnification of 1000mm/5mm = 200x. I would buy
whichever one of these eyepieces that gives you 150x to 200x:

https://www.highpointscientific.com/store/listCategoriesAndProducts.asp?idCategory=7015

Dennis

Date: 25 May 2007 19:52:33
From: Jim Klein
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

Lauren the Ravishing <lauren_the_ravishing@yahoo.com > wrote:

>Looking in the Orion catalog I can spend anywhere from $25 to $700 on
>an eyepiece. I'd like to spend about $75, but only if I can get
>something that will work reasonably well to view Saturn. I suppose I
>want the most magnification I can for my 5" reflection scope.
>
>Right now I have what came with my Celestron: a crappy 3x Barlow, a
>4cm and a usable 20cm.
>
>Can anyone help me figure out what's the best thing to get? I'm
>thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
>first I want to focus (ha ha) on the eyepiece.
>
>~ L

Figure a maximum mag of 50-75X per inch. That is 250 to 375 x. Take
the EFL and divide by the total magnification to get the efl of the
desired eyepiece.

Make sure you use the same units for the efl and the eyepiece. An
orthoscopic will probably be all you will need and I would think
$75.00 ought to get you a really nice eyepiece. You might also want a
good achromatic barlow as well.

Suppose you have a 5" f/15 which yields an efl of 5x15 = 75 inches or
1905 mm. Divided by 375 yields 5.08 mm so a 4, 5 or 6 mm eyepiece will
work fine. For shorter EFL apocromats, you will probably need a barlow
of 2 or 3 x.

Jim Klein

James E. Klein
jameseklein@earthlink.net

Engineering Calculations
http://www.ecalculations.com
ecalculations@ecalculations.com
Engineering Calculations is the home of
the KDP-2 Optical Design Program
for Windows.
1-818-507-5706 (Voice and Fax)
1-818-823-4121

"KDP2, not quite easy enough for a Caveman to use" :-)

Date: 26 May 2007 05:56:54
From: David Nakamoto
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

You should add that those magnification figures are for nights of fine
seeing. Most nights you can't push them that high; perhaps 30x to 50x
is more reasonable most nights. So it begs for two eyepieces, perhaps a
Barlow and an eyepiece, so the telescope can operate at 40x and on
nights of steady seeing you can use the Barlow to go to 80x.

--- Dave

Jim Klein wrote:
> Lauren the Ravishing <lauren_the_ravishing@yahoo.com> wrote:
>
>> Looking in the Orion catalog I can spend anywhere from $25 to $700 on
>> an eyepiece. I'd like to spend about $75, but only if I can get
>> something that will work reasonably well to view Saturn. I suppose I
>> want the most magnification I can for my 5" reflection scope.
>>
>> Right now I have what came with my Celestron: a crappy 3x Barlow, a
>> 4cm and a usable 20cm.
>>
>> Can anyone help me figure out what's the best thing to get? I'm
>> thinking of replacing the Barlow eventually with a Tri-Mex 3x, but
>> first I want to focus (ha ha) on the eyepiece.
>>
>> ~ L
>
> Figure a maximum mag of 50-75X per inch. That is 250 to 375 x. Take
> the EFL and divide by the total magnification to get the efl of the
> desired eyepiece.
>
> Make sure you use the same units for the efl and the eyepiece. An
> orthoscopic will probably be all you will need and I would think
> $75.00 ought to get you a really nice eyepiece. You might also want a
> good achromatic barlow as well.
>
> Suppose you have a 5" f/15 which yields an efl of 5x15 = 75 inches or
> 1905 mm. Divided by 375 yields 5.08 mm so a 4, 5 or 6 mm eyepiece will
> work fine. For shorter EFL apocromats, you will probably need a barlow
> of 2 or 3 x.
>
> Jim Klein
>
> James E. Klein
> jameseklein@earthlink.net
>
> Engineering Calculations
> http://www.ecalculations.com
> ecalculations@ecalculations.com
> Engineering Calculations is the home of
> the KDP-2 Optical Design Program
> for Windows.
> 1-818-507-5706 (Voice and Fax)
> 1-818-823-4121
>
> "KDP2, not quite easy enough for a Caveman to use" :-)

Date: 25 May 2007 16:08:03
From: Dennis Woos
Subject: Re: Best Eyepiece for 5" Scope to View Saturn

>
> Figure a maximum mag of 50-75X per inch. That is 250 to 375 x. Take
> the EFL and divide by the total magnification to get the efl of the
> desired eyepiece.

This is most probably way too much magnification.

>
> An
> orthoscopic will probably be all you will need and I would think
> $75.00 ought to get you a really nice eyepiece.

An orthoscopic in the fls we are talking about is totally unusable for
anyone who wears glasses, and is very uncomfortable even for folks who
don't.

Dennis