Under the "graphical plots" PLOP gives you the location of the various
points on each part - the center, the ends etc. - in cartesian
coordinates relative to the mirrors center. If this seems unclear then,
get some graph paper and start drawing things out using these
coordinates. It will become clear very quickly how this translates into
part dimensions, as in - for example - subtracting one x coordinate
from another to get the length of the side of a triangle and so on.
Joe


--- In bigdob@yahoogroups.com, "schmintan" <schmintan@...> wrote:
>
>
> I have downloaded PLOP and inputted my mirror details. it has
generated
> an 18 point design,but i have no idea how to find the dimensions of
my
> mirror cell.
>
> im first trying to find the 3 points where the collomation bolts will
> go, so i will be able to work out the spacing of the bars in the
> tailgate.
>
> how do i work out the measurements from what plop gives me? all plop
> gives are x,y coordinates of the points of the triangles and of the
> bars. i cannot work out dimensions from this, or atleast, I do not
know
> how to.
>

Something that I've never understood clearly and hope someone here
could answer.  I understand all the formulae concerning exit pupil, fov
and magnification, I understand, with a given telescope and 14mm
eyepiece there is, for example, a 60 arcmin fov [approx twice the
dimeter of the full moon], z mm exit pupil, and x magnification;

and with an similiar type of eyepiece of 7mm focal length there is a 30
arcmin fov [approx, the full moon], z/2 mm exit pupil, and 2x
magnification.

The 7mm FL eyepiece has an fov entering the eye of the entire full moon
[the full moon will be approx the entire fov of the 7mm eyepiece].  But
the exit pupil is also 1/2 the diameter of the exit pupil of the 14mm
eyepiece, so the size of the moon's image entering the eye should be
the same with either eyepiece.   How does the image of the moon on the
retina become 2x as large?

Thanks for Any Insight,  Ken

----- Original Message ----

> From: bret7237 <krconn@...>
>
> Something that I've never understood clearly and hope someone here
> could answer.  I understand all the formulae concerning exit pupil, fov
> and magnification, I understand, with a given telescope and 14mm
> eyepiece there is, for example, a 60 arcmin fov [approx twice the
> dimeter of the full moon], z mm exit pupil, and x magnification;
>
> and with an similiar type of eyepiece of 7mm focal length there is a 30
> arcmin fov [approx, the full moon], z/2 mm exit pupil, and 2x
> magnification.
>
> The 7mm FL eyepiece has an fov entering the eye of the entire full moon
> [the full moon will be approx the entire fov of the 7mm eyepiece].

Well that also depends on the focal length of the scope.

>  But
> the exit pupil is also 1/2 the diameter of the exit pupil of the 14mm
> eyepiece, so the size of the moon's image entering the eye should be
> the same with either eyepiece.   How does the image of the moon on the
> retina become 2x as large?

Because the light rays entering the eye do so at larger angles.
It seems pretty evident from your question that when you say you "understand"
the formulae, all you really mean is that you _memorized_ them, but don't
actually understand what's really happening at all.  See
<http://jmmahony1.home.comcast.net/~jmmahony1/optics/>
it gives a geometric picture of what happens to light rays going through a
scope, and uses mostly simple proportions to show how magnification, focal
length, FOV, etc, all interrelate as a result of the geometry of the light rays.

-John

See comments in text below.


--- In bigdob@yahoogroups.com, John Mahony <jmmahony@...> wrote:
>
> ----- Original Message ----
>
> > From: bret7237 krconn@...
> >
> > Something that I've never understood clearly and hope someone here
> > could answer. I understand all the formulae concerning exit pupil,
fov
> > and magnification, I understand, with a given telescope and 14mm
> > eyepiece there is, for example, a 60 arcmin fov [approx twice the
> > dimeter of the full moon], z mm exit pupil, and x magnification;
> >
> > and with an similiar type of eyepiece of 7mm focal length there is a
30
> > arcmin fov [approx, the full moon], z/2 mm exit pupil, and 2x
> > magnification.
> >
> > The 7mm FL eyepiece has an fov entering the eye of the entire full
moon
> > [the full moon will be approx the entire fov of the 7mm eyepiece].
>
> Well that also depends on the focal length of the scope.


That was stated as a given not as a question.




> > But
> > the exit pupil is also 1/2 the diameter of the exit pupil of the
14mm
> > eyepiece, so the size of the moon's image entering the eye should be
> > the same with either eyepiece. How does the image of the moon on the
> > retina become 2x as large?
>
> Because the light rays entering the eye do so at larger angles.

That and the cited article does explain it.  But....


> It seems pretty evident from your question that when you say you
"understand" the formulae, all you really mean is that you _memorized_
them, but don't actually understand what's really happening at all.

For many many years I've been into astrophotography and imaging only,
because of very poor vision until recent eye surgury. Now I can see
somethin thru the eyepiece.  But Believe me that I "understand the
formulae", what I don't understand is what I never see in any
explanation, the math that calculates the size of the image on the
retina in relation to the other parameters.  With 2 math degrees and
many acturial exams and 30+ yrs of actuarial experience, I know that all
the explanitions in the world are BS if the math isn't there, the suit
type execs always want to go by a slick verbal explanition and ignore
the math.

Ken

See
> <http://jmmahony1.home.comcast.net/~jmmahony1/optics/>
> it gives a geometric picture of what happens to light rays going
through a scope, and uses mostly simple proportions to show how
magnification, focal length, FOV, etc, all interrelate as a result of
the geometry of the light rays.
>
> -John
>




[Non-text portions of this message have been removed]

----- Original Message ----

> From: bret7237 <krconn@...>
>
> See comments in text below.
>
> --- In bigdob@yahoogroups.com, John Mahony wrote:
> >
> > ----- Original Message ----
> >
> > > From: bret7237 krconn@...
> > >
> > > Something that I've never understood clearly and hope someone here
> > > could answer. I understand all the formulae concerning exit pupil,
> fov
> > > and magnification, I understand, with a given telescope and 14mm
> > > eyepiece there is, for example, a 60 arcmin fov [approx twice the
> > > dimeter of the full moon], z mm exit pupil, and x magnification;
> > >
> > > and with an similiar type of eyepiece of 7mm focal length there is a
> 30
> > > arcmin fov [approx, the full moon], z/2 mm exit pupil, and 2x
> > > magnification.
> > >
> > > The 7mm FL eyepiece has an fov entering the eye of the entire full
> moon
> > > [the full moon will be approx the entire fov of the 7mm eyepiece].
> >
> > Well that also depends on the focal length of the scope.
>
>
> That was stated as a given not as a question.
>
>
>
>
> > > But
> > > the exit pupil is also 1/2 the diameter of the exit pupil of the
> 14mm
> > > eyepiece, so the size of the moon's image entering the eye should be
> > > the same with either eyepiece. How does the image of the moon on the
> > > retina become 2x as large?
> >
> > Because the light rays entering the eye do so at larger angles.
>
> That and the cited article does explain it.  But....
>
>
> > It seems pretty evident from your question that when you say you
> "understand" the formulae, all you really mean is that you _memorized_
> them, but don't actually understand what's really happening at all.
>
> For many many years I've been into astrophotography and imaging only,
> because of very poor vision until recent eye surgury. Now I can see
> somethin thru the eyepiece.  But Believe me that I "understand the
> formulae", what I don't understand is what I never see in any
> explanation, the math that calculates the size of the image on the
> retina in relation to the other parameters.

Well the eye is just another optical instrument, so if you understand basic
optics then that should be easy.  If you want the size on the retina in linear
units rather than angle, then you'll need to consult an opthamology text to find
the size of the average eyeball.

-John

>  With 2 math degrees and
> many acturial exams and 30+ yrs of actuarial experience, I know that all
> the explanitions in the world are BS if the math isn't there, the suit
> type execs always want to go by a slick verbal explanition and ignore
> the math.
>
> Ken
>
> See
> >
> > it gives a geometric picture of what happens to light rays going
> through a scope, and uses mostly simple proportions to show how
> magnification, focal length, FOV, etc, all interrelate as a result of
> the geometry of the light rays.
> >
> > -John
> >
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>

Seasons Greetings!



I do not know how many folks in the astronomical arena are aware of it, but
this past fall Rob Teeter built a 12.5" truss tube Teeter Telescope and
outfitted it with accessories donated by various manufacturers and
suppliers, yours truly included.  The completed telescope was donated to
Stellafane with the purpose in mind that it would be sold in one manner or
another to raise funds for Stellafane.  A detailed article was written and
published about the telescope in the November issue of Astronomy Technology
Today.



The telescope currently is being auctioned on eBay
(http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260328267262>
&item=260328267262).  If you are in the market for an outstanding telescope,
fully equipped with a ServoCAT GoTo and Argo Navis system and all the other
goodies, check out this once in a lifetime opportunity.  The telescope is
brand new and is equipped to the max.  Don't wait too long to place your
bid.  The end date is December 13!



Carpe Noctem!



Best regards,



Charlie Starks
MarklessT Astronomics
http://www.marklessastronomics.com <http://www.marklessastronomics.com/>

Accessories for Obsessions and other Big Dobs







[Non-text portions of this message have been removed]

Hi Charlie,

Hey, are those two boundry layer fans mounted on the back of the mirror
box?

Kyle

I am not sure, Kyle, but they look like it.  Rob Teeter could answer that
question, however.  He installed them.



Charlie



   _____

From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On Behalf Of
kyle_baron
Sent: Friday, December 12, 2008 12:05 PM
To: bigdob@yahoogroups.com
Subject: [bigdob] Re: Stellafane Donantion Telescope



Hi Charlie,

Hey, are those two boundry layer fans mounted on the back of the mirror
box?

Kyle



[Non-text portions of this message have been removed]

Perhaps you're not looking at it the right way.
The telescope produces an image on its final focal plane.  The scale
of that image is based on the focal length of the scope.  An eyepiece
is merely a simple magnifier of that focal plane image.  The higher
the inherent magnification of the eyepiece, the larger you will see
the image in the eyepiece.  High power eyepieces have smaller field
stops, too, so see a smaller segment of the final focal plane of the
scope.
The exit pupil doesn't determine the field of view you see; it merely
determines how large the image will be when it hits your eye (and the
retina).  The image scale determines how large the object will
appear, and a higher power magnifier (eyepiece) magnifies the image
on the telescope's focal plane more.
For instance, if the 7mm eyepiece had a field stop twice as large as
the 14, the true field of view would be the same size in both
eyepieces.  If you stopped down the field of view on the second
eyepiece, the object's image would be the same size--only the
apparent field would be shrunken.  So the image size of the Moon
entering the eye would be larger than in the 14mm because the image
in the exit pupil IS larger.
DonP

--- In bigdob@yahoogroups.com, "bret7237" <krconn@...> wrote:
>
> Something that I've never understood clearly and hope someone here
> could answer.  I understand all the formulae concerning exit pupil,
fov
> and magnification, I understand, with a given telescope and 14mm
> eyepiece there is, for example, a 60 arcmin fov [approx twice the
> dimeter of the full moon], z mm exit pupil, and x magnification;
>
> and with an similiar type of eyepiece of 7mm focal length there is
a 30
> arcmin fov [approx, the full moon], z/2 mm exit pupil, and 2x
> magnification.
>
> The 7mm FL eyepiece has an fov entering the eye of the entire full
moon
> [the full moon will be approx the entire fov of the 7mm eyepiece].
But
> the exit pupil is also 1/2 the diameter of the exit pupil of the
14mm
> eyepiece, so the size of the moon's image entering the eye should
be
> the same with either eyepiece.   How does the image of the moon on
the
> retina become 2x as large?
>
> Thanks for Any Insight,  Ken
>

----- Original Message ----

> From: pensack1 <Pensack1@...>
>
> Perhaps you're not looking at it the right way.
> The telescope produces an image on its final focal plane.  The scale
> of that image is based on the focal length of the scope.  An eyepiece
> is merely a simple magnifier of that focal plane image.  The higher
> the inherent magnification of the eyepiece, the larger you will see
> the image in the eyepiece.  High power eyepieces have smaller field
> stops, too, so see a smaller segment of the final focal plane of the
> scope.

In general, yes, but the _apparent_ FOV is also involved.  A narrow AFOV low
power EP _can_ have a smaller field stop than a wide angle higher power EP.  But
if the AFOV is the same, then the field stop size is proportional to EP focal
length.

> The exit pupil doesn't determine the field of view you see; it merely
> determines how large the image will be when it hits your eye (and the
> retina).

Well, for a given scope that's true.  They're inversely proportional to each
other.

>  The image scale determines how large the object will
> appear, and a higher power magnifier (eyepiece) magnifies the image
> on the telescope's focal plane more.
> For instance, if the 7mm eyepiece had a field stop twice as large as
> the 14, the true field of view would be the same size in both
> eyepieces.

No, it would be twice as large (true field is directly proportional to field
stop size), but this is very unlikely, because then the _apparent_ FOV of the
7mm would be 4X larger than the AFOV of the 14mm.

I think you meant to reverse those? - in your next two sentences you compare the
"second EP" to the 14mm.
If the AFOV is the same, then the 14mm EP will have a field stop twice the size
of the 7mm.  I

>  If you stopped down the field of view on the second
> eyepiece, the object's image would be the same size--only the
> apparent field would be shrunken.

Right, and this will have no effect on exit pupil size.

>  So the image size of the Moon
> entering the eye would be larger than in the 14mm because the image
> in the exit pupil IS larger.

There is no "image in the exit pupil".  As you correctly stated, the image is in
the focal plane.  It is then refocused on the retina by the EP.  But in between
there is no focused image.

-John


> --- In bigdob@yahoogroups.com, "bret7237" wrote:
> >
> > Something that I've never understood clearly and hope someone here
> > could answer.  I understand all the formulae concerning exit pupil,
> fov
> > and magnification, I understand, with a given telescope and 14mm
> > eyepiece there is, for example, a 60 arcmin fov [approx twice the
> > dimeter of the full moon], z mm exit pupil, and x magnification;
> >
> > and with an similiar type of eyepiece of 7mm focal length there is
> a 30
> > arcmin fov [approx, the full moon], z/2 mm exit pupil, and 2x
> > magnification.
> >
> > The 7mm FL eyepiece has an fov entering the eye of the entire full
> moon
> > [the full moon will be approx the entire fov of the 7mm eyepiece].
> But
> > the exit pupil is also 1/2 the diameter of the exit pupil of the
> 14mm
> > eyepiece, so the size of the moon's image entering the eye should
> be
> > the same with either eyepiece.   How does the image of the moon on
> the
> > retina become 2x as large?
> >
> > Thanks for Any Insight,  Ken
> >
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>

Seasons greetings, Everyone!



This is a brief announcement about a new product from Markless Astronomics.
It is a heavy duty (#8 AWG) power cable to run from a battery or 12 volt DC
power source to your telescope's Powered Ground Board (A ServoCAT option).
It connects in parallel with your existing XLR/PGB wiring.  You do not
remove the XLR/PGB wiring from the telescope, or disturb it.   Once the #8
HD cable system is installed, it is used in lieu of the XLR wiring, which is
still present and can be used as a backup system.



The gist of the power cable is #8 AWG wiring and 50-amp Anderson power
connectors.  There are three major parts to the package - a 13-foot long #8
AWG main cable, a short #10 AWG load cable for the powered ground board
(PGB), and a short #10 AWG source cable for your DC power source.



As always, only the best materials have gone into this MA product.



The purpose of the cable is not to boost the current carrying ability of the
power cable (which isn't needed, but it does), but rather to reduce the
resistance and accompanying voltage drop along the input power cable.  All
electrical wiring has a voltage drop equal to the current flowing in it
multiplied by the total resistance of the cable.  The resistance of the wire
is a factor of the metal used, its diameter, its total length, its
temperature, and the frequency of the signal on it.  In this case, it is 12
volts direct current (DC).   All things considered, #8 AWG wire has 1/10th
of the resistance of #18 gauge wire and consequently 1/10th of the voltage
drop.



Who can benefit from this cable system?  Any owner with a telescope equipped
with a PGB, especially if it has equipment that draws a lot of current;
e.g., a laptop, multiple cooling fans, and multiple dew heaters in
conjunction with a ServoCAT.  It is especially helpful if you use a DC-DC
converter to power your laptop from the power rail.  OTOH, you may just want
a cool-looking, heavy duty power cable that can really take abuse (think
star parties!).



I invite you to take a look at my website to review this new product at your
convenience.  Please click on Product #13.





Best regards,



Charlie Starks
MarklessT Astronomics
http://www.marklessastronomics.com <http://www.marklessastronomics.com/>

Accessories for Obsessions and other Big Dobs







[Non-text portions of this message have been removed]

John,
Thanks.
I stated:
"For instance, if the 7mm eyepiece had a field stop twice as large as
the 14, the true field of view would be the same size in both
eyepieces."
You were right to point out the error.
What I meant to say (thought it but typed something else) was:
"For instance, if the 7mm eyepiece had an apparent field twice as large
as the 14mm, the true field of view would be the same in both
eyepieces.  For this to be true, both eyepieces would have identically-
sized field stops."

Don

--- In bigdob@yahoogroups.com, John Mahony <jmmahony@...> wrote:
>
> ----- Original Message ----
>
> > From: pensack1 <Pensack1@...>
> >
> > Perhaps you're not looking at it the right way.
> > The telescope produces an image on its final focal plane.  The scale
> > of that image is based on the focal length of the scope.  An
eyepiece
> > is merely a simple magnifier of that focal plane image.  The higher
> > the inherent magnification of the eyepiece, the larger you will see
> > the image in the eyepiece.  High power eyepieces have smaller field
> > stops, too, so see a smaller segment of the final focal plane of the
> > scope.
>
> In general, yes, but the _apparent_ FOV is also involved.  A narrow
AFOV low power EP _can_ have a smaller field stop than a wide angle
higher power EP.  But if the AFOV is the same, then the field stop size is
proportional to EP focal length.
>
> > The exit pupil doesn't determine the field of view you see; it merely
> > determines how large the image will be when it hits your eye (and
the
> > retina).
>
> Well, for a given scope that's true.  They're inversely proportional to
each other.
>
> >  The image scale determines how large the object will
> > appear, and a higher power magnifier (eyepiece) magnifies the
image
> > on the telescope's focal plane more.
> > For instance, if the 7mm eyepiece had a field stop twice as large as
> > the 14, the true field of view would be the same size in both
> > eyepieces.
>
> No, it would be twice as large (true field is directly proportional to
field stop size), but this is very unlikely, because then the _apparent_
FOV of the 7mm would be 4X larger than the AFOV of the 14mm.
>
> I think you meant to reverse those? - in your next two sentences you
compare the "second EP" to the 14mm.
> If the AFOV is the same, then the 14mm EP will have a field stop
twice the size of the 7mm.  I
>
> >  If you stopped down the field of view on the second
> > eyepiece, the object's image would be the same size--only the
> > apparent field would be shrunken.
>
> Right, and this will have no effect on exit pupil size.
>
> >  So the image size of the Moon
> > entering the eye would be larger than in the 14mm because the
image
> > in the exit pupil IS larger.
>
> There is no "image in the exit pupil".  As you correctly stated, the
image is in the focal plane.  It is then refocused on the retina by the EP.
But in between there is no focused image.
>
> -John
>
>
> > --- In bigdob@yahoogroups.com, "bret7237" wrote:
> > >
> > > Something that I've never understood clearly and hope someone
here
> > > could answer.  I understand all the formulae concerning exit
pupil,
> > fov
> > > and magnification, I understand, with a given telescope and
14mm
> > > eyepiece there is, for example, a 60 arcmin fov [approx twice the
> > > dimeter of the full moon], z mm exit pupil, and x magnification;
> > >
> > > and with an similiar type of eyepiece of 7mm focal length there is
> > a 30
> > > arcmin fov [approx, the full moon], z/2 mm exit pupil, and 2x
> > > magnification.
> > >
> > > The 7mm FL eyepiece has an fov entering the eye of the entire
full
> > moon
> > > [the full moon will be approx the entire fov of the 7mm
eyepiece].
> > But
> > > the exit pupil is also 1/2 the diameter of the exit pupil of the
> > 14mm
> > > eyepiece, so the size of the moon's image entering the eye
should
> > be
> > > the same with either eyepiece.   How does the image of the
moon on
> > the
> > > retina become 2x as large?
> > >
> > > Thanks for Any Insight,  Ken
> > >
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
>

Was the scope actually sold?  I cannot tell from the Ebay page.

Rob



--- In bigdob@yahoogroups.com, "C. Starks" <cstarks@...> wrote:
>
> I am not sure, Kyle, but they look like it.  Rob Teeter could
answer that
> question, however.  He installed them.
>
>
>
> Charlie
>
>
>
>   _____
>
> From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On
Behalf Of
> kyle_baron
> Sent: Friday, December 12, 2008 12:05 PM
> To: bigdob@yahoogroups.com
> Subject: [bigdob] Re: Stellafane Donantion Telescope
>
>
>
> Hi Charlie,
>
> Hey, are those two boundry layer fans mounted on the back of the
mirror
> box?
>
> Kyle
>
>
>
> [Non-text portions of this message have been removed]
>

Yes, it was.  When I went to the eBay site, I scrolled down the page and
found the sold information.  It sold for ~$6700.



Charlie



   _____

From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On Behalf Of
albireo13
Sent: Thursday, December 18, 2008 1:40 PM
To: bigdob@yahoogroups.com
Subject: [bigdob] Re: Stellafane Donantion Telescope



Was the scope actually sold? I cannot tell from the Ebay page.

Rob

--- In bigdob@yahoogroups. <mailto:bigdob%40yahoogroups.com> com, "C.
Starks" <cstarks@...> wrote:
>
> I am not sure, Kyle, but they look like it. Rob Teeter could
answer that
> question, however. He installed them.
>
>
>
> Charlie
>
>
>
> _____
>
> From: bigdob@yahoogroups. <mailto:bigdob%40yahoogroups.com> com
[mailto:bigdob@yahoogroups. <mailto:bigdob%40yahoogroups.com> com] On
Behalf Of
> kyle_baron
> Sent: Friday, December 12, 2008 12:05 PM
> To: bigdob@yahoogroups. <mailto:bigdob%40yahoogroups.com> com
> Subject: [bigdob] Re: Stellafane Donantion Telescope
>
>
>
> Hi Charlie,
>
> Hey, are those two boundry layer fans mounted on the back of the
mirror
> box?
>
> Kyle
>
>
>
> [Non-text portions of this message have been removed]
>





[Non-text portions of this message have been removed]

I just bought a couple of University Optics Orthos (4mm and 6mm) mainly
for planetary viewing in my WO 80mm refractor. I have an 18" f4.3 Dob
as well and wondered how good such eyepieces could be for hi-power
views of DSOs (such as planetary nebula and especially their central
stars) or small distant galaxies?

  I have a barlow which is useful but I am a believer that less (glass
that is) is more...eyepieces with less elements typically have higher
light throughput. I have experienced this effect dramatically with my
30mm Widescan II eyepeice on the Veil nebula and compared to more
complex eyepieces (Naglers, Panoptics, etc...) and they cannot compare
to the simpler design/ more light-throuput. Would this generally hold
true for smaller focal length eyepieces as well?

Happy Holidays...

Mike Klosterman
Yorktown, VA

----- Original Message ----

> From: kloster12000 <kloster12000@...>
>
> I just bought a couple of University Optics Orthos (4mm and 6mm) mainly
> for planetary viewing in my WO 80mm refractor. I have an 18" f4.3 Dob
> as well and wondered how good such eyepieces could be for hi-power
> views of DSOs (such as planetary nebula and especially their central
> stars) or small distant galaxies?
>
> I have a barlow which is useful but I am a believer that less (glass
> that is) is more...eyepieces with less elements typically have higher
> light throughput. I have experienced this effect dramatically with my
> 30mm Widescan II eyepeice on the Veil nebula and compared to more
> complex eyepieces (Naglers, Panoptics, etc...) and they cannot compare
> to the simpler design/ more light-throuput. Would this generally hold
> true for smaller focal length eyepieces as well?

Sure (as long as the AR coatings are good), although the reasons for preferring
less glass is a bit different for planets.  They're bright, so you don't need
more light.  But fewer air/glass surfaces also means less scattered light
(better contrast) and fewer ghost images.

But a downside to orthos for dobs is the small FOV, unless your dob is driven.

-John

Thanks John. Yes my Telekit now has ServoCat so for certain objects,
FOV is not an issue. I have heard excellent things about the UO Abbe
Orthos especially since they are so inexpensive!

Happy Holidays
Mike

--- In bigdob@yahoogroups.com, John Mahony <jmmahony@...> wrote:
>
> ----- Original Message ----
>
> > From: kloster12000 <kloster12000@...>
> >
> > I just bought a couple of University Optics Orthos (4mm and 6mm)
mainly
> > for planetary viewing in my WO 80mm refractor. I have an 18" f4.3
Dob
> > as well and wondered how good such eyepieces could be for hi-
power
> > views of DSOs (such as planetary nebula and especially their
central
> > stars) or small distant galaxies?
> >
> > I have a barlow which is useful but I am a believer that less
(glass
> > that is) is more...eyepieces with less elements typically have
higher
> > light throughput. I have experienced this effect dramatically
with my
> > 30mm Widescan II eyepeice on the Veil nebula and compared to more
> > complex eyepieces (Naglers, Panoptics, etc...) and they cannot
compare
> > to the simpler design/ more light-throuput. Would this generally
hold
> > true for smaller focal length eyepieces as well?
>
> Sure (as long as the AR coatings are good), although the reasons
for preferring less glass is a bit different for planets.  They're
bright, so you don't need more light.  But fewer air/glass surfaces
also means less scattered light (better contrast) and fewer ghost
images.
>
> But a downside to orthos for dobs is the small FOV, unless your dob
is driven.
>
> -John
>

There is a discussion now on Cloudy Nights ATM on alternative laminates
for  alt and azimuth bearings.
What have you had success with now that Ebony Star isn't available?

Ah, but it is still available. ScopeStuff bought a boat load of the
stuff and still has a bunch. See http://www.scopestuff.com/ss_lexx.htm


davidfpitre wrote:
>
> There is a discussion now on Cloudy Nights ATM on alternative laminates
> for alt and azimuth bearings.
> What have you had success with now that Ebony Star isn't available?
>
>

The new stuff seems to have a different surface texture, like 1000 grit
sandpaper. 

Ross

--- On Wed, 12/24/08, Jim Chandler <jim@...> wrote:
From: Jim Chandler <jim@...>
Subject: Re: [bigdob] Alternative bearings for alt bearings
To: bigdob@yahoogroups.com
Date: Wednesday, December 24, 2008, 7:16 PM











             Ah, but it is still available. ScopeStuff bought a boat load of the

stuff and still has a bunch. See http://www.scopestu ff.com/ss_ lexx.htm



davidfpitre wrote:

>

> There is a discussion now on Cloudy Nights ATM on alternative laminates

> for alt and azimuth bearings.

> What have you had success with now that Ebony Star isn't available?

>

>
























[Non-text portions of this message have been removed]

Jim,
  Scopestuff has it in strips for alt bearings and in narrow-cut rings
for small az bearings. They don't sell it in squares or full circles
though; and the az bearing circles they offer are not big enough for
larger dobs. It seems the azmuth bearing circles they sell are mainly
for  Synta dob bearings.

David,

When you asked about Ebony Star, I assumed you were looking for alt.
bearing material. You're building an 18", correct? Look for FRP
(fiberglass reinforced plastic), the white, bumpy stuff, also known as
Glasboard. That's the material Obsession uses for az bearings (at least
for 18" and up) and I've always been satisfied with the performance.

Jim



davidfpitre wrote:
>
> Jim,
> Scopestuff has it in strips for alt bearings and in narrow-cut rings
> for small az bearings. They don't sell it in squares or full circles
> though; and the az bearing circles they offer are not big enough for
> larger dobs. It seems the azmuth bearing circles they sell are mainly
> for Synta dob bearings.
>
>

I have used the glass board on the AZ on small scopes such as the Antares 12"
tube dob with success. It does seem to be a bit smoother with heavier scopes
though. If I had enough of the old EbonyStar on hand, I would have used that for
the Antares.

Pat M.

-------------- Original message from Jim Chandler <jim@...>:
--------------

David,

When you asked about Ebony Star, I assumed you were looking for alt.
bearing material. You're building an 18", correct? Look for FRP
(fiberglass reinforced plastic), the white, bumpy stuff, also known as
Glasboard. That's the material Obsession uses for az bearings (at least
for 18" and up) and I've always been satisfied with the performance.

Jim

davidfpitre wrote:
>
> Jim,
> Scopestuff has it in strips for alt bearings and in narrow-cut rings
> for small az bearings. They don't sell it in squares or full circles
> though; and the az bearing circles they offer are not big enough for
> larger dobs. It seems the azmuth bearing circles they sell are mainly
> for Synta dob bearings.
>
>



[Non-text portions of this message have been removed]

Ahhh!
Thanks for the tip.

David

--- In bigdob@yahoogroups.com, Jim Chandler <jim@...> wrote:
>
> David,
>
> When you asked about Ebony Star, I assumed you were looking for
alt.
> bearing material. You're building an 18", correct? Look for FRP
> (fiberglass reinforced plastic), the white, bumpy stuff, also known
as
> Glasboard. That's the material Obsession uses for az bearings (at
least
> for 18" and up) and I've always been satisfied with the performance.
>
> Jim
>
>
>
> davidfpitre wrote:
> >
> > Jim,
> > Scopestuff has it in strips for alt bearings and in narrow-cut
rings
> > for small az bearings. They don't sell it in squares or full
circles
> > though; and the az bearing circles they offer are not big enough
for
> > larger dobs. It seems the azmuth bearing circles they sell are
mainly
> > for Synta dob bearings.
> >
> >
>

I think FRP is even preferred over ebony star for az bearings on larger dobs.

It's available at most of the big home improvement stores, about $25 (IIRC) for
a 4'X8' panel.  It's commonly used as wall covering material in restaurant
kitchens and public bathrooms.

-John




----- Original Message ----
> From: Jim Chandler <jim@...>
>
> David,
>
> When you asked about Ebony Star, I assumed you were looking for alt.
> bearing material. You're building an 18", correct? Look for FRP
> (fiberglass reinforced plastic), the white, bumpy stuff, also known as
> Glasboard. That's the material Obsession uses for az bearings (at least
> for 18" and up) and I've always been satisfied with the performance.
>
> Jim

Why would it be preferred?
How is the application different than for alt bearings?
It seems like you have similar forces and the need for similar
friction.

David

--- In bigdob@yahoogroups.com, John Mahony <jmmahony@...> wrote:
>
> I think FRP is even preferred over ebony star for az bearings on
larger dobs.
>
> It's available at most of the big home improvement stores, about
$25 (IIRC) for a 4'X8' panel.  It's commonly used as wall covering
material in restaurant kitchens and public bathrooms.
>
> -John
>
>
>
>

----- Original Message ----

> From: davidfpitre <davidfpitre@...>
>
> Why would it be preferred?
> How is the application different than for alt bearings?
> It seems like you have similar forces and the need for similar
> friction.

I'm not quite sure myself, but I've only heard of it being used for az bearings,
not alt.  One possible reason is that it's a stiffer material, so I don't know
if it would bend to fit the curved alt bearing surface well.

-John


> --- In bigdob@yahoogroups.com, John Mahony wrote:
> >
> > I think FRP is even preferred over ebony star for az bearings on
> larger dobs.
> >
> > It's available at most of the big home improvement stores, about
> $25 (IIRC) for a 4'X8' panel.  It's commonly used as wall covering
> material in restaurant kitchens and public bathrooms.
> >
> > -John
> >
> >
> >
> >
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>

My 10-year-old Obsession 25 has FRP for both alt and az bearings, from
the factory. It works fine. My much newer 30, on the other hand, has FRP
az and Ebony Star alt bearings. It works fine too. Go figure.

Jim


John Mahony wrote:
>
> ----- Original Message ----
>
> > From: davidfpitre <davidfpitre@...
> <mailto:davidfpitre%40yahoo.com>>
> >
> > Why would it be preferred?
> > How is the application different than for alt bearings?
> > It seems like you have similar forces and the need for similar
> > friction.
>
> I'm not quite sure myself, but I've only heard of it being used for az
> bearings, not alt. One possible reason is that it's a stiffer
> material, so I don't know if it would bend to fit the curved alt
> bearing surface well.
>
> -John
>
>
> > --- In bigdob@yahoogroups.com <mailto:bigdob%40yahoogroups.com>,
> John Mahony wrote:
> > >
> > > I think FRP is even preferred over ebony star for az bearings on
> > larger dobs.
> > >
> > > It's available at most of the big home improvement stores, about
> > $25 (IIRC) for a 4'X8' panel. It's commonly used as wall covering
> > material in restaurant kitchens and public bathrooms.
> > >
> > > -John
> > >
> > >
> > >
> > >
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
>
>

True.  It is preferred for ALT bearings on larger Dobs.



Charlie



   _____

From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On Behalf Of
John Mahony
Sent: Thursday, December 25, 2008 9:35 PM
To: bigdob@yahoogroups.com
Subject: Re: [bigdob] Re: Alternative bearings for alt bearings



I think FRP is even preferred over ebony star for az bearings on larger
dobs.

It's available at most of the big home improvement stores, about $25 (IIRC)
for a 4'X8' panel. It's commonly used as wall covering material in
restaurant kitchens and public bathrooms.

-John


----- Original Message ----
> From: Jim Chandler <jim@... <mailto:jim%40bigdob.net> >
>
> David,
>
> When you asked about Ebony Star, I assumed you were looking for alt.
> bearing material. You're building an 18", correct? Look for FRP
> (fiberglass reinforced plastic), the white, bumpy stuff, also known as
> Glasboard. That's the material Obsession uses for az bearings (at least
> for 18" and up) and I've always been satisfied with the performance.
>
> Jim





[Non-text portions of this message have been removed]

For the underside of the mirror box, I like to use FRP, which stands for
Fiberglass Reinforced Plastic.  There are several makers of it, a well-known
brand being GlasBoard.  However, I recently saw FRP at Lowes in our area,
with the random sized and random oriented bumps - the right stuff!  It is
sold in 4x8 sheets for about $28.



Charlie

Charlotte, NC



   _____

From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On Behalf Of
davidfpitre
Sent: Thursday, December 25, 2008 1:41 PM
To: bigdob@yahoogroups.com
Subject: [bigdob] Re: Alternative bearings for alt bearings



Jim,
Scopestuff has it in strips for alt bearings and in narrow-cut rings
for small az bearings. They don't sell it in squares or full circles
though; and the az bearing circles they offer are not big enough for
larger dobs. It seems the azmuth bearing circles they sell are mainly
for Synta dob bearings.





[Non-text portions of this message have been removed]