I've never heard any authoritative comments about gold diagaonals
which I have heard about, kid of like ancient rumors about El
Dorado, but never seen in action.  Do they have anything to
recommend them?

regards
Greg N

--- In ap-ug@yahoogroups.com, ocean779@a... wrote:
> yeah, but chuck you're missing the point...1/20th wave is more
perfect than
> 1/10th wave.  Whether such perfection can be "utilized" or not
does not assail
> the integrity of the perfection :)
>

In a message dated 8/3/2004 6:51:20 AM Central Daylight Time,
tim71pos@... writes:


> I've never heard any authoritative comments about gold diagaonals
> which I have heard about, kid of like ancient rumors about El
> Dorado, but never seen in action.  Do they have anything to
> recommend them?
>

No.

Roland Christen


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

Well that's the short answer (to wit: No).  What would be the
nominal misleading reason to get a gold diagonal, and why is it
fallacious?  Or is it just something people do, like Mag wheels on
cars?

thanks
Greg N



--- In ap-ug@yahoogroups.com, chris1011@a... wrote:
> In a message dated 8/3/2004 6:51:20 AM Central Daylight Time,
> tim71pos@h... writes:
>
>
> > I've never heard any authoritative comments about gold
diagaonals
> > which I have heard about, kid of like ancient rumors about El
> > Dorado, but never seen in action.  Do they have anything to
> > recommend them?
> >
>
> No.
>
> Roland Christen
>
>
> [Non-text portions of this message have been removed]

Greg,
  Gold mirrors produce gold colored images. That makes them unsuitable
for telescope use at visual wavelengths. However, gold exhibits high
reflectivity (~95%) across a wide range of wavelengths in the far
infrared.

Richard

So, they are appropriate for the scads of amateurs who are doing
imaging in infrared....

...but wouldn't we want a gold *primary* too, for that sort of thing?

BTW if memory serves that was an infrared image of the shadow side
of Venus in S&T?  Or was it a different wavelength?

thanks,
Greg N


--- In ap-ug@yahoogroups.com, "zeeemu" <syzygy42@e...> wrote:
> Greg,
>  Gold mirrors produce gold colored images. That makes them
unsuitable
> for telescope use at visual wavelengths. However, gold exhibits
high
> reflectivity (~95%) across a wide range of wavelengths in the far
> infrared.
>
> Richard

"...but wouldn't we want a gold *primary* too, for that sort of
thing?"

  I suppose so but aluminum and silver are adequate for near infrared
wavelengths. Gold is typically used at much longer wavelengths.

"BTW if memory serves that was an infrared image of the shadow side
of Venus in S&T?  Or was it a different wavelength?"

  The images I remember were obtained at visible and UV wavelengths.

http://vestige.lmsal.com/TRACE/transits/venus_2004/

http://sohowww.nascom.nasa.gov/

http://www.n3kl.org/sun/index.html

Richard

--- In ap-ug@yahoogroups.com, "gnowellsct" <tim71pos@h...> wrote:
> So, they are appropriate for the scads of amateurs who are doing
> imaging in infrared....
>
> ...but wouldn't we want a gold *primary* too, for that sort of thing?
>
> BTW if memory serves that was an infrared image of the shadow side
> of Venus in S&T?  Or was it a different wavelength?
>
> thanks,
> Greg N
>
>
> --- In ap-ug@yahoogroups.com, "zeeemu" <syzygy42@e...> wrote:
> > Greg,
> >  Gold mirrors produce gold colored images. That makes them
> unsuitable
> > for telescope use at visual wavelengths. However, gold exhibits
> high
> > reflectivity (~95%) across a wide range of wavelengths in the far
> > infrared.
> >
> > Richard

Unless you are working out beyond the MWIR band of about 5 microns,
the difference in reflectivity between a gold or silver mirror coating
is negligible.  The images of Venus as I rememeber were taken around 1
micron.  In that case, stick with the silver and get better reflection
in the blue and green for other purposes.  If you want to image out
beyond the MWIR band, then gold is best, but you also have many other
things to worry about in your optical design, not withstanding the
price of the camera.

Frank Z...

Those of you many who were on sci.astro or on the original AOL refractor
newsgroup will remember that Vernonscope and its many iterations over the
years were no strangers to hyperbole.

glenmore



> From: "paulatkinson22" <paulatkinson22@...>
> Reply-To: ap-ug@yahoogroups.com
> Date: Tue, 03 Aug 2004 02:20:17 -0000
> To: ap-ug@yahoogroups.com
> Subject: [ap-ug] New $445 Digaonal?
>
> Has anyone else seen this?  New product showcase in Sept. S&T
> magazine has profiled a new Vernonscope 2" 1/20th wave (or better)
> VERNONscope Quartz Star Diagonal Mirror. Each diagonal mirror comes
> with an indivdual Zygo interferometer printout for proof of flatness
> and is 98% or better reflectivity.  This bad boy cost $445 dollars!!!
>
> So exactly what does this thing offer that the three Maxbrights that
> I own don't?  Figure this is the best place on earth for honest talk
> on optics.
>
> Paul Atkinson

Yes.  There were some interesting claims for some of their
smaller telescopes.

Rich

> Those of you many who were on sci.astro or on the original AOL refractor
> newsgroup will remember that Vernonscope and its many iterations over the
> years were no strangers to hyperbole.
>
> glenmore
>
>
>
> > From: "paulatkinson22" <paulatkinson22@...>
> > Reply-To: ap-ug@yahoogroups.com
> > Date: Tue, 03 Aug 2004 02:20:17 -0000
> > To: ap-ug@yahoogroups.com
> > Subject: [ap-ug] New $445 Digaonal?
> >
> > Has anyone else seen this?  New product showcase in Sept. S&T
> > magazine has profiled a new Vernonscope 2" 1/20th wave (or better)
> > VERNONscope Quartz Star Diagonal Mirror. Each diagonal mirror comes
> > with an indivdual Zygo interferometer printout for proof of flatness
> > and is 98% or better reflectivity.  This bad boy cost $445 dollars!!!
> >
> > So exactly what does this thing offer that the three Maxbrights that
> > I own don't?  Figure this is the best place on earth for honest talk
> > on optics.
> >
> > Paul Atkinson
>
>
>
>
> To UNSUBSCRIBE, or for general information on the ap-ug list
> see http://groups.yahoo.com/group/ap-ug
> Yahoo! Groups Links
>
>
>
>
>

Thank you for the spectacular links.  I'm sorry not to be more
specific but with painting the living room the house is more chaotic
than usual and I can't find my S&T.   But the image in question was

(a) taken through a C14 and
(b) "the shadow of venus" to which I referred, easily misread as a
reference to the transit, was in fact the dark side of venus--if you
will "the old Venus in the New Venus' arms".  No relationship to the
transit.

It is the first known amateur picture to capture features on the
dark side disk of Venus using wavelengths (methinks IR) that can
make it through the clouds.  Dark albedo features were visible. The
crescent was overexposed to permit the weaker dark-side features to
come through.

regards
Greg N


--- In ap-ug@yahoogroups.com, "zeeemu" <syzygy42@e...> wrote:
>  "...but wouldn't we want a gold *primary* too, for that sort of
> thing?"
>
>  I suppose so but aluminum and silver are adequate for near
infrared
> wavelengths. Gold is typically used at much longer wavelengths.
>
> "BTW if memory serves that was an infrared image of the shadow
side
> of Venus in S&T?  Or was it a different wavelength?"
>
>  The images I remember were obtained at visible and UV wavelengths.
>
> http://vestige.lmsal.com/TRACE/transits/venus_2004/
>
> http://sohowww.nascom.nasa.gov/
>
> http://www.n3kl.org/sun/index.html
>
> Richard

Greg,
  You're correct! While looking through September's S&T last night I
found the near IR picture of Venus on page 20.

Richard

Gold coatings from Edmund Sci are highly reflective above 600nm up
to 97% from 800-2000nm.

Will gold coatings last longer than aluminum coatings?

Don

"Will gold coatings last longer than aluminum coatings?"

Don,
  It depends. Gold doesn't oxidize but is quite soft. I have a few gold
coated mirrors that still look new after thirty years. If properly
overcoated and cared for, gold coatings can last indefinitely.

Richard

Hi Roland

> Think of it this way. On the receiving end of this super-duper flatness
> diagonal is an eyepiece of perhaps 2" diameter clear aperture into which
1/20 wave
> of light is passing almost directly without much change.  Now, there is no
> eyepiece on earth, and even if God himself designed it, that would have
anything
> close to diffraction limited performance over this size aperture. In fact,
the
> fanciest 2" eyepiece (smaller sizes would not need the entire diagonal
> aperture to be perfect, eh?) has about 20 to 40 WAVES of spherical
wavefront error
> over its entire aperture.

Would you expand on this? I knew there was considerable error, and the
ability (at that point in the optical train) to hide a great deal of error,
but had never thought of quantifying it. (IIRC, someone on the atm list was
putting together a selection of eyepiece Oslo files. I may need to dig those
out and do some playing.)

What sort of a range of errors are we all looking at in our favorite
eyepieces? And do we really want to know!  :^0

Clear Skies

Chuck Taylor

In a message dated 8/5/2004 5:54:13 PM Central Daylight Time,
chucktaylor@... writes:


> What sort of a range of errors are we all looking at in our favorite
> eyepieces? And do we really want to know!  :^0
>
>

Each star image occupies a very tiny portion of the surface of each of the
lenses in an eyepiece. It is minuscule compared to the full aperture of the
eyepiece. Play with it in Oslo and you will instantly have one of those "DUH"
moments. Then, expand the F-ratio of the incoming beam and see what happens to
the
star diameters at the focus point of the ocular. You will be utterly amazed.

You can also simulate a full aperture image with any eyepiece where you can
remove the 1.25" barrel. Then allow a star to come to focus on a ground glass
behind the telescope. Place the eyepiece up to the ground glass to see the
resultant image. Now go inside and outside of focus to see the horrendous
spherical aberration. Remove the ground glass and examine the image again. the
spherical will be gone. Why does the ground glass introduce spherical? Because
it
changes the F-ratio from whatever the scope is to whatever maximum the eyepiece
allows. Draw it out on paper to see what I mean. Interesting stuff, optics.

Roland Christen


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

Hi all;
Safety aside, is there potential for harm to the objective lens of a
refractor when using a Herschel wedge?  Specifically for the AP
refractors--Traveler, in my case--are the lens materials/oils
susceptible to color center formation/breakdown from full exposure to
incident sunlight?

Thanks for any advice,
George
http://www.digibird.com

> Each star image occupies a very tiny portion of the surface of each of the
> lenses in an eyepiece. It is minuscule compared to the full aperture of
the
> eyepiece. Play with it in Oslo and you will instantly have one of those
"DUH"
> moments.

Just like the diagonal, only here it is an even smaller part of each lens.
That much I already saw. Field curvature would be a far greater problem. But
what is the typical (overall) error that eyepiece manufacturers allow? At
what point does it become noticable to the observer (at f/4? at f/8?) What
caught me in your original post was quantifying it at 20-40 waves. I knew it
could be big for the same reason as the diagonal quality question, (but far
more so, being practically on top of the focal plane), but 40 waves was more
than I would have guessed. However, now that I think and picture the
approximate ray trace, it does not seem unreasonable.

> Then, expand the F-ratio of the incoming beam and see what happens to the
> star diameters at the focus point of the ocular. You will be utterly
amazed.

I haven't played with it in oslo, but have put cheap eyepieces into fast
scopes!  :-(

From what I am hearing, part of the problem is the design, with tremendous
aberation inherent in the designs. But would it also be made worse if the
focal ratio was fast enough to expose quality problems as well? At what
speed (and at what surface errors in manufacturering) would quality problems
come into play enough to be seen, assuming the design had sufficient
correction for that focal ratio? My guess is that even very poor quality
control in each surface is not going to be exposed, but that wedge problems
might show up?

I lost oslo due to a drive failure, and I understand LT is no longer
available. Does the raytrace software from AP import oslo files?

> You can also simulate a full aperture image with any eyepiece where you
can
> remove the 1.25" barrel. Then allow a star to come to focus on a ground
glass
> behind the telescope. Place the eyepiece up to the ground glass to see the
> resultant image. Now go inside and outside of focus to see the horrendous
> spherical aberration. Remove the ground glass and examine the image again.
the
> spherical will be gone. Why does the ground glass introduce spherical?
Because it
> changes the F-ratio from whatever the scope is to whatever maximum the
eyepiece
> allows. Draw it out on paper to see what I mean.

More fun to draw it in your head  :-)  It took me a minute to realize why
the ground glass made a difference and allowed a different focal ratio.

> Interesting stuff, optics.

Understatement! Understanding the optics is as much fun as understanding the
objects we view through them.

Now to create a piece of ground glass and have some fun! Or maybe use a
pinhole source?

Thanks

Chuck Taylor


> Roland Christen

George;

I use Astro-Physics refractors for years to observe the sun with a
Herschel wedge. Is was sure for me and for the scope.

You have not to worry about anything and believe me, I wouldn´t tell
you that if I wasn´t absolutely sure about it.

The lens of the scope let only pass the parallel light which comes
from the sun. The lens is not exposed to a hot light cone of focussed
light. (The same as you looking to Venus near the Sun). Exposed to a
heated light cone is only true for the Herschel wedge, but no problem
for it as well because it was built for that.

Nevertheless, to take care of the Herschel Wegde, I covered the
aperture of the scope from time to time, lets say, after one hour or
so.

I hope that helps.

Stefan

http://www.astromeeting.de


--- In ap-ug@yahoogroups.com, "George" <graiche@d...> wrote:
> Hi all;
> Safety aside, is there potential for harm to the objective lens of a
> refractor when using a Herschel wedge?  Specifically for the AP
> refractors--Traveler, in my case--are the lens materials/oils
> susceptible to color center formation/breakdown from full exposure
to
> incident sunlight?
>
> Thanks for any advice,
> George
> http://www.digibird.com

In a message dated 8/6/2004 12:22:33 AM Central Daylight Time,
chucktaylor@... writes:


> But
> what is the typical (overall) error that eyepiece manufacturers allow

It is not what a manufacturer allows, since it is virtually impossible to
produce anyhting but a perfect sphere on all these tiny surfaces. It is the
design or type of ocular itself that governs the amount of spherical aberration
at
different F-ratios. Thus a Plossl would have a certain amount at F10, an Ortho
a different amount, etc.

Roland Christen


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

> > But
> > what is the typical (overall) error that eyepiece manufacturers allow
>
> It is not what a manufacturer allows, since it is virtually impossible to
> produce anyhting but a perfect sphere on all these tiny surfaces.

What, no zonal control!  <vbg>

Actually, I had someone telling me the other day that his eyepieces had
aspherical surfaces.  ;-)

For manufacturing quality, I was thinking of tolerances on the radii and
thickness. Would wedge show up quicker?

But mainly I meant what the manufacturer allows in the design -- ie how much
spherical aberation could be tolerated in the design before being noticable
at reasonable focal ratios.

BTW, congrats on the new construction.

Clear Skies

Chuck Taylor


> It is the
> design or type of ocular itself that governs the amount of spherical
aberration at
> different F-ratios. Thus a Plossl would have a certain amount at F10, an
Ortho
> a different amount, etc.
>
> Roland Christen
>
>
> [Non-text portions of this message have been removed]
>
>
>
>
> To UNSUBSCRIBE, or for general information on the ap-ug list
> see http://groups.yahoo.com/group/ap-ug
> Yahoo! Groups Links
>
>
>
>
>
>

In a message dated 8/6/2004 2:07:12 PM Central Daylight Time,
chucktaylor@... writes:


>
> BTW, congrats on the new construction.
>
>

Thanks.

Roland Christen


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

Hi All -

I must be travelling at something like 99.96% of the speed of light
judging by the way time seems to have slowed to a near standstill in
the world around me.  The reason for these relativistic effects?  My
Big Mak is at home getting to know his new playmates, a new 1200GTO
and Monolith pier, and waiting for dark.

After nearly four years of anticipation, I finally got everything
assembled last night, albeit in my living room.  Let me tell you,
the cat wasn't the only one who was impressed.  What a setup!
Familiarity with the individual components simply didn't prepare me
for the gestalt of the whole.  The first time I switched it on and
watched it slew was like a religious experience, which in itself is
something considering my atheist inclinations.

So tonight the plan is to get it out into the backyard and under the
stars.  If all goes well at home, Saturday night will see us at one
of the local observing spots.  I'm more than ready to trade my
longstanding photon deprivation for some good old american sleep
deprivation (Sunday morning pedestrians on Page Mill Rd may want to
take note.)

I'll have plenty more to report once I actually SEE something, but
for now I'll go back to watching the second hand sweep over the same
real estate ad nauseum.

Rob Hunt

p.s. - George, what is all this talk about a Herschel wedge?  Don't
you think you'd be better served with a few more essential items -
such as a diagonal, a good slo-mo head, or an eyepiece other than
your lonely 10 Radian?  The Baader film (about 20 bucks at a store
near you) will get you 95% of the way there anyway.  If your solar
budget is really so big, why not just save some more and get into h-
alpha?

> >
> > BTW, congrats on the new construction.
> >
> >
>
> Thanks.
>
> Roland Christen
>


Undercover spy shots of  the new AP facility...?
http://www.scopenews.com/ap_expansion.jpg

In a message dated 8/6/2004 3:35:01 PM Central Daylight Time,
mike@... writes:


> Undercover spy shots of  the new AP facility...?
> http://www.scopenews.com/ap_expansion.jpg
>

Close!

Rolando


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

Hey Rob, what do you really think?

Just kinda wondering about the Herschel as I was reviewing
erecting prisms.  I will cross my fingers for you in the hope that
Los Trancos is fog-free tonight!  Of course, you could attempt to
find Jupiter before sunset... :)

George
http://www.digibird.com

> p.s. - George, what is all this talk about a Herschel wedge?
Don't
> you think you'd be better served with a few more essential
items -
> such as a diagonal, a good slo-mo head, or an eyepiece other
than
> your lonely 10 Radian?  The Baader film (about 20 bucks at a
store
> near you) will get you 95% of the way there anyway.  If your
solar
> budget is really so big, why not just save some more and get
into h-
> alpha?

Pursuant to discussions from a few days ago:

1.  If I understand a rather cursory note rightly, the hole in the
mirror is covered by the primary lock nut which acts to mask the
rough edge of the mirror hole (i.e. overlaps the mirror).  Thus
the "edge is clean" in those cases where the secondary does
not "cast a shadow" over the lock nut.

2.  The designs vary.  In the C5 and C8, the lock nut diameter is
the SAME as the secondary CO. In the 9.25 and C14, the lock nut is
SMALLER than the secondary CO...by significant margins of 1/3 to
almost 1/2 inch respectively.  In the C11 the lock nut is LARGER
than the secondary CO by one tenth of one inch.  A C11 owner might
measure his central obstruction at the corrector plate as 35.45% but
the true CO is 36.36%. The C11's effective CO is thus functionally
equivalent to the 9.25 (36.49%).

This information was provided by Celestron.  I've prepared an Excel
table but won't post it to the files till they've doublechecked its
accuracy.  I don't think there is any effort on Celestron's part to
put out wrong information.  I do think that with five basic
telescopes and three different sets of relationships between the
secondary CO and the primary obstruction that there is a lot of
opportunity for spreadsheet error.  Moreover, explaining that on
this scope we measure the lock nut, on this scope the secondary: all
that gets complicated.  The only really unusual case is the C11, and
if for consistency's sake they stick with the secondary obstruction
measurement rather than the primary lock nut, the inaccuracy is less
than 1% of total aperture by diameter.  I wouldn't consider that a
significant issue.

regards
Greg N

"All cats look grey in the dark", Thomas Lodge (1558-1625)

Hmmmm... is it possible that Renaissance prognosticators foretold of
catadioptric issues centuries before their introduction ?!? (Sorry, couldn't
resist! :o)

Paul

PS: While on a roll (of being a jerk) I'll share a bit of astro-whimsy with ya'
(the clouds and "work-demons" have polluted my mind! :o)

This was tossed together as a demo for gradient correction:

SNIP---> (if image does not appear, use this link: http://tinyurl.com/6y56m )



The images here are reduced sized versions of the actual images used to produce
this:

http://www.astro-nut.com/sun-ha-04jul21.html


Notice that only a small amount of tweak is used, as I wanted to lighten up the
outlying limb only a tad. While difficult
to detect the darkened limbs in the reduced size original grayscale shown here,
their prominence --- pun intended ---
is readily discernable in the large-scale version.

Perhaps they will touch on these aspects of image processing techniques during
the seminar.

Cheers,

Paul

PS: I gotta' be careful... I'm skating on thin ice here. If I divulge too many
of the details behind solar processing tricks,

the Solar-Magicians Users Group (AKA the SMUG) may move to ex-communicate me!

--- http://www.astro-nut.com ---

(Okay, okay... I'll consider changing the name of my site name to astro-ass.com
heheheh!)



--- http://www.astro-nut.com ---



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

Mike,
How did you do that? I laughed so hard when I saw it. I don't believe anything I
see in a photo anymore. <g>

Clear skies,
Marj Christen
Astro-Physics, Inc.
11250 Forest Hills Road
Rockford, IL 61115
Phone: 815-282-1513
Fax: 815-282-9847
www.astro-physics.com
Please include this e-mail with your response.


>-----Original Message-----
>From: Mike C [mailto:mike@...]
>Sent: Friday, August 06, 2004 3:33 PM
>To: ap-ug@yahoogroups.com
>Subject: Re: [ap-ug] New $445 Digaonal?
>
>
>
>> >
>> > BTW, congrats on the new construction.
>> >
>> >
>>
>> Thanks.
>>
>> Roland Christen
>>
>
>
>Undercover spy shots of  the new AP facility...?
>http://www.scopenews.com/ap_expansion.jpg
>
>
>
>
>
>
>
>To UNSUBSCRIBE, or for general information on the ap-ug list
>see http://groups.yahoo.com/group/ap-ug
>Yahoo! Groups Links
>
>
>
>
>
>

Hi Marj

Glad to supply a laugh... Adobe Photoshop is the choice tool for adjusting
pictures.

Mike



> Mike,
> How did you do that? I laughed so hard when I saw it. I don't believe anything
I see in a photo anymore. <g>
>
> Clear skies,
> Marj Christen

nebula through my 100mm f6 achro was NO different than any of you who
waited, and spent thousands of dollars for an AP.
Tom