Hello everyone recently I have become interested in double stars and
Refractors, so I was wondering which type of refractor would be best for this
type of astronomy.  I was thinking along the lines of a TEC 140 or a D&G 6inch
F12. Now I know we are not comparing like with like but would the extra inch
plus the greater focal length of the D$G compansate for the fact it is not an
APO. The optical tube would be going on a Losmandy G11 Mount, bearing in mind
also the D$G is half the price of the TEC.

I've owned one of these for almost 2 years.  (140)  Great scope.

Jim

--- In Refractors@yahoogroups.com, "Richard F.L.R. Snashall" <rflrs@...> wrote:
>
> Scott Walker wrote:
> > Would still expect the NeoAchro to have a lot of chromatic aberation. The
Petzval design only improves chromatic aberation a modest amount. One needs to
combine the Petzval design with special glasses to achieve the great color
correction that is seen in scopes like the NP101. I would expect the chromatic
aberation to be similar to a f8 to f9 achro of the seem aperture.
> Re: NeoAchro 140
>
> I wonder what their particular definition of "Petzval like" is...
>

I would vote for the D&G. Faint close pairs should benefit fron the extra inch
for resolving power and light grasp, and at f/12, I don't think CA will be a
problem. Also, I think you'll probably have less out-of-pocket. D&G has a fine
reputation.

Scott Holland
Lowell, NC 28098

Celestron/Vixen C-102 f/9 (plus a lot of other toys)


   ----- Original Message -----
   From: patconlon
   To: Refractors@yahoogroups.com
   Sent: Saturday, November 14, 2009 2:57 PM
   Subject: [Refractors] Refractor for Double Stars



   Hello everyone recently I have become interested in double stars and
Refractors, so I was wondering which type of refractor would be best for this
type of astronomy. I was thinking along the lines of a TEC 140 or a D&G 6inch
F12. Now I know we are not comparing like with like but would the extra inch
plus the greater focal length of the D$G compansate for the fact it is not an
APO. The optical tube would be going on a Losmandy G11 Mount, bearing in mind
also the D$G is half the price of the TEC.





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

I agree with you, Scott.
Doug

On Sat, Nov 14, 2009 at 6:16 PM, Scott Holland <holl8127@...>wrote:

>
>
> I would vote for the D&G. Faint close pairs should benefit fron the extra
> inch for resolving power and light grasp, and at f/12, I don't think CA will
> be a problem. Also, I think you'll probably have less out-of-pocket. D&G has
> a fine reputation.
>
> Scott Holland
> Lowell, NC 28098
>
> Celestron/Vixen C-102 f/9 (plus a lot of other toys)
>
> ----- Original Message -----
> From: patconlon
> To: Refractors@yahoogroups.com <Refractors%40yahoogroups.com>
> Sent: Saturday, November 14, 2009 2:57 PM
> Subject: [Refractors] Refractor for Double Stars
>
> Hello everyone recently I have become interested in double stars and
> Refractors, so I was wondering which type of refractor would be best for
> this type of astronomy. I was thinking along the lines of a TEC 140 or a D&G
> 6inch F12. Now I know we are not comparing like with like but would the
> extra inch plus the greater focal length of the D$G compansate for the fact
> it is not an APO. The optical tube would be going on a Losmandy G11 Mount,
> bearing in mind also the D$G is half the price of the TEC.
>
> [Non-text portions of this message have been removed]
>
>
>



--
Doug
Truckstop Astronomer


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

http://www.vixenoptics.com/refractors/ax103.html depicts the f/8
system. The AX103S page has a CA diagram but its unscaled so
meaningless. Its a 'scope designed for imaging, but f/8 is a tad slow
for deep sky photography. You'd have to add the dedicated f/5.6 FF. I
assume the 140 f/5.7 system is similar, i.e. triplet air spaced OG +
Petzval type field corrector.

Chris Lord

On Nov 14, 2009, at 19:33, Richard F.L.R. Snashall wrote:

> Scott Walker wrote:
>  > Would still expect the NeoAchro to have a lot of chromatic
> aberation. The Petzval design only improves chromatic aberation a
> modest amount. One needs to combine the Petzval design with special
> glasses to achieve the great color correction that is seen in scopes
> like the NP101. I would expect the chromatic aberation to be similar
> to a f8 to f9 achro of the seem aperture.
>  Re: NeoAchro 140
>
>  I wonder what their particular definition of "Petzval like" is...
>


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

No, get the TEC140APO. The Strehl of the achro when focussed in green
will be about 90% but less than 80% at C & F, whereas the Strehl of the
TEC140 is ~98% across the visual spectrum. Its not simply a question of
how much green & folding you have to part with. There's also the matter
of how well the 'scope holds value. The D&G may cost half as much as
the TEC, but after a decade the TEC will have a resale value ~ what you
paid, whereas the D&G resale value will be like that of a used car. In
the meantime you'll have enjoyed the superb view, instead of wishing
you'd gone for the real deal.

Chris Lord

On Nov 14, 2009, at 19:57, patconlon wrote:

>  Hello everyone recently I have become interested in double stars and
> Refractors, so I was wondering which type of refractor would be best
> for this type of astronomy. I was thinking along the lines of a TEC
> 140 or a D&G 6inch F12. Now I know we are not comparing like with like
> but would the extra inch plus the greater focal length of the D$G
> compansate for the fact it is not an APO. The optical tube would be
> going on a Losmandy G11 Mount, bearing in mind also the D$G is half
> the price of the TEC.
>
>


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

Chris Lord wrote:
> http://www.vixenoptics.com/refractors/ax103.html depicts the f/8
> system. The AX103S page has a CA diagram but its unscaled so
> meaningless. Its a 'scope designed for imaging, but f/8 is a tad slow
> for deep sky photography. You'd have to add the dedicated f/5.6 FF. I
> assume the 140 f/5.7 system is similar, i.e. triplet air spaced OG +
> Petzval type field corrector.
With "Petzval like", wouldn't that imply that the four
lenses in two groups would be more like two doublets?
You wouldn't as much need a triplet for an achromat.

Not true. The D&G's hold their original value quite well, and it has the
advantage of costing Much Less than the TEC, while still providing a really
good view.
Doug

On Sun, Nov 15, 2009 at 2:30 AM, Chris Lord <
chrislord@...> wrote:

> No, get the TEC140APO. The Strehl of the achro when focussed in green
> will be about 90% but less than 80% at C & F, whereas the Strehl of the
> TEC140 is ~98% across the visual spectrum. Its not simply a question of
> how much green & folding you have to part with. There's also the matter
> of how well the 'scope holds value. The D&G may cost half as much as
> the TEC, but after a decade the TEC will have a resale value ~ what you
> paid, whereas the D&G resale value will be like that of a used car. In
> the meantime you'll have enjoyed the superb view, instead of wishing
> you'd gone for the real deal.
>
> Chris Lord
>
> On Nov 14, 2009, at 19:57, patconlon wrote:
>
> >  Hello everyone recently I have become interested in double stars and
> > Refractors, so I was wondering which type of refractor would be best
> > for this type of astronomy. I was thinking along the lines of a TEC
> > 140 or a D&G 6inch F12. Now I know we are not comparing like with like
> > but would the extra inch plus the greater focal length of the D$G
> > compansate for the fact it is not an APO. The optical tube would be
> > going on a Losmandy G11 Mount, bearing in mind also the D$G is half
> > the price of the TEC.
> >
> >
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>


--
Doug
Truckstop Astronomer


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

Long focus and good quality refractors are a good choice. Using my old Royal
Astro Optical 76mm f/16 refractor Ihave been able to do splitting of doubles
that sometimes is surprising. Maksutovs are good at this too.

Guido

--- On Sat, 11/14/09, Scott Holland <holl8127@...> wrote:

From: Scott Holland <holl8127@...>
Subject: Re: [Refractors] Refractor for Double Stars
To: Refractors@yahoogroups.com
Date: Saturday, November 14, 2009, 10:16 PM







 









       I would vote for the D&G. Faint close pairs should benefit fron the extra
inch for resolving power and light grasp, and at f/12, I don't think CA will be
a problem. Also, I think you'll probably have less out-of-pocket. D&G has a fine
reputation.



Scott Holland

Lowell, NC 28098



Celestron/Vixen C-102 f/9 (plus a lot of other toys)



----- Original Message -----

   From: patconlon

   To: Refractors@yahoogro ups.com

   Sent: Saturday, November 14, 2009 2:57 PM

   Subject: [Refractors] Refractor for Double Stars



Hello everyone recently I have become interested in double stars and Refractors,
so I was wondering which type of refractor would be best for this type of
astronomy. I was thinking along the lines of a TEC 140 or a D&G 6inch F12. Now I
know we are not comparing like with like but would the extra inch plus the
greater focal length of the D$G compansate for the fact it is not an APO. The
optical tube would be going on a Losmandy G11 Mount, bearing in mind also the
D$G is half the price of the TEC.



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

























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

That's one of the uses my 80mm f/15 Carton excels at too.
Doug

On Sun, Nov 15, 2009 at 8:41 AM, Guido Santacana <foxam2001@...>wrote:

>
>
> Long focus and good quality refractors are a good choice. Using my old
> Royal Astro Optical 76mm f/16 refractor Ihave been able to do splitting of
> doubles that sometimes is surprising. Maksutovs are good at this too.
>
> Guido
>
> --- On Sat, 11/14/09, Scott Holland
<holl8127@...<holl8127%40bellsouth.net>>
> wrote:
>
> From: Scott Holland <holl8127@... <holl8127%40bellsouth.net>>
> Subject: Re: [Refractors] Refractor for Double Stars
> To: Refractors@yahoogroups.com <Refractors%40yahoogroups.com>
> Date: Saturday, November 14, 2009, 10:16 PM
>
>
>
> I would vote for the D&G. Faint close pairs should benefit fron the extra
> inch for resolving power and light grasp, and at f/12, I don't think CA will
> be a problem. Also, I think you'll probably have less out-of-pocket. D&G has
> a fine reputation.
>
> Scott Holland
>
> Lowell, NC 28098
>
> Celestron/Vixen C-102 f/9 (plus a lot of other toys)
>
>
> ----- Original Message -----
>
> From: patconlon
>
> To: Refractors@yahoogro ups.com
>
> Sent: Saturday, November 14, 2009 2:57 PM
>
> Subject: [Refractors] Refractor for Double Stars
>
> Hello everyone recently I have become interested in double stars and
> Refractors, so I was wondering which type of refractor would be best for
> this type of astronomy. I was thinking along the lines of a TEC 140 or a D&G
> 6inch F12. Now I know we are not comparing like with like but would the
> extra inch plus the greater focal length of the D$G compansate for the fact
> it is not an APO. The optical tube would be going on a Losmandy G11 Mount,
> bearing in mind also the D$G is half the price of the TEC.
>
> [Non-text portions of this message have been removed]
>
> [Non-text portions of this message have been removed]
>
>
>



--
Doug
Truckstop Astronomer


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

Petzval's original camera lens comprised a pair of doublets, the
leading doublet air spaced, the field doublet cemented.

The principal is that of an achromatic objective and an achromatic
field flattener/corrector. But I suppose you could stretch the
principal to an triplet objective and a single field corrector, that
comprise a fully corrected system. The idea is that the field corrector
corrects Petzval curvature.

My inclination is that the off colour correction would be as good as a
triplet apo and dedicated field flattener. I'd be happier if the CA
diagram was scaled so I could make a comparison.

Chris Lord

On Nov 15, 2009, at 11:45, Richard F.L.R. Snashall wrote:

> Chris Lord wrote:
>> http://www.vixenoptics.com/refractors/ax103.html depicts the f/8
>> system. The AX103S page has a CA diagram but its unscaled so
>> meaningless. Its a 'scope designed for imaging, but f/8 is a tad slow
>> for deep sky photography. You'd have to add the dedicated f/5.6 FF. I
>> assume the 140 f/5.7 system is similar, i.e. triplet air spaced OG +
>> Petzval type field corrector.
> With "Petzval like", wouldn't that imply that the four
> lenses in two groups would be more like two doublets?
> You wouldn't as much need a triplet for an achromat.
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>


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

The ability of a telescope to resolve unequal doubles near the Rayleigh
limit is determined by the Strehl ratio. A Littrow doublet had a
significantly lower Polychromatic Strehl ratio than an FPL53 triplet
apo. Take a look at this CN article
<http://www.cloudynights.com/item.php?item_id=1869> and the attached
jpeg run by Roland Christen for a 160F7 triplet.

The f/15 doublet will not have superior resolving power on unequal
doubles than the triplet apo. Its not a matter of focal plane image
scale, but PSF size.

Forget the D&G, and get the TEC.

Chris Lord


   ----------


On Nov 15, 2009, at 08:30, Chris Lord wrote:

> No, get the TEC140APO. The Strehl of the achro when focussed in green
> will be about 90% but less than 80% at C & F, whereas the Strehl of the
> TEC140 is ~98% across the visual spectrum. Its not simply a question of
> how much green & folding you have to part with. There's also the matter
> of how well the 'scope holds value. The D&G may cost half as much as
> the TEC, but after a decade the TEC will have a resale value ~ what you
> paid, whereas the D&G resale value will be like that of a used car. In
> the meantime you'll have enjoyed the superb view, instead of wishing
> you'd gone for the real deal.
>
> Chris Lord
>
> On Nov 14, 2009, at 19:57, patconlon wrote:
>
>>  Hello everyone recently I have become interested in double stars and
>> Refractors, so I was wondering which type of refractor would be best
>> for this type of astronomy. I was thinking along the lines of a TEC
>> 140 or a D&G 6inch F12. Now I know we are not comparing like with like
>> but would the extra inch plus the greater focal length of the D$G
>> compansate for the fact it is not an APO. The optical tube would be
>> going on a Losmandy G11 Mount, bearing in mind also the D$G is half
>> the price of the TEC.

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

Thanks folks for the replies I think I will  go with the TEC  if at all
possible I was wondering Chris if you have any advice on eyepieces  to use with
it . I have a nice U.O. 6MM which I like  the rest are a mixed bag , also I
have a Celestron barlow which I do not like  what barlow would you recomend to
use with the TEC. 

THANKS AGAIN   PAT.







--- On Sun, 15/11/09, Chris Lord <chrislord@...> wrote:

From: Chris Lord <chrislord@...>
Subject: Re: [Refractors] Refractor for Double Stars
To: Refractors@yahoogroups.com
Date: Sunday, 15 November, 2009, 19:24







 









       The ability of a telescope to resolve unequal doubles near the Rayleigh

limit is determined by the Strehl ratio. A Littrow doublet had a

significantly lower Polychromatic Strehl ratio than an FPL53 triplet

apo. Take a look at this CN article

<http://www.cloudyni ghts.com/ item.php? item_id=1869> and the attached

jpeg run by Roland Christen for a 160F7 triplet.



The f/15 doublet will not have superior resolving power on unequal

doubles than the triplet apo. Its not a matter of focal plane image

scale, but PSF size.



Forget the D&G, and get the TEC.



Chris Lord



----------



On Nov 15, 2009, at 08:30, Chris Lord wrote:



> No, get the TEC140APO. The Strehl of the achro when focussed in green

> will be about 90% but less than 80% at C & F, whereas the Strehl of the

> TEC140 is ~98% across the visual spectrum. Its not simply a question of

> how much green & folding you have to part with. There's also the matter

> of how well the 'scope holds value. The D&G may cost half as much as

> the TEC, but after a decade the TEC will have a resale value ~ what you

> paid, whereas the D&G resale value will be like that of a used car. In

> the meantime you'll have enjoyed the superb view, instead of wishing

> you'd gone for the real deal.

>

> Chris Lord

>

> On Nov 14, 2009, at 19:57, patconlon wrote:

>

>>  Hello everyone recently I have become interested in double stars and

>> Refractors, so I was wondering which type of refractor would be best

>> for this type of astronomy. I was thinking along the lines of a TEC

>> 140 or a D&G 6inch F12. Now I know we are not comparing like with like

>> but would the extra inch plus the greater focal length of the D$G

>> compansate for the fact it is not an APO. The optical tube would be

>> going on a Losmandy G11 Mount, bearing in mind also the D$G is half

>> the price of the TEC.



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

























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

An F/16 doublet of excellent quality  has so little if any color that it would
probably give a good run to any triplet of equal aperture. I don't think that
the difference would be that much at least at the lower apertures.It would be
interesting to check this on a side by side test.

Guido

--- On Sun, 11/15/09, Chris Lord <chrislord@...> wrote:

From: Chris Lord <chrislord@...>
Subject: Re: [Refractors] Refractor for Double Stars
To: Refractors@yahoogroups.com
Date: Sunday, November 15, 2009, 5:24 PM







 









       The ability of a telescope to resolve unequal doubles near the Rayleigh

limit is determined by the Strehl ratio. A Littrow doublet had a

significantly lower Polychromatic Strehl ratio than an FPL53 triplet

apo. Take a look at this CN article

<http://www.cloudyni ghts.com/ item.php? item_id=1869> and the attached

jpeg run by Roland Christen for a 160F7 triplet.



The f/15 doublet will not have superior resolving power on unequal

doubles than the triplet apo. Its not a matter of focal plane image

scale, but PSF size.



Forget the D&G, and get the TEC.



Chris Lord



----------



On Nov 15, 2009, at 08:30, Chris Lord wrote:



> No, get the TEC140APO. The Strehl of the achro when focussed in green

> will be about 90% but less than 80% at C & F, whereas the Strehl of the

> TEC140 is ~98% across the visual spectrum. Its not simply a question of

> how much green & folding you have to part with. There's also the matter

> of how well the 'scope holds value. The D&G may cost half as much as

> the TEC, but after a decade the TEC will have a resale value ~ what you

> paid, whereas the D&G resale value will be like that of a used car. In

> the meantime you'll have enjoyed the superb view, instead of wishing

> you'd gone for the real deal.

>

> Chris Lord

>

> On Nov 14, 2009, at 19:57, patconlon wrote:

>

>>  Hello everyone recently I have become interested in double stars and

>> Refractors, so I was wondering which type of refractor would be best

>> for this type of astronomy. I was thinking along the lines of a TEC

>> 140 or a D&G 6inch F12. Now I know we are not comparing like with like

>> but would the extra inch plus the greater focal length of the D$G

>> compansate for the fact it is not an APO. The optical tube would be

>> going on a Losmandy G11 Mount, bearing in mind also the D$G is half

>> the price of the TEC.



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

























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

 Thanks again. Sorry on being slow to respond. I understand. Because of the
tree line  
atmospheric dispersion is not a problem.
--- On Wed, 11/11/09, William Hamblen <wrhamblen@...> wrote:


From: William Hamblen <wrhamblen@...>
Subject: Re: [Refractors] Meade LXD 75 AR6 Refractor
To: Refractors@yahoogroups.com
Date: Wednesday, November 11, 2009, 9:36 PM


 



It's not quite the position of the eye but looking through the eyepiece
at an angle. If the color is in the objective high power makes it
worse. If the color is in your eye position low power makes it worse.
Also watch out for atmospheric dispersion.

Bud

bonview@verizon. net wrote:
> Thanks, I did have my eye to the glass - from edge to edge. I replace the Mead
focuser with a ScopeStuff focuser plus I was using the new 14.5mm Orion edge-on
planetry eyepiece. I was like a kid in the candy store. This scope is so much
better than it was for such a small investment. Next moon I will try it with a
higher power eyepiece.
> Thanks
> gary saunders
>
>
>
>
>
>
> i
>
> --- On Tue, 11/10/09, William Hamblen <wrhamblen@yahoo. com> wrote:
>
>
> From: William Hamblen <wrhamblen@yahoo. com>
> Subject: Re: [Refractors] Meade LXD 75 AR6 Refractor
> To: Refractors@yahoogro ups.com
> Date: Tuesday, November 10, 2009, 9:42 PM
>
>
>
>
>
>
> bonview@verizon. net wrote:
>
>> I did a collimation on this scope but when I look at the moon I have blue
light to the sun side and yellow to the dark side. Are the lens out with respect
to each other? Can I tweak this myself? Can this be tweak with this scope? I
take it that this scope has two air spaced lens.
>>
> Even with a reflector your eyepiece will give you blue on one side of
> the Moon and yellow on the other when your eye is not in the center.
> This is very noticeable with a low power eyepiece.
>
> Bud
>
>
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------ --------- --------- ------
>
> Yahoo! Groups Links
>
>
>
>
>








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

Sky & Telescope did an article about these prisms 3 or 4 years ago. My
understanding was it only helped with the atmosphere issue.

--- On Fri, 11/13/09, Warp <warpcorp@...> wrote:


From: Warp <warpcorp@...>
Subject: Re: [Refractors] Re: Meade LXD 75 AR6 Refractor
To: Refractors@yahoogroups.com
Date: Friday, November 13, 2009, 11:18 AM


 



I don't think these will do much for the inherent false color due to the achro
nature of the doublet lens.  Careful collimation of the front cell will work
best for this.  This device is only for atmospheric induced color (which I have
never noticed).
 
Or... am I wrong and does this device actually help cut down on CA?
 
It also seems to add a fair amount of glass to the optical path - what effect
does this have on light transmission and the brightness and contrast of the
target?
 
Would be good to have more info from an actual user.
 
Warp
 

--- On Fri, 11/13/09, Frank <mega75mark@sisna. com> wrote:

From: Frank <mega75mark@sisna. com>
Subject: [Refractors] Re: Meade LXD 75 AR6 Refractor
To: Refractors@yahoogro ups.com
Date: Friday, November 13, 2009, 8:43 AM

 

I have an atmospheric dispersion prism and they do work. With Jupiter at a
rather low declination this year the prism removes the red and blue fringe
around the planet and gives it a clean edge. Adirondack sells them, but they are
pricey.

Frank K.

--- In Refractors@yahoogro ups.com, "Rich" <astronut1001@ ...> wrote:
>
> Anothher thing which can cause or contribute to this is atmospheric dispersion
when viewing below about 45 to 60 degrees. In fact low angle wedge prisms have
been offered for eyepiece installation to correct this for fanatical planetary
viewers. I have seen them mentioned but have never seen one.
>
> Rich Wood
>
>
> --- In Refractors@yahoogro ups.com, "bonview@" <bonview@> wrote:
> >
> > I did a collimation on this scope but when I look at the moon I have blue
light to the sun side and yellow to the dark side. Are the lens out with respect
to each other? Can I tweak this myself? Can this be tweak with this scope? I
take it that this scope has two air spaced lens.
> > gary saunders
> >
>

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








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

Well, my first telescope was a 3-inch f/16 Littrow refractor. I put it
together in 1969 and eventually sold it in 1988. I used it for double
star observing, and as you remark it had little false colour (secondary
spectrum). The power could be pushed to x50 per inch before break down.
If you look at my monograph on the resolution of unequal binaries, in
the appendix is a list of some of the critical pairs I observed in
order to accumulate the necessary data for my analysis in 1993.

What I do know is that my Megrez90 ED doublet can achieve a better
resolution limit on unequal pairs than my old 3-inch f/16, taking into
account the difference in Rayleigh Limit for a 75mm & a 90mm OG. The
tighter PSF from C - F makes a noticeable difference for pairs with mag
diffs >4m.

During the 1970's I had unrestricted access to the 6.5-inch f/13.5
Cooke refractor at Rossall School's Assheton Observatory. I used it
with a bifilar micrometer to measure pairs, especially unequal pairs.
My 5.5-inch f/7 TEC knocks spots off the Cooke, which is still there,
still as useable as when I curated the observatory almost 40 years ago.

On Nov 15, 2009, at 21:48, Guido Santacana wrote:

> An F/16 doublet of excellent quality  has so little if any color that
> it would probably give a good run to any triplet of equal aperture. I
> don't think that the difference would be that much at least at the
> lower apertures.It would be interesting to check this on a side by
> side test.
>
>  Guido

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

--- In Refractors@yahoogroups.com, Chris Lord <chrislord@...> wrote:
>
> Well, my first telescope was a 3-inch f/16 Littrow refractor. I put it
> together in 1969 and eventually sold it in 1988. I used it for double
> star observing, and as you remark it had little false colour (secondary
> spectrum). The power could be pushed to x50 per inch before break down.
> If you look at my monograph on the resolution of unequal binaries, in
> the appendix is a list of some of the critical pairs I observed in
> order to accumulate the necessary data for my analysis in 1993.
>
> What I do know is that my Megrez90 ED doublet can achieve a better
> resolution limit on unequal pairs than my old 3-inch f/16, taking into
> account the difference in Rayleigh Limit for a 75mm & a 90mm OG. The
> tighter PSF from C - F makes a noticeable difference for pairs with mag
> diffs >4m.
>
> During the 1970's I had unrestricted access to the 6.5-inch f/13.5
> Cooke refractor at Rossall School's Assheton Observatory. I used it
> with a bifilar micrometer to measure pairs, especially unequal pairs.
> My 5.5-inch f/7 TEC knocks spots off the Cooke, which is still there,
> still as useable as when I curated the observatory almost 40 years ago.


I can confirm your experience.
My vintage BORG 125mm F/8 ED doublet beats almost perfect 6" F/10 achromat
(which was a collimator on an optical test bench) in splitting unequal binaries
and in planetary details.

Valery.

I prefer TMB Mono's & Zeiss Abbé Ortho's followed closely by pre war
Zeiss Abbé's and also Brandon Ortho's. I have a set of UO HD Ortho's
which are fine eyepieces, but not in the same league as the former. I
don't use Barlows for double star work, I use TAK HiLE Ortho's for the
highest powers, 2.8mm & 3.6mm.

No longer made, but worth acquiring as & when are the E-Z view. They
came as a threesome, 3.6; 5.5; 9.5mm.

If you're interested in measuring doubles visually, a great accessory
to find is a filar micrometer and position circle, or a Lyot double
image micrometer.

For Lunar imaging I use an Antares 1.6x Barlow, or a 2x TV Big Barlow.
The snag is they do ghost if you have most of the bright portion of the
Moon outside the field stop. I also use a x4TV Powermate, which is more
or less telecentric, it doesn't ghost.

My favourite gadget is the TEC 5-port turret, which I have loaded with
the TMB Mono's. I also have a Unitron Giant UniHex loaded with pre war
6; 9; 12.5mm Zeiss Abbé's and a pair of Ottway Mono's, 6mm & 8mm, and a
48mm Brandon Ortho.

If you can find them series 1 TV Plössls or better still Ets Clavé
Plössls are good, as are type I Königs.

Keep an eye on APM's used eyepieces listings. You get some real gems
from time to time. Such as the Zeiss 2-1 aspheric 25mm Ortho.

You also need to consider lowest useful powers & widest real fields. I
have a Rodenstock F40/70º that gives ~2º.8 fov & a ~6mm exit pupil.
Ideal for turning the TEC into an RFT.

Chris Lord

On Nov 15, 2009, at 20:57, patconlon conlon wrote:

>
>  Thanks folks for the replies I think I will  go with the TEC  if at
> all possible I was wondering Chris if you have any advice on
> eyepieces  to use with it . I have a nice U.O. 6MM which I like  the
> rest are a mixed bag , also I have a Celestron barlow which I do not
> like  what barlow would you recomend to use with the TEC. 
>
>  THANKS AGAIN   PAT.

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

The excellent 76 and 80mm doublets of yesterday with those high f numbers are
virtually unavailable today. My only experience with a triplet is observing
Jupiter with a 60mm Tak ( I think it was a Tak) and coming out quite impressed
at the detail level that was discernible. I have kept my f/16 for the last 42
years. The first objective was accidentally damaged. The telescope had a 75mm
1970s Edmund objective for many years until just recently I was able to acquire
an original Royal Astro Optical objective to replace it. Both the Edmund and the
Royal are excellent but the Edmund with a 75mm diameter had to be fitted in the
original cell creating centering problems. Today it will probably be better to
go with ED doublets or triplets at these apertures. Of course, apochromats would
also be great at high apertures but then the $ky is the limit.

Best,

Guido

--- On Mon, 11/16/09, Chris Lord <chrislord@...> wrote:

From: Chris Lord <chrislord@...>
Subject: Re: [Refractors] Refractor for Double Stars
To: Refractors@yahoogroups.com
Date: Monday, November 16, 2009, 6:26 AM







 









       Well, my first telescope was a 3-inch f/16 Littrow refractor. I put it

together in 1969 and eventually sold it in 1988. I used it for double

star observing, and as you remark it had little false colour (secondary

spectrum). The power could be pushed to x50 per inch before break down.

If you look at my monograph on the resolution of unequal binaries, in

the appendix is a list of some of the critical pairs I observed in

order to accumulate the necessary data for my analysis in 1993.



What I do know is that my Megrez90 ED doublet can achieve a better

resolution limit on unequal pairs than my old 3-inch f/16, taking into

account the difference in Rayleigh Limit for a 75mm & a 90mm OG. The

tighter PSF from C - F makes a noticeable difference for pairs with mag

diffs >4m.



During the 1970's I had unrestricted access to the 6.5-inch f/13.5

Cooke refractor at Rossall School's Assheton Observatory. I used it

with a bifilar micrometer to measure pairs, especially unequal pairs.

My 5.5-inch f/7 TEC knocks spots off the Cooke, which is still there,

still as useable as when I curated the observatory almost 40 years ago.



On Nov 15, 2009, at 21:48, Guido Santacana wrote:



> An F/16 doublet of excellent quality  has so little if any color that

> it would probably give a good run to any triplet of equal aperture. I

> don't think that the difference would be that much at least at the

> lower apertures.It would be interesting to check this on a side by

> side test.

>

>  Guido



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

























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

>My inclination is that the off colour correction would be as good as a
triplet apo and dedicated field flattener. <

After a series of reflectors up to 12" the 140NA is my first refractor.  I use
it for galaxy and other faint fuzzy hunting.  On clear cold nights I can track
down sub 13mag. galaxies w/averted vision.  It does throw up color on Jupiter
and the moon.  Not objectionable to me but it's definitely there.  I've seen
photo's taken with it and there is a blue bloom associated with it.  For visual
deep sky work I love it.  Recently unbeknownst to me I had an extremely steady
night.  When wrapping up I decided to look at Jupiter.  Normally seeing peeks
out at 166x (5mm).  The image was rock steady.  I dropped in a 4mm (200x), rock
steady.  Jupiter looked like a hand painting with a caligraphers pen. 
Significantly better view than any photo except fly by's.  I 3x barlowed a 9mm
ep.  The exit pupil got me here with a dim image but Jupiter was barely
quavering.  What a night and the scope didn't let me down.

Jim

Unless it is against the rules, I will be posting in the files section a summary
description of two OTA's I am putting up for sale.  One will be a classic Meade
102ED APO 102mm / 920mm - f/9 APO refractor with Williams Optics 2" dual speed
Crayford focuser and brand new 2" 99% dielectric diagonal.
 
Also... a brand new 8" Meade SCT with UHTC coatings, crayford focuser, 2" 99%
Stellarvue Diagonal, full baffled dew shield, Bob's knobs and the Peterson
Focuser upgrade. 
 
Please feel free to contact me if you need more information and are interested.
 
Thanks
Warp 

--- On Mon, 11/16/09, Chris Lord <chrislord@...> wrote:


From: Chris Lord <chrislord@...>
Subject: Re: [Refractors] Refractor for Double Stars
To: Refractors@yahoogroups.com
Date: Monday, November 16, 2009, 2:26 AM


 



Well, my first telescope was a 3-inch f/16 Littrow refractor. I put it
together in 1969 and eventually sold it in 1988. I used it for double
star observing, and as you remark it had little false colour (secondary
spectrum). The power could be pushed to x50 per inch before break down.
If you look at my monograph on the resolution of unequal binaries, in
the appendix is a list of some of the critical pairs I observed in
order to accumulate the necessary data for my analysis in 1993.

What I do know is that my Megrez90 ED doublet can achieve a better
resolution limit on unequal pairs than my old 3-inch f/16, taking into
account the difference in Rayleigh Limit for a 75mm & a 90mm OG. The
tighter PSF from C - F makes a noticeable difference for pairs with mag
diffs >4m.

During the 1970's I had unrestricted access to the 6.5-inch f/13.5
Cooke refractor at Rossall School's Assheton Observatory. I used it
with a bifilar micrometer to measure pairs, especially unequal pairs.
My 5.5-inch f/7 TEC knocks spots off the Cooke, which is still there,
still as useable as when I curated the observatory almost 40 years ago.

On Nov 15, 2009, at 21:48, Guido Santacana wrote:

> An F/16 doublet of excellent quality  has so little if any color that
> it would probably give a good run to any triplet of equal aperture. I
> don't think that the difference would be that much at least at the
> lower apertures.It would be interesting to check this on a side by
> side test.
>
> Guido

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








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

HELLO Chris thank you for all the information on eyepieces I have been away this
last two days so only got your post now so I will have to study it a before I
make a up my mind which to go for. As for measureing  with a micrometer I would
like to go in that direction in the future, by the way do you know of any firm
selling micrometers at the present time.  Recently I have come across a firm
called GPU OPTICAL they make 140mm by 1200 oiled triplet Refractors does anyone
know what they are like they are selling at 3999 euroes plus vat.       PAT

Pat,

I met Andras Papp at Kelling Heath in April 2005, He was staying with a
dealer called Chris Garvey. To the best of my knowledge GPU is still a
going concern. Apart from TEC they're the only company making oiled
triplets similar to the Zeiss APQ. They make them in the same way Yuri
Petrunin does. Read the discussion on their website in favour of the
oiled triplet apo.
<http://www.gpuoptical.com/osl_introduction.htm>

I have seen the smaller 'scope 102/640 but not looked through it.
However I have heard they are very good, and enjoy a well earned
reputation in Europe. If the 140/1200 has the same performance as the
TEC140/980, then it is an apo that will give you apo performance with
the plate scale of a modern achro. Could be the best of both worlds.

Chris Lord


On Nov 17, 2009, at 21:21, patconlon wrote:

> HELLO Chris thank you for all the information on eyepieces I have been
> away this last two days so only got your post now so I will have to
> study it a before I make a up my mind which to go for. As for
> measureing with a micrometer I would like to go in that direction in
> the future, by the way do you know of any firm selling micrometers at
> the present time. Recently I have come across a firm called GPU
> OPTICAL they make 140mm by 1200 oiled triplet Refractors does anyone
> know what they are like they are selling at 3999 euroes plus vat. PAT
>
>


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

--- In Refractors@yahoogroups.com, "patconlon" <ploughc@...> wrote:
>
> HELLO Chris thank you for all the information on eyepieces I have been away
this last two days so only got your post now so I will have to study it a before
I make a up my mind which to go for. As for measureing  with a micrometer I
would like to go in that direction in the future, by the way do you know of any
firm selling micrometers at the present time.  Recently I have come across a
firm called GPU OPTICAL they make 140mm by 1200 oiled triplet Refractors does
anyone know what they are like they are selling at 3999 euroes plus vat.      
PAT
>
Pat,

There are only two companies that I know of that make bifilar micrometers -
Retel Ltd in England and van Slyke in the U.S. Here is the van Slyke link:
http://www.observatory.org/bfm.htm  I believe the contact information for Retel
Ltd. is in the "double star section" of the Webb Society's site:
http://www.webbdeepsky.com/index.html

Regards,
PJ Anway

Hello Chris sorry for going on about this but what did you think of the build
quality of the GPU telescope you seen I know it was a while ago so it might be
hard to remember but if you do how does it compare to say the TEC. The
mechanical quality of the scope is almost as important as the optics. Thanks for
all the information so far.                 PAT.

I don't really know. The focuser looks well made, but I prefer TEC's
focuser. The OTA I saw was finely crafted. Try asking GPU for the full
spec.

Chris Lord

On Nov 19, 2009, at 12:45, patconlon wrote:

> Hello Chris sorry for going on about this but what did you think of
> the build quality of the GPU telescope you seen I know it was a while
> ago so it might be hard to remember but if you do how does it compare
> to say the TEC. The mechanical quality of the scope is almost as
> important as the optics. Thanks for all the information so far. PAT.

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

Funny how it can be a hot product.
Has anyone actually seen one?
Nice price $270  and specs can be seen on Astronomics site.

Don

A large Zeiss or Alvan Clark refractor is a wonderful instrument for double
stars.

I wonder if D&G can capture the some magic (strehl) with their 8" f/12 achromat?

Don

The Strehl of a two element achromat when focused in green dips at the
red and blue ends, and vice versa. It typically dips to just below 0.8.

There's a man in London who is building refractors (4-inch f/15) that
look very similar to a Cooke Troughton & Simms from the 1920's. Richard
Day, Skylight Telescopes. But I think its a tad expensive at £2k for
the OTA. & you have to find a suitably styled German Equatorial to
accompany it. The ads show it on a Cooke Equatorial.

Neil English, who has a Springer Practical Astronomy Series book about
refractors coming out next summer, has an article in the current issue
of Astronomy Now.

The rule-of-thumb for acceptable CA error (within Rayleigh criterion)
is f/# = ~3 x aperture in inches.

I spent most of the 70's observing and measuring doubles with a 6 Paris
Inch (6.3-inches) 86-inch focal length Cooke equatorial, clock driven,
refractor. From the measurements I logged, when I compare them to
similar measurements of separation made with my TEC140APO, I cannot in
all honesty say it performed better. I put this down to the TEC's more
accurately figured OG, and its fairly flat polychromatic Strehl curve.

A modern apo does however lack the nostalgia factor.

Chris Lord


On Nov 27, 2009, at 04:42, glasspusher2001 wrote:

> A large Zeiss or Alvan Clark refractor is a wonderful instrument for
> double stars.
>
>  I wonder if D&G can capture the some magic (strehl) with their 8"
> f/12 achromat?
>
>  Don


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