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130mm Apochromat vs 152mm Achromat



 
 
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  #1  
Old June 4th 16, 10:24 PM posted to sci.astro.amateur
Sketcher
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Default 130mm Apochromat vs 152mm Achromat

After 19 more days I will have had my 6-inch f/6.5 achromat for one full year. Last night - for the first time - I set up Excalibur (130mm f/6 apochromat) and The Beast (152mm f/6.5 achromat) side-by-side.

For the planets (Jupiter, Mars and Saturn) a Fringe-Killer filter was kept in The Beast. Not surprisingly, a few planetary details were better when The Beast was used at full aperture while most seemed better stopped down to 120mm. High contrast details (apparent sizes of Jupiter's moons and Cassini's Division) faired better at full aperture. Regardless, all planetary details (excepting only Jupiter's moons) were better with Excalibur.

I found myself often picking out details with Excalibur that I would later look for with The Beast - and usually I would be able to see them with The Beast, but it wasn't nearly as easy. Excalibur's images were 'cleaner'. Excalibur was the clear winner on planetary detail.

M5, a globular star cluster, showed significant resolution with both telescopes using a 6mm eyepiece. I picked out a faint star conveniently located between brighter stars for comparison purposes. The first test was between views in The Beast with and without the Fringe-Killer filter. I concluded that the view without the filter was better. The second test was between the two telescopes. I concluded that the globular test was too close to call. The Beast's extra light grasp was reasonably well balanced by Excalibur's tighter star images. I'll call this one a tie - at least on this particular night.

Next was NGC 6118. Once again, The Beast did better without the Fringe-Killer than with it. Both telescopes showed the galaxy as a distinct, faint-fuzzy at low and medium powers. The views were better at medium magnifications. The Beast's extra aperture was enough to provide better views. It wins the faint-fuzzy category - though a single galaxy may not be a very clear test.

Original plans, in addition to the above, called for targeting the Trifid Nebula followed by an attempt at sighting Pluto, but I was cold and tired. Tonight should provide even better conditions than last night; but plans haven't been finalized yet.

Sketcher,
To sketch is to see.


  #2  
Old June 4th 16, 10:32 PM posted to sci.astro.amateur
Sam Wormley[_2_]
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Default 130mm Apochromat vs 152mm Achromat

On 6/4/16 4:24 PM, Sketcher wrote:
After 19 more days I will have had my 6-inch f/6.5 achromat for one
full year. Last night - for the first time - I set up Excalibur
(130mm f/6 apochromat) and The Beast (152mm f/6.5 achromat)
side-by-side.

For the planets (Jupiter, Mars and Saturn) a Fringe-Killer filter was
kept in The Beast. Not surprisingly, a few planetary details were
better when The Beast was used at full aperture while most seemed
better stopped down to 120mm. High contrast details (apparent sizes
of Jupiter's moons and Cassini's Division) faired better at full
aperture. Regardless, all planetary details (excepting only
Jupiter's moons) were better with Excalibur.

I found myself often picking out details with Excalibur that I would
later look for with The Beast - and usually I would be able to see
them with The Beast, but it wasn't nearly as easy. Excalibur's
images were 'cleaner'. Excalibur was the clear winner on planetary
detail.

M5, a globular star cluster, showed significant resolution with both
telescopes using a 6mm eyepiece. I picked out a faint star
conveniently located between brighter stars for comparison purposes.
The first test was between views in The Beast with and without the
Fringe-Killer filter. I concluded that the view without the filter
was better. The second test was between the two telescopes. I
concluded that the globular test was too close to call. The Beast's
extra light grasp was reasonably well balanced by Excalibur's tighter
star images. I'll call this one a tie - at least on this particular
night.

Next was NGC 6118. Once again, The Beast did better without the
Fringe-Killer than with it. Both telescopes showed the galaxy as a
distinct, faint-fuzzy at low and medium powers. The views were
better at medium magnifications. The Beast's extra aperture was
enough to provide better views. It wins the faint-fuzzy category -
though a single galaxy may not be a very clear test.

Original plans, in addition to the above, called for targeting the
Trifid Nebula followed by an attempt at sighting Pluto, but I was
cold and tired. Tonight should provide even better conditions than
last night; but plans haven't been finalized yet.

Sketcher, To sketch is to see.



Thank You.

--

sci.physics is an unmoderated newsgroup dedicated
to the discussion of physics, news from the physics
community, and physics-related social issues.

  #3  
Old June 4th 16, 11:04 PM posted to sci.astro.amateur
SlurpieMcDoublegulp
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Posts: 134
Default 130mm Apochromat vs 152mm Achromat

On Saturday, June 4, 2016 at 4:24:21 PM UTC-5, Sketcher wrote:
After 19 more days I will have had my 6-inch f/6.5 achromat for one full year. Last night - for the first time - I set up Excalibur (130mm f/6 apochromat) and The Beast (152mm f/6.5 achromat) side-by-side.

For the planets (Jupiter, Mars and Saturn) a Fringe-Killer filter was kept in The Beast. Not surprisingly, a few planetary details were better when The Beast was used at full aperture while most seemed better stopped down to 120mm. High contrast details (apparent sizes of Jupiter's moons and Cassini's Division) faired better at full aperture. Regardless, all planetary details (excepting only Jupiter's moons) were better with Excalibur.

I found myself often picking out details with Excalibur that I would later look for with The Beast - and usually I would be able to see them with The Beast, but it wasn't nearly as easy. Excalibur's images were 'cleaner'. Excalibur was the clear winner on planetary detail.

M5, a globular star cluster, showed significant resolution with both telescopes using a 6mm eyepiece. I picked out a faint star conveniently located between brighter stars for comparison purposes. The first test was between views in The Beast with and without the Fringe-Killer filter. I concluded that the view without the filter was better. The second test was between the two telescopes. I concluded that the globular test was too close to call. The Beast's extra light grasp was reasonably well balanced by Excalibur's tighter star images. I'll call this one a tie - at least on this particular night.

Next was NGC 6118. Once again, The Beast did better without the Fringe-Killer than with it. Both telescopes showed the galaxy as a distinct, faint-fuzzy at low and medium powers. The views were better at medium magnifications. The Beast's extra aperture was enough to provide better views. It wins the faint-fuzzy category - though a single galaxy may not be a very clear test.

Original plans, in addition to the above, called for targeting the Trifid Nebula followed by an attempt at sighting Pluto, but I was cold and tired. Tonight should provide even better conditions than last night; but plans haven't been finalized yet.

Sketcher,
To sketch is to see.


I've been doing side by side with a 160mm Mak-Cass compared to a 130 F6.3 Apo refractor. Both scopes were made by myself and have similar high correction. The Mak-Cass has a 45mm diameter 28% obstruction. Rule of thumb is that on the planets an unobstructed aperture is equal to an obstructed one minus the central obstruction. That would mean that the 160mm with 45mm C.O. would act more or less like a 115mm unobstructed scope on low contrast detail on the planets.

What I observed was that the 130mm had a slight edge showing low-contrast detail on Jupiter, but the Mak had similar or slightly higher resolution of the higher contrast features. Both scopes had similar brightness levels on deep sky objects, although the refractor definitely had a darker background..

In the past I have compared an 8" Apo refractor against a 10" Mak-Cass with 23% C.O. The Mak would theoretically have similar contrast performance to the refractor if the above rule of thumb is correct. In looking at Mars, both instruments showed lots of low contrast features but the 10" Mak showed some linear features near the poles as finer and thinner than the refractor.. So I would say that aperture with reasonably small C.O. has the edge on resolution.

I also have a 10" SCT that is fairly well corrected, but with a 35% C.O. That instrument does not show features on Mars very well, and is severely affected by seeing. If I increase the Mak-Cass C.O. to 35%, it also deteriorates to a great degree.

Finally, I have compared images of Jupiter under sub-arc sec seeing in Chile with both an 8" fluorite refractor and a 12" Portaball-Zambuto mirror scope with 16% C.O., and conclude that the 12" was the clear winner, on both planetary and deep sky. The refractor, however can cover a 70mm field on an imaging camera with pinpoint stars to the corners.
  #4  
Old June 4th 16, 11:50 PM posted to sci.astro.amateur
RichA[_6_]
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Posts: 1,076
Default 130mm Apochromat vs 152mm Achromat

On Saturday, 4 June 2016 17:24:21 UTC-4, Sketcher wrote:
After 19 more days I will have had my 6-inch f/6.5 achromat for one full year. Last night - for the first time - I set up Excalibur (130mm f/6 apochromat) and The Beast (152mm f/6.5 achromat) side-by-side.

For the planets (Jupiter, Mars and Saturn) a Fringe-Killer filter was kept in The Beast. Not surprisingly, a few planetary details were better when The Beast was used at full aperture while most seemed better stopped down to 120mm. High contrast details (apparent sizes of Jupiter's moons and Cassini's Division) faired better at full aperture. Regardless, all planetary details (excepting only Jupiter's moons) were better with Excalibur.

I found myself often picking out details with Excalibur that I would later look for with The Beast - and usually I would be able to see them with The Beast, but it wasn't nearly as easy. Excalibur's images were 'cleaner'. Excalibur was the clear winner on planetary detail.

M5, a globular star cluster, showed significant resolution with both telescopes using a 6mm eyepiece. I picked out a faint star conveniently located between brighter stars for comparison purposes. The first test was between views in The Beast with and without the Fringe-Killer filter. I concluded that the view without the filter was better. The second test was between the two telescopes. I concluded that the globular test was too close to call. The Beast's extra light grasp was reasonably well balanced by Excalibur's tighter star images. I'll call this one a tie - at least on this particular night.

Next was NGC 6118. Once again, The Beast did better without the Fringe-Killer than with it. Both telescopes showed the galaxy as a distinct, faint-fuzzy at low and medium powers. The views were better at medium magnifications. The Beast's extra aperture was enough to provide better views. It wins the faint-fuzzy category - though a single galaxy may not be a very clear test.

Original plans, in addition to the above, called for targeting the Trifid Nebula followed by an attempt at sighting Pluto, but I was cold and tired. Tonight should provide even better conditions than last night; but plans haven't been finalized yet.

Sketcher,
To sketch is to see.


Good that you re-iterated the truism that (unless a telescope's optics are grossly poor) aperture wins over absolute optical refinement. I remember when there were people pretending a 130mm apo was a match for a good 200mm reflector and that was impossible owing to the sheer aperture advantage. Star images, etc., might be rudimentarily tighter in an apo, planetary detail might be more distinct, but it depends on seeing. However, you can't look at an unresolved extended object like a galaxy or nebula and beat a scope with three times the light-gathering area.
  #5  
Old June 5th 16, 01:27 AM posted to sci.astro.amateur
Quadibloc
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Posts: 7,018
Default 130mm Apochromat vs 152mm Achromat

On Saturday, June 4, 2016 at 4:50:49 PM UTC-6, RichA wrote:

Good that you re-iterated the truism that (unless a telescope's optics are
grossly poor) aperture wins over absolute optical refinement.


Yes, indeed.

The Questar, when it first came out, was worth an exorbitant price, because at the time no other telescope existed which was both compact and which had a comparatively large aperture.

But those days are now past.

However, the expensive apochromatic refractors still have one valid market -
people who need a very compact telescope, owing to limited space, might well
have money to spend on getting the best possible telescope for which they have
room. This is why they sell well in Japan.

People who live in North American suburbs with cars in their garages will, of
course, prefer a Dob.

John Savard
  #6  
Old June 5th 16, 02:56 AM posted to sci.astro.amateur
oriel36[_2_]
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Default 130mm Apochromat vs 152mm Achromat

You are such strange people in that you have no respect whatsoever for astronomy and the great mathematical component within the Book of Revelation. The Johannine work remains impenetrable to minds who are mediocre as the author takes time out to point out that unbelief is preferable to mediocre belief in his letter to the Church of Laodicia and with very good reason.

"In this case wisdom is needed: Let the person who has understanding calculate the total number of the beast, because it is a human number, and the sum of the number is 666. " Revelation 13

https://www.biblegateway.com/passage...&version=NABRE

http://www.jesuswalk.com/christian-s...389vatican.jpg

https://en.wikipedia.org/wiki/Talk:Quasicrystal

The bridge between 666 and 153 is partly geometrical,partly numeric and a true structural miracle for those who come within its atmosphere of hope, love and faith.Watching somebody use 666 for trivial reasons can be quaint as the book and the values within it represents achievements like no other and truly a revelation for those who are Christian and who really accept wisdom is needed.

Giving telescopes descriptive names is childish anyway.


















  #7  
Old June 5th 16, 03:16 AM posted to sci.astro.amateur
Quadibloc
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Default 130mm Apochromat vs 152mm Achromat

On Saturday, June 4, 2016 at 7:56:03 PM UTC-6, oriel36 wrote:

The bridge between 666 and 153 is partly geometrical,


And 153 is also mentioned in the Bible, being the number of fish in the net
pulled in by Peter at one point...

John Savard
  #8  
Old June 5th 16, 04:14 AM posted to sci.astro.amateur
Davoud[_1_]
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Default 130mm Apochromat vs 152mm Achromat

Quadibloc:
The Questar, when it first came out


....and long afterward...

was worth an exorbitant price


Whether the price was or is exorbitant is a matter of opinion. After 34
years of reliable service the Questar that I bought in 1982 doesn't
seem very costly at all. Next year's total eclipse will occur in its
35th anniversary month.

because at the time no other telescope existed which was both compact and which had a
comparatively large aperture.


Indeed. I was a world traveler. There was not in 1954 and there is not
today a telescope besides the Questar with highest quality optics and
mechanicals that can fit in its carrying case under an airliner seat,
equatorial mount and all. That's why I bought mine.

People who live in North American suburbs with cars in their garages will, of
course, prefer a Dob.


Some, perhaps. Nothing wrong with that. I have a garage and an SUV. But
I prefer my refractors, a 150mm and a 106mm, in addition to my Questar
http://primordial-light.com/observatory.html#twoscopes.

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  #9  
Old June 6th 16, 12:10 PM posted to sci.astro.amateur
[email protected]
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Default 130mm Apochromat vs 152mm Achromat

On Saturday, June 4, 2016 at 11:14:03 PM UTC-4, da'void wrote:
Quadibloc:
The Questar, when it first came out


...and long afterward...

was worth an exorbitant price


Whether the price was or is exorbitant is a matter of opinion. After 34
years of reliable service the Questar that I bought in 1982 doesn't
seem very costly at all. Next year's total eclipse will occur in its
35th anniversary month.


35 years is not old for a telescope, so one shouldn't be impressed by a 35-year old Questar either.

As for cost, for virtually everyone, obtaining a Questar will present a cash-flow problem. It would be difficult to finance one over a 35 year period.

  #10  
Old June 6th 16, 12:37 PM posted to sci.astro.amateur
[email protected]
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Posts: 9,472
Default 130mm Apochromat vs 152mm Achromat

On Saturday, June 4, 2016 at 8:27:32 PM UTC-4, Quadibloc wrote:
On Saturday, June 4, 2016 at 4:50:49 PM UTC-6, RichA wrote:

Good that you re-iterated the truism that (unless a telescope's optics are
grossly poor) aperture wins over absolute optical refinement.


Yes, indeed.

The Questar, when it first came out, was worth an exorbitant price, because at the time no other telescope existed which was both compact and which had a comparatively large aperture.

But those days are now past.

However, the expensive apochromatic refractors still have one valid market -
people who need a very compact telescope, owing to limited space, might well
have money to spend on getting the best possible telescope for which they have
room. This is why they sell well in Japan.

People who live in North American suburbs with cars in their garages will, of
course, prefer a Dob.


With telescopes, as with most anything, it's impossible to use the word "best" without resorting to a tautology.
 




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