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#26 BigC

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Posted 21 October 2016 - 06:48 PM

I have the SeaRs 76mm and another classic in 80/1200. I think 1200mm is a quite usable length and that achromats of that length in apertures of 60-150mm still have merit.Obviously telescope manufacturers think there is insufficient economic incentives.
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#27 aa6ww

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Posted 21 October 2016 - 11:43 PM

 When one wants a long tube classic looking scope, only a long tube will do. Its not just about the optics, because they are all excellent optically. The appeal of a long tube refractor pointing way up in the sky, is in itself the driving factor for many to want them. 

  

 ...Ralph

 

 

 

 That Starwave 102/f11 is a beautiful looking scope....but add $100 and you can get a Skywatcher 100ED f9 .

 

 BOTH scopes are doublets.

 

If one insists on traditional crowm and flint objectives the choices are limited.



#28 MartinPond

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Posted 21 October 2016 - 11:44 PM

Everything has its traits...

 

-----------------------------------"

Have any side-by-side comparisons been made between a 3" f/15 achro and an 80ED for planetary?

------------------------------------"

 

3" ....like that 76mm x 1200mm?  Nice size...  one-arm portable. 80mm isn't quite.

If you're looking for chromatics on planetary, you would have to push both  past 150x to see it.

And...at that point, they both start fuzzing from diffraction and they're dim.

The main difference at that point is that the achromat can't give you the ow power/wide-field the shorter ED can.

Most of the ED benefit is spent on that goal.

 

---------------------------"

For an OTA of that length, I might as well be using a 10" f/5 Newt.

---------------------------"

Weight-wise, with tripod, the Newt would be a lot heavier.

Short reflectors don't handle suburban light polllution that well here at the star parties.

Some doctrine says that can't be, but I keep seeing it.

I haven't seen a hooded  shortie yet though.



#29 Rutilus

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Posted 22 October 2016 - 08:37 AM

A traditional 3"f15 versus the 80ED is more the comparison in mind.

A did some testing a few years  ago with the following scopes.

76.2mm f/16 (made in the 1960s) , 80mm f/15 (70s model),  80mm f7 Triplet ED (2006),

150mm f/8 Achromat (2007, fitted with 80mm aperture mask) and my Tak TSA-102(again fitted

with 80mm mask).

 

Targets observed were Lunar, Mars and Jupiter. While all the achromats showed some C.A., the

actual detail visible was exactly the same in all the scopes. The three more modern scopes had a little less

light scatter around Jupiter, which I put down to better/more modern  lens coatings. 


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#30 Astrojensen

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Posted 22 October 2016 - 09:17 AM

I did multiple side-by-side comparisons of a TV 76 ED f/6.3 vs. a 80mm f/15 Vixen and the Vixen totally smoked the TV on Mars, Saturn, the Moon and the Sun, despite actually having the worst star test of the two, with more spherical aberration, but it had by far the most stable, sharp image. This was seen repeatedly, again and again, on many nights for several months.

 

The TV 76 had *impressive* color correction, the best I've seen in such a short focus scope. By contrast, the Vixen had images with a clear yellow hue, but this didn't appear to result in a loss of planetary details at all. Martian details in particular seemed to be in some way *enhanced* by the color shift, and the seas appeared greenish and stood out with better contrast than in the TV 76, where they were a much duller brown hue that didn't stand out very well at all, compared to the ochre surface. It was the same on Saturn, albeit not to the same degree. In combination with the much steadier, sharper image, the Vixen always pulled far ahead.  

 

On the Moon, the yellow hue was starkly apparent, when you jumped from the TV 76 to the Vixen, but as you kept looking, it disappeared. Despite the yellow hue, small lunar details, such as rilles, wrinkle ridges, domes, etc., were easier seen in the Vixen. 

 

I could usually see the same detail in the TV 76, as in the Vixen, but it would often take a lot of patience to fish them out of the image. It never seemed to focus steadily. I would always be tempted to fiddle with the focuser, hunting for a sharper image that would never come. On the Vixen, you would plop an eyepiece in the diagonal, turn the focuser and *bam*, tack-sharp images that just stayed that way. 

 

So, a modern, lightweight 100mm f/15 achromat? Yes please. Even better, a 100mm f/12 ED, with the same glass as in the Sky-Watcher 100mm f/9, but nobody wants to build it and few wants to buy it. 

 

 

Clear skies!
Thomas, Denmark


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#31 Sarkikos

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Posted 22 October 2016 - 09:46 AM

 

 When one wants a long tube classic looking scope, only a long tube will do. Its not just about the optics, because they are all excellent optically. The appeal of a long tube refractor pointing way up in the sky, is in itself the driving factor for many to want them. 

  

 ...Ralph

 

:thinking:  So you want the sizzle, not the steak?  Ad men must love you guys.

 

:grin:

Mike


Edited by Sarkikos, 22 October 2016 - 09:47 AM.


#32 Sarkikos

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Posted 22 October 2016 - 09:55 AM

---------------------------"

For an OTA of that length, I might as well be using a 10" f/5 Newt.

---------------------------"

Weight-wise, with tripod, the Newt would be a lot heavier.

Short reflectors don't handle suburban light polllution that well here at the star parties.

Some doctrine says that can't be, but I keep seeing it.

I haven't seen a hooded  shortie yet though.

In my circumstances, having to go down a flight of stairs in my house, out the front door, onto a porch, and then down another flight of stairs, both the 3" f/15 and the 10" f/5 would take two trips to get out onto the ground.  So for me, they would be substantially equivalent in terms of effort involved ... but not equivalent as far as planet image produced.  The 10" would show much more.

 

If a short reflector can't handle light pollution in the 'burbs, it's because the owner didn't prepare it properly.  There should be a long flocked light shield on the front, the interior of the OTA should be flocked, and a baffle should be attached below the primary.

 

Mike



#33 Sarkikos

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Posted 22 October 2016 - 09:59 AM

I did multiple side-by-side comparisons of a TV 76 ED f/6.3 vs. a 80mm f/15 Vixen and the Vixen totally smoked the TV on Mars, Saturn, the Moon and the Sun, despite actually having the worst star test of the two, with more spherical aberration, but it had by far the most stable, sharp image. This was seen repeatedly, again and again, on many nights for several months.

 

The TV 76 had *impressive* color correction, the best I've seen in such a short focus scope. By contrast, the Vixen had images with a clear yellow hue, but this didn't appear to result in a loss of planetary details at all. Martian details in particular seemed to be in some way *enhanced* by the color shift, and the seas appeared greenish and stood out with better contrast than in the TV 76, where they were a much duller brown hue that didn't stand out very well at all, compared to the ochre surface. It was the same on Saturn, albeit not to the same degree. In combination with the much steadier, sharper image, the Vixen always pulled far ahead.  

 

On the Moon, the yellow hue was starkly apparent, when you jumped from the TV 76 to the Vixen, but as you kept looking, it disappeared. Despite the yellow hue, small lunar details, such as rilles, wrinkle ridges, domes, etc., were easier seen in the Vixen. 

 

I could usually see the same detail in the TV 76, as in the Vixen, but it would often take a lot of patience to fish them out of the image. It never seemed to focus steadily. I would always be tempted to fiddle with the focuser, hunting for a sharper image that would never come. On the Vixen, you would plop an eyepiece in the diagonal, turn the focuser and *bam*, tack-sharp images that just stayed that way. 

 

So, a modern, lightweight 100mm f/15 achromat? Yes please. Even better, a 100mm f/12 ED, with the same glass as in the Sky-Watcher 100mm f/9, but nobody wants to build it and few wants to buy it. 

 

 

Clear skies!
Thomas, Denmark

Maybe you should have tested a full 80mm ED against the 80mm f/15?   :grin:

 

In any case, there is a clear winner whenever I view planet/lunar with the C80ED f/7.5, compared to what the Vixen A80MF f/11.4 can deliver.  The image from the 80 f/11 isn't bad at all.  But the C80ED is better.  Sharper and more contrasty.  Obviously so when viewing the Moon.  

 

Mike


Edited by Sarkikos, 22 October 2016 - 10:00 AM.


#34 Mark9473

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Posted 22 October 2016 - 10:11 AM

 

Bresser is certainly not ES. ES is a brand owned by JOC of China. It is simply a retailing organisation for JOC. Bresser is a long existing european telescope company, originally owned by the Bresser family and then sold to Meade. In recent years the Bresser family reacquired the business from Meade ( who was letting it run into the ground). Bresser now has a solid business in europe again. 

In addition, JOC is one of the main shareholders of Bresser, and Bresser owns the European branch of ES.

I think that's about as clear as mud. ;)



#35 BarrySimon615

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Posted 22 October 2016 - 10:24 AM

My achros which come closest to the "standard," arranged in order of color correction, starting with the best:

 

Towa 60 f/15, CA ratio 5.7, better than Conrady

A70LF f/12.9, CA ratio 4.69, almost Conrady

A80MF f/11.4, CA ratio 3.62, better than Sidgwick

C102 f/9.8, CA ratio 2.45, worse than Sidgwick

 

Mike

Mike,

 

Your ratio for the Towa 60/15, the CA ratio, is 6.35, even better than the 5.7 you calculated.  May be even a bit better if the objective cell design reduces the clear aperture of the objective to something less.

 

Amongst my herd of telescopes, my best are my Milo 76 mm f/18.4 which has a CA ratio of 6.16, my Antares 105 x 1500 mm (as the objective cell design and a strengthening ring immediately behind the objective stops it down to a 95 mm equivalent, so it works as an f/15.8 and it's CA ratio is 4.22) and my Jaegers 54 mm whose cell stops it down to 51 mm and it has a focal length of 1039 mm so it works as an f/20.4 scope, giving it a CA ratio of 10.2!

 

Barry Simon


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#36 BigC

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Posted 22 October 2016 - 10:37 AM

Important point: the ubiquitous modern 80 f11 is not classic length .There is significant difference between f11 and f15 .

And I believe a 100mm ED f12 would sell as well,perhaps better,since those buying the 100f9 often mention planetary,lunar,and doubles .

The Belgian scope maker is planning an f12 but at $3000 it is too expensive.An f12 doublet ED of 100mm should sell around $800.Basically just stretch the Skywatch 100.

It may be that the Japanese classic objectives are better figured and polished than today's scopes.
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#37 Astrojensen

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Posted 22 October 2016 - 10:42 AM

 

 

Maybe you should have tested a full 80mm ED against the 80mm f/15?   :grin:

In any case, there is a clear winner whenever I view planet/lunar with the C80ED f/7.5, compared to what the Vixen A80MF f/11.4 can deliver.  The image from the 80 f/11 isn't bad at all.  But the C80ED is better.  Sharper and more contrasty.  Obviously so when viewing the Moon. 

Mike

Maybe. I initially thought the fight was going to be much harder, so I thought I'd give the older achromat with its MgFl2 coatings a slight aperture advantage, as the newer TV 76 had a fully multicoated objective and superior color correction. Images appeared equally bright in them. 

 

Frankly, I was surprised by the results myself. 

 

 

Clear skies!

Thomas, Denmark


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#38 Sarkikos

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Posted 22 October 2016 - 12:26 PM

 

My achros which come closest to the "standard," arranged in order of color correction, starting with the best:

 

Towa 60 f/15, CA ratio 5.7, better than Conrady

A70LF f/12.9, CA ratio 4.69, almost Conrady

A80MF f/11.4, CA ratio 3.62, better than Sidgwick

C102 f/9.8, CA ratio 2.45, worse than Sidgwick

 

Mike

Mike,

 

Your ratio for the Towa 60/15, the CA ratio, is 6.35, even better than the 5.7 you calculated.  May be even a bit better if the objective cell design reduces the clear aperture of the objective to something less.

 

Amongst my herd of telescopes, my best are my Milo 76 mm f/18.4 which has a CA ratio of 6.16, my Antares 105 x 1500 mm (as the objective cell design and a strengthening ring immediately behind the objective stops it down to a 95 mm equivalent, so it works as an f/15.8 and it's CA ratio is 4.22) and my Jaegers 54 mm whose cell stops it down to 51 mm and it has a focal length of 1039 mm so it works as an f/20.4 scope, giving it a CA ratio of 10.2!

 

Barry Simon

 

You're right.  The CA ratio is calculated:  f number / aperture in inches.  So the CA ratio for my Towa 60 f/15 would 15/2.36 = 6.35.  I'm not sure where that 5.7 came from. I probably just copied it from another source without calculating it myself.  Thanks for the correction.

 

I went back and deleted the original post and reposted it with the correction.  Funny how CN will let you delete a post for an indefinite length of time - how long? - but only gives you a couple days to edit and correct a post.

 

:grin:

Mike


Edited by Sarkikos, 22 October 2016 - 08:10 PM.


#39 Sarkikos

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Posted 22 October 2016 - 12:28 PM

My achros which come closest to the "standard," arranged in order of color correction, starting with the best:

Towa 60 f/15, CA ratio 6.35, better than Conrady
A70LF f/12.9, CA ratio 4.69, almost Conrady
A80MF f/11.4, CA ratio 3.62, better than Sidgwick
C102 f/9.8, CA ratio 2.45, worse than Sidgwick

Mike


Edited by Sarkikos, 22 October 2016 - 12:29 PM.


#40 MartinPond

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Posted 22 October 2016 - 01:52 PM

--------------------------------------- "

In my circumstances, having to go down a flight of stairs in my house, out the front door, onto a porch, and then down another flight of stairs, both the 3" f/15 and the 10" f/5 would take two trips to get out onto the ground.  So for me, they would be substantially equivalent in terms of effort involved ... but not equivalent as far as planet image produced.  The 10" would show much more.

------------------------------------ "

 

A 10-in Dob would be about 60 pounds.  

An 80mm f/15 refractor, altogether, clocks in at around 30 pounds.

However, if the latter is an equatorial, the clumsiness makes that two trips and a take-down.

 

 

 

--------------------------------------- "
If a short reflector can't handle light pollution in the 'burbs, it's because the owner didn't prepare it properly. 

There should be a long flocked light shield on the front, the interior of the OTA should be flocked,

and a baffle should be attached below the primary.

----------------------------------- "

 

Good to have that confirmed. 

The long flocked lightshield, the extra internal flocking,

   and the  and the extra baffle need to be added to the 60 pounds.   :p

 

My trip is down the stairs, into the car, and down the road

   1-1/2 miles to an office park (the trees surround me).

 

But, to adjust your point for a trickier haul:

   How would an 8-inch Dob.  (45lb total), F/5.9 (reduces hooding req. a bit) compare?

  I could see hoisting it in one piece .... (just)... and the hood would hide in the trunk.

 

I usually check the sky out first with a 70mm F10 on a gutted diecast goto mount.

The motion isn't fluid, but it's close.   Total weight:  7 pounds.

The low Western sky is often murky....no fun.

It's the plume from the Penn/Ohio coal/electric plants.

Masking the 70x700 to 60 makes it Conrady ready.


Edited by MartinPond, 22 October 2016 - 01:58 PM.


#41 Sarkikos

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Posted 22 October 2016 - 02:22 PM

--------------------------------------- "

In my circumstances, having to go down a flight of stairs in my house, out the front door, onto a porch, and then down another flight of stairs, both the 3" f/15 and the 10" f/5 would take two trips to get out onto the ground.  So for me, they would be substantially equivalent in terms of effort involved ... but not equivalent as far as planet image produced.  The 10" would show much more.

------------------------------------ "

 

A 10-in Dob would be about 60 pounds.  

An 80mm f/15 refractor, altogether, clocks in at around 30 pounds.

However, if the latter is an equatorial, the clumsiness makes that two trips and a take-down.

 

The length of the OTA also should be taken into consideration when negotiating around turns in a stairway, avoiding overhangs at the base of the staircase, going through a doorway.  This is also why for me a C102 f/9.8 or SW120ED is a two-trip telescope.  Put a long tube on any mount and you can have problems getting it outside all in one trip.

 

Mike


Edited by Sarkikos, 22 October 2016 - 02:23 PM.


#42 Sarkikos

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Posted 22 October 2016 - 02:29 PM

But, to adjust your point for a trickier haul:

   How would an 8-inch Dob.  (45lb total), F/5.9 (reduces hooding req. a bit) compare?

  I could see hoisting it in one piece .... (just)... and the hood would hide in the trunk.

I've owned an 8" f/6 Dob.  It is a two-trip scope as well.  I wouldn't advise hoisting it in one piece with the Dob mount unless you are a weight lifter.  

 

A couple years ago, I had a discussion with another observer on CN about this very subject, of lifting up and moving around an 8" f/6 Dob, scope and mount together.  I said I would never do it.  I couldn't do it.  Too heavy and too awkward.  He said he could do it, no problem.  Pick up the whole setup and carry it outside.  Pick it up and carry it around the yard.  

 

Yeah.  Turns out he was a weight lifter!   :rofl:

 

QED

 

By the way, I also used a long light shield on the 8" f/6 Dob.  It was a Z8.  Most manufacturers have the secondary too close to the end of the OTA for adequate glare prevention.  The length of the OTA below that point doesn't matter.   I put a light shield on all my Newts.

 

:grin:

Mike


Edited by Sarkikos, 22 October 2016 - 02:33 PM.


#43 stevew

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Posted 22 October 2016 - 03:33 PM

 

 When one wants a long tube classic looking scope, only a long tube will do. Its not just about the optics, because they are all excellent optically. The appeal of a long tube refractor pointing way up in the sky, is in itself the driving factor for many to want them. 

  

 ...Ralph

 

Ralph is correct. There is definitely something special about observing with a long focus refractor.

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#44 BigC

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Posted 22 October 2016 - 05:56 PM

A D&G 12"f30 would be an awesome scope!😀

#45 MartinPond

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Posted 22 October 2016 - 06:05 PM

It's not just the drama.....a really long barrel makes precise focusing and

   eyepiece performance far less costly.     

 

An interesting situation is making itself evident:

 

----I have a 70x700 that is not just one-trip but one-arm:  7 lbs total.

---Then there is an 80x910 that is 27 lbs, but also awkward enough that it is 2 trips.

    (taking that to F15 just adds a little to the issue)

----and those Dobs are twice that weight and 2 trips...

 

70-->80mm is looking like a dramatic hinge-point in a refractor for portability.

Seems like I should be able to go just a bit further than the 70 and still stay with one trip.

 

I suppose this is where someone could chime in again about the "ED-lite" scopes

  like the Orion ED80 or the Lunt 80x560.. There is a niche, at the less-fast-ED level.


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#46 MartinPond

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Posted 22 October 2016 - 06:06 PM

A D&G 12"f30 would be an awesome scope!

Not as awesome as the motorized building and chair you would use :D



#47 n2068dd

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Posted 22 October 2016 - 06:42 PM

Hi, there.

 

Here's brand new achromat F15 telescopes in Japan.

STL80A-MAXI link below

https://translate.go...html&edit-text=

The company head, Mr.Takashi Onuma , have the strong insist for 'good and well made F15 achromat never worse than fast ED telescopes'. He himself surprised to see that vintage F15 3inch refracter will surpass the ED telescopes on planet view.

STL80A-MAXI lens design is all the same of vintage Mizar. He find out the polishing dish at Tohoku district, Kubota Kougaku.

He ordered 100set at first and thought it would be the last ,but then it made best selling telescope.

now He made it ordinary stock. we can buy it not expensive 350$.

Maybe, He will accept the international order, I think.

How about to try one?

 

Regards

Hiromu

Japan

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Edited by n2068dd, 22 October 2016 - 06:48 PM.

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#48 BigC

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Posted 22 October 2016 - 07:14 PM

Domo arigato

#49 BigC

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Posted 22 October 2016 - 07:28 PM

That STL80A-MAXI really looks good. And with the escalating prices of its surviving ancestors $350 is a fair price for a first quality OTA.

Definitely going on my wish list despite already owning too many scopes .
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#50 Sarkikos

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Posted 22 October 2016 - 08:12 PM

 

 

 When one wants a long tube classic looking scope, only a long tube will do. Its not just about the optics, because they are all excellent optically. The appeal of a long tube refractor pointing way up in the sky, is in itself the driving factor for many to want them. 

  

 ...Ralph

 

Ralph is correct. There is definitely something special about observing with a long focus refractor.

 

Now that looks like a two trip scope!

 

:grin:

Mike




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