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Equipment Discussions >> Refractors

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junomike
Carpal Tunnel
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Reged: 09/07/09

Loc: Ontario
Re: Triplet APO or Doublet APO? new [Re: hfjacinto]
      #5864091 - 05/16/13 10:13 AM

Helder, If your pics are unedited (to remove CA) then they are impressive. I do see some CA in this pic though (from about 2 o'clock - 6 o'clock). It not intrusive (as they say) but It does bother me.

Quote:

My friend had a TAK 130 and an FSQ 106. The FSQ106 is color free, but the TAK 130 was as color free as was the 120MM. After looking through my 120, he sold the TAK 130 and brought a mount and a 9.25 as we all know aperture rules on DSO




My experience was the opposite! CA never really bothered me until I viewed through Maks and Dobs. Then I craved that "pure, clean" Image in a Refractor as well.

Quote:

I know some people are sensitive to CA but for some of us, its not that big deal and we don't see it.




This is the main key I believe! What one actually sees and what bothers that same person is also an issue. You may see CA and not bother commenting on It (or to a lesser degree) because It's minor to you. Or you may really not see It at all.

Quote:

I also have expeirenced the "I paid a lot for my NP101, AP, TEC, etc so of course its better than your 18" reflector".




This probably does happen, but there's also the flip side where someone has to settle (due to finances, mount limitations, etc) and tries to rationalize the performance of their scope to one they can never obtain.

Too many times "good enough for me" or "similar to" is often put forth as "equal to" or "the same as".
I'm not saying you're doing this, but in general It happens with Astronomy gear all the time.

Quote:

What I am saying is that while a triplet can be good, a lot of people use doublets and they work really well also. I have also looked through a lot of doublet and triplets and the only pure color free refractor that I ever looked through is an FSQ.




Agreed! The Doublets can work very well. I will however add that sometimes the idea of having one can be different than actually making the plunge to own one. What I'm referring to is the Markus Ludes 152ED. When It was In the discussion phase there were many people interested in one.
Now that It's available, where are all the potential buyers?
Is It that the economy is not as good as It was last year?
Or Is It that for $4G's they'd rather forgo the extra 20mm and get a TMB 130SS with FPL-53? (Especially after James Ling's reivew/comparison)
I know which one I'd be more happy with?

There's also the true situation of the fellow who had an FS-152, sold It, acquired a TEC 140 and Immediately missed the FS-152 (he was lucky enough to find another one close by).

I guess It's a matter of taste. Because I see CA doesn't mean others will....But because you don't see It doesn't mean others won't either.

Mike


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hfjacinto
I think he's got it!
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Reged: 01/12/09

Loc: Land of clouds and LP
Re: Triplet APO or Doublet APO? new [Re: junomike]
      #5864152 - 05/16/13 10:46 AM

Mike,

I see you and I "actually" agree on a lot.

As to this "Helder, If your pics are unedited (to remove CA) then they are impressive. I do see some CA in this pic though (from about 2 o'clock - 6 o'clock). It not intrusive (as they say) but It does bother me. "

There is CA in that picture, that was actually one of my first images and it used eyepiece projection. Its not good.The focus is also soft. That was done in 2010.

Compare it to this one. This one was in November 2012, http://www.astrophotogallery.org/moon-and-sun/p10662-moon-on-11-29-2012.html

I got a little better imaging I also don't run any CA removal routines. I actually don't really over process my images, I think lots of the AP out there while nice is not really accurate, the tricolors are beautiful but they don't exist in nature (although I admit I do make star spikes for artistic reasons )

About Premiun optics, I also agree with you, I looked through a TEC 140 and that essentialy was a perfect scope for me. I also would love the NP127.

But I have access to a 178MM Astro Physics that shows CA and the 127MM ES (while a really nice scope) shows more CA than the 120MM EON. So not every premium scope or triplet is perfect.

But even doublets have issues, my 80MM EON has lots of field curvature so you need a field flatner to make it work, actually all my images use a Hutech field flatner, which probably also removes some CA.

So to the OPs original question, a Triplet "can" be better than a doublet, but a doublet can also be a great scope. As to whether the $$$$ is worth it, only you can make that decision.


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Fomalhaut
scholastic sledgehammer


Reged: 08/16/08

Loc: Switzerland
Re: Triplet APO or Doublet APO? new [Re: hfjacinto]
      #5864318 - 05/16/13 11:54 AM

a) If made to exacting standards, doublets with one element of fluorite are better than with FPL-53, because it is more difficult to find an appropriate partner-glass for the latter.
b) In "Telescopes, Eyepieces, Astrographs" (WB-2012) they confirm that a 100mm fluorite doublet should be no faster than f/9 - which has been realized by Vixen. By scrutinizing the spot diagrams it becomes obvious that f/8 is the fastest focal ratio which allows a 100mm-doublet to have essentially perfect color-correction - which has been realized by Tak.
c) Besides Tak's FC100 f/8 there was also an f/10 made (the FC100N), suggesting that Tak themselves considered f/8 a bit sub-optimal for color-correction.
d) Tak's FC150, in spite of being f/11.3, was rumoured not to be totally free of false colors, demonstrating that scaling up objective's diameter should go together with scaling up focal ratio proportionally for same color correction.
e) Tak's FS-152 f/8 doublet was given score 88 by Mr. Yoshida's group testing planetary performance. By comparison, TOA-150 and Zeiss APQ-150 triplets got scores 95 and 96.
f) Tak's FS-128 fluorite doublet and TSA-120 FPL-53 triplet were scored equal (73 both), which also demonstrates the triplets' bigger potential, once the objectives' diameter having grown substantially over 100 mm.
g) In comparison with f), TOA-130 and APQ-130 triplets scored 84 each.

Of course, this is no mathematical proof - however these are all evidences pointing into the same direction...

Chris

PS My FCT100 f/6.4 triplet is distinctly better color corrected (inside, outside plus IN focus) than any FC100 or FS102 f/8 doublet which I have ever seen...


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JoseBorrero
Post Laureate
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Reged: 09/04/09

Loc: Puerto Rico Island
Re: Triplet APO or Doublet APO? new [Re: hfjacinto]
      #5864362 - 05/16/13 12:09 PM

Is there a guy that can put down any triplet is this guy http://www.starhopper.at/

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Triplet APO or Doublet APO? new [Re: JoseBorrero]
      #5864426 - 05/16/13 12:39 PM

http://www.astrophotogallery.org/data/878/Closer_Moon.jpg

hfjacinto I see a little CA in your shot, but it is very acceptable to my eyes.
However I haven't been spoiled by $$$$ optics yet LOL.


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hfjacinto
I think he's got it!
*****

Reged: 01/12/09

Loc: Land of clouds and LP
Re: Triplet APO or Doublet APO? new [Re: audioaficionado]
      #5864479 - 05/16/13 12:57 PM

Quote:

http://www.astrophotogallery.org/data/878/Closer_Moon.jpg

hfjacinto I see a little CA in your shot, but it is very acceptable to my eyes.
However I haven't been spoiled by $$$$ optics yet LOL.




LET ME POST AGAIN, this is an OLD image using Eyepiece Projection, compare to a new image. http://www.astrophotogallery.org/moon-and-sun/p10662-moon-on-11-29-2012.html


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GHarris
super member


Reged: 06/06/09

Re: Triplet APO or Doublet APO? new [Re: junomike]
      #5864505 - 05/16/13 01:05 PM

Quote:

Quote:

What I am saying is that while a triplet can be good, a lot of people use doublets and they work really well also. I have also looked through a lot of doublet and triplets and the only pure color free refractor that I ever looked through is an FSQ.




Agreed! The Doublets can work very well. I will however add that sometimes the idea of having one can be different than actually making the plunge to own one. What I'm referring to is the Markus Ludes 152ED. When It was In the discussion phase there were many people interested in one.
Now that It's available, where are all the potential buyers?
Is It that the economy is not as good as It was last year?
Or Is It that for $4G's they'd rather forgo the extra 20mm and get a TMB 130SS with FPL-53? (Especially after James Ling's reivew/comparison)
I know which one I'd be more happy with?

There's also the true situation of the fellow who had an FS-152, sold It, acquired a TEC 140 and Immediately missed the FS-152 (he was lucky enough to find another one close by).

I guess It's a matter of taste. Because I see CA doesn't mean others will....But because you don't see It doesn't mean others won't either.

Mike




Regarding the 152ED I'm not sure what you are expecting to see that you aren't seeing. There are only 50 scopes (plus some lens cells) being made in this first production run, worldwide, and they haven't been delivered to customers yet (though it shouldn't be much longer now). I'm waiting for one myself. Now that I'd made my purchasing choices and am just waiting for delivery there isn't a lot about the scope for me to discuss on forums. I can't say what my opinions of the scope are until I have it, people can't ask me questions with a view to making their own decision to purchase one, etc etc. Empty speculation seems futile when I'm soon to take delivery of the item.

What fraction of a forum community "lurks" (reads while rarely or never posting), and what fraction post a lot? It must vary from forum to forum but I believe I've seen figures in the past demonstrating that the posters are vastly outnumbered by the lurkers. If there are only 50 scopes worldwide, how many are going to be owned by active members of this forum? I myself am more of a lurker and am probably not going to be all that vociferous when the scope does arrive, as I'm not very knowledgeable and would not want to give anybody inaccurate information. I'll post whatever general impressions I feel I am qualified to give, which might not amount to a lot.

You're right about the attraction of the 152ED being a matter of taste. I for example love the idea of a 6 inch refractor but view traditional 6" f/8 achromats as being too compromised by CA to make much sense, while I view 6" apo triplets as being too far off the deep end in terms of value for money. The doublet is only "somewhat" cheaper than a triplet, but it has good enough performance for me, plus better cooldown times and lower weight (it is bound to be less front-heavy in particular). To me, it's a sensible compromise for a visual user with reasonable expectations who wants something moderately better than an achromat. I admit though that before the 152ED came into existence I wondered whether there could possibly be enough people fitting that description to make it financially viable. I hope there will turn out to be but we don't know yet and the minority (or majority) will probably remain pretty silent until we have some hardware in our hands to talk about.


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hfjacinto
I think he's got it!
*****

Reged: 01/12/09

Loc: Land of clouds and LP
Re: Triplet APO or Doublet APO? new [Re: JoseBorrero]
      #5864513 - 05/16/13 01:12 PM

Quote:

Is there a guy that can put down any triplet is this guy http://www.starhopper.at/




Same scope I have except mine is the EON. Shows what a doublet can do. Like I said in probably every post here, a doublet can be an excellent scope. The people that post that the CA is not acceptable in a doublet for imaging are plain wrong.


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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Triplet APO or Doublet APO? new [Re: hfjacinto]
      #5864585 - 05/16/13 01:34 PM

Quote:

Quote:

http://www.astrophotogallery.org/data/878/Closer_Moon.jpg

hfjacinto I see a little CA in your shot, but it is very acceptable to my eyes.
However I haven't been spoiled by $$$$ optics yet LOL.




LET ME POST AGAIN, this is an OLD image using Eyepiece Projection, compare to a new image. http://www.astrophotogallery.org/moon-and-sun/p10662-moon-on-11-29-2012.html




Awesome moon mosaic.


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Triplet APO or Doublet APO? new [Re: hfjacinto]
      #5864715 - 05/16/13 02:20 PM

Quote:


No offense taken but look at the moon image, they have no color, I have used over 300 power before I noticed some CA and that was with a Nagler. With an Ortho I could see no false color.




My hope here is that there an unbiased discussion of the realities of the differences between doublets and triplets. I have some, limited experience with the 120mm F/7.5, I think it's a reasonable scope and were I interested in a 5 inch ED/apo, it's the one I would most likely choose, it seems to be a good value and a good scope.

But in my mind, this discussion is about the differences at the high end, how good is the color correction under the most difficult conditions, not 300x viewing the moon, which is relatively forgiving, but 300x viewing Venus... in my experience Venus is the ultimate test.

Jon Isaacs


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StarsAbove
sage


Reged: 09/09/05

Re: Triplet APO or Doublet APO? new [Re: hfjacinto]
      #5865521 - 05/16/13 06:41 PM

That is simply beautiful!

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CounterWeight
Postmaster
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Reged: 10/05/08

Loc: Palo alto, CA.
Re: Triplet APO or Doublet APO? new [Re: StarsAbove]
      #5865955 - 05/16/13 09:50 PM

What about a Hatori-Honso triplet?

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olivdeso
super member


Reged: 02/20/11

Loc: Paris FR
Re: Triplet APO or Doublet APO? new [Re: Jon Isaacs]
      #5865973 - 05/16/13 10:01 PM

Quote:

300x viewing Venus... in my experience Venus is the ultimate test.

Jon Isaacs




x300 on Venus ?! the atmophere will have a hudge chromatic dispersion effect. This will be the first limiting factor.
You will have to use a well tuned ADC (Atmospheric Dispersion Corrector) to cancel the chromatic error, then you might be able to juge the scope chromatic error.

Another way to cancel the atmosphere chromatic dispersion effect is to use a filter which will narrow the spectrum, but this will also cut the secondary spectrum of the refractor if any.

Olivier


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Triplet APO or Doublet APO? new [Re: olivdeso]
      #5866419 - 05/17/13 04:14 AM Attachment (9 downloads)

Quote:

Quote:

300x viewing Venus... in my experience Venus is the ultimate test.

Jon Isaacs




x300 on Venus ?! the atmophere will have a hudge chromatic dispersion effect. This will be the first limiting factor.
You will have to use a well tuned ADC (Atmospheric Dispersion Corrector) to cancel the chromatic error, then you might be able to juge the scope chromatic error.

Another way to cancel the atmosphere chromatic dispersion effect is to use a filter which will narrow the spectrum, but this will also cut the secondary spectrum of the refractor if any.

Olivier




Olivier:

I am curious if you have spent much time observing Venus at higher magnifications? Certainly there are situations when Venus shows a significant amount of atmospheric dispersion but this is not a given, the maximum elongation of Venus is about 45 degrees so it's can be free from the effects of atmospheric effects.

At it's brightest, Venus is about 2.3 magnitudes brighter than the moon at it's brightest, that's 8 times brighter than the moon at it's brightest. This is what makes Venus such a challenge for a refractor.

Even when Venus is lower on the horizon and atmospheric effects a visible, it takes quite good color correction to show the orange side that results from the atmospheric dispersion because it is ovewhelmed by purple haze of the refractors chromatic aberration. Out of focus tests can also be instructive.

Of course there are situations where a test using Venus is not particularly useful.

Jon

Edited by Jon Isaacs (05/17/13 04:20 AM)


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olivdeso
super member


Reged: 02/20/11

Loc: Paris FR
Re: Triplet APO or Doublet APO? new [Re: Jon Isaacs]
      #5867176 - 05/17/13 01:16 PM

Quote:


I am curious if you have spent much time observing Venus at higher magnifications? Certainly there are situations when Venus shows a significant amount of atmospheric dispersion but this is not a given, the maximum elongation of Venus is about 45 degrees so it's can be free from the effects of atmospheric effects.

Jon




Hi Jon,

Until now I never had a chance to see Venus free of atmospheric dispertion here in France.
Even last year when it was well positioned, the color dispersion was obvious with the TEC160ED for instance.

The paradox with high end large APO like the TEC160ED is that they show a very high contrast and excelent color correction that result also in high sensitivity to atmospheric dispersion.
Even on Mars, the dispersion is enoying as soon as Mars is more than 1h away from the meridian.

So I invested in an ADC at the end.

That said I will try again, following your advice, but I a not optimistic at all. The analysis will not be easy anyway...migh be it could be easier in a drier place...

Olivier


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hfjacinto
I think he's got it!
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Reged: 01/12/09

Loc: Land of clouds and LP
Re: Triplet APO or Doublet APO? new [Re: olivdeso]
      #5867210 - 05/17/13 01:36 PM Attachment (29 downloads)

Last year when Venus was its highest, I was able to capture it, air was stagnant and seeing was essentially perfect. I was also new at this planetary imaging so the picture isn't the best, but when the atmosphere is stable the planet can lose most its shine and color, this was imaged right at sunset and a red filter was used to dim the view. I only shot red so this is only the red channel.

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SteveG
Post Laureate
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Reged: 09/27/06

Loc: Seattle, WA
Re: Triplet APO or Doublet APO? new [Re: Jon Isaacs]
      #5867268 - 05/17/13 02:04 PM

Quote:

At it's brightest, Venus is about 2.3 magnitudes brighter than the moon at it's brightest, that's 8 times brighter than the moon at it's brightest. This is what makes Venus such a challenge for a refractor.


Jon




Perhaps I'm misunderstanding you here? Isn't the moon at about magnitude -13 always brighter than Venus at about magnitude -4?

Edited by SteveG (05/17/13 02:10 PM)


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SteveG
Post Laureate
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Reged: 09/27/06

Loc: Seattle, WA
Re: Triplet APO or Doublet APO? [Re: SteveG]
      #5867273 - 05/17/13 02:07 PM

I had my best view ever of Venus last year when it was fairly high in the sky and through a very slight upper atmosphere haze. Rock steady and no false color - and I detected the chevron shaped faint markings on the cloud tops.

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Mike Clemens
Frozen to Eyepiece
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Reged: 11/26/05

Loc: Alaska, USA
Re: Triplet APO or Doublet APO? [Re: hfjacinto]
      #5867319 - 05/17/13 03:08 PM

Quote:

After processing.




This is what I'd expect from a doublet (awesome results) but Iota Orionis there at mag 2.77 has a glowing blue sphere around it.


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Triplet APO or Doublet APO? [Re: SteveG]
      #5867363 - 05/17/13 03:28 PM

Quote:

Quote:

At it's brightest, Venus is about 2.3 magnitudes brighter than the moon at it's brightest, that's 8 times brighter than the moon at it's brightest. This is what makes Venus such a challenge for a refractor.


Jon




Perhaps I'm misunderstanding you here? Isn't the moon at about magnitude -13 always brighter than Venus at about magnitude -4?




I am sorry, I was referring to surface brightness. The moon is much brighter overall due to it's large surface area but Venus is much smaller so the intensity, the surface brightness, can be considerably greater. It's the surface brightness and it's small size that brings out the chromatic aberration when viewing Venus.

Jon

Edited by Jon Isaacs (05/17/13 03:29 PM)


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