Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Altair ASCENT 102mm F11ED Refractor vs Skywatcher 120ED for Visual Astronomy

  • Please log in to reply
43 replies to this topic

#1 aa6ww

aa6ww

    Mercury-Atlas

  • *****
  • topic starter
  • Posts: 2,591
  • Joined: 23 Oct 2011
  • Loc: Sacramento, Calif.

Posted 21 November 2019 - 06:41 PM

I'm wondering what refractor lovers thoughts are on the comparisons of these two excellent ED refractors.

I've owned a SW120ED for 3 or so years now, and it’s always been an excellent performer. I have yet to find any flaws in this scope. I bought mine used and installed a matching white Williams Optics Digital dual speed focuser on mine before I even received the scope, so I don't know how the stock focusers really perform. I'm sure the William optics is a substantial upgrade however.

Nevertheless, I'm a huge fan of long tube refractors. Long but not over powering. The new Altair Ascent 102ED F11 is still manageable on an AVX size mount or GM8, something with a 30 pound payload capacity.

My SW 120ED is also manageable and solid on an AVX also.

Aside from the very cool looks of how the long tube 102ED F11 would look mounted on a nice equatorial mount, I’m wondering if there would be any advantages the 102ED would have over the 120ED, or visa versa.

First off, I’m throwing out the idea that the Altair F11ED is less manageable then the Skywatcher. Physically, these scopes could be nearly identical in actual length since one has a retractable dew shield despite it being 200mm longer in focal length. In the world of usable telescopes, since both are under 15 pounds, both are very manageable.

Regarding color correction, the SW120ED is as color free as any refractor I’ve ever owned. It does have the trendy FPL53 and at F7.5 it needs that glass to be color free. I’m guessing it would be too close to call, vs the F11ED with its lesser known ED Glass but at very long comfortable less demanding F11 for color correction.

I wonder how the F11ED compares during Star Splitting. It’s easier to use slower larger eyepieces for high magnification views when using longer focal length refractors. 900mm to 1100mm are still close numbers.

I think the better focuser goes hands down to the Altair F11ED. I can’t say from experience but it seems well made and well thought out with 3 thumbscrews to tighten down a 2” diagonal.

For binoviewers, the Altair F11ED is a big winner, since it converts to a shorter physical length by removing the back section. No optical corrector needed.

I do believe the F11ED requires a more solid mount then the Skywatcher 120ED. My SW120ED is solid with the legs fully extended on my GP-DX but when using a friend’s 102 F11 Planet Hunter, my GP-DX was horrible for shakes during focusing. I’m told the tripod is the blame and I've verified this to be true also since with the tripod full retracted, the F11 102 was much more stable, but definitely not practical with tripod legs being so short.

For planets, probably the 120ED has the edge. Mostly because of the larger aperture. If conditions won’t allow all 120mm to perform fully, the 102ED F11 could be competitive. I don’t consider a 102 or 120 size apertures planetary apertures, but if it’s what you’re using, every mm should mater.

I'm curious about the 102ED F11. Not to replace my SW 120ED but just having a slick long tube classic looking 102 with excellent optics that my light weight AVX mount can fully support

Any thoughts or opinions on these two scopes?

Thanks for reading and sharing your inputs.

..Ralph in Sacramento

#2 nicoledoula

nicoledoula

    Apollo

  • *****
  • Posts: 1,180
  • Joined: 31 Jan 2018

Posted 21 November 2019 - 07:08 PM

I can't think of any advantages except looks.....  That said it's droolworthy.   AVX might like it better than the 120ED



#3 mikeDnight

mikeDnight

    Apollo

  • ****-
  • Posts: 1,231
  • Joined: 19 Apr 2015
  • Loc: Wild Wild West - North West England

Posted 21 November 2019 - 07:21 PM

I loved my Equinox 120ED and used it for many years, thrilling constantly at its remarkable optics and piercingly sharp, high contrast views of moon, planets and DSO's. Yet when I ran my 120ED in a side by side comparison with my newly acquired Tak FC100DC back in March/April of 2015, you could have knocked me down with a feather as the 100mm left the 120ED standing regarding Jupiter. May be the 120 was more affected by the seeing conditions with the 100mm seeing through the seeing, but whatever it was it was a difference that took my breath away. It wasn't a one off either, as on every occasion for about a month the 100mm stole the show. Eventually I sold the 120ED as the 100mm did all I asked of it and more. 

 I'm not suggesting you sell your 120ED in preference to a 102 F11, and it may sound counter intuitive, but you might find a 102mm will give you some remarkable views on occasion,  even outstripping the superlative 120ED. I suppose much will depend on the optical figure of the 102ED F11.


  • SteveG, Sasa and Steve Allison like this

#4 aa6ww

aa6ww

    Mercury-Atlas

  • *****
  • topic starter
  • Posts: 2,591
  • Joined: 23 Oct 2011
  • Loc: Sacramento, Calif.

Posted 21 November 2019 - 07:53 PM

I used my 80mm F15 last weekend and that's fun, but after setting that up last weekend in my backyard, I kept thinking the new ED 102F11 would make a nice star splitter for my light weight AVX and still give it that cool long tube refractor looks we all think of when we see them mounted on a mount. That's what got me thinking about asking about this comparisons.

Here is my 80 f/15 with a 2" focuser on my AVX with G11 Tripod. Pretty cool but the 102 F11ED would be the cats meow!

https://www.cloudyni...y/#entry9776391

...Ralph

#5 Bean614

Bean614

    Apollo

  • *****
  • Posts: 1,182
  • Joined: 05 Nov 2015
  • Loc: Mass.

Posted 21 November 2019 - 09:03 PM

I used my 80mm F15 last weekend and that's fun, but after setting that up last weekend in my backyard, I kept thinking the new ED 102F11 would make a nice star splitter for my light weight AVX and still give it that cool long tube refractor looks we all think of when we see them mounted on a mount. That's what got me thinking about asking about this comparisons.

Here is my 80 f/15 with a 2" focuser on my AVX with G11 Tripod. Pretty cool but the 102 F11ED would be the cats meow!

https://www.cloudyni...y/#entry9776391

...Ralph

Which do you prefer,  looking AT your refractors, or through them?


  • Rollo likes this

#6 stevew

stevew

    Now I've done it

  • *****
  • Posts: 6,522
  • Joined: 03 Mar 2006
  • Loc: British Columbia Canada

Posted 21 November 2019 - 11:22 PM

102 F-11 HFK61 vs 120 F-7.5 FPL53  

If both scopes had the same level of polish, and figuring I'd say the 120 mm would be the all around better scope for visual astronomy due to the extra resolution.


  • Wildetelescope likes this

#7 aa6ww

aa6ww

    Mercury-Atlas

  • *****
  • topic starter
  • Posts: 2,591
  • Joined: 23 Oct 2011
  • Loc: Sacramento, Calif.

Posted 22 November 2019 - 07:51 PM

When they are mounted in my house, I like looking at them.
when I'm setting them up, and its still daylight, I like looking at them.

Once the skies are dark, I like to look through them.

...Ralph


Which do you prefer,  looking AT your refractors, or through them?


  • Celerondon likes this

#8 Gary Riley

Gary Riley

    Viking 1

  • *****
  • Posts: 725
  • Joined: 01 Dec 2011
  • Loc: White Bluff, TN

Posted 22 November 2019 - 08:34 PM

I would think that the SW 120 would still be the preferred scope. I have the same scope and really love the views it puts up.

#9 Tyson M

Tyson M

    Aurora

  • *****
  • Posts: 4,821
  • Joined: 22 Jan 2015
  • Loc: Canada

Posted 22 November 2019 - 09:09 PM

I have used the 120ED and found it outstanding.  Given the two scopes I'd probably choose it over the TS102ED F11.



#10 drd715

drd715

    Viking 1

  • *****
  • Posts: 547
  • Joined: 07 Jan 2015
  • Loc: Fort Lauderdale

Posted 22 November 2019 - 10:49 PM

I have used the 120ED and found it outstanding. Given the two scopes I'd probably choose it over the TS102ED F11.

The 120ED is s VERY good scope. At twice the price though and even then worth it for light gathering ability, slightly better potential resolution, better ED glass and slightly shorter than the F-11 in length. All pluses.

But the F-11 by its nature (F-11 Ed) has sharp pinpoint stars, a dark black image background, very contrasty view, snappy focus point easier positioning focus, and slightly higher magnification per a given eyepiece mm.

On the down side the F-11 doesn't have as wide of a view as the F-7.5.

They are just different. Each has its strong points. The F-11ed is great value for the economy dollars. The F-7.5 Ed is also great value for its reasonable price dollars, just more dollars. Just depends on the amount of cash you are comfortable spending.

Both need about the same size mount.

Sent from my SM-N950U using Tapatalk

#11 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 86,544
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 23 November 2019 - 03:34 AM

 I have the Eon version of the 120 mm Skywatcher scope. For those who want a telescope to look at, it's a beauty.

 

For close doubles, the 18 mm of aperture certainly gives the 120 ED the advantage.

 

Color correction should be very similar.

 

Jon



#12 aa6ww

aa6ww

    Mercury-Atlas

  • *****
  • topic starter
  • Posts: 2,591
  • Joined: 23 Oct 2011
  • Loc: Sacramento, Calif.

Posted 23 November 2019 - 05:10 AM

My APM 152 throws out a fairly wide field of view with my 41 Pan and 31 Nagler. The F11ED should be even wider. 

The strenght of the 102ED F11 isnt its wide field appeal though.

 

 

 

...Ralph

 

 

 

The 120ED is s VERY good scope. At twice the price though and even then worth it for light gathering ability, slightly better potential resolution, better ED glass and slightly shorter than the F-11 in length. All pluses.

But the F-11 by its nature (F-11 Ed) has sharp pinpoint stars, a dark black image background, very contrasty view, snappy focus point easier positioning focus, and slightly higher magnification per a given eyepiece mm.

On the down side the F-11 doesn't have as wide of a view as the F-7.5.

They are just different. Each has its strong points. The F-11ed is great value for the economy dollars. The F-7.5 Ed is also great value for its reasonable price dollars, just more dollars. Just depends on the amount of cash you are comfortable spending.

Both need about the same size mount.

Sent from my SM-N950U using Tapatalk



#13 jag767

jag767

    Kinesis Custom Machining and Refinishing

  • *****
  • Vendors
  • Posts: 1,220
  • Joined: 20 Jun 2013
  • Loc: Massapequa, NY

Posted 23 November 2019 - 05:26 AM

So I actually went from the 120 ed to the F11. Imo, its not a fair comparison for obvious reasons. The 120 will show marginally more, as to be expected. As far as optical figure, of my to samples the f11 put up a better star test (again, to be expected). The build quality of the f11 is also much nicer. Also, its 40% the price of the 120. Fwiw, I regret nothing opting for another f11 over a 120.
  • Terra Nova and drd715 like this

#14 drd715

drd715

    Viking 1

  • *****
  • Posts: 547
  • Joined: 07 Jan 2015
  • Loc: Fort Lauderdale

Posted 23 November 2019 - 11:01 AM

So I actually went from the 120 ed to the F11. Imo, its not a fair comparison for obvious reasons. The 120 will show marginally more, as to be expected. As far as optical figure, of my to samples the f11 put up a better star test (again, to be expected). The build quality of the f11 is also much nicer. Also, its 40% the price of the 120. Fwiw, I regret nothing opting for another f11 over a 120.

The F-11 ed is probably the most cost effective bargain telescope that produces the best possible image in the 100mm class.

The long F-11 fl with an Ed element lens really does it. To get that kind of correction in a short F-6 or so you would have to spend 5 times as much on a triplet.

The 120ED F7.5 (FPL-53) and the 100ED F-9 are both quite good scopes too, but the F-11 is a real bargain that performs.

Now the question is which brand, Altair, TS or other version of the same scope. Are there differences between the brands? Differences between brand pricing? Better to get from a stateside vendor in case the optics are not up to a high figure quality (ie: returnable/exchangeable)? Any dealer that can pre-check the optical quality before shipping (and actually knows how do a critical test not superficial and cares) , which hopefully would avoid any returning hassle?

I've been considering purchasing one of these F-11 ED scopes for some time. It would be used as a bit of a "knock about" camping scope on an alt/az mount for some fun visual viewing, maybe binoviewer. Don't want to drag out the Apm 152ED on non dedicated astronomy trips, just something that produces a best quality image. Don't really care for the short tube scopes, they just don't seem to provide a sharp contrasty image. Oh well we'll see what Christmas will bring.

Sent from my SM-N950U using Tapatalk
  • vkhastro1 likes this

#15 aa6ww

aa6ww

    Mercury-Atlas

  • *****
  • topic starter
  • Posts: 2,591
  • Joined: 23 Oct 2011
  • Loc: Sacramento, Calif.

Posted 23 December 2019 - 12:09 AM

Id go with TNR since they are as good as it gets for service. 

 

https://www.landseas...ed-focuser.html

 

The load bearing focuser is a nice touch vs the one on the Achro Planet Hunter 102 F/11. I have a friend who has one and his focuser cant handle the big 2" eyepieces. 

 

It should be pretty solid on my new Avx with my G11 Tripod with 12" pier. Should be high enough also, something the Avx tripod lacks without sitting down.

 

...Ralph


  • Terra Nova likes this

#16 db2005

db2005

    Apollo

  • *****
  • Posts: 1,219
  • Joined: 23 Dec 2017
  • Loc: Living in Denmark, under Bortle 5/6 skies.

Posted 23 December 2019 - 03:17 AM

I have no experience with the two telescopes in question, but I have spent quite some time comparing the visual performance of several scopes of different size, focal ratio and optical quality, including both of the 120's smaller siblings.

 

A real challenge when making such hypothetical "X vs Y" comparisons is the implied premise that "all other things are equal"... which they never are. Of course, both scopes receive a lot of praise from owners and personally I don't think I would be unhappy with either of them, except that both scopes are probably slightly too large for my requirements. There are however a few things worth keeping in mind when comparing scopes mainly from their specifications:

  • A manufacturer specification of the used ED glasses alone don't tell you how good the optics are. I have owned scopes with FPL-53 glass with vastly different optical performance, both in terms of CA and SA. The mating element for the ED glass is equally important, as is the quality of the optical figure and polish. IME higher-end telescope brands tend to be much better at utilizing the full potential of the optics; better choice of mating element, better optical figure and polish, and better QC.
  • Optical quality is a real thing. My own SW ED100 was my primary scope for a few years, and is indeed a solid performer. But when I got my hand on a vintage Tak FC-100 scope I was astonished by its performance; Cleaner views, much better CA control, and significantly better planetary contrast. Even my FC76Q (quadruplet) and my SD81S have more contrast visually on planets than my ED100. Yes, optical quality is a real thing. We pay more for the quality of the workmanship put into the lens than the materials it's made of.
  • The most important information about the scope is rarely found in specification sheets. For instance: Many ED doublets tend to perform relatively poorly in the red end of the visual spectrum, making reddish objects like Mars look fuzzy and with poor "focus snap", and generally causing loss of contrast. The best ED doublets and fluorite doublets perform much better (I was finally convinced when I compared my ED80 with my Vixen SD81S, both using FPL-53 glass). Since the majority of  telescope makers don't specify polychromatic Strehl, consumers are frequently left with the impression that all FPL-[whatever] scopes are made equal. Well... they aren't. IME the most reliable predictor of optical quality is price.

That being said, and now returning the the OP's question: If all other things are (roughly) equal I would guess the F/11 would likely have the "better" and more contrasty optics simply on account of having the smaller and slower lens, meaning it's easier to make, figure and polish while keeping SA and CA under tight control. But the 120mm has a clear aperture advantage (but needs longer time to acclimatize, meaning that the optimum optical performance can only be accomplished if you take your time). Personally, if I could have only one of the scopes I would likely take the 120, but the choice would have to be a very close call.


Edited by db2005, 23 December 2019 - 05:32 AM.

  • Erik Bakker, Uwe Pilz, Astrojensen and 4 others like this

#17 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • Posts: 13,255
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 23 December 2019 - 03:23 AM

I'd say that if you already have an APM 152, an EON 120 brings very little new to the table, except wider fields of view, which to you seems less important, since you focus so heavily on double stars and planets. 

 

The 4" f/11 DOES bring something new over the APM 152, though, namely DRASTICALLY shorter cool-down time. This can mean all the difference in the world on an evening when clear skies catch you by surprise. 

 

 

Clear skies!
Thomas, Denmark


  • db2005 likes this

#18 dscarpa

dscarpa

    Skylab

  • *****
  • Posts: 4,164
  • Joined: 15 Mar 2008
  • Loc: San Diego Ca.

Posted 25 December 2019 - 04:52 PM

The longer FL would make the Altair somewhat  less seeing sensitive. My had for 12 years WO ZS110 F7  triplet and new buy Vixen 130ED SS doublet both with text book star tests are about the same size difference as the Altair 102 and SW 120. The Vixen outperforms the WO for everything by a fair margin and is only about 3 lbs heavier.  I really enjoy the WO's performance and don't see myself parting with it but if  I'd bought the Vixen first probably wouldn't have got it. David


Edited by dscarpa, 25 December 2019 - 05:06 PM.


#19 BillP

BillP

    ISS

  • *****
  • Posts: 20,336
  • Joined: 26 Nov 2006
  • Loc: Spotsylvania, VA

Posted 26 December 2019 - 09:16 AM

I usually operate at f/8 because it is easier on eyepiece designs while still affording generous TFOVs.  I recently acquired an f/9 Apo and was rather astonished at now much better classic eyepiece designs work in it vs. the f/8s.  So a very distinct advantage for the f/11 will be that most any eyepiece design, new or old, will perform to excellent-levels in their off-axis.  I also noted that TMB Supermonos perform much more resolutely on-axis at the longer focal ratios as well.  For me, all this is of significant advantage because I have and like many of the old classic and simple eyepiece designs.  So when they work excellently in a modern scope then it opens up a whole new aspect to observing for me that I enjoy immensely.  Of course, with my 100 f/9 scope it is still not so long and easily manageable.  Adding another 8" to the length for an f/11 would not IMO change any of that.  With the f/11 your max TFOV, while not so generous, still sits at a level that I think is fine for general purpose observing, about 2.4 degrees with a 40mm wide field.  So even at f/11 I would find it quite capable across all targets big and small.  Operating a classic long line refractor is also a whole different level from shorter scopes.  Point is very intuitive with them and it gives observing IMO a more lay back and waltzy feeling which I enjoy. 

 

I don't really think that f/11 over f/7.5 would be of any particular advantage as far as how it performs on celestial targets.  So no advantage either way excepting as already mentioned that the f/11 will open up a whole new world of eyepieces for you that will work excellently and also cost little comparatively.  And yes, while smaller apertures are sometimes better when the seeing is less than optimum, but the120  f/7.5 can simply be masked to achieve the same focal ratio, although at a reduced aperture of around 82mm for f/11.  So all scopes can be masked to smaller apertures to better handle some observing situations when the seeing is not so stable.  What comes to mind most for me is double star observing.  When the seeing is such that there is just too much undulation and star point flaring of the view that it becomes a less pleasing session, or when the seeing is just not good enough to get to the magnifications necessary at whatever aperture to get a good somewhat stable airy disk, then masking does wonders since the spurious disk is larger and less magnification needed to get there.  With the 100 f/11 you could mask that thing to 65mm for an f/17 scope!  That would be killer IMO as you would get good doubles performance in poorer seeing and gobs of depth of focus too!  And at that focal ratio even wider AFOV Konig designs are razor sharp at the field stop!

 

Basically, I think you might be surprised how different the "operation" of observing is with the 100 f/11 vs. the 120 f/7.5.  It will be a completely different experience, and a better one as far as I'm concerned.  Observing is about a whole lot more than simply what aperture brings.  If you are attuned to those other intrinsic aspects of the craft, then the Altair might breathe a whole different life into the observing experience for you.


Edited by BillP, 26 December 2019 - 12:24 PM.

  • Galicapernistein, Astrojensen, eros312 and 3 others like this

#20 BillP

BillP

    ISS

  • *****
  • Posts: 20,336
  • Joined: 26 Nov 2006
  • Loc: Spotsylvania, VA

Posted 28 December 2019 - 08:17 PM

I don't really think that f/11 over f/7.5 would be of any particular advantage as far as how it performs on celestial targets.  So no advantage either way excepting as already mentioned that the f/11 will open up a whole new world of eyepieces for you that will work excellently and also cost little comparatively.  And yes, while smaller apertures are sometimes better when the seeing is less than optimum, but the120  f/7.5 can simply be masked to achieve the same focal ratio, although at a reduced aperture of around 82mm for f/11.  So all scopes can be masked to smaller apertures to better handle some observing situations when the seeing is not so stable.  What comes to mind most for me is double star observing.  When the seeing is such that there is just too much undulation and star point flaring of the view that it becomes a less pleasing session, or when the seeing is just not good enough to get to the magnifications necessary at whatever aperture to get a good somewhat stable airy disk, then masking does wonders since the spurious disk is larger and less magnification needed to get there. 

 

Wanted to give you an example of the masking.  Tonight out observing with my 100 f/9 ED scope.  Looking at Gamma And (Almaak) I masked it to 50mm, the size of the smaller hole in the objective cap supplied.  At 75x Almaak then showed two beautifully perfect airy disks and the color saturation was still quite vivid blue-deep yellow.  Gorgeous!  Taking the mask off and back to 100mm and the airy disks were now gone, everything else the same since seeing fairly steady here tonight.  When I turned to observe M45 with the 24mm ES68 I did the same thing, much nicer masked to 50mm as the background became pure black and all but the dimmest stars at 100mm still perfectly visible.  Much more aesthetic observation.
 


Edited by BillP, 28 December 2019 - 08:17 PM.

  • Astrojensen, paul m schofield and db2005 like this

#21 db2005

db2005

    Apollo

  • *****
  • Posts: 1,219
  • Joined: 23 Dec 2017
  • Loc: Living in Denmark, under Bortle 5/6 skies.

Posted 29 December 2019 - 07:58 AM

Much more aesthetic observation.

+1 waytogo.gif A lot can indeed be said in favor of aesthetics, especially when a hobby like amateur astronomy should be enjoyable.

 

Aesthetic views is IMO another reason why smallish (~3") APOs are so popular. Things just look pretty through a small high-quality scope that is relatively insensitive to poor seeing and tube currents and uses glass that acclimatizes quickly and benignly.

 

Larger instruments - while more powerful and able to produce "scientifically more accurate" results/observations aren't always more enjoyable to look through, and are certainly less manageable in daily operation than small scopes. This doesn't imply a conflict between "hobby-inclined"  amateur astronomy and "scientifically inclined" amateur astronomy, but it is a useful reminder that we always benefit from choosing the right tools for the job.


Edited by db2005, 29 December 2019 - 07:59 AM.

  • BillP and Astrojensen like this

#22 Erik Bakker

Erik Bakker

    Cosmos

  • *****
  • Moderators
  • Posts: 8,868
  • Joined: 10 Aug 2006
  • Loc: Netherlands, Europe

Posted 29 December 2019 - 10:25 AM

I have no experience with the two telescopes in question, but I have spent quite some time comparing the visual performance of several scopes of different size, focal ratio and optical quality, including both of the 120's smaller siblings.

 

A real challenge when making such hypothetical "X vs Y" comparisons is the implied premise that "all other things are equal"... which they never are. Of course, both scopes receive a lot of praise from owners and personally I don't think I would be unhappy with either of them, except that both scopes are probably slightly too large for my requirements. There are however a few things worth keeping in mind when comparing scopes mainly from their specifications:

  • A manufacturer specification of the used ED glasses alone don't tell you how good the optics are. I have owned scopes with FPL-53 glass with vastly different optical performance, both in terms of CA and SA. The mating element for the ED glass is equally important, as is the quality of the optical figure and polish. IME higher-end telescope brands tend to be much better at utilizing the full potential of the optics; better choice of mating element, better optical figure and polish, and better QC.
  • Optical quality is a real thing. My own SW ED100 was my primary scope for a few years, and is indeed a solid performer. But when I got my hand on a vintage Tak FC-100 scope I was astonished by its performance; Cleaner views, much better CA control, and significantly better planetary contrast. Even my FC76Q (quadruplet) and my SD81S have more contrast visually on planets than my ED100. Yes, optical quality is a real thing. We pay more for the quality of the workmanship put into the lens than the materials it's made of.
  • The most important information about the scope is rarely found in specification sheets. For instance: Many ED doublets tend to perform relatively poorly in the red end of the visual spectrum, making reddish objects like Mars look fuzzy and with poor "focus snap", and generally causing loss of contrast. The best ED doublets and fluorite doublets perform much better (I was finally convinced when I compared my ED80 with my Vixen SD81S, both using FPL-53 glass). Since the majority of  telescope makers don't specify polychromatic Strehl, consumers are frequently left with the impression that all FPL-[whatever] scopes are made equal. Well... they aren't. IME the most reliable predictor of optical quality is price.

That being said, and now returning the the OP's question: If all other things are (roughly) equal I would guess the F/11 would likely have the "better" and more contrasty optics simply on account of having the smaller and slower lens, meaning it's easier to make, figure and polish while keeping SA and CA under tight control. But the 120mm has a clear aperture advantage (but needs longer time to acclimatize, meaning that the optimum optical performance can only be accomplished if you take your time). Personally, if I could have only one of the scopes I would likely take the 120, but the choice would have to be a very close call.

+1 waytogo.gif



#23 BillP

BillP

    ISS

  • *****
  • Posts: 20,336
  • Joined: 26 Nov 2006
  • Loc: Spotsylvania, VA

Posted 29 December 2019 - 12:43 PM

Larger instruments - while more powerful and able to produce "scientifically more accurate" results/observations....

From a relative perspective very true that a 12" optic, as example, will provide a more detailed observation providing one a more "accurate" assessment of the object.  But as far as that being scientifically useful, I would say very much no as either the 4" or 12" Earth-bound optic in a visual configuration would be of absolutely no scientific value whatsoever in the context of today's needs in astronomy and cosmology, and either of them will visually only produce the crudest of renditions of the target making them useless for science in that configuration.  That being the case, both are really just for personal enjoyment and edification, scientifically inclined user or not.  If the goal is to do modern science, or visualize scientifically accurate/useful renditions of the target, then your astronomical toolbox is not very likely to ever contain an eyepiece unless you have need of a paper weight. lol.gif  One of the reasons I don't bother with larger aperture amateur instruments since none of them in a visual mode can even scratch the surface of what we know of these objects found through cutting-edge research using sensor-driven data gathering.  So when my scientifically inclined bug starts giving me an itch, which it does often, visual through a telescope is the least productive place I go as that will tell me next to nothing, if not entirely nothing useful about the object!


Edited by BillP, 29 December 2019 - 12:48 PM.

  • db2005 likes this

#24 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • Posts: 13,255
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 29 December 2019 - 01:18 PM

 But as far as that being scientifically useful, I would say very much no as either the 4" or 12" Earth-bound optic in a visual configuration would be of absolutely no scientific value whatsoever in the context of today's needs in astronomy and cosmology, and either of them will visually only produce the crudest of renditions of the target making them useless for science in that configuration.

This is absolutely wrong. Visual estimates of variable stars are STILL HIGHLY SCIENTIFICALLY USEFUL. There are so many variable stars out there, that the professionals are completely overwhelmed and can't keep track of them all. This is especially true of highly irregular variables, which are sometimes also the most scientifically important to keep an eye on. Here an early alert from an amateur or a long series of visual brightness estimates can be worth its weight in gold. There are still variable star classes we don't understand the mechanisms behind. 

 

Don't just take my word for it. Here it's straight from AAVSO: https://www.aavso.or...isual-observers

 

Even a visual planetary observation of a transient phenomena, such as an impact, are of tremendous value, if done carefully.  

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 29 December 2019 - 01:33 PM.

  • Terra Nova and db2005 like this

#25 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 26,876
  • Joined: 01 Feb 2006

Posted 29 December 2019 - 01:20 PM

Looks are looks, and if you like the way it looks and that is important to you, then get it.

 

Now that being said, I married a couple of women that were knockouts, but that did not make them the right people to be my wife. LOL. Those were both expensive mistakes.

 

And that is what we have here.  It may be that you are attracted to the looks, but the question is what happens if it does not have any of the great magic we often read about here on CN that turns out to be more like cheap parlor tricks when we actually get them.  

 

If you find that you don't like it as much as some of the testaments suggest, you will take a beating on resale because, well, you take a beating on resale for anything bought new.   If you love the look of it and decide that it performs equally to your current scope and you decide to sell that, then you take an even bigger hit or resale.

 

Or, you keep them both, denying you the opportunity to recover some of those funds for a 106mm Takahashi because we absolutely know that the Tak, being a Tak will blow them both not only off the highway, but in to the weeds in the next state because Taks lenses are made from compressed  FPLZ Unicron corneas and are therefore immune to the laws of physics.

 

So, I am not going to suggest what you should buy, but I am going to suggest that things like this rarely make the difference the forum seems to suggest they will make, and what is left is what to do if the outcome does not thrill you.  

 

You are the one that has to live with that outcome, not us.  Do what you think is best for you, and ignore what we think. 


Edited by Eddgie, 29 December 2019 - 01:22 PM.

  • Dougal and db2005 like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics