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Starwave 102ED f11 (yes, ED)

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#126 jrbarnett

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Posted 20 January 2019 - 01:03 PM

Thanks Jon, I thought I was missing something crucial that would explain why a slower focal ratio scope would show a blacker sky at any given exit pupil than a faster focal ratio. I figured it was just the longer tube/baffling as Ralph said, but I doubt it is a hard and fast rule considering some tubes are not painted/flocked/baffled well and some are done extraordinarily well

Likewise surface polish, cleanliness and coating/surface suitability (for the design and glass materials), all impact scatter, ghosting, transmission and resulting contrast as well as perceived brightness,

 

Best,

 

Jim


Edited by jrbarnett, 20 January 2019 - 01:14 PM.

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#127 Astrojensen

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Posted 20 January 2019 - 01:03 PM

Objectives with longer focal lengths/higher focal ratios produce much less steep optical cone angles with cone elements closer to parallel so there is less internal tube scatter and baffling can be less critical, hence the tendency towards darker fields and higher contrast, all other things being equal.

I'm not buying that at all, I'm afraid. I've used a few homemade refractors, both long and short, with absolutely no baffling at all and when you look up through the tube against the nighttime sky, the inside of the tube is just absolutely jet black, even without any baffling at all. The slight amount of light coming from the nighttime sky and hitting the tube sides, simply isn't enough to cause harm, if the tube is just properly blackened inside. And the contrast on deep-sky objects is just as good as we expect of any refractor. 

 

It does make a difference, when observing the Moon, though. 

 

 

Clear skies!

Thomas, Denmark


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#128 25585

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Posted 20 January 2019 - 02:23 PM

I think it's nostalgia from pre-ED days. Long refractors are the quintessential icon of a telescope, the thing most people think of when they hear the word. Since the glass wasn't as good, they had to have slow focal ratios, as I'm sure you know. Nowadays we can make much faster refractors with just as good or better correction thanks to ED/SD glass and compatible mating glass. There really is no need for a super slow (say, f/15) refractor in today's day and age. There is something to be said about the potential benefits of going slow, though. In the case of this Starwave, I bet if the lenses were tuned like the recent Stowaway (re-spaced and rotated to achieve maximum correction, only so much to do with a doublet though) it would have completely color-free optics with great spherical correction. Heck, take something like an f/7.4 FC-100DF and make it f/11. You just took some of the best 4" doublet optics in the world and made them essentially perfect, just by reducing the amount of visible error (oversimplified).

 

I can see the allure of a long and slow ED refractor if it would already be at great levels of correction at, say, f/7. I considered buying one of these just to see for myself what all the fuss is (or could be) about, because it's the first pretty-slow Chinese ED doublet I've seen. If the correction was epic, I would have no choice but to try one for myself. But it seems that while it is good, it's not amazing. I will of course wait for more of Thomas' impressions, and probably be tempted again a few times. 

 

TL;DR: The only merit to long and slow refractors is that the optics can be better with lesser glass and lesser effort. Today they don't serve much of a purpose other than nostalgia. Paired with ED glass, though, a slow design could provide epic correction.

My DL Tak with its Q1.6x extender is F14. 


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#129 jay.i

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Posted 20 January 2019 - 02:42 PM

My DL Tak with its Q1.6x extender is F14. 

I have read very good things about the FC-76DCU with the EX-CQ extender, plus the Extender-Q for the Sky90 apparently fixes all of its problems? lol. The FC-100DL doesn't need to be f/14 to deliver amazing images though, and gains (what I would expect to be) very little performance which would be only visible on the most challenging of targets on a good night. Still, I have no doubt it improves things. It's just unnecessary for excellent images, and that's why we have shorter refractors now. Great views with very little CA/SA can be delivered in a more compact package, which is added convenience for everyone, especially people who don't have a lot of room for a long tube, or money/room for a mount large enough to hold a large, long refractor (5" f/12 for example). A long Unitron is out of the picture too - an FC-100DF probably puts up just as good of views and it's half the length, maybe even shorter than the long 4" f/15 Unitrons I've seen.



#130 Jon Isaacs

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Posted 20 January 2019 - 02:47 PM

Objectives with longer focal lengths/higher focal ratios produce much less steep optical cone angles with cone elements closer to parallel so there is less internal tube scatter and baffling can be less critical, hence the tendency towards darker fields and higher contrast, all other things being equal.

 

The angles at which the light enters the scope are trivial.  They are determined by the TFOV.  At the same exit pupil pupil and AFoV , these are identical in identical apertures. And how a significant amount of light would be scattered forward by a knife edge is difficult to imagine.  

 

I'm with Thomas on this . Careful tests are difficult , a 10% difference in exit pupil is a 21% difference in brightness. 

 

In the comparisons I have done between my 80 mm F/7 FPL-53 doublet (WO ) and my Meade/Mizar 310 80 mm F/11.3, the differences i saw were due to transmission . The Meade is likely uncoated . In any event,  the skies were dimmer but so were the stars . I could see stars in the F/7 that could not be seen in the F/11. And that was when tried any available eyepiece in the 310.

 

Jim:

 

I believe my WO FPL-53 doublet is LP or KU,  AT-80 LE is also. The Eon was Synta LP . The ED-80 was Synya.  

 

FPL-51 Class include WO-66, AT-72ed , AT-102ED .  

 

These are the scopes I have owned that i remember.  I have spent time with others.  I have observed a consistent difference in the color correction of these two groups,  consistent with the difference in the ED glasses. 

 

Jon



#131 jrbarnett

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Posted 20 January 2019 - 02:48 PM

I have read very good things about the FC-76DCU with the EX-CQ extender, plus the Extender-Q for the Sky90 apparently fixes all of its problems? lol. The FC-100DL doesn't need to be f/14 to deliver amazing images though, and gains (what I would expect to be) very little performance which would be only visible on the most challenging of targets on a good night. Still, I have no doubt it improves things. It's just unnecessary for excellent images, and that's why we have shorter refractors now. Great views with very little CA/SA can be delivered in a more compact package, which is added convenience for everyone, especially people who don't have a lot of room for a long tube, or money/room for a mount large enough to hold a large, long refractor (5" f/12 for example). A long Unitron is out of the picture too - an FC-100DF probably puts up just as good of views and it's half the length, maybe even shorter than the long 4" f/15 Unitrons I've seen.

But adding a tele-extender to the on-paper "already optically perfect" DL does up the target acquisition difficulty considerably.  Kind of like the astronomy equivalent of a hair shirt for anti-goto fundamentalists.  That and a 30mm Plossl will get you 200x.  :p

 

Best,

 

Jim


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#132 Sasa

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Posted 20 January 2019 - 02:54 PM

I'm not buying that at all, I'm afraid. I've used a few homemade refractors, both long and short, with absolutely no baffling at all and when you look up through the tube against the nighttime sky, the inside of the tube is just absolutely jet black, even without any baffling at all. The slight amount of light coming from the nighttime sky and hitting the tube sides, simply isn't enough to cause harm, if the tube is just properly blackened inside. And the contrast on deep-sky objects is just as good as we expect of any refractor.

It does make a difference, when observing the Moon, though.


Clear skies!
Thomas, Denmark


Alas, this is also the case of my FOA-60Q. Not much of baffles could be seen. When you look to the eyepiece from a distance, you immediately see bright ring. The telescope and the focuser would definitely benefit from a better light control. As I said, nothing is perfect.

#133 jay.i

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Posted 20 January 2019 - 02:58 PM

But adding a tele-extender to the on-paper "already optically perfect" DL does up the target acquisition difficulty considerably.  Kind of like the astronomy equivalent of a hair shirt for anti-goto fundamentalists.  That and a 30mm Plossl will get you 200x.  tongue2.gif

 

Best,

 

Jim

Very true! It narrows the field of view quite considerably. However, a 30mm Plossl in a 100/1440 refractor would provide 48x mag with just over a 2mm exit pupil.

 

That is one important thing about long refractors/slow focal ratios as well - with older eyepieces like Plossls and orthos that have very short eye relief on the short focal lengths, I imagine people liked to use longer focal length eyepieces for the longer eye relief. They don't produce enough magnification with short scopes, but a 2x Barlowed 20mm Plossl would provide 144x with a nice amount of eye relief (extended by the Barlow lens).

 

These days we have a lot more options for longer eye relief, albeit with more expensive eyepieces. The benefit of these more expensive eyepieces with newer designs (compared to a Plossl or Abbe ortho) is that they also have better correction for the faster focal ratios they may be subjected to. In that regard, Plossls/orthos are truly suited for slow focal ratios on long scopes. So now, do we not only have the technology/glass to make short "APOs" that perform as well or better as the long, well-corrected achros of yestermillennium, but we also have the technology/glass to make eyepieces with generous eye relief that perform well in said short APOs.

 

Again, going slow today with ED glass presents an opportunity for epic correction if the design and execution are good, which is why this Starwave is exciting!


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#134 jay.i

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Posted 20 January 2019 - 03:07 PM

Alas, this is also the case of my FOA-60Q. Not much of baffles could be seen. When you look to the eyepiece from a distance, you immediately see bright ring. The telescope and the focuser would definitely benefit from a better light control. As I said, nothing is perfect.

I noticed a significant white ring with looking at the eyepiece from a distance, in my TMB105, but only during daytime or lunar viewing. I wanted to paint the focuser adapter and even the machined FTF baffles but never got around to it. My FC-76DC's FTF also exhibits this. Turns out the machined baffles are quite shiny! It had nothing to do with tube baffling or flocking from what I could tell. Just to clarify, that solid white ring is from the sliding drawtube on the TMB105 that allows it to be super compact; it's not light from the OTA itself.

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Edited by jay.i, 20 January 2019 - 03:08 PM.


#135 Bomber Bob

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Posted 20 January 2019 - 04:00 PM

And comparing scopes of very different aperture is simply so difficult to do fairly that I sometimes wonder why people bother.

 

I make the comparisons out of curiosity; and, to help me decide whether hauling out the bigger gun is worth the effort; and, whether I'm gonna keep a particular scope.  A Vixen VMC200L is my largest aperture scope, yet my APM 152ED out-performs it on lunar/planetary, but the CAT is much lighter and much easier to set up & use.  I get even more selective on work nights.  My Vixen FL80S gets used a lot during the week!


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#136 Astrojensen

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Posted 20 January 2019 - 04:12 PM

And comparing scopes of very different aperture is simply so difficult to do fairly that I sometimes wonder why people bother.

 

I make the comparisons out of curiosity; and, to help me decide whether hauling out the bigger gun is worth the effort; and, whether I'm gonna keep a particular scope.  A Vixen VMC200L is my largest aperture scope, yet my APM 152ED out-performs it on lunar/planetary, but the CAT is much lighter and much easier to set up & use.  I get even more selective on work nights.  My Vixen FL80S gets used a lot during the week!

We all do that sort of comparisons all the time. In that respect, comparing a small and a large scope is fair game! You DO want to establish where on the "is-it-worth-bothering" scale any given scope is placed. 

 

I was thinking more of comparing optical quality alone, which is almost impossible, since there's so much more to a telescope than mere optical quality. Sorry for not being more specific and clear.

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 20 January 2019 - 04:12 PM.

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#137 Bomber Bob

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Posted 20 January 2019 - 04:30 PM

I was thinking more of comparing optical quality alone, which is almost impossible, since there's so much more to a telescope than mere optical quality.

 

True, and even comparing like to like can be inconclusive.  On paper, my Tak FC-50 F8 fluorite should trounce my older Swift (Tak) 838 F14 achromatic... but visually, it doesn't, so I'm keeping both.  Or, Royal vs. Unitron 3" F15s that I went back & forth over.  Better views in the former, more flexible hardware in the latter...

 

On Topic:  Based on your posts, I'd favor the F11 ED over an F8 or shorter version.


Edited by Bomber Bob, 20 January 2019 - 04:37 PM.


#138 HARRISON SCOPES

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Posted 20 January 2019 - 04:38 PM

One simple reason long refractors exhibit good contrast is actual tube length. Stray light has a much harder time reaching the eyepiece in a long black tube than a short one. The angles available for stray light are far more limited.

Edited by HARRISON SCOPES, 20 January 2019 - 05:45 PM.

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#139 Tyson M

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Posted 20 January 2019 - 04:44 PM

We all do that sort of comparisons all the time. In that respect, comparing a small and a large scope is fair game! You DO want to establish where on the "is-it-worth-bothering" scale any given scope is placed. 

 

I was thinking more of comparing optical quality alone, which is almost impossible, since there's so much more to a telescope than mere optical quality. Sorry for not being more specific and clear.

 

 

Clear skies!
Thomas, Denmark

Comparing optical quality between apertures and designs is dubious, as highlighted by you and many others.

 

I like trying various equipment, I will readily admit.  Even just for curiosity sake.  Sometimes I report them here, sometimes I don't. 

 

I like my eyepieces, and I like to use these eyepieces and mounting solutions in different telescope designs and compare how the totality of observing experience is. 

 

Ergonomics, viewing experience, optical quality, how nice it plays with my EP's all play a role.  The sum of it all is what I like to report.

 

Lunar comparisons are particularly hard, unless you match exit pupil exactly.  Even off by a bit is noticeable and throws off the comparison completely, like you also mentioned.  


Edited by Tyson M, 20 January 2019 - 04:46 PM.

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#140 aa6ww

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Posted 20 January 2019 - 06:28 PM

I never need to do calculations to explain to me what my eyes tell me when I look though a telescope.

 

The quality of "Everything" you look at in a longer tube refractor, with the same glass as a shorter tube refractor, will always be better!

 

...Ralph


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#141 mic1970

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Posted 21 January 2019 - 03:07 PM

Sadly, the scope is not as well corrected for spherical aberration as I had hoped. Inside focus the rings in the diffraction disk are sharp and crisp, while outside it's just a mush. It appears to be around 1/4 wave undercorrection, judging by how prominent the first diffraction ring is when in focus, but it was a little hard to tell, due to the mediocre seeing. There was a little too much "junk" floating around the spurious disk and first ring, as well as some faint flares hinting at slight miscollimation (but the diffraction disk inside focus was completely concentric, so I do think the collimation is spot on) but this might also be due to the seeing, so please take this with a grain of salt, until I get a night of amazing seeing, so I can test the scope more accurately.   I'm new to the technical side of scopes.  I thought the purpose of the long focal length was to eliminate spherical aberration. 

 

 

Another thing: I've seen people use the same eyepiece, for example a big, low power wide-field one, on both a f/6 and a f/15 scope and then remark just how much blacker the background is in the f/15 and how amazing the contrast is. Well, duh!  Not duh... some of use have not been playing this game as long as a lot of you. 



#142 Astrojensen

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Posted 21 January 2019 - 03:34 PM

 

I'm new to the technical side of scopes.  I thought the purpose of the long focal length was to eliminate spherical aberration.

Yes and no. Long focal length isn't needed to eliminate spherical aberration per se, but it makes it exponentially easier to do so and at the same time keep the optics simple and easy to make. 

 

 

Not duh... some of use have not been playing this game as long as a lot of you.

It isn't a matter of having played the game long, it's a matter of understanding the rules of the game, so to speak. 

 

 

Clear skies!
Thomas, Denmark


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#143 25585

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Posted 21 January 2019 - 03:56 PM

Long/er focal lengths, and that includes my DL F14, allow the use of longer FL eyepieces, that have longer eye relief.

 

With refractors there is the benefit of using any 2 inch eyepieces, something only larger SCTs allow. Newtonians are more versatile and modifiable.

 

1440mm allows me to get just under 120x with a 12mm ES 92, 111x with a Vixen 14mm LVW, 100x with a 14mm Morpheus, 50x with ES MV 28mm, 25x with TV 55mm Plossl. Etc. 

 

No problems, pure comfort, and breathtaking in a Brandon 48mm EFL. 

 

Exit pupils get too tiny so that restricts what is practical.

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Edited by 25585, 21 January 2019 - 04:17 PM.


#144 Joe Gervin

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Posted 22 January 2019 - 02:31 PM

Hi Thomas

I just received one of these scopes today. I want to use it with the small section removed & using an extension tube similar to your last image on page 5. When I removed the focuser the first part unscrewed easily but the black ring part could only be unscrewed with my son holding the main tube_ it was that tight! However,  the black ring part with the 3 screw holes attached to the main tube won't budge. I think it is cross-threaded & will be speaking to the supplier tomorrow. I was wondering if you could confirm that this part is unscrewed anticlockwise like the other parts ( I don't want to damage the scope) and also if any instructions/information came with your package.  Hopefully,  this makes sense & I will try to send photos but I'm not that technical

Again thanks in advance for any feedback

Joe



#145 Astrojensen

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Posted 22 January 2019 - 03:03 PM

Hi Joe

 

 

When I removed the focuser the first part unscrewed easily but the black ring part could only be unscrewed with my son holding the main tube_ it was that tight!

I'm guessing that you're saying that the focuser itself unscrewed from the black, threaded ring that attaches it to the tube of the scope itself. Is that so? If so, the focuser on mine sits *extremely tightly* in said ring. The ring itself was easy enough to screw in and out of either the extension tube or the main tube.

 

I must add that the focuser should not need to be removed from the black ring that goes between it and the telescope tube/small tube section.

 

 

However,  the black ring part with the 3 screw holes attached to the main tube won't budge. I think it is cross-threaded & will be speaking to the supplier tomorrow.

Mine was very tight as well and hard to loosen the first time. I needed to mount the scope, so I could grip the small tube section with both hands. It is unscrewed anticlockwise, the threads on the focuser assembly black ring are supposed to fit into the main tube, instead of the small tube section, so naturally, the threads are the same. 

 

There were no instructions whatsoever with my scope. None that I found, at least...

 

 

Clear skies!
Thomas, Denmark

 

PS: What serial number does your scope have? Mine is number 18. 


Edited by Astrojensen, 22 January 2019 - 03:04 PM.


#146 Joe Gervin

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Posted 22 January 2019 - 03:23 PM

Hi Thomas

Thanks for that. I never thought about holding the tube on the mount for a better grip! I now know it needs to be unscrewed. I'll try that tomorrow after I speak with the supplier about the problem & any other advice on the problem.

The cardboard box states _ C/No:5-177 and on the lens it states_ Sn0008

Again many thanks for the quick response

Joe



#147 Astrojensen

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Posted 22 January 2019 - 05:50 PM

Has been outside for two hours under crystal clear skies (some clouds for the first half hour) and decent seeing. Not perfect seeing, but quite good. 

 

And the lunar views were just completely, flipping outstanding. At first, as there were still some clouds and the seeing was not so good, I used just 45x (25mm Zeiss) on the bino and the images were sharp right away, even after just five minutes cooldown.

 

After the clouds disappeared the seeing improved dramatically and I could increase the power to around 115x-120x (25mm Zeiss plus either 2.6x GPC or projection with 40mm TS Superview, exact magnification not known in either case) and the views were mindblowingly good. 

 

To give you an idea of just how well this scope performs, I could discern subtle shade differences in the illuminated SIDE of the Petavius Rille... 

 

The reasonably good seeing also clearly improved the color correction to the point where I had to look carefully for it, when in best focus at 239x (4.7mm ES82), but it was there. It was fairly visible at 561x (2mm Sky-Watcher LER), but the lunar views were still very surprisingly good at this magnification. I actually spent some time looking at Petavius at this magnification. 

 

A star test at 239x on a not too bright star (Procyon) revealed a much tighter and cleaner image than last time. Best focus showed a superbly clean airy disk, surrounded by one, very crisp and well-defined ring, that was perhaps a tad too bright, but nothing serious, surrounded by a few, very faint outer rings that flared in and out in the seeing. 

 

The star test was less impressive, but more telling at 561x. The spurious disk was vaguely hexagonal, hinting at slightly pinched optics, and there were more diffraction rings to the left side than to the right, plus that the spurious disk could sometimes be seen to have a red fringe to one side and a blue to the other, instead of a symmetrically distributed halo of color. This hints at very slight miscollimation. It is entirely possible that if the collimation is improved, then so will the color correction be. I've seen this before in my 72mm f/6 ED.  

 

So, in short: Not perfect, but certainly very, very usable optics. I had a very hard time tearing myself away from the eyepieces of the binoviewer, but, alas, it's a workday tomorrow.

 

 

Clear skies!
Thomas, Denmark


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#148 jrbarnett

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Posted 22 January 2019 - 11:12 PM

The biggest appeal / advantage of the F11 refractor vs an F/7 if both glass types are the same, are the back ground skies. It's an immediate difference you don't have to wonder about if you see them both looking at the same object side by side.

 

 Nothing wrong with an F/7 ED view, not by a long shot, but the same object in an F/11 or longer scope is going to show you the same object with darker back ground skies, so you get more contrast on the object. Deep space objects just stand out more in the long tube refractor, planets have more contrast, its just a win win situation. Its an immediate difference you notice. The natural light baffle of the long tube is whats doing this, just less stray light gets to the eyepiece when you go longer.  The quality of "Everything" you look at in a longer tube refractor, with the same glass as a shorter tube refractor, will be better!

 

 The longer focal length scope doesn't even need ED glass to show this improvement. My AstroTech 102ED F/7 will show a lighter back ground sky when compared to my friends 102 F/11 Non ED refractor in the same skies. The F11 is considerably darker and objects just stand out more. Its not a slight difference, its a considerable difference in back ground skies.

 

 Focusing is another big advantage of the longer tube refractors. Focusing isn't so hair trigger, you don't have to be dead on accurate to find that one sweet spot you need to achieve focus. In short FL refractors, people talk about "Snap Focus," that one spot when focusing is dead on. APO guys act like "Snap Focusing" is something that only comes from APO refactors and that everyone wants that. 

 The reality is you get that "Snap" because you have one tiny spot on your focuser where you achieve that focal point. The shorter the focal length, the more important that sweet spot becomes, the more you need to find that "Snap". Its also more important as magnification increases. Its also more obvious when seeing conditions are better because your not fighting atmospheric turbulence which is the downside of bad seeing conditions. Its also the downside when focal lengths are shorter. Focusing is more difficult when your focal length is shorter. We know this because we rack our focusers in and out and in and out and in and out with our shorty refractors till we find that sweet spot.

 

Shorter focal length scopes made micro focusers popular, because its more challanging to find that one tiny sweet spot to achieve focus.

 

 In longer focal length scopes, you have more depth of focus, so focusing on an objects is easier. I've said this in other threads. The Classic refractor group knows all about all of this already.

As focal length increases on "Refractors" you don't just have one tiny sweet spot to focus, you have a range where the scope stays in focus. Focusing is just easier, I call it "relaxed or lazy focus."  Wind turbulence or atmospheric conditions don't disrupt focusing so much as with shorter focal length refractors. This makes the scope easier to focus and just as important,  "hold focus" in less than perfect conditions. These effects are more obvious as focal lengths increase. as you move toward F/15 focal lengths and longer. 

 

My eyes generally focus different then my friends eyes when we are out observing. On shorter focal length scopes, I have to refocus the same object a friend may have just looked at. We all do this. On longer focal length scopes, sometimes we both say the focus is dead on, with both of our eyes on the same object because of that "range" where your scope is focused, its not just a sweet spot, its a range. You can actually move the focus slightly in either direction and you will notice you are still in focus. 

 This helps again, in less then perfect conditions. The focus isn't so effected by turbulence. It also helps as your eyes get older or as your observing session is longer and our eyes get more tired, since our ability to focus isn't what is use to be.

 

One other note also, is that a 102 F/11 is not a narrow field of view telescope, as some have mentioned out here. Like any scope, if you limit your eyepiece selection to narrow field eyepieces, then blame your eyepieces on your narrow field of view not your scope.

 

1100mm F/L with a 41 Panoptic gives you 2.6 degs actual field of view.  Few objects are going to need more field of view to observe then this. Of course there are objects like the North America Nebula, or the entire Veil nebula which will require more field of view to see in its entirety, or Markarians chain, to name 3 examples. Basically the entire messier catalog can easier fit into this range, including the M31, since visually, you cant see the fine edges of that galaxy in a 4" scope.

 

. This scope to me is really the "Planet Hunter" the Non ED version of this scope claims to be. At least for a 4" refractor. Planets require a decent amount of magnification to really be appreciated. The ED glass will help considerably on Jupiter for color correction and sharpness and contrast. Its also just easier also to observe planets with longer focal length telescopes. You can hit higher magnifications without adding barlows, which to me is a huge advantage since you are trying to ring out every bit of sharpness and contrast you can, and adding more glass to the light path is never a good thing when you don't need to.

 

Once you start pushing your focal length out to F/11 and above in refractors in this aperture size, especially with ED glass, those of us who have owned and experienced longer tube refractors, F/11. F/13, F/15 and above, no longer make color correction the topic. The other real advantages of what longer focal length scopes are know for, starts to shine brighter. The overall quality of the entire view in the eyepiece becomes more the focal point, not just the color correction. 

 

Like every scope, this scope has its limitations also. Overall. its just nice to see another great idea put into a nice scope that is relatively affordable.

 

....Ralph 

Of course, the biggest advantage of an f/15 over an f/11 are the background skies...:grin:

 

That's why I am holding out for an f/15 4" ED doublet.

 

- Jim



#149 mikeDnight

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Posted 23 January 2019 - 06:11 PM

I have read very good things about the FC-76DCU with the EX-CQ extender, plus the Extender-Q for the Sky90 apparently fixes all of its problems? lol. The FC-100DL doesn't need to be f/14 to deliver amazing images though, and gains (what I would expect to be) very little performance which would be only visible on the most challenging of targets on a good night. Still, I have no doubt it improves things. It's just unnecessary for excellent images, and that's why we have shorter refractors now. Great views with very little CA/SA can be delivered in a more compact package, which is added convenience for everyone, especially people who don't have a lot of room for a long tube, or money/room for a mount large enough to hold a large, long refractor (5" f/12 for example). A long Unitron is out of the picture too - an FC-100DF probably puts up just as good of views and it's half the length, maybe even shorter than the long 4" f/15 Unitrons I've seen.

I bought a 1.6x extender Q for my FC100DC, though I didn't pay full price for it. It really is the most transparent amplifier I have ever used. Comparing the performance of my DC with and without the Q attached, I can honestly say I could detect no observable difference in star image quality or colour correction, which is superb at F7.4. Where the Q really shone though,  was in its ability to amplify the image and remain utterly invisible. I remember slowly studying the high spring moon while around first quarter with the Q and my binoviewer with 2x barlow, and being in utter disbelief at the incredible level of sharpness. My stomach rolled as I unexpectedly and suddenly drifted over the edge of the Apennine mountains. The extender Q is not essential for getting the FC to perform with text book perfection, but it is a wonderful tool for pushing the scope into the realms extreme high power in conjunction with a binoviewer and 2x barlow. 

I admit this new F11 ED appeals to me as I'm primarily a lunar and planetary nut these days. I'm also certain it will be a great deep sky scope, having used a 102mm F13 achromat for many years for fuzzy hunting. That 102 F13 gave some terrific views of brighter DSO's, and I remember thinking while looking at M82 "wow, why would anyone want anything more than this"!? Even today, over thirty years down the line, my only telescope is still a 4" refractor, though now its a Tak, and I'm am still totally content. 

I'd love to have a classic Unitron to observe with and to cherish, but I think with modern glasses and better coatings, the new F11 ED and definitely the Tak FC100D, will give the Unitron serious competition. 


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#150 daquad

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Posted 23 January 2019 - 07:40 PM

I bought a 1.6x extender Q for my FC100DC, though I didn't pay full price for it. It really is the most transparent amplifier I have ever used. Comparing the performance of my DC with and without the Q attached, I can honestly say I could detect no observable difference in star image quality or colour correction, which is superb at F7.4. Where the Q really shone though,  was in its ability to amplify the image and remain utterly invisible. I remember slowly studying the high spring moon while around first quarter with the Q and my binoviewer with 2x barlow, and being in utter disbelief at the incredible level of sharpness. My stomach rolled as I unexpectedly and suddenly drifted over the edge of the Apennine mountains. The extender Q is not essential for getting the FC to perform with text book perfection, but it is a wonderful tool for pushing the scope into the realms extreme high power in conjunction with a binoviewer and 2x barlow. 

I admit this new F11 ED appeals to me as I'm primarily a lunar and planetary nut these days. I'm also certain it will be a great deep sky scope, having used a 102mm F13 achromat for many years for fuzzy hunting. That 102 F13 gave some terrific views of brighter DSO's, and I remember thinking while looking at M82 "wow, why would anyone want anything more than this"!? Even today, over thirty years down the line, my only telescope is still a 4" refractor, though now its a Tak, and I'm am still totally content. 

I'd love to have a classic Unitron to observe with and to cherish, but I think with modern glasses and better coatings, the new F11 ED and definitely the Tak FC100D, will give the Unitron serious competition. 

I love long focus refractors, being the owner of a 4" f/15 Jaegers and a previous owner of a 4" f/15 Unitron. Maybe I'm splitting hairs, but I think, in your last sentence, your characterization of the Tak and the Kunming f/11 ED is an understatement of their optical excellence. 


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