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5" APO verses BEST 7" MAK CASS

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#1 De Lorme

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Posted 18 January 2019 - 02:16 PM

Hello everybody,

 

I really like my ES 5" FCD100 but at times I would like a little more power with the same optical quality I get from the FCD100.

Would a  7"  Mak Cass deliver? If so what brand makes the best?  Since my skies here are mediocre I just look at open clusters the moon and planets which I think the Mak Cass should be able to handle the fov.

 

Thanks for all opinions and advice.

 

Clear Skies,

 

De Lorme



#2 Codbear

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Posted 18 January 2019 - 02:48 PM

With the "what brand makes the best" question, you are opening yourself up to the entire gamut of Mak-Casses, which is indeed a wide range of quality and cost.

 

I can only speak from personal experience of course. I have a Questar 7" and have owned an AP130GT and currently own an Esprit 100, TV NP127 and TEC180.

 

My Questar so thoroughly destroyed my AP130GT that I sold it. My Esprit 100 is a grab n go so that serves a different function. I have kept my NP127 however, since it gives incredible wide-field views with pinpoint stars and is a great complement to my Q7. Since you are looking for more power though, the NP127 is probably not the route to take.

 

A shootout I performed between the TEC180 and the Questar 7 was incredibly close but, with no central obstruction, the 180 won - as expected. The difference of course is my 180 is about 4 ft long and weighs close to 40 lbs with rings, while my Q7 weighs in at 19 lbs and is less than 2 ft. in length.

 

I hope this has helped.

 

Sam


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#3 Astro-Master

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Posted 18 January 2019 - 03:10 PM

I have the Russian Intes 180 Mak-Cass with the 1/10 wave optics.  It was better on double stars than my friend's TEC 140.  I paid $1400 for it used about 4 yrs. ago.  I had to buy a moonlight focuser, because the focuser was bad.

The f ratio is f 10 so its better on DSO's.


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#4 De Lorme

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Posted 18 January 2019 - 03:17 PM

How Good or bad are the Sky Watcher and Orion Mak Cass?   I can easily hit 300x with the 5" FCD100. Looking for much higher power on the moon and planets.  Is the optical quality of the Sky Watcher or Orion of excellent quality that it would take me to 500x with a cooperating sky of course?


Edited by De Lorme, 18 January 2019 - 03:39 PM.


#5 photoracer18

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Posted 18 January 2019 - 04:13 PM

If you really want an MCT that better than a 5" APO I suggest one of Yuri's from TEC. But it will cost more than the APO for sure. An Intes in the 7-9" would likely also. In reality the seeing will determine how high you can go, and for Lunar and planetary work you need one of those once-in-a-lifetime heavy, still air conditions of pre-fog (at least in my Mid-Atlantic region where I have had only one useful event of that in about 10 years [Mars 2005 Opposition]) when I reached over 500X with both my early first run C9.25 and a Jaegers 6" F15 built by Barry Griner (D&G). Most of the time in my region 200x is about all the power you can use, especially on Jupiter, due to seeing conditions with any scope.


Edited by photoracer18, 18 January 2019 - 04:14 PM.

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#6 junomike

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Posted 18 January 2019 - 04:34 PM

How Good or bad are the Sky Watcher and Orion Mak Cass?   I can easily hit 300x with the 5" FCD100. Looking for much higher power on the moon and planets.  Is the optical quality of the Sky Watcher or Orion of excellent quality that it would take me to 500x with a cooperating sky of course?iM

IME exceeding 300X is rare due to the seeing, and 500X is something very few have access to (due to location)

For those types of magnifications a large mirror (10"+) is best as things get dim otherwise (at lest for me).


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#7 spongebob@55

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Posted 18 January 2019 - 05:07 PM

Hi De Lorne,

I had a 180mm Orion and it was fantastic.  Tight pinpoint stars and great contrast.  I can't say if it was better than a 5" APO, but with the convenience of its size and weight, (and price) I wouldn't have bothered.  I just recall 2 experienced buddies of mine looking through it and saying 'wow'.....

I ended up selling it b/c I only had a GEM at the time, and I found repositioning sitting, diagonal and EP annoying and somewhat painful due to multiple orthopedic maladies.  .   But now I expected to buy another since I now have a good alt/az mount.

One thing to know is that if you buy a Mak from Orion, you can check it out for 30 days.  If you don't like it for whatever reason, you can return it for $9.95, no questions asked, by just printing out a label online on their site and shipping it from a UPS store.

Good luck

SB



#8 De Lorme

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Posted 18 January 2019 - 05:10 PM

A 10" used SCT is within my price range but the optical quality isn't do to my dissatisfaction of not knowing just what your

getting. Would rather stay smaller and sharper than bigger that can't handle being pushed.  

 

Reviews so far on the Orion Mak Cass are good and it's a little cheaper than the Sky Watcher but if the conditions are right can it take me to 500x? 



#9 SeattleScott

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Posted 18 January 2019 - 05:14 PM

Keep in mind a Mak is not nearly as efficient. Maybe 70-75% of the light reaches the eyepiece compared to maybe 97% with your Apo. Let’s round up to 75% for the Mak and 100% for the Apo. So the Mak has twice the light grasp but the views will only be 50% brighter. An excellent one might get you to 450x. In practice I normally hear about people pushing these 7” Maks to about 350x. Although maybe their skies are not as steady as yours. If you really want 500x I think you are looking at a premium 8” Mak ($$$$$$).

Scott
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#10 SeattleScott

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Posted 18 January 2019 - 05:17 PM

A 10" used SCT is within my price range but the optical quality isn't do to my dissatisfaction of not knowing just what your
getting. Would rather stay smaller and sharper than bigger that can't handle being pushed.

Reviews so far on the Orion Mak Cass are good and it's a little cheaper than the Sky Watcher but if the conditions are right can it take me to 500x?


I think the SW comes with more accessories. So it depends on whether you need the diagonal and if you like the paint job on the SW. Seems like people either love it or hate it.

Scott

#11 De Lorme

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Posted 18 January 2019 - 05:21 PM

Thanks spongebob@55, and everybody else for the info.

 

Spongebob55, when the seeing would allow what range of high powers could you push the Orion Mak?  Here in Killeen I can really only observe open clusters, gobblers{to some extent}the moon{which I really like}and the planets.

 

What alt/az mount do you have?  Like you I'm tired of moving the diagonal to a better position.  Is the focuser workable?

Doesn't have to be great just usable.

 

Clear Skies,  De Lorme



#12 De Lorme

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Posted 18 January 2019 - 05:24 PM

I have a BBHS so I wouldn't need the diagonal.



#13 spongebob@55

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Posted 18 January 2019 - 05:51 PM

Thanks spongebob@55, and everybody else for the info.

 

Spongebob55, when the seeing would allow what range of high powers could you push the Orion Mak?  Here in Killeen I can really only observe open clusters, gobblers{to some extent}the moon{which I really like}and the planets.

 

What alt/az mount do you have?  Like you I'm tired of moving the diagonal to a better position.  Is the focuser workable?

Doesn't have to be great just usable.

 

Clear Skies,  De Lorme

I would be able to use my 10mm regularly, but using a 7mm was rare due to the normally less than good seeing here in NJ.   Pretty much like my SCTs......   I too would use it for the moon, planets and bright DSOs.   I remember vividly the view of M13....spectacular.

I have the Orion Atlas Pro Alt/Az.   Works great, except for the lack of a cord wrap setting, so you have to be careful with the cord, and also a very good battery supply since it uses more power than most.

The focuser is just like all the other mass SCTs and Maks out there.  Its fine.  I use a larger knob to get a little more accuracy on the focus.  It should snap to focus if its acclimated  (or insulated)

Regards

Bob



#14 luxo II

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Posted 19 January 2019 - 06:30 AM

De Lorne I’ve been and done this. A couple of years ago I bought a nice TS Photoline 130mm ED triplet APO mostly to see if the refractor hype really stacked up.

I also had a SW. 180mm f/15 mak with excellent optics, a really nice scope - and put the two of them side by side on a push-to mount (Losmandy AZ8).

In short side by side the mak was the scope I used most, by far. There really wasn’t anything that the refractor could do that the mak didn’t do better.

End result was I concluded the refractor hype was just that - hype - and sold the APO.

IMHO the SW 180mm maks are a bargain - they are a very nice size for a portable scope, their optics have been consistently good lately.

Visually at a dark site they’re just big enough to pull in many galaxies which are simply beyond 5” refractors, and on the planets it will slay the refractor for resolution.

A secondhand Intes-Micro M715D - if you can find one - would probably have slightly better optics for extreme high power however the field of view is smaller, whereas the SW mak has a 2” back and can work quite nicely at 60X with a 2” 50mm eyepiece.

I now have a 9” mak as my only scope.

Edited by luxo II, 19 January 2019 - 06:33 AM.

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#15 Asbytec

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Posted 19 January 2019 - 07:08 AM

How Good or bad are the Sky Watcher and Orion Mak Cass?   I can easily hit 300x with the 5" FCD100. Looking for much higher power on the moon and planets.  Is the optical quality of the Sky Watcher or Orion of excellent quality that it would take me to 500x with a cooperating sky of course?

Hitting 300x in your FCD100 provides a 0.4mm exit pupil and a workable image for a range of high resolution observing.

 

I generally find about 0.6mm exit pupil about the maximum for Jupiter with my Orion 150 MCT. And that is not definite because that is where the eyepiece magnification step takes me. It could be a little higher, but it's not 300x (0.5mm exit pupil) because the image is too dim for my eye to resolve small planetary detail. Using that as a guide, I would imagine a 180 MCT could hit 290x or more on Jupiter without much trouble.

 

I suspect you can hit higher magnification in your 127mm clear aperture because it has nice throughput and contributes to the image surface brightness giving you a little more oomph at smaller exit pupils. In comparison, that woudl be 375x in my 150 MCT and way out of the question. Not so much because the image "breaks down" because it's a bad optic, but because the image is too dim up that high at very small exit pupils...at least for Jupiter's bright low contrast detail. The larger high contrast detail is still seen, but forget the low contrast detail. YMMV due to physiology and light throughput.  

 

Mars is a separate issue altogether. I have hit well over 400x on Mars to good effect. I believe Mars surface brightness is a little brighter and it's major features are higher contrast. So, on the eye, the image can survive smaller exit pupils. Same with Saturn's higher contrast features. I observed Saturn at 300x regularly, when it was well placed in the sky a few years ago, in a 150mm aperture. The 180mm MCT can probably hit 400x easily enough (at ~0.5mm exit pupil). 

 

Lunar is the same, really, about 0.5mm exit pupil (300x) or smaller...down to about 0.4mm (375x) or so is fine for the 150mm MCT. Approaching 0.3mm exit pupil (450x), it begins to dim noticeably with no new detail seen up that high, anyway. In fact, much higher and you might begin to lose detail as the image dims further. Scaling that up to 180mm aperture should take you well above 300x for lunar observing when seeing permits, maybe as high as 450x, give or take. 

 

So, hitting 500x on all planets and the moon is kind of a mixed bag of answers. So much has to do with exit pupil and the resulting magnification and image surface brightness as well as the throughput of your telescope (lenses, mirrors, coatings, obstruction, etc.). A 180mm MCT might do 500x fairly well on bright high contrast objects like the moon, but I think Jove will be dimmed and washed out up that high. Mars will likely be okay, still, I've had good views at aout 450 +/- in a 150mm aperture MCT under good tropical seeing. 

 

Some will say optical quality matters in terms of image surface brightness. Maybe. The Sky Watcher and the Orion version are not premium optics, but they are not bad optics, either. They can take magnification as well as most and usually, when prepped for observing, they are only limited by the low contrast detail and low surface brightness of the image itself. 


Edited by Asbytec, 19 January 2019 - 07:11 AM.

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#16 astroneil

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Posted 19 January 2019 - 07:10 AM

nota bene;

 

https://www.cloudyni...tural-exchange/

 

 

et

 

 

https://www.cloudyni...v-in-the-field/


Edited by astroneil, 19 January 2019 - 07:29 AM.

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#17 bobhen

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Posted 19 January 2019 - 08:12 AM

HERE is a link to a review between a Tak TOA 130 and a STF 180 Mirage Mak. Both are very high quality scopes. 

 

Bob



#18 CHASLX200

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Posted 19 January 2019 - 09:56 AM

My SW150 Mak would just beat out my AT102ED on planets.  It was a very sharp Mak. I would say a top of the line 7" Mak will beat out most any 5" APO on the planets when it comes to showing color on Jupiter.


Edited by CHASLX200, 19 January 2019 - 09:57 AM.

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#19 Eddgie

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Posted 19 January 2019 - 11:26 AM

How Good or bad are the Sky Watcher and Orion Mak Cass?   I can easily hit 300x with the 5" FCD100. Looking for much higher power on the moon and planets.  Is the optical quality of the Sky Watcher or Orion of excellent quality that it would take me to 500x with a cooperating sky of course?

I am not giving you an definitive answer.  Rather, it is better to provide some objective testing and let you judge for yourself.The quality varies greatly on these imported MCTs:

 

http://teleskop-spez...-teleskope.html

 

Few are excellent, many are good, and a few are not so good.

 

Here is a very large compilation of tests with various size MCTs.  While there may not be many 180mms in the test, there are plenty of 6" and 5", and one would think that if they quality on the smaller siblings varies to such a great degree, it should not be expected that the larger scopes would do better.

 

Scope #49 in the tests above is a Skywatcher 180.  You can see some SA, but more importantly, there is a significent S zone at 60%.   This scope is not a bad scope, but it is not at all an excellent scope.  Ditto for scope #58. A touch more SA, and perhaps a zone error close to center.  Again, not great, not bad.

 

By comparison, take a look at scope 88.  This is a Celestron EdgeHD 8".  Very smooth optics with no sign of zonal error or turned edge, and very well corrected for SA.   Better than the two MCTs above.. I know, that is heresy that an SCT could be made better than an MCT, but some are.

 

If you want to see a good example of a bad scope, the Meade 8"  #144 is one of the poorest in all of these scopes tested.  How that scope could get past a good QA inspection?

 

Some further musing..   Skywatcher 120E (#68 in the above testing).  This scope has a reputation for good optics.  The one I owned was quite excellent.  The one tested here show very good quality. Scope #60 is another 120ED, and once again, very nice optics. Scope #1.. Another 120ED and another nice quality instrument. I owned one of these and quality was excellent.   It is not surprising to me that 4" and 5" refractors often put up higher contrast images than many 5" and 6" MCTs or SCTs.   

 

Scope #9. Vixen 102FL.  Not many bench tests, but lots of subjective tests (which is hard to have high confidence in) say excellent.  This tests shows excellence. 

 

CN would have you believe that every MCT ever sold had great optics.   I would treat those claims with a healthy dose of skepticism. 

Skywatcher 120ED?  Yeah, that one has enough published test data to expect it to be very good to excellent.


Edited by Eddgie, 19 January 2019 - 11:44 AM.

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#20 terraclarke

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Posted 19 January 2019 - 12:43 PM

You might just consider a used C9.25. About the same cost, weight, length, and cool down time as a 7” Mak, 75% more surface aperture for light gathering, and about a third more aperture diameter for angular resolution.  The longer focal length (higher F-stop) produces darker fields and much more Mak-like views than a C8, so very nice on planets, globular clusters and double stars. Sorry, I didn’t mean to side-track things.


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#21 Magnus Ahrling

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Posted 19 January 2019 - 03:02 PM

That Teleskope-Spezialisten link is very intressting to scroll through. 

 

Magnus



#22 De Lorme

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Posted 19 January 2019 - 06:17 PM

Thanks Eddgie, The  for the advice.   My concern  was  consistency of the optics. I would probably go with the Sky Watcher

because I get the impression there willing to make sure that the one you get won't be mediocre.

 

Have to think about this a bit.  Thanks all for the great advice.

 

Clear Skies,

 

De  Lorme



#23 Asbytec

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Posted 19 January 2019 - 07:40 PM

That Teleskope-Spezialisten link is very intressting to scroll through. 

 

Magnus

It is interesting to see the actual star and Ronchi tests. One thing I find interesting is the MCT star tests, they look pretty ugly and different of both sides of focus. But, we have to be more careful when evaluating the star test of these complex designs because they do not test like a parabola which can form a more or less spherical wavefront with some classic primary spherical present. MCTs have a large amount of secondary spherical induced by the meniscus as a function of it's design. However, the combination of higher order SA from the meniscus cannot be canceled by lower order SA from the primary. They will not test in the more classic sense of primary spherical aberration alone including the shadow breakout (the preferred 33% obstruction aside). And if done well, the result is a very low RMS value and a high Strehl.

 

The result is not a spherical wavefront, but one that approximates a sphere by smoothly undulating around a reference sphere. The resulting undulating waveform affects the star test and they will not be the same on either side of focus as each zone comes to focus in a slightly different point. If you notice, almost consistently, the MCT has a brighter outer ring outside focus (marginal zone) and some indication of an inner ring inside focus (paraxial zone). It's almost and generally like an undercorrected condition with each zone focusing differently. This also seems to show in the Ronchi tests, but it is not a classic undercorrection of primary spherical alone and the star test should not be interpreted as such. I believe this is what Roland was talking about in his (in)famous article on complex designs. They can be made to "please the star test crowd" using an asphere and touching up some zones, but performance in focus is not really improved. 

 

What the star tests seem to be telling me is the effect of balancing the higher order from the meniscus with opposite amount of lower order from the primary is working as deigned and it suggests no aspheric term was employed (often debated and seen in the Meade). The desired wavefront is being achieved somewhat consistently. Then performance is improved further with balancing with defocus to the point along the caustic of best diffraction focus (at the ~70% zone) where spherical aberration is again minimized.

 

The MCT has no higher order term built into the meniscus as an SCT does, and you may notice the SCTs tend to test more in a classical sense (with the higher order term dealt with) and any residual lower order SA can be easily seen. Not so in the MCT because of it's complex design. This ugly star test does not mean the MCT is a bad optic. In fact, there can be as much as 0.4 PV wave of higher order SA and the MCT will still be diffraction limited. This is because each undulation of the resulting wavefront closely approximates a reference sphere (perfect wavefront) and each zone covers only a small area of the wavefront and the RMS can be very good.

 

Fast APOs also have residual higher order spherical due to their steeply curved surfaces. In this sense, Maks kind of are refractor-like. :) 

 

http://www.csun.edu/.../startest2.html

 

Some pertinent quotes from the link above:

 

"When the optical system gets more complex than a simple parabolic mirror, then there are inherent aberrations that affect the star test."

 

"Machines exist now that can lay down a 1/20 wave or better spherical surface on a piece of glass without any human intervention."

 

"In this pure form, the Mak-Cass has left over 5th order aberrations and, depending on design, these can be less than 1/10 wave on the wavefront."

 

"By the way, fast Apo refractors have these same aberrations also. The RMS value will be better than 1/50 RMS and the Strehl ratio will be exceedingly high."

 

"When tested on the night sky, the inside and outside diffraction patterns will be quite different."

 

"I can tell you that it is easy to do some rough compensation with quick local polishing at several zones to get more equal inside and outside star patterns, but the result will almost certainly be a loss of contrast."

 

More info here:

https://www.telescop...n_telescope.htm

 

"An interesting aspect of the commercial Maksutov-Cassegrain is the question of its star test. There is a notion that its optics has special properties, making it sort of exception in that its intra and extra focal pattern are not supposed to be identical, even when it is near perfectly corrected. Or, put somewhat differently, that it doesn't need to have near-perfect star test for near-perfect performance.

 

The answer to this special status is in its higher order spherical aberration. Due to its steeply curved optical surfaces, especially those of the meniscus corrector, Maksutov-Cassegrain systems generate 6th-order spherical aberration that can't be cancelled (w/o aspheric surface terms), only minimized by balancing it with the 4th-order aberration. While roughly as much noticeable in the star test as the lower-order spherical aberration for given P-V wavefront error (FIG. 189), the balanced form is considerably less detrimental to image quality." 


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#24 luxo II

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Posted 20 January 2019 - 02:44 AM

Asbytec the star test appearance depends on the type of mak. I agree for the SW 180 maks there is a difference between inside and outside focus - and in addition some spherochromatism is visible if you look very closely.

But in the case of my MK91 (rumak), MN56 (Intes mak newt) and the intes M715D (also a rumak) the appearance of the star test on all of these inside and outside focus is precisely identical and spherochromatism is not visible.

Regarding the OPs question there is a difference between

a) “the best 7” mak - bar none” (the unicorns) - vs
b) “the best mak you can currently buy new at reasonable cost” vs
c) “the best mak you can currently buy new irrespective of cost”

The SW 180 is in category (b), while Questar is in ©. Intes / Intes Micro is the only one in (a) - for a 7”.

Edited by luxo II, 20 January 2019 - 03:50 AM.


#25 Asbytec

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Posted 20 January 2019 - 03:15 AM

Asbytec the star test appearance depends on the type of mak. I agree for the SW 180 maks there is a difference between inside and outside focus - and in addition some spherochromatism is visible if you look very closely.

But in the case of my MK91 (rumak), MN56 (Intes mak newt) and the intes M715D (also a rumak) the appearance of the star test on all of these inside and outside focus is precisely identical and spherochromatism is not visible.

Sure, you're right. I was only speaking to the Gregory MCTs in the test. 




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