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5" APO verses BEST 7" MAK CASS

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#101 Kevin Barker

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Posted 01 February 2019 - 05:05 PM

The allure of the Mak-Cass is real to me, as my observing interests are mainly planetary.  They are short, easy to mount, and their long F/L makes it easy to achieve the magnifications needed.  I owned a TEC6 f12 which I compared extensively with my 4" and 5" apos.  I concluded that for planetary it was likely equal to a 4.5" apo.  My experience with the TEC6 led me to purchase a TEC8 f15.5.  I used that to compare with my 6" and 7" apo and concluded it was probably the equal to a 6.5" apo for planetary.  Fast forward to today and I have a TEC7 f15.  Given the established data points, if one extrapolates the performance it would therefore be a safe assumption that this quality 7" MC would be the equal of a 5.5" apo for the planets. Certainly the TEC7 would outperform a 5" apo.  I've had mine out with my 130GT and can confirm this to be so.  Again, I can attest only to planetary.

 

Some notes from the field:

1) MC's need significantly more time to cool down. As such, not an optimal quick peek scope.

2) MC's are more prone to be affected by seeing by virtue of the CO. On bad-seeing nights, one would probably do better with a 4" apo than a 6" MC. Same holds true for a 5" apo vs a 7" MC.  Apos are more consistent more often. 

3) The TEC8 f15.5 gathered significantly more light than the 6" apo. Whereas I found Jupiter too dim at 300x with the apo, it was still pleasing with the MC.

 

Just my experience, hope it helps.

 

-Evan

Interesting comments. My experience with some large Maks (I own 6,7 and 8 inch Intes Maks) is on planetary low contrast the 7 inch Mak (IM703 f-10) will not quite keep up with my Zeiss APQ 130/1000 which is a true apochromatic refractor. The 8 inch Mak (IM815 f-15) will beat out the Zeiss APQ130/1000 but not by much. 815 has 24% CO and the 703 (32%).

 

I wonder when folks say a Questar 7 with 33% CO beats out a 5 inch Apo on planetary whether the apo being compared are as good as say a Zeiss APQ or a Tak TOA  on the low contrast planetary stuff etc I have yet to see my IM 703 do it. But then again seeing is believing. Maybe I have yet to get the very best of seeing where the 7 inch  Mak can win??

 

All three of my Maks are collimated and I live in a temperate climate.

 

On deep sky the 7 and 8 inch Maks will go deeper than the APQ 130 refractor, but the refractor still shows some of the hard to see details in nebulosity due to it's high contrast for it's lower image brightness.

 

I spent quite a bit of time with my 6 inch f-10  Mak IM 603 over Xmas when travelling around in a motorhome. I was really pleased with the images it produced. I did not have a refractor next to it but suspect it was producing deep sky images not far from what a 4.5-5.0  inch apo would produce. I did not use it on planetary. At a star party other observers using large Dobsonians (10-20 inches) kept coming back for views. Although dimmer the IM603 was delivering razor sharp images.


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#102 Kevin Barker

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Posted 01 February 2019 - 06:24 PM

Further to my comments above on a 7 inch mak. I corresponded with the previous owner of the 703 deluxe I own. 

He also owned an Astrophysics 155 refractor. He told me he felt the Mak was about the same on deep sky viewing but the 6 inch refractor was  a bit better on planetary. 

 

My twin brother owns an excellent SW 180 and we have compared 7 inch Mak's over a couple of evenings. The f-15 SW did seem to show a bit more low contrast detail on Jupiter. (Pretty close though). The SW also  showed a few extra faint stars in open clusters but this was also quite subtle. We would have used similar eyepieces.

 

Both scopes have snap into focus views when cooled. The Intes 703 seemed to cool a bit quicker than the SW 180. The SW 180 is a fair bit heavier than the IM 703. From the defocused star images the IM 703 seemed to have slightly more CO.


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#103 De Lorme

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Posted 02 February 2019 - 01:15 AM

Thanks Kevin for your thoughts also.  The 7" Sky Watcher came day before yesterday{Wednesday}and I've got it mounted on the AVX with the bubble wrap around the tube,dew heater}{with battery on top}and black flocked dew shield done.  Looking

through the collimation cap with the scope pointed at the wall the collimation looks just about perfect with the 7 o'clock position just ever so slight bigger than the 1 o" clock. The secondary shadow was perfect so I left it alone. Will do a star test just to see how far off it really is. My wife could not tell a difference. 

 

Supposed to be cloudy and rainy for the foreseeable future. Will report back first chance I get to look up.


Edited by De Lorme, 02 February 2019 - 01:16 AM.


#104 precaud

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Posted 02 February 2019 - 09:53 AM

Hope you enjoy yours, DeLorme. The SW180 is quickly becoming my favorite scope. Had mine out again last night and was smiling the whole time.

My 8" dob is feeling increasingly redundant. It told me so as I walked by it this morning...

 

(BTW, don't count out the stock 2" diagonal, its well-made with 3-point-silicon-mounted mirror. Mine is superb.)


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#105 Max Lattanzi

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Posted 02 February 2019 - 11:34 AM

If I may, I would add a swift personal experience to Evan's and Kevin's contributions above.

 

As a matter of fact, I've had here for several months two SW180, one Meade Mak 7", two FS-128, one LZOS 130/9.25.
Well, given the instruments are perfectly (and I mean perfectly) collimated and cooled, there are still differences.

 

Maks are handier and easier to carry around (although the FS-128 it remarkably remains the lighter of all the OTAs above).
And brighter, of course (not twice as bright, but a good 40% yes).
And yes of course they are much cheaper.
And if you just have a quick shallow look, you may think they mimic, if not overtake, the refractors (I am talking planetary).

 

But, yes, they are *extremely* more demanding in terms of seeing.
Furthermore, if you look well, there are some subtle low contrast features that in the Maks are *way* closer to the threshold of undetectability; so much that, sometimes, they become plainly invisible.

In short, in all these months, there was never something the three Maks above showed (equally well, I have to say), that the three Apos did not show as well (slightly dimmer, of course).

The opposite was not true. Several times.

 

And this was always "none of the three" and "all of the three". So it is a clear (albeit subtle, but still clear) and consistent difference in rendition.

 

Moving to TEC (i.e. scaling up the quality of Mak manufacturing), my sole experience is with the TEC 250/20, which is a truly excellent instrument; but certainly not up to the 200ED/9 I had it against.

Again, I am talking planetary.

Unfortunately I did not have the occasion of a side by side with the AP180EDT, which would have been interesting, given how close the AP180 and the 200ED were in several occasions. So cannot say anything first-hand.

OTOH, I recall well that Roland always reported that his 10" Mak was overtaking the 180EDT in excellent seeing. But "as soon as the seeing started deteriorating" (if I am not mistaken he used exactly this expression), the 180EDT pulled ahead.

 

Once more, price-wise there is simply no contest.
Performance-wise things are bit different, and certainly less tranchantes.

 

Hope these impressions can be of help.
-- Max

 

 

Disclaimer: as said more than once, and despite running something called "Refractorland", I own and (happily) use at least as many (if not more) Maksutovs than Refractors.
So I have really zero bias in this regard; not to mention obviously the very highest esteem in the work and achievements of Dmitrij Dmitrievič.


Edited by Max Lattanzi, 02 February 2019 - 11:37 AM.

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#106 vahe

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Posted 02 February 2019 - 12:21 PM

"Moving to TEC (i.e. scaling up the quality of Mak manufacturing), my sole experience is with the TEC 250/20, which is a truly excellent instrument; but certainly not up to the 200ED/9 I had it against.

Again, I am talking planetary.

Unfortunately I did not have the occasion of a side by side with the AP180EDT, which would have been interesting, given how close the AP180 and the 200ED were in several occasions. So cannot say anything first-hand.

OTOH, I recall well that Roland always reported that his 10" Mak was overtaking the 180EDT in excellent seeing. But "as soon as the seeing started deteriorating" (if I am not mistaken he used exactly this expression), the 180EDT pulled ahead."

 

 

And speaking of TEC 250/20 I sold mine a couple of months ago, I owned this Mak for exactly 20 years, but the old age along with a major surgery forced me to give up this magnificent instrument as I could no longer carry and mount it in our backyard. Looking back at the big Mak the cooling was always a real issue but once I learned to deal with this limitation it offered superb high contrast planetary views.

.

Fortunately some 10 years ago a TEC fanatic contacted me and offered to sell me his TEC 200/20, I bought it, it was the very last one produced in 2002 and had the same 22% co, it is much lighter and easily portable for me at my old age. After that Yuri switched to 200/15.5 which turned out to be more popular model.

The 200/20 came with two internal mixing fans at opposite ends of Ota, I wrap it with 1/2" foam insulation and that really makes a big difference. 

.

Under excellent seeing the 200/20 outperforms my AP 155EDT f/9, surprisingly at higher powers the Mak offers better contrast on Jupiter than the refractor, I attribute this to dimmer image in the refractor affecting its contrast compared to the Mak.

.

Vahe 


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#107 Kevin Barker

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Posted 02 February 2019 - 02:49 PM

The insights from Max, Vahe and de Lorme and others are fascinating.

 

I certainly hope the SW 180's being sold are as consistent as the sample my twin was sold.

It is interesting comparing a 1/3 CO obstructed Mak of larger aperture with a smaller refractor.

There is an old wisdom that a reflector's aperture minus the central obstruction will show similar detail in planetary.

This approximation is probably about right if the reflector has a CO of around 1/3 or 33% of it's aperture.

There is of course the assumption that the optics are of a high quality, collimated and cooled. Also that seeing is such as to facilitate the scope's potential. The comparable refractor also needs high quality optics. I suspect SA has a greater effect on reducing contrast than a small amount of CA.

 

As the CO reduces the differences between an obstructed scope and an unobstructed one of the same aperture gets smaller and smaller.

So it is no surprise that a 200 mm f-15.5 Mak with 24% CO ?? may outperform an AP 155. Perhaps at 20% obstruction has little effect on contrast. Another example would be my twins 180 SW which outperforms his 115 mm ED doublet on Jupiter's low contrast stuff.

 

One thing to consider is the view through a 33% CO Mak scope compared to an unobstructed refractor with an aperture slightly more than the Mak's minus it's obstruction. It is to some extend apples v oranges. It is my experience the subtle low contrast garlands and equatorial belt etc are ever so easier to see with the refractor. Some may not be picked up by the Mak but might be seen with patience. Sharper higher contrast features appear a bit sharper in the unobstructed scope(Yes a fair bit dimmer if at the same mag) but they are also there in the Mak albeit a bit fuzzy.

If comparing similar exit pupils, there is no doubt the larger aperture will take more magnification. The Mak also has better resolution.

 

When Jupiter comes around again I will certainly test it out again with the 130 apo and my Intes 703. It will be interesting to confirm if there are certain features visible in one scope which are invisible in the other.

 

The Mak is a lot easier to mount. They are so compact compared to refractors around f-8.

As an aside for many years I did not see the Trapezium's F star in my 80 mm f 1-.5 refractor.  I would try every time I could. One evening it showed perfectly. Perhaps there will be a day when the Mak will show something my venerable old APQ will not show?? My impression so far is this will not happen but we will see......


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#108 De Lorme

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Posted 02 February 2019 - 03:12 PM

Thanks Precaud,Max,and Vahe, for your comments. This is so exciting.  Was just looking for a little more ump in magnification{Oh! alright I was looking for a big UMP LOL}from my 5" FCD100 but could not afford a real 6" triplet.

 

To me it's the quality of{and of course the figure}of the glass then the size. 

 

Precaud,{and everyone else}when at high magnification{starting at 275x}does your 7" Sky Watcher{or any other 7" Mak Cass} stay razor sharp on the moon and the planets? Just how high of consistent magnification on the moon and planets have you been able to go when the seeing cooperates?  If the seeing in Killeen Texas is bad the 5" FCD100 doesn't do well on deep sky but I can still look at the moon which seems to do better with bad seeing.

When viewing{at low powers}open clusters and gobblers at around 75x to 250x are the stars still pin points of light like very good refactors?

 

Thanks for telling me.

 

Clear Skies,  De Lorme



#109 Stopforths

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Posted 02 February 2019 - 03:33 PM

Vahe's observations re 155 astro physics versus 10 inch f20 mak doesn't surprise me.  The 8 inch will be brighter have better resolution and even contrast given its only got a 22% obstruction.

 

They are both made as well as possible this is exactly what would be expected. I believe a 7 inch scope even a questar would not beat a 155mm astro physics on planets it would be close but the obstruction just pushes too much light out of the airy disc to match the refractory.  If the Questar was under 25% and optics equal in quality it would be very very close.

 

Re Question does a 7 inch Mak go well on deep sky at 75-250 yes it does.  My SW180 is superb at these magnifications.  In good seeing it handles 400 plus on doubles with no apparent breakdown of image.  Its particularly good at 87X with 31mm Hyperion no vignetting and really sharp to the edge wonderful on Omega Centaurus and 47 Tukana at this power.   

 

I prefer around 230 x on Jupiter with the sw180 lovely image very good contrast lots of detail.


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#110 De Lorme

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Posted 02 February 2019 - 04:06 PM

Thanks Stopforths for telling me.  Really look forward to looking up. Can't wait.



#111 makeitso

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Posted 02 February 2019 - 04:47 PM

Question to you all. When you mention CO, are you talking about by diameter or % of area.

 

Thanks, Jack



#112 chuckscap

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Posted 02 February 2019 - 05:21 PM

diameter


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#113 salico

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Posted 02 February 2019 - 05:44 PM

hm, in the AP 10" Mak thread people stated, that the AP can outperform fracs of nearly the same aperture... though it has CO. So aperture - CO is not always correct?

 

Sal



#114 Kevin Barker

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Posted 02 February 2019 - 10:45 PM

Sal

Yes you are right. The 10 inch AP Mak will likely have a very small central obstruction around 20% so the aperture minus obstruction rule for 33% obstructions does not really apply. It would not surprise me that a Mak of this quality could indeed match a true apo refractor of similar aperture in all manner of observing.

 

I wonder just how many 10 inch apo refractors are out there for comparison. Very few I would guess. They would be very difficult to make, expensive and massive.

 

My 8 inch Mak IM 815 is similar to mount to my APQ 130. It is slightly heavier and slightly shorter. An 8 inch apo would be a monster in comparison.



#115 luxo II

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Posted 03 February 2019 - 06:17 AM

I wonder just how many 10 inch apo refractors are out there for comparison. Very few I would guess.

For a scope with a CO well below 30% the CO is of little consequence, hence the performance of the AP 10" will be superb. Frankly I doubt there's a 10" refractor that could match them.

 

I've spent many nights with a 9" f/16. While the 9" was useable on planets at 700X my MK91 isn't far behind, I've used 660X and images in the 9" refractor were not entirely colour-free whereas the MK91 has no colour. Zip, nada, none.

 

But the 9" required an enormous permanent mounting and observatory, and as for the observing position... you had to chase the eyepiece around at the end of the monstrous tube with an adjustable reclining sofa. The MK91 and mount fits easily in the boot of my car, and the observing position is vastly superior.

 

IMHO the scopes where the CO really hurts are those with CO at 30% or more - even the Intes ones, as well as all Celestron/Meade SCTs.

 

And a 9" or 10" mak is at most 10% (and quite likely less) than the cost of the equivalent refractor - to that add  mount and a building and the land to put it on.


Edited by luxo II, 03 February 2019 - 06:45 AM.

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#116 precaud

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Posted 03 February 2019 - 10:39 AM

Precaud,{and everyone else}when at high magnification{starting at 275x}does your 7" Sky Watcher{or any other 7" Mak Cass} stay razor sharp on the moon and the planets?

 

I have not been pushing the mags yet, except to verify that it was capable of it, so the other guys can answer to that. Splitting doubles at 400x is not my "thing", I'll probably stay below 200X until Jupiter is back on the evening menu.

 

When viewing{at low powers}open clusters and gobblers at around 75x to 250x are the stars still pin points of light like very good refactors?

 

Absolutely.

 

If your SW180 is a good one (and it probably is) I predict that, within its FOV capability, it will outperform your 5" frac on most targets.



#117 Asbytec

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Posted 03 February 2019 - 08:55 PM

I have not seen color in a MCT, save for atmospheric dispersion.

 

As we all know, the CO does affect the intensity distribution between the peak central disc and the rings. An APO refractor will work at it's polychromatic Strehl and residual higher order SA but without added diffraction. A 0.20 obstruction will bring peak intensity from perfect = 1 to about 0.92. Then multiplied by its Strehl, say 0.94, gives a nominal peak intensity of 0.87 normalized to 1. Still well above diffraction limited performance. Likewise, a 0.30 obstruction will bring peak intensity from perfect = 1 to about 0.83. Then multiplied by its Strehl, say 0.94, gives a nominal peak intensity of 0.78 normalized to 1 and flirting with the diffraction limit in terms of performance.

 

The above is just an approximation. It includes the shading effect of the obstruction which does not affect contrast, but may help with a rough approximation accounting for some small amount of aberration. And it ignores the small boost in peak intensity of the central disc caused by the additional diffraction from the obstruction. In theory, the volume under the PSF remains the same, but the base is somewhat smaller so the peak increases slightly. In practice, that is very hard to observe. 

 

No doubt a difference in the intensity distribution can be seen between a well corrected APO at it's polychromatic Strehl and a 0.30 obstructed scope at the same aperture. The difference is, in practice, apparently more difficult to notice at 0.20 obstruction with about a 0.10 spread between 'perfect' and obstructed peak intensity. Again, at the same aperture. But, we almost never compare the same aperture when talking about equivelent planetary contrast. The Airy disc of a 127mm aperture is ~ 1.1" arc. The first offending ring of the obstructed 180mm is 185/Dmm ~ 1" arc. So a lot of the contrast damage (obstructed first diffraction ring) is hidden in the lower resolution (Airy disc) of the 5" APO. 

 

This is what gives us that extrapolated curve of the larger obstructed aperture on the MTF which seems to lend some credence to the D - CO rule of thumb when comparing different apertures as far a small scale planetary contrast is concerned. So, the difference between a 5" APO and a well made 180mm modestly obstructed MCT should be very close in terms of planetary contrast. However, the high contrast resolution, of the moon for example, of the 180mm will be greater. The 180mm should retain it's edge in being "sharp" on lunar and equal doubles. 

 

I like to think of my 150 MCT a having the planetary contrast of a 4" APO, the throughput of a 5" APO, and the resolution of a 6" APO. Not a bad line up. I imagine the 180 MCT will be an inch larger in each category. In my experience, MCTs can take magnification worthy of their long focal lengths with no "image breakdown" so long as the image retains sufficient surface brightness on the eye. As Roland says in his article on Star Testing Complex Designs, a well corrected MCT can have an exceedingly good RMS. They can have as much as 0.4 waves PV of residual higher order and still be diffraction limited at about 1/14 waves RMS.

 

They are good scopes for a fraction of the cost of a similar aperture APO. I find this to be true when cooled and operating in good seeing. 


Edited by Asbytec, 03 February 2019 - 08:59 PM.

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#118 fred1871

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Posted 03 February 2019 - 09:40 PM

For a scope with a CO well below 30% the CO is of little consequence, hence the performance of the AP 10" will be superb. Frankly I doubt there's a 10" refractor that could match them.

 

I've spent many nights with a 9" f/16. While the 9" was useable on planets at 700X my MK91 isn't far behind, I've used 660X and images in the 9" refractor were not entirely colour-free whereas the MK91 has no colour. Zip, nada, none.

 

But the 9" required an enormous permanent mounting and observatory, and as for the observing position... you had to chase the eyepiece around at the end of the monstrous tube with an adjustable reclining sofa. The MK91 and mount fits easily in the boot of my car, and the observing position is vastly superior.

 

IMHO the scopes where the CO really hurts are those with CO at 30% or more - even the Intes ones, as well as all Celestron/Meade SCTs.

 

And a 9" or 10" mak is at most 10% (and quite likely less) than the cost of the equivalent refractor - to that add  mount and a building and the land to put it on.

Curious, luxo II - the refractor you describe was the old Oddie achromat at Mt Stromlo Observatory, near Canberra, that was destroyed in the firestorm of 2003. 

 

The comparison is odd because it was not an apochromat, being a late-1800s achromat by Grubb. The observing position was very awkward because it had been made without provision for a star diagonal, and was heritage listed so could not be modified to add a modern diagonal. So it was much more awkward than some other old refractors I've encountered. A modern apochromat would not require as much space or be as awkward. I used that scope back in the 1980s, and in particular recall excellent images of Mars at the 1986 Opposition, and some spectacular Lunar close-ups, including Petavius under a low Sun at 600x or so magnification, enough detail to make one feel in an Apollo mission Lunar orbit.

 

Of course you're correct about the modest size and ease of use of modern Maks and similar scopes. And if they're optically top rate they will outperform a smaller apochromat overall, simply because "aperture wins". This doesn't mean that all claims about the virtues of refractors are merely hype. Various respondents in this thread have spelled that out from their experiences with the differing scope types, and the superior performance relative to aperture that high-grade refractors can give.

 

If I compare what I see with my 140mm achromat refractor with what I see with my Mewlon 210, very unsurprisingly the Mewlon wins on most things - more light, more resolution, because of more aperture. But the Mewlon doesn't do wide-field for star clusters. It has visible coma, unlike the refractor, even with a 40' field. It doesn't have chromatic aberration, but that's not an issue for every type of object.

 

I also have a C9.25, optically good but not outstanding. Definitely less than Tak quality optics. Over the last 10+ years I've looked at a lot of double stars, and in recent times compared my notes using the 140 mm refractor and 235mm SCT. (The Mewlon is a more recent acquisition). The SCT wins easily on doubles of about equal brightness. It also wins on the really faint pairs (a full extra magnitude of light).

 

Where they're very close is on unequal close pairs that are not particularly faint. Very little difference - the extra light put in the diffraction rings of the SCT from its over-30% secondary obstruction makes it less capable, relative to aperture, than the refractor. So they end up similar. Chromatic aberration I don't find to be a big deal in this. This particular refractor has very good optics, so sharpness is high and there's not a lot of scattered light. It gives a neat Airy disc at 570x (2.5x Powermate with 3.5mm Nagler).

 

So, like a lot of other folk, I have use for more than one telescope. And, as a bonus, I like the aesthetics of refractor star images.



#119 contrailmaker

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Posted 04 February 2019 - 07:57 AM

De Lorme

 

Congratulations on your purchase. I got mine (Orion version) as an interim scope while I waited for an AP130 refractor. The optics on my MCT are fantastic. It shows the best star test of any telescope that I have owned. From my viewing site near the ocean I have been able to have some of my best-ever views of Jupiter, Saturn and the moon at over 400x. I live in the tropics so cool-down is never an issue. I like it so much that I kept it even after obtaining my GTX.  Hope you enjoy yours as much.

 

CM


Edited by contrailmaker, 04 February 2019 - 08:57 AM.

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#120 bobhen

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Posted 04 February 2019 - 08:42 AM

Just my 2 cents...

 

I live in PA with mediocre seeing 99% of the time and telescope acclimation needs to be taken seriously and the planets don’t get as high as they do farther south. So take that into consideration.

 

I owned a 7” Meade Mak OTA that was very good. I liked it, as most people do. I purchased a AP 155 and the Mak didn’t stay around much longer after that. S & T did a review of the Meade 7” Mak and in the review they compared it to an AP 155 and came to pretty much the same conclusion.

 

I now own a Tak TSA 120 refractor and a Mewlon 210 and have used them many times “side-by-side” on a twin alt az mount, so it’s pretty easy to compare the views in real time. So no distorted memory views but real-time side-by-side views under the same conditions.

 

On “lunar planetary” the Mewlon will pull slightly ahead but only when the seeing allows a significant part of the Mewlon’s aperture advantage to be put to good use. Here in PA those nights are not as many as one would want. And the Mewlon is a lot more fussy with acclimation and seeing and tube currents.

 

On "deep sky" the Mewlon goes deeper and objects are easier to see but not all that much deeper. With my light pollution, I don’t remember seeing an object in the Mewlon that was invisible in the refractor. And of course the refactor has a wider field of view. The refractor is also more conducive to solar viewing as well.

 

With the luxury of a 2 scope solution, I can enjoy the Mewlon’s aperture advantage when conditions warrant and when that happens I’m glad I have the Mewlon. But the Mewlon is really a second scope luxury while the Tak TSA 120 is a workhorse scope.

 

If I were forced to keep just one scope it would be the Tak 120, because of it ease of use and versatility and its ability to never seem to disappoint, even in iffy conditions.

 

If the choice were between a 7” Mak and a high quality 5” refractor (say a Tak TOA 130) where I live (again WHERE I LIVE and with MY conditions) I would pick the refractor without question.

 

Bob


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#121 Asbytec

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Posted 04 February 2019 - 09:10 AM

...(again WHERE I LIVE and with MY conditions) I would pick the refractor without question.

 

Bob

Makes sense, Bob. It's nice to chose a type and aperture that can flourish in local conditions.

 

I observe in the tropics with seeing so steady I can watch the Poisson spot kick off the next diffraction ring as I slowly scroll through focus (not always, but often). It starts with a tiny hole in the center of the Poisson spot, which is an amazing thing to see. I have seen the first bright ring close to focus break out, albeit briefly, into several thinner rings (and no idea that was the case nor do I understand why that happens.) Under such conditions, I have seen full crater forms to below Dawes and detail on Ganymede in a modest aperture. 

 

Seeing and thermal stability are so important, and it also allows great collimation. Lastly, with modest ambient, cooling is never a problem. So, the scope is peeked for performance in near lab-like conditions where we can really see what it can do. A refractor would be at it's best, too, and no doubt stunning. Maybe even more so. I often get fractitis, but after a night of observing I ask myself why. I appreciate as much as anyone the beauty of a dead calm, etched image of the moon or planets. And doubles with a diffraction ring that does not move. Even if the aperture is smaller with less resolution, there is some magic in a calm image. 

 

Often, matching your scope's strengths to your conditions just makes sense in that way. It's something to behold in either a Mak or a nice refractor. And now My 8" f/6 is growing on me, too. But, I'll leave the aperture rules debate for another time. Point being, when your scope can perform nicely to its limits, that's where it's at. It's a beautiful thing, so I can and do understand. 



#122 iKMN

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Posted 04 February 2019 - 11:09 AM

Just to add to the discussion, I have a 6” ES CH Mak-Newt. Certainly not in the same league as many of the premium Maks in the thread. However, I gotta say I am very surprised out how good it is compared to a smaller 115-130mm APO. The contrast and overall performance with my MN is very close to APO and I’ve spent a lot of time with 4-5” APOs. I absolutely love this scope for the price. Don’t get me wrong, I don’t want to exaggerate... I’d rather have a 5” APO and this was a compromise for me but I’m very pleased. Anyway, my point is a 7” Mak with higher quality optics must be even better. Best wishes with whatever you get.

Cheers

K

#123 De Lorme

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Posted 05 February 2019 - 03:56 AM

Much thanks everybody for your opinions.  I really like my ES 5" FCD100 but just want another 100x-150x more power, larger image size with the same image quality that the FCD100 puts up on the moon, planets and open clusters. 

I could not afford a 6"-7" triplet which would also require a bigger mount.  Could not justify the substantial increase in cost of either APM's doublets{although I'm sure there nice}because the glass type in the 6" and and only a half an inch more in the

140mm.  With the price difference I was able to get a Binotron and 2" BBHS mirror.

 

My seeing here in Killeen is ok I guess. Could be better. But if I was in Colorado Springs right now I would not be looking up

at all. Just to cold and to much snow. So I'm grateful.

 

I collimated{needed something to do}the Sky Watcher tonight and tomorrow I'm going to measure for aperture loss when using the Binotrons with the OCS.  I did a measure of just the mirror by itself and it's a full 7". 

 

I'm really hooked on the Binotrons. There just great. Equal to whatever I'm looking up with because of the sheer convenience. Hoping the 82% more light compared to the 5" is really going to get me over the hump with the Binotrons. 

 

I won't be able to find out just how much brighter and how far I can push the magnification with either using the Binotrons

or an eyepiece{on the moon} for at least a week because of the weather.  You how time is, it's either really dragging by

or going by like the wind. Well now it's just dragging by. LOL

 

Really enjoy rereading the threads here. Love the anticipation of the launch. LOL



#124 contrailmaker

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Posted 05 February 2019 - 09:52 AM

De Lorme

 

Looking forward to your observing reports with the new scope. I observe almost exclusively with Denk standard binoviewers and Pentax XL eyepieces. I think your Binotrons will work great.

 

CM



#125 chuckscap

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Posted 06 February 2019 - 09:01 AM

"Moving to TEC (i.e. scaling up the quality of Mak manufacturing), my sole experience is with the TEC 250/20, which is a truly excellent instrument; but certainly not up to the 200ED/9 I had it against.

Again, I am talking planetary.

Unfortunately I did not have the occasion of a side by side with the AP180EDT, which would have been interesting, given how close the AP180 and the 200ED were in several occasions. So cannot say anything first-hand.

OTOH, I recall well that Roland always reported that his 10" Mak was overtaking the 180EDT in excellent seeing. But "as soon as the seeing started deteriorating" (if I am not mistaken he used exactly this expression), the 180EDT pulled ahead."

 

 

And speaking of TEC 250/20 I sold mine a couple of months ago, I owned this Mak for exactly 20 years, but the old age along with a major surgery forced me to give up this magnificent instrument as I could no longer carry and mount it in our backyard. Looking back at the big Mak the cooling was always a real issue but once I learned to deal with this limitation it offered superb high contrast planetary views.

.

Fortunately some 10 years ago a TEC fanatic contacted me and offered to sell me his TEC 200/20, I bought it, it was the very last one produced in 2002 and had the same 22% co, it is much lighter and easily portable for me at my old age. After that Yuri switched to 200/15.5 which turned out to be more popular model.

The 200/20 came with two internal mixing fans at opposite ends of Ota, I wrap it with 1/2" foam insulation and that really makes a big difference. 

.

Under excellent seeing the 200/20 outperforms my AP 155EDT f/9, surprisingly at higher powers the Mak offers better contrast on Jupiter than the refractor, I attribute this to dimmer image in the refractor affecting its contrast compared to the Mak.

.

Vahe 

 Previously used a "legendary Orange C14"  that was previously owned by David J in San Diego, an exquistite Mewlon 250 with in baffle corrector, and now a TEC 7 Mak.  I have to say for planetary and double stars the TEC 7 Mak beats them all for clarity and contrast.   I hope to get to our annual star party this year in Colorado and look through some really awesome larger apos and have their owners compare the views through my little TEC 7.  I still own the exquisite Orange C14, hope some day to permanently mount it again once I move back to dark skies.


Edited by chuckscap, 06 February 2019 - 11:33 AM.



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