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7" Mak versus an 8" SCT

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#1 azure1961p

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Posted 29 July 2014 - 10:06 PM


I've always been curious about this comparison. I've read more than one 6" Mak users exclaims that his 6" can match or outdo a C8, then here in CN we have an article comparing a 7" Mak to a C11 and the former presenting a more pleasing lunar image!! Even after collimation and cooling of the big C.

I'm curious here. Say we have a typical 7" Mak going head to head on Saturn for example with a good sample C8. Not the one in a million, just a decent C8.

How would the image of Saturn fare? It'd be a little dimmer perhaps, but what about Cassinis boldness, banding, the subtle polar region, the subtle belt bisecting the EZ.

I welcome pure conjecture as much as practical hands in accounts.

Thanks in advance.

Pete

#2 rg55

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Posted 29 July 2014 - 10:52 PM

Check thread #5636646.

#3 Patricko

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Posted 29 July 2014 - 11:08 PM

Hi Pete,

In my experience this would be a close call. The determining factors would probably be seeing, scope acclimation, diagonal performance, and eyepiece selection. My thinking is that subtle details visible in one would also be seen in the other under most circumstances. The 203mm aperture of the SCT would allow for more color saturation while the smaller CO of the Mak helping to balance the playing field. Unless one really wants to own both instruments I think either/or would suffice. Me....I'd chose the C8 for greater light grasp because DSOs are my thing.

#4 jzeiders

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Posted 30 July 2014 - 12:34 AM

I would suggest there are no magic optical configurations. There are far more SCT scopes out there and the quality varies widely, as does collimation.

There is a much smaller Mak population to compare and rarely will you find one bigger then 7" as they get very expensive and heavy. they also take longer to reach equilibrium due to the thicker corrector.

I have a couple SCT tube assemblies and currently two Maks. A few years ago I had a Questar 7 Mak-Cass. and it took forever to cool down and in summer never did reach equilibrium with short nights and big temperature swings, from mid 90s in the day to 30s at night.

Some of this may be "mine is better than yours" or simple pride of ownership. I have seen enough variation to suspect a specific scope may work better at a given time and place yet not perform as well given different circumstances. Also there is usually sample variation within the products of a single manufacturer even though exactly the same model.

All scopes have their good and bad points.

If you pay $5k to $10k or more, it must be great, right? Well...

YMMV

Jack

#5 Asbytec

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Posted 30 July 2014 - 05:14 AM

Check thread #5636646.


Rich, how do you search for that thread, please? 'Scuse my ignorance...

Pete, I dunno. I'd say, right off, if both scopes are prepped and ready to observe, they would both obey the laws of physics that relate to their aperture. I do not know if there is anything magical about the Mak over the SCT. I love the Mak design, for some reason, but just have not been able to pin point the reason why. They are CATs of a different design, and there may actually be a design advantage to the Mak. I just could not tell you what it is nor, not having compared both side by side, if it's even real.

I've often wondered if the purely spherical (for smaller apertures) meniscus is somehow superior to the Schmidt corrector. They prep the incoming wavefront differently. The former should rely on balancing low/high order SA and this improves RMS. Is this somehow superior to reducing HSA at the corrector? That's the main difference, so if there might be an advantage to the Mak it might be found there or maybe in the tighter baffling. But, again, I don't know the answer.

The answer may be pride of ownership and excellent tropical seeing, for all I know. I suspect it's the latter leading to the former.

#6 Illinois

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Posted 30 July 2014 - 06:56 AM

I used C8 years ago and now I have 7" Mak-Cass. I see Saturn, Jupiter and Mars on both telescope. Not much different but my 5 inch refractor....Wow! I plan to sell my 7 inch Mak-Cass! 7" Mak Cass is nice but lot of time on cooling and put it outside few hours before dark. Easy see good but also easy to see bad! Depends on how good night is and how long cooling time.

#7 Asbytec

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Posted 30 July 2014 - 07:10 AM

Cooling to ambient is so important, IME, and it takes anything from minor prep to aggressive steps and may or may not be successful. So is seeing very important.

If you got both, you off to the races. The scope, unless it's a lemon, will perform as it should. So, if we assume we're cooled, or make the effort, and operating in at least the same seeing what do we expect from each?

Edit: Okay, it's interesting there is a thread raging in the refractor forum about some professional comments made concerning the MCT. Of course, the smaller APO wins hands down due to better contrast, according to the argument. But, what's interesting is the thread quickly turned into an APO bashes SCT argument. What happened to the MCT comparison with APO? Are APOs, those SCT bashing scopes, afraid to do battle against a MCT? Are APOs on the defensive and have to pick on the little guy. LOL

Sometimes we hear the MCT is APO-like. Normally some probably mean the view. But, they are actually APO-like in one important way: they both have very high secondary SA and both /should/ use the balanced low/High form of correction to reduce RMS. So, I'll ask it again, is this form of correction somehow superior to the Schmidt corrector? Does this form of correction help make a larger Mak achieve a smaller APO-like view (when considering cooling of each and the obstruction of the MCT)?

I dunno, do you?

#8 spencerj

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Posted 30 July 2014 - 08:43 AM

These comparisons are fun, but I don't think there is a definitive answer. In my experience it comes down to the specific scopes and not the design. A good scope is a good scope.

I used to own a C8. It was ok. I'll be nice and say the optics were diffraction limited and leave it at that. I currently have a Intes Micro M703. It is not a deluxe version, but the optics are 1/6 to 1/7 wave. Really good, but not perfect.

Both of those scopes were F10 so the central obstructions were similar. The M703 was clearly better. High power images were sharper and even at lower powers, stars were tighter. When you factor in the flatter field of the M703, I found it to be a better all-around scope than the C8.

Again, that is just one comparison of two specific scopes. I would be interested to get a look through a C8 Edge as I have a feeling a good sample of that scope would outperform my M703. Now a M715 deluxe against a C8 Edge on high-power planetary detail . . . that would be interesting.

#9 gatorengineer

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Posted 30 July 2014 - 08:59 AM

7" (Russian) Mak all day everyday and twice on Sundays....

I would put my MN86 up against any C11 ever made....

#10 mdowns

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Posted 30 July 2014 - 09:01 AM

Pete,
Your location can have alot to do with the outcome of the two set up side by side.Here in southern Florida,were we get a fairly high number of nights with steady air,the 7" always won.I had a very good c8 at the same time and often compared one against the other.The c8 always delivered a pleasing view with steady air while the 7"orion mak I had would go above and beyond.For example the c8 deliverd sharp images up to 350x or so while I could always crank the mak up a bit more and to me its contrast levels were better.For me,side by side,the mak was it.One of my favorite all time scopes.However,if you live somewhere else,say like the midwest or NE,with air less steady, your results could be just the opposite.Even different examples of the mak can produce very different results.I have an observing buddy who comes down our way each winter with his 7"meade mak.Its nice but does'nt impress me the way my old orion did.Earlier in this thread several have mentioned cooling times which can be a real concern if you travel to view.I always set my mak up (in the backyard) hours before I actually observed.

#11 gatorengineer

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Posted 30 July 2014 - 09:02 AM

But seeing in your sig line that you have an 8" F9 Newt, if it has good optics it would run real close with the MN86,just bigger and bulkier... I had some 8 F8's that were very high quality primaries, and they ran with the MN86... Kept the MN86 because it was wider and easier to deal with, I can carry it on a DM6.....

#12 RAKing

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Posted 30 July 2014 - 09:02 AM

I have owned some very nice Maks from 6 - 8 inches and when properly acclimated they provided incredible views. I would certainly choose my TEC Mak over a standard SCT, but would my TEC 6 beat a Celestron 8 inch Edge? Based on my past experience with the Edge, I doubt it. It might equal it in some areas, but I think my old Edge would show a slightly brighter view and the details would be determined more by seeing conditions.

My Intes-Micro M703 would definitely give the standard SCT a run for its money. But the view would still be brighter in the SCT. The major difference in these designs would be the sharper image off-axis. Side by side with a decent Mak, the coma of the SCT is very distracting. The Edge and ACF designs level the field and those would be the scopes to compare. You asked about Saturn and that is mostly on-axis, so the standard SCT has a chance - as long as you only looked at planets with it. But how many people limit themselves to that?

Aside from the little TEC and the I-M, I also had a beautiful 8 inch STF-Mirage MCT. Properly cooled, it was more than equal to my C925 Edge parked next to it on several occasions. The contrast difference was especially noticeable on faint DSO. I could see them clearly in the Mak and could barely see them in the bigger Edge - despite the aperture difference. The problem was the acclimation. There were too many nights where the STF never settled down enough to strut its stuff and on those nights, the C925 was the clear winner. In fact, the best view I ever had of Saturn was through the C925 Edge. Stunning! Unfortunately for me, both of those scopes exceeded the doctor's weight limit when I had to have spinal surgery in 2012. :(

It's a very difficult choice for me. The slightly smaller scopes with better optics do show more contrast and the views are sharper than the mass produced larger scopes. But the thick meniscus retards the acclimation so much in my mid-Atlantic area it's rare when I get to see that beautiful view. So my little Mak is currently reserved for moderate spring and fall nights when our temperatures don't have the drastic changes and I use the refractors during most of the warm weather months. But I am dreaming of the day I can try something bigger, like another C925 Edge.

That's my experience with these things, for better or worse. YMMV! :cool:

Ron

#13 spencerj

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Posted 30 July 2014 - 09:15 AM


Sometimes we hear the MCT is APO-like. Normally some probably mean the view. But, they are actually APO-like in one important way: they both have very high secondary SA and both /should/ use the balanced low/High form of correction to reduce RMS. So, I'll ask it again, is this form of correction somehow superior to the Schmidt corrector?


"Apo-like views" is one of the most ambiguous and over-used terms on the CN forums. A good Apochromatic is an impressive telescope especially when you get over 4". There is a reason they cost what they do. When I hear the term Apo-like, I assume they mean tight stars and great contrast. I have owned two non-refractors that I would say meet this criteria: an MN66 with outstanding optics and small central obstruction and my current 10" Starmaster with an F6 Zambuto primary and the smallest secondary mirror I have ever seen on a similar size Newtonian.

So for me, secondary obstruction and optical quality are the two biggest factors in the equation. If you have a small secondary obstruction and outstanding optical quality, you can "approach" the view of a similar sized Apo.

#14 astroneil

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Posted 30 July 2014 - 12:33 PM



Sometimes we hear the MCT is APO-like. Normally some probably mean the view. But, they are actually APO-like in one important way: they both have very high secondary SA and both /should/ use the balanced low/High form of correction to reduce RMS. So, I'll ask it again, is this form of correction somehow superior to the Schmidt corrector?


"Apo-like views" is one of the most ambiguous and over-used terms on the CN forums. A good Apochromatic is an impressive telescope especially when you get over 4". There is a reason they cost what they do. When I hear the term Apo-like, I assume they mean tight stars and great contrast. I have owned two non-refractors that I would say meet this criteria: an MN66 with outstanding optics and small central obstruction and my current 10" Starmaster with an F6 Zambuto primary and the smallest secondary mirror I have ever seen on a similar size Newtonian.

So for me, secondary obstruction and optical quality are the two biggest factors in the equation. If you have a small secondary obstruction and outstanding optical quality, you can "approach" the view of a similar sized Apo.


Eye. Ken. ;)

Best,

Neil. ;)

#15 Ed Holland

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Posted 30 July 2014 - 12:37 PM

I have an 8"SCT, are you saying I have to get a 7" Mak now?

What should I tell Mrs H :question: :help:

#16 astroneil

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Posted 30 July 2014 - 01:00 PM

Hello Ed,

Ach, no, I would never presume.

I thought about the 180mm Maksutov and one came my way. I was lucky, that's all.

The Maksutov images are about midway between a fine refractor and a SCT.

Regards,

Neil. ;)

#17 jimb1001

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Posted 30 July 2014 - 01:01 PM



Sometimes we hear the MCT is APO-like. Normally some probably mean the view. But, they are actually APO-like in one important way: they both have very high secondary SA and both /should/ use the balanced low/High form of correction to reduce RMS. So, I'll ask it again, is this form of correction somehow superior to the Schmidt corrector?


"Apo-like views" is one of the most ambiguous and over-used terms on the CN forums. A good Apochromatic is an impressive telescope especially when you get over 4". There is a reason they cost what they do. When I hear the term Apo-like, I assume they mean tight stars and great contrast. I have owned two non-refractors that I would say meet this criteria: an MN66 with outstanding optics and small central obstruction and my current 10" Starmaster with an F6 Zambuto primary and the smallest secondary mirror I have ever seen on a similar size Newtonian.

So for me, secondary obstruction and optical quality are the two biggest factors in the equation. If you have a small secondary obstruction and outstanding optical quality, you can "approach" the view of a similar sized Apo.


I've owned several examples of both.

If you are conducting testing in a laboratory environment or on one of those 3-4 nights where seeing is special, you might see a perceptible difference. Might. If you can switch diagonals and eyepieces before the air cells move. Outside, at night, its almost never a controlled environment and the differences are small when comparing "best of breeds."

Most of the time (nearly all) other factors (mainly seeing) will have a much greater impact than the inherent differences between an APO refractor, a good quality SCT or a MAK.

#18 Asbytec

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Posted 30 July 2014 - 06:08 PM



Sometimes we hear the MCT is APO-like. Normally some probably mean the view. But, they are actually APO-like in one important way: they both have very high secondary SA and both /should/ use the balanced low/High form of correction to reduce RMS. So, I'll ask it again, is this form of correction somehow superior to the Schmidt corrector?


"Apo-like views" is one of the most ambiguous and over-used terms on the CN forums. A good Apochromatic is an impressive telescope especially when you get over 4". There is a reason they cost what they do. When I hear the term Apo-like, I assume they mean tight stars and great contrast. I have owned two non-refractors that I would say meet this criteria: an MN66 with outstanding optics and small central obstruction and my current 10" Starmaster with an F6 Zambuto primary and the smallest secondary mirror I have ever seen on a similar size Newtonian.

So for me, secondary obstruction and optical quality are the two biggest factors in the equation. If you have a small secondary obstruction and outstanding optical quality, you can "approach" the view of a similar sized Apo.


Eye. Ken. ;)

Best,

Neil. ;)


Yea, that sounds reasonable.

But is the Mak such a good design it can overcome an inch larger SCT aperture? Are they the same? Is there something inherent in their designs that would cause the OP to ask such a question?

#19 aa6ww

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Posted 30 July 2014 - 06:59 PM

Maybe in Pennsylvania but never in Calif where the skies are clear, the weather is stable, and aperture always rules.

Darker skies beat larger aperture every time when going deep.
Stable seeing conditions beat better optics, when looking for resolution.

..Always!

...Ralph

7" (Russian) Mak all day everyday and twice on Sundays....

I would put my MN86 up against any C11 ever made....



#20 cbwerner

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Posted 30 July 2014 - 08:47 PM

Check thread #5636646.


Rich, how do you search for that thread, please? 'Scuse my ignorance...


I didn't see this answered, so in case it's still needed, that thread can be found here.

#21 Ed D

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Posted 30 July 2014 - 09:41 PM

Solely on the basis of the equipment I have used, the conditions where I live, and that I observe planets, the Maks appears to have an edge in resolution over SCTs. Change any of the criteria and the outcome can change.

Pete, sent you a PM.

Ed D

#22 Asbytec

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Posted 31 July 2014 - 05:52 AM

Thank you, Chris.

#23 azure1961p

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Posted 31 July 2014 - 11:41 PM

A lot of interesting posts here. I've been working long long days this week. Id like to add something when I'm less tired.

Ed - read your message. Thank you Ill be replying tomorrow.

Pete

#24 Asbytec

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Posted 01 August 2014 - 04:49 AM

As Pete knows, I am enthralled with the Mak design. I am sure a good 8" SCT is no slouch, either. But is there a difference in design that gives one an edge over another? Mechanically they are obstructed apertures, but each uses a different "corrector" lens. Does that make a tiny bit of difference in RMS, contrast, or whatever that might cause someone to make the claim a 7" MCT is as good or better than an 8" SCT? My first impression through the MCT was stunning enough to think so, but that's just a subjective impression done in excellent seeing and not a comparison. The MCT is a great design, IMO, but is it actually better in any way? Dunno. Does anyone?

#25 Mark Costello

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Posted 01 August 2014 - 08:31 AM

As Pete knows, I am enthralled with the Mak design. I am sure a good 8" SCT is no slouch, either. But is there a difference in design that gives one an edge over another? Mechanically they are obstructed apertures, but each uses a different "corrector" lens. Does that make a tiny bit of difference in RMS, contrast, or whatever that might cause someone to make the claim a 7" MCT is as good or better than an 8" SCT? My first impression through the MCT was stunning enough to think so, but that's just a subjective impression done in excellent seeing and not a comparison. The MCT is a great design, IMO, but is it actually better in any way? Dunno. Does anyone?


I recall seeing on Astromart a thread on this question which included a post from Roland Christen. A MCT and SCT would have the same design characteristics (diameter and focal length) and be built to the limits associated with the design. IIRC, his response was that the MCT would have the advantage of the SCT, I wish I recall why, I should have saved that response....






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