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Maks VS SCTs

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#1 Darren Drake

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Posted 24 December 2012 - 09:05 PM

If we assume identical apertures which scope design tends to be the better planetary performer the Mak Casses or SCTs? The Maks tend to be considerably more expensive especially in the larger apertures and also are slower and not easy to collimate. They also tend to have slightly smaller obstructions and perhaps smoother surfaces. My 1980's C8 has proven to be an outstanding performer and would hold it's own against anything in its'class and would love to see how such a scope would compare in a head to head detailed match up. Thoughts?

#2 mdowns

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Posted 24 December 2012 - 09:29 PM

I once had another very good c8 like yours. At the same time I owned a 7" mak.The planetary views provided by the mak were spectacular under steady skies,always better than the c8.Tighter focus with more intricate details visible when set up side by side. The c8 was really a good one often performing very well at 400x, But even with the brighter image it could not stay up with the mak. At that time ,besides those two,I had a 10" meade sct and an antares 4"f15 rfr.The mak always came in at number 1,the c8 second,the 4" rfr third and then the 10" sct.The rfr was handicapped by its smaller aperature,not its performance. The meade suffered from poor contrast levels that always seemed to hide details.

#3 mdowns

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Posted 24 December 2012 - 09:34 PM

BTW,if you can collimate your sct,you'll be able to collimate your mak.It is more complicated involving say 9 adjustment screws compared to 3.Nonetheless,once you've done it,its relatively simple,just more time consumming.

#4 azure1961p

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Posted 24 December 2012 - 09:54 PM

Downs,

Interesting comparisons. The way I understand it is the spherical surfaces of the Mak are easier to produce with repeatable precision where as the sct is not. I'm guessing that dished out corrector is where a lot of the extra expense goes into. Might be easier to perfect but possibly a time eater in manufacturing. This is going to be a good thread.

Pete

#5 Asbytec

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Posted 24 December 2012 - 10:20 PM

The interesting difference between the designs is the way they handle spherical aberration. The Schmidt corrector, with an aspheric higher order term, delivers an 'aberrated' wavefront to the spherical primary. Best focus at 0.7D appears to be unaffected while marginal zones are corrected. The marginal wavefront is delayed just a bit so they reflect off the primary very close to a perfect reference sphere centered on best focus. This has the potential for some very good correction. However, I believe the central zones might also be delayed a bit, too, by the thicker central zone on the corrector. So there may be less paraxial correction (covered by the secondary) as the central wavefront lags the reference sphere. If so, that would seem to give a larger P-V error.

The Mak produces a convex wavefront to the spherical primary, and if done correctly, can provide a well corrected wavefront balanced for HSA. (Interestingly, the final wavefront, as I see it, has very similar shape to the Schmidt's higher order surface: the central and marginal zones lead the prefect reference sphere centered on best focus. I believe this offers a little better P-V error.) A Mak cannot completely eliminate HSA, like a good Schmidt corrector can. But the affected portion of the wavefront is negligible, if correcting for the lower order surface approximation is done correctly. In the Mak, all zones, including best focus at 0.7D, have a longer radius resulting from adding aberration of opposite sign (and a longer focal ratio.)

So, both will have some correction error, but the Mak will have some residual HSA since it is impossible to grind a perfect sphere (approximated in the lower order terms, as I understand it.) However, this HSA can be very minimal. So, really, it boils down to how well each scope is made. A good Schmidt can provide better correction to a sloppily made Mak with significant residual higher order aberration. However, a well made, all spherical Mak (of moderate aperture) can provide better images than a sloppy Schmidt surface. Obviously, right?

So, which is easier to make consistently well and smooth? Probably an all Spherical Mak of 6" or less aperture where HSA is not excessive to begin with. Much over 7", and it requires an aspheric term because its' higher order SA becomes exponentially more significant. So, at 6" or less, I would lay bets on the Mak being more consistently good than an equal aperture SCT due to relative ease of laying down a 1/20th wave sphere. (The calculations for Mak radii are the difficult part, grinding to tolerance should be pretty straight forward.) However, once both scopes require an aspheric term, all bets are off. In mass produced models, it will be the luck of the draw. With some hand re-figuring, the higher end Maks can give a better wavefront across most samples for a price. And, it's possible hand figuring a Mak aspheric will be a bit smoother than machine driven Schmidt aspherics.

But, this is nothing a 'premium' SCT could not do, either. Question is, do they? If not, I would give a nod to the Mak. If so, however, all bets are off again. They are both potentially very good designs, the Schmidt has even better potential to correct for SA, as I understand it. So, it probably depends heavily on how well each is made or how lucky you are to have a good one, IMO. (I have a good 6" Mak that seems well balanced for higher order SA and the views are just stunning. But, again, a 6" Mak is in that all spherical sweet zone, and it's probably nothing a good Schmidt cannot deliver. In this case, the discriminating factor might well be the central obstruction.)

I don't want to speak to the EDGE design since I know nothing about them. Heck, I can barely grasp the above, but I think it's at least close to being correct. My two cents, pay pal, please.

#6 coopman

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Posted 25 December 2012 - 07:48 AM

Each person is different, of course, but I would find the small FOV of a Mak to be a major issue. I'd have to buy a tracking mount, and probably one with go-to as well, for a f/15 Mak. All of my current mounts are alt-az.

#7 jrbarnett

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Posted 25 December 2012 - 10:23 AM

As mass-produced scopes go, the Gregory Maks are generally easier to fabricate to a given level of quality than an SCT. That said, when you luck out and get a really good SCT (not too common in my experience), the SCT will generally put through a lot more light at a given aperture than the Maks. The multicoatings used on SCTs are much better than the coatings applied to Maks made by the same fabricator (Synta).

So one one hand you have modern coating technology and on the other you have better average optical quality. Tough choice, really.

- Jim

#8 Eddgie

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Posted 25 December 2012 - 01:32 PM

Identical aperture, Identical CO size, and identical quality, they will perform more or less exactly the same.

But these three things are rarely all the same.

If you make the CO smaller (Easy at f/15), or the quality better (think Intes Micro), expect the MCT to perform better on planets but the SCT will have a much wider field capability, and this allows it to perform better as a general use instrument. It is no accident that commercial SCTs are f/10. It is about as fast as the design can be made and still deliver acceptable off axis performance.

I have plotted the MTF curves for the Intes Micro M715 against the C8. The C8 would have to be perfect optically (a sure thing with the Intes Micro, a rare thing with the C8) for the C8 to come in even to the Intes Micro M715.

Not to say that there are not a few perfect C8s out there, but most are not.

But even a very good one will give planetary performance that is similar enough that it will be hard to see the difference.

After owning 4 or 5 dozen scopes, I have come to believe that clear aperture is the easiest way to compare planetary performance on telescopes. The more clear aperture, the better. But quality counts, and when the clear aperture is the same, the scope with the best optical quality will win out.

Both the C8 and the M715 have about the same clear aperture (134mm for the C8 VS 135mm for the M715), but finding C8s that match the quality of the Intes Micro M715 would be difficult. Not impossible. I think there many out there that are this good. But there are far far more out there that are not this good.

But again, for all other observing, the C8 to me would be preferable because of the bigger image scale for the same exit pupil when viewing extended objects, and for the ability to provide a far bigger true field than the M715.

Once again, I will repeat this message... Scopes differ far more in their off axis characteristics than their on axis characteristices, and if you got a really excellent C8, it would equal an M715 on planets, but bet better on just about everything else.

Not bad for the price. Not bad at all.

#9 gnowellsct

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Posted 25 December 2012 - 04:58 PM

99% of what we argue about is the 1% of performance that we *might* get if our instruments were all well maintained and the sky was cooperative.

#10 azure1961p

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Posted 25 December 2012 - 05:25 PM

Actually it 5%.

Pete

#11 orion61

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Posted 25 December 2012 - 09:33 PM

I love this Thread some very interesting posts and I agree with them all, for the most part. I have one of the Meade
7" Maks. It comes down to QC.. period.. I had one of these before and was not impressed with it, the one I got from escher here is much better. I don't believe he realizes it.
I don't mind the smaller field of view, the added contrast
makes up for it. I simply "like" the view through the Maks.
The Synta 127 (Celestron 127 NexStar SLT) I believe is an instant classic. Planetary views are pretty respectible.
I have an above average C8, an old Orange tube that performs
very well, so the answer to settle this is....
YA GOTTA HAVE EM BOTH....

#12 vct123

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Posted 25 December 2012 - 10:58 PM

I had (2) Intes m703 maks and an m6511 which I found all three to be excellent lunar scopes, probably the best I have owned, but due to the co of similar size to a c8, I found them to be no big deal for planetary detail or similar to the many c8's I have owned depending on the particular sample of sct. I did notice them all to be slightly dimmer compared to other scopes of similar size most likely due to the inferior coatings. They did offer a flatter edge of field but if given the choice I would take a C8 Edge

#13 RAKing

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Posted 26 December 2012 - 10:36 AM

I agree with all the above, more or less.

I have owned half a dozen C8 regular SCT and none of them could hold a candle to my 8 inch f/10 STF-Mirage Deluxe MCT. Some of them were okay on-axis, but the edges were soft and the coma was bad (not so important for planetary). I have owned two C8 Edge and they compare quite well with my Mak, but in the end, the Mak scores better for both optical and mechanical quality.

The Edge requires corrective lenses in the baffle to compete with its assembly line optics, while the Mak just uses smoother 1/10 wave surfaces. My STF has machined front and rear cells, so collimation has stayed perfect since the day it shipped from Moscow. Plus, the focuser mechanics are smoother and more stable on the Mak. (I changed out the Edge focusers for FeatherTouch Micros.) My STF Mak is an f/10, but has a slightly smaller CO than the SCT (30.5 percent). Added bonus: The STF comes with a decent bolt-on dew shield. It's solid and works well enough to make dew straps redundant. :)

The only knock on the Mak is the cool down time. It take a good two hours to stabilize, but the views are magnificent.

My .02 based on personal expense and experience. :cool:

Ron

#14 orion61

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Posted 26 December 2012 - 11:06 AM

Yes the cool down time on my 7" LX200 is a long time with that 8 lb weight in there. Even when I keep it oin my unheated garage it still takes 45 minutes!
But like the above poster says nothing beats it for
Planetary Except a high $ Apo of similar size.
I'd have to be hard pressed to sell her.
I dont think many Planetary/Double Star viewers will
pick the SCT over a good MCT, My Meade 102 ED
comes close but is dimmer, (there is one for sale in the S&S
thread right now CEAP!)

#15 Asbytec

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Posted 26 December 2012 - 11:29 AM

Shhh! :lol:

You know, on cooling...the Mak seems to have a bad reputation. Personally, I have absolutely ZERO OTA thermal issues with a little prep in moderate climates. Conversely, some of my previous larger, more massive SCTs would (at times) present thermals well into the evening even in the tropics. In fairness, that was long before I began to realize how to prep them for observing.

So, point being, since both Maks and SCTs are very similar in their gut (enclosed massive mirror and supporting structure.) I'd guess there is little disparity in cool down across each design given similar conditions. The meniscus is a bit thicker but, much like a refractor objective, it's exposed to open air and can dissipate more readily that the enclosed primary mirror. Both correctors will dew over.

No testing, really, or proof other than anecdotal to support that assertion. Just some application of theory, correct or otherwise. If I were to form a hypothesis for testing, that would be it: both have similar thermal characteristics and it might be proportional to mass (aperture.)

#16 Darren Drake

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Posted 26 December 2012 - 11:45 AM

Of course an MNT is a different story over an MCT as the mak newt has a much smaller obstruction and should beat out the other designs all things being equal.

#17 Darren Drake

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Posted 26 December 2012 - 01:01 PM

Here is a series of very revealing comparisons from Rohr's site. I think the best SCT here is maybe the C8 Nextstar from 2005 and the best Mak is the 8 inch Intes Alter. Rohr has many other examples on his website but this is a revealing series nontheless.

http://translate.goo...1&ie=UTF8&ru...

#18 GeneT

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Posted 26 December 2012 - 05:11 PM

Identical aperture, Identical CO size, and identical quality, they will perform more or less exactly the same.
But these three things are rarely all the same.


I agree with this statement. If I was going to buy a SCT, I would pay extra for the Edge HD.

#19 aolo

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Posted 26 December 2012 - 07:17 PM

Darren,

You reviewed a F/10 LOMO 180 many years back. I happen to have one due to that review. All SCT I've seen are F/10. I've seen MCT between F/10 and F/15. Not apples and apples, but what are your thoughts on the 7" Lomo F/10 MCT vs the C8? Would a 7" f15 Mak may offer compete with a 8" F/10 SCT on Planets and Double Stars?

#20 Darren Drake

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Posted 26 December 2012 - 07:26 PM

Darren,

You reviewed a F/10 LOMO 180 many years back. I happen to have one due to that review. All SCT I've seen are F/10. I've seen MCT between F/10 and F/15. Not apples and apples, but what are your thoughts on the 7" Lomo F/10 MCT vs the C8? Would a 7" f15 Mak may offer compete with a 8" F/10 SCT on Planets and Double Stars?


Yes my review of that scope is here on CN. I would suspect that the C8 would beat out the LOMO. It was ok but not great as I recall as I think there was some spherical aberration and the C8 is very good. How does yours perform?

#21 Darren Drake

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Posted 26 December 2012 - 10:34 PM

So just how good is my C8? By placing an artificial star in my optically excellent 12 inch dob and aiming the C8 right into the 12 and placing a straight edge in the C8 I was able to get a good null test. It took a bit of patience but I was able to get a good and very revealing pic of the surface of the C8 similar to what Rohr does.

Attached Files



#22 Darren Drake

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Posted 26 December 2012 - 10:38 PM

Here is one of the better pics I was able to get. The sensitivity is extremely high. When I put my hand in front of the C8 or the furnace comes on the air currents become very visible and the test is impossible to conduct. The very subtle surface errors that are visible are real as they were repeatedly visible in all my test pics. Overall this is a very good scope.

Attached Files



#23 Gord

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Posted 26 December 2012 - 11:01 PM

Darren,

Could you elaborate on how you did this? I don't understand the "straight edge" in the C8 part.

Thanks,

#24 Darren Drake

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Posted 26 December 2012 - 11:04 PM

It's a bit long to explain. I did write an article on it here a few years ago. Check it out and maybe that will help.
http://www.cloudynig...hp?item_id=1637

#25 titanio

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Posted 27 December 2012 - 09:54 AM

I prefer Maks to STCs, for me Mak-Newtons are even better. I have had one IM 815 Deluxe, one MN78, One C11, one C8 and I have a MN86 Deluxe and a C9,25 HD. The only SCT that can perform similar or even better than a very nice Mak is the C 9,25 edge HD, I could say it is better than the M815 Deluxe and maybe similar to the MN78. The C8 I had was very nice only with the stars colors the star colors look like originals and very nice, but I didn´t like other thinks. Many STC telescope are goods and many of them are not so goods but they are cheaper. Mak-Cass and Mak-News normally are good or very good but you have to pay extra money for them, moreover you have the guaranty that your telescope will be good and normally a report comes with them.

Regards

Toni






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