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6" Apo vs. 6" Maksutov

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#1 Larry Geary

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Posted 06 September 2009 - 01:22 PM

Could someone give me an impression of how a 6" Apo refractor would perform compared to a 6" Maksutov, particularly on planets? I know the theory, but I'm curious about any head-to-head comparisons using high quality instruments.

#2 Joe Ogiba

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Posted 06 September 2009 - 01:57 PM

I will take the 6" APO over a 6" Mak everyday for all objects.

#3 isramirez

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Posted 06 September 2009 - 02:04 PM

I believe a premium 6"APO from AP, Taka or APM is a lot for a 6"MakCass but per sure a 6"MNF6 or 6"MNF8 will do a fantastic match! :)

#4 Luigi

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Posted 06 September 2009 - 02:40 PM

If you know the theory, you know the answers with respect to effect of the size of the CO, focal length and max TFOV, CA, flatness of field, equilibration, etc.. This provides better and more accurate guidance than subjective impressions. However, if you want my subjective impression, I'd say a high quality f/15 25% CO 6" MCT would be awesome, but a 6" APO would be more awesomer. ;)

#5 Fomalhaut

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Posted 06 September 2009 - 05:39 PM

In theory, a perfect 8 (eight!)-inch-Mak-Cass with 30 - 35% obstruction could or would equal a perfect 6-inch Apo on planets, but under real world circumstances (cooling, seeing and so on) the 6-inch Apo would better the 8-inch MC in 9 out of 10 nights.
Chris

#6 isramirez

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Posted 06 September 2009 - 06:47 PM

In theory, a perfect 8 (eight!)-inch-Mak-Cass with 30 - 35% obstruction could or would equal a perfect 6-inch Apo on planets, but under real world circumstances (cooling, seeing and so on) the 6-inch Apo would better the 8-inch MC in 9 out of 10 nights...

I think the above theory is wrong... the resolution of 8in aperture will easly kill the 6in APO

#7 ltha

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Posted 06 September 2009 - 07:05 PM

Depends on how you interpret the post. As I read it, it does not say a 6" will beat an 8", only that it will provide better performance more of the time. In my experience, a 6" APO will match seeing more often than an 8" scope (Mak, Newtonian, SCT, etc). And anything with a 30% to 35% is not going to match the image of an APO. Again, in my experience using many Maks (MN 56, MN 76, 6" Mak-cass and a 10" Mak-Cass F/12.5 APM Wirth custom) the effect of the CO is very obvious when it gets over 20%. The image is not as hard: the APO makes planetary detail look etched, the others rendered. And I am not down on Maks or an APO snob, I just ordered a large Dall-Kirkham as my primary planetary instrument. I will bet that you would see the same thing in side by side comps under identical seeing.

Having said that, I agree that when everything comes together, a high quality 8" scope can beat a 6" APO: an old Cave 8" F/8 Newtonian I own when next to the TMB 175 APO is amazingly close in planetary detail and image sharpness. Yes the APO bests it but at a new cost of over $15,000 for the OTA alone it darn well better. The Cave has a 17% obstruction and a superb mirror. It does exhibit diffraction due to the spider and tube currents can be an issue. BUt is still turns in an amazing image and considering I paid roughly $800 for the entire set up, scope and mount, it is not hard to figure out which is the better deal in dollars per performance.

If you mean deep sky where the sharpness is not such an issue, larger will almost always be better given very good to excellent optics AND seeing. match seeing

As far as the original question: I have owned and compared both and a 6" APO will out perform the 6" mak-cass. The 6" MN scopes come closer, but the APOs still provide a sharper, brighter image with better contrast.

#8 Midnight Dan

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Posted 06 September 2009 - 07:33 PM

I've compared a 6" Astrophysics to my 8" SCT side by side under dark skies at Cherry Springs. I found them to be very close. The refractor had a *tiny* bit better contrast, the SCT pulled in more light. But the fact of the matter is, I had to look long and hard, back and forth many times, to see much difference between the two.

But in the same aperture, 6" APO vs. 6" Mak, I don't think there's any question ... the refractor will be better.

If you just run the numbers, and account for the central obstruction, here's the comparison (I did this for an SCT since I don't have the specs on a Mak):

Compared to a 6" refractor, an 8" SCT will have:

160% of the light gathering capability
133% of the resolution
92% of the contrast

Compared to a 6" refractor, a 6" SCT will have:

84% of the light gathering capability
99% of the resolution
62% of the contrast

Note that this does not account for the additional light scattering (more air/glass interfaces) that occurs in an SCT or Mak which will reduce contrast and light transmission a wee bit more.

-Dan

#9 chuckscap

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Posted 06 September 2009 - 07:36 PM

If it's an Intes 815 (25% CO) vs a top flight 6" APO, I would expect the result to be much closer.

Chuck

#10 Midnight Dan

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Posted 06 September 2009 - 07:59 PM

As my GPS often says, "Recalculating". :grin:

Compared to a 6" Refractor, a 6" Intes with a 25% CO will have:

98% of the light gathering capability
100% of the resolution
85% of the contrast.

So, right you are Chuck! (Again the caveat about other factors such as light scatter)

[EDIT]
OOOPS! It was late last night and I must have typed those numbers into my calculating spreadsheet incorrectly. The right numbers are:

94% of the light gathering capability
100% of the resolution
75% of the contrast.

Thanks to jcrilly for catching it! :bow:

-Dan

#11 Moonglum

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Posted 06 September 2009 - 08:03 PM

There is a review of a TEC MAC 8" F15.5 vs a TEC 160 APO. In it he said the MAC was noticably better. Sorry no link, I'm sure it would be easy to find. I believe the review was in french.

#12 jrcrilly

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Posted 06 September 2009 - 08:03 PM

Compared to a 6" Refractor, a 6" Intes with a 25% CO will have:

98% of the light gathering capability


Is that a typo? Square root of 25 is greater than 2; more like 5 (yielding 95%) - and then you have to consider the mirror losses.

#13 Bob Abraham

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Posted 06 September 2009 - 08:48 PM

I believe the review referred to by Moonglum is this:

http://www.astrosurf...ent/apo140e.htm

The review explicitly compares a TEC 140 to an 8" TEC Mak. I also have a TEC140 and TEC MC200 (8" Mak) and agree with everything said in this review.

Bob

#14 stevew

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Posted 06 September 2009 - 08:48 PM

My wallet would certainly see a big difference.

Steve

#15 coopman

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Posted 07 September 2009 - 07:35 AM

I suggest that you look into getting a MN66 instead. These scopes offer views that approach refractor-like quality with much less cool down time than a 6" Mak. The fov of the MN66 is wider than the Mak too, making it easier to find what you're looking for. The MN scopes can be bought from Teton Telescopes in Idaho.

#16 RAKing

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Posted 07 September 2009 - 08:19 AM

I guess if you remove the theory, then what is left are our subjective opinions.

My new 6 inch f/12 Mak has made me forget all about my 5 inch apo. I suppose a 6 inch apo would be better than the Mak, but it would certainly not be as portable nor as easy to set up and use.

My 5 inch apo required a taller pier than the Mak and I would also have to upgrade to a better mount for a 6 inch apo. If I can assume that someone else will do all the grunt work for me, then I probably would favor the 6 inch unobstructed view of the apo. But in real life, the views out of my 6 inch, long focal length Mak are excellent and I definitely prefer the more compact scope.

My .02 - YMMV :cool:,

Ron

#17 ltha

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Posted 07 September 2009 - 08:38 AM

Hi Ron,

You have distilled the advantage of the Mak-cass well: very compact, easy to handle, transport and mount compared to equal sized refractors. Combined with excellent optical performance, they are really a nice package. I have owned and sold two Questars. Superb optics and mechanics, take anywhere size but just too small aperture for me. Spoiled I guess, but I like more light!

Back to the original question, I found notes from a comp of near-sized scopes several years back:

"20 December 2002

MK67 v 5" Meade APO

Just a quick test run in preparation for a more detailed comparison later. The target was Saturn and seeing was moderate with a fair amount of turbulence. Saturn was decidedly cleaner in the APO and detail presented much sharper in moments of better seeing. I did not try to set exact power matches but was content to just get into the same area and see if there was much of a difference. The Meade blew the MK67 away in sharpness. Detail on the globe and in the rings was clearer and cleaner through the APO. Focus was pretty much a snap in the APO but a bit more uncertain in the MK. I had both on Polaris as well and though each easily showed the companion star, the Meade did it more clearly. The biggest advantage to the MK was it's light weight and easy set up. I can easily carry it out with one hand.


26 December 2002

Cold and clear (for this area) night with a seemingly steady atmosphere. Took the 5" Meade APO and 7" MN76 out for an hours cool-down. By the time I was ready to set them up, the sky had become unusually steady.

My first target was Saturn. Given the nearly identical focal lengths ( the Meade at 45" v the MN at 42") I decided to start with 7mm Pentax SMC orthos (lucky to have a pair on hand!). The Meade was turning in a rock solid, highly detailed image. Four moons were clearly defined as was Cassinis all the way around the ring. The outer ring was distinctly darker than either the B ring or the Crepe ring. Saturn's globe was a pastel olivine green with a darker band half way between the ring and the pole. From the band up to the pole the color darkened quite a bit. The Crepe ring was quite obvious against the globe. Contrast was very good with the sky nearly black behind the image of Saturn.

Turning to the MN76 there was a pronounced increase in image brightness. Saturn was sharply defined and if anything, Cassinis was even darker and clearer-especially in the very front of the ring- than it had been in the Meade. The image was inverted relative to the Meade which made direct comparisons a bit tough. All of the features mentioned in the Meade were seen easier in the MN76. Not sharper, the Meade held a steadier and possibly sharper image but the MN was just a world brighter which made everything easier to see. There was a bit of fluctuation in image sharpness- the image would go in and out of being razor sharp. This was not noticed nearly as much in the Meade. Color more pleasing in the Meade, richer. MN seems to overwhelm with light.

The stock Crayford focuser on the MN76 is garbage. During critical focusing I found it difficult to reach the best focus. But I always did after futzing around a bit. A JMI DX1 has been ordered to fix this problem. The rotating tube rings were a God-sent and made positioning the focuser and the image of Saturn a breeze.

Switching to the 4mm Brandon pushed the power to about what the conditions could hold. The Meade presented a good image but was starting to dim. The MN76 was sharp as a tack and I was able to glimpse Encke's minima. I could not do this with the Meade. The 6mm Pentax SMC ortho was the best image in the Meade. Stunningly clear and detailed. The 4mm softened things up in the Meade more than in the MN76.

Jupiter was just coming into calm air around midnight. Back to the 7mm SMCs in both scopes. The Meade image was the best I have ever seen it turn in. Much like the evening Shoemaker-Levy hit Jupiter a few years back. Wonderfully detailed with the Great-Used-To-Be-Red Spot prominently displayed. Several bands present including two disjointed in the south equatorial region.

The MN was brighter but the Meade was better at showing low contrast features in the cloud bands. The background was a bit darker in the Meade as well. Again, things were easier to see in the MN due to the advantage in light gathering but the APO (really semi-APO as there was a bit of color showing) had higher contrast in the image.

Next I tried M42 paying particular attention to the Trapezium. Using the 6mm SMC ortho the APO pulled all six stars pretty easily. Interestingly, switching to the UO 6mm made it harder to see the two faint stars and I found I was using averted vision in it but not in the SMC. The MN with the 6mm SMC was brighter and all six stars were easy whether the UO or SMC was in the focuser. The APO surrounded the brighter stars with crisp diffraction rings. The MN was just about there but not as good as the APO. The star images were "tighter" in the APO but it was a small difference.

Rigel: both scopes easily showed the companion star. The Meade had a "muddy" series of diffraction rings that were showing blue as the image flickered. The MN was essentially the same.

CONCLUSION:

I know these are different enough that the comparison was stacked in favor of the MN but I was curious to try it anyway. The Meade had just had the new lens cell installed and been cleaned and collimated. When all is said and done, if I had to pick one scope it would likely be the MN76. The contest was really close- it is a matter of personal preference given the MN's brighter images. The Meade is a more convenient scope to use, gives a bit more contrast and is ever-so-slightly sharper. Sitting is a major advantage in comfort. The MN suffers from a *BLEEP* focuser and the need to stand frequently-at least on the G-11. I could live happily with either but would take the larger scope and change a few of the annoying elements."

#18 Midnight Dan

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Posted 07 September 2009 - 08:50 AM

Is that a typo? Square root of 25 is greater than 2; more like 5 (yielding 95%)


Indeed it is! I edited my post above with the correct numbers. Thanks for catching that!

-Dan

#19 Larry Geary

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Posted 07 September 2009 - 02:06 PM

Thanks to everybody. I appreciate the information and visual impressions.

#20 Erik Bakker

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Posted 08 September 2009 - 09:21 AM

Hi Larry,

I sold my AP130 after comparing it to my Questar 7. In equal apertures, the quality APO will win in all respects except portability and mountability. Only you can decide what is important to you. In favour of the apo is the bigger fov, in favor of the Mak is it's longer focal ratio (I like f/16 and longer). Thus the APO is great for widefields as well. The Mak can more easily achieve high magnifications, thus allowing for more viewing comfort due to the longer focal lenght eyepieces used.

Clear skies,

Erik

#21 SteveC

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Posted 09 September 2009 - 09:10 PM

Could someone give me an impression of how a 6" Apo refractor would perform compared to a 6" Maksutov, particularly on planets? I know the theory, but I'm curious about any head-to-head comparisons using high quality instruments.


Hi Larry,

I own a 7" IM Mak and TEC140 and they are comparable except when tempuratures are dropping. My Mak has a fan, but it never seems to be able to stabilize here in NJ during the Winter. Spring, Summer, Fall, it's a very good scope. DSO are brighter with the Mak, planets more contrast and perhaps sharper in the TEC140.

#22 NewAstronomer

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Posted 10 September 2009 - 09:35 AM

Hi Steve, I have trouble even in the summer (only had my C11 a few months this summer). Temps are dropping 3-4° F until 11pm (from about 7pm) some nights (cold summer). Coupled with air conditioning runnning in my house, it seems to be a problem.

I'm working on a home made "CAT cooler" now to see if that would help.

Of course, seeing is a whole 'nuther problem....:)

#23 stanislas-jean

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Posted 10 September 2009 - 01:48 PM

Mora than a long write here with a 6 " cass

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#24 stanislas-jean

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Posted 10 September 2009 - 01:49 PM

now also with the same scope
Stanislas

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#25 stanislas-jean

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Posted 10 September 2009 - 01:51 PM

and the last with a 10" scope
stanislas

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