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Maksuton-Newtonian vs Schmidt-Cassegrain

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#26 RogerRZ

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Posted 28 January 2013 - 03:19 PM

My MN65 is listed as having a 26% CO, along with a .97-ish Sthrel. I don't know if this is average for the breed (they seem quite scarce), but it does throw up very nice views that are more similar than different to my 2012 vintage C8.

#27 JohnH

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Posted 28 January 2013 - 06:36 PM

My MN65 is listed as having a 26% CO, along with a .97-ish Sthrel. I don't know if this is average for the breed (they seem quite scarce), but it does throw up very nice views that are more similar than different to my 2012 vintage C8.


My old MN-61 with its 18% obstruction. The MN-76 it replaces has a 7.1" clear aperture with just a 1.125" obstruction, making for 15.8% obstruction, a fair improvement but the increase in size is more noticed.

#28 Patrick

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Posted 28 January 2013 - 11:24 PM

My old MN-61 with its 18% obstruction. The MN-76 it replaces has a 7.1" clear aperture with just a 1.125" obstruction, making for 15.8% obstruction, a fair improvement but the increase in size is more noticed.



I always wonder what size the 100% field illumination is with scopes like these. If I had to guess, it's pretty small. That's perfectly fine for planetary work, but aren't these mainly visual scopes?

Patrick

#29 jsrj98

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Posted 29 January 2013 - 02:44 AM

I always wonder what size the 100% field illumination is with scopes like these. If I had to guess, it's pretty small. That's perfectly fine for planetary work, but aren't these mainly visual scopes?


The two Mak-Newts (MN56, MN55) I've owned were fine visual instruments, but had serious limitations for imaging. I loved both scopes, and claimed I'd never sell them-- but ended up doing that in both cases. I also vowed I'd never buy a SCT-- and recently did just that. I've had my EdgeHD 8 for less than a week now, but WOW, what a great scope.

The MN55 wouldn't even come to focus with a new filter wheel I purchased, so replaced it with an MN55. It had more back focus, but when I changed cameras to one with an APS sized chip, the illumination was poor. While I could correct the image with flats, I couldn't get over the fact that I was losing so much data. Without flats, there's no way to make an acceptable image with a Mak-Newt IMO-- and I did that for years with them. I eventually moved on to smaller ED refractors and APO's (90mm to 100mm).

From a visual perspective, for me actually looking thru the APO was always a more pleasing experience than with my Mak-Newts. With them I was always fighting cool down issues (and the MN55 had a fan), plus they are bulky and heavy for their aperture. I never owned a Nagler at the same time as my Mak-Newts, but I can't image they would come close to fully illuminating a 22mm Nagler, let alone a 31mm.

When I decided I wanted more aperture than my smallish APOs could give me (but still have the same viewing experience with a Nagler) I bought an EdgeHD 8. Because I'd read nothing bad about one, I felt confident I'd probably get good to excellent optics. Mine shows a very good star test, and so far I'm extremely happy with the decision. When Celestron ships my dedicated reducer, I suspect I'll be even happier.

#30 orion61

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Posted 29 January 2013 - 08:17 AM

If you look back a couple pages there is quite an exhaustive
thread about central obstruction and images and it doesn't seem to degrade the views nearly as much as people believe it does. A good example is the Meade RCX, fantastic optics with a larger secondary, brightness well, that may be a different story.

#31 Patrick

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Posted 29 January 2013 - 09:16 AM

I always wonder what size the 100% field illumination is with scopes like these. If I had to guess, it's pretty small. That's perfectly fine for planetary work, but aren't these mainly visual scopes?

when I changed cameras to one with an APS sized chip, the illumination was poor.


That's kind of what I figured. I think that's one reason Explore Scientific decided to go with the larger CO on their Comet Hunter. The large secondary means the scope is capable of being used as an astrograph. Mine is actually an f/4.8, but you can see that in some loss of contrast visually.

For imaging, the CO contrast loss doesn't matter, and the larger 100% full illumination circle is very useful. Still, it is a big instrument for only being 6" of aperture.

For Mak Newts, rather than make comparisons to SCT's, I think they should be compared to APO refractors because they have more in common in terms of f/ratio and focal lengths. My Comet Hunter has a focal length of 731mm at f/4.8 with 6" of aperture. The ES 127 f/7.5 Triplet APO has a focal length of 952mm at f/7.5. With a 0.8x focal reducer that gets much closer to the Comet Hunter (762mm at f/6).

Also, the comparison in physical size is closer between a large refractor and the MN.

Patrick

#32 spencerj

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Posted 29 January 2013 - 10:00 AM

From a visual perspective, for me actually looking thru the APO was always a more pleasing experience than with my Mak-Newts. With them I was always fighting cool down issues (and the MN55 had a fan), plus they are bulky and heavy for their aperture. I never owned a Nagler at the same time as my Mak-Newts, but I can't image they would come close to fully illuminating a 22mm Nagler, let alone a 31mm.


This comes up a lot on this forum. Someone has never tried a wide field eyepiece in their Mak Newt (or doesn't even own a Mak Newt), but they are sure the view would be unacceptable. Well . . . I owned a MN66 (smaller secondary than the MN55 or MN65) and I own a 26mm Nagler T5. I have used that eyepiece in that scope several hundred times. While there is a mathematical drop-off in light (that I am sure causes an issue in deep sky imaging) for visual use, the combination works very well.

I loved viewing 2* plus areas of the sky with the 26mm Nagler. The view was flat and sharp to the edge. The illumination drop off does not affect the visual view—certainly not to the extent that some with (or without) experience claim. Outside of an Apo refractor or a Newtonian with a very large secondary mirror, there is always a drop off in illumination at the edge of the field in all telescope designs. The SCT is certainly not immune to this. Until the recent release of the HD SCTs, field curvature as well as edge illumination was an issue in a standard C8. Basically, I could choose to either focus the stars in the middle of the field or the stars at the edge of the field in my C8 with the 26mm Nagler. (Unless I chose something in between where everything was just a little blurry.) So the Mak Newt is held to a higher standard in edge of field illumination because the standard SCT has so much field curvature that illumination drop off is not the biggest issue?

The C8 I had did not have great optics. It was a black tube version from the 90s. My MN66 killed in every way except for light grasp, but the sharper image in the MN66 minimized that advantage the C8 had. The MN66 showed more detail on Mars, Jupiter. Gave cleaner views of double stars. Showed flat, wide-field views that the C8 could never dream of producing. And it cooled down faster. A lot faster. Again, my C8 was not great, but it was not a lemon either. It was somewhere in between and probably well within the bell curve for what was being produced at the time.

Mak Newts are bulky and heavy for their aperture. For me that was the real weakness. As far as cool down goes, that has never been a problem for me either. Certainly not if the comparison is an SCT. The Mak Newt has an oversized tube and light only passes through the tube twice (not 3 times like in a Mak Cass or SCT). Those two features make the Mak Newt superior to those scopes for cool down. Does a standard Newtonian or refractor cool down faster? Sure, but cool down is not a big drawback to the Mak Newt design.

#33 JohnH

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Posted 29 January 2013 - 10:18 AM

Between my MN-61 and now the MN-76, I have used both a 26mm Nagler and a 41mm Panoptic. I had not noticed any serious light fall off across the field of view while observing.

#34 jsrj98

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Posted 29 January 2013 - 10:38 AM

Between my MN-61 and now the MN-76, I have used both a 26mm Nagler and a 41mm Panoptic. I had not noticed any serious light fall off across the field of view while observing.


On my MN55 (which was theoretically optimized for imaging, with a larger secondary and more back focus) the light loss at the outer 1/4 edge of an image taken with a QHY8 CCD camera (slightly larger than a normal DSLR) was more than 50%. I just couldn't get over that, which is why I eventually sold it. At the time I never owned a Nagler, so I could not make a visual comparison.

In theory, the Mak-Newt should experience less cool down issues than an SCT. I've only had my EdgeHD 8 for less than a week, so I guess I'll eventually find out. Having said that I was always disappointed how long it took the views to get really good on my two Mak-Newts.

From a quality perspective (star test), the MN56 and MN55 were always first rate-- and I had the 'papers' from ITE to prove their high Strehl. Of course my new Edge didn't come with any 'proof' of quality (which is why it took me so long to pull the trigger on it), but it's star test is virtually the same on both sides of focus-- which I thought was amazing for a mass produced scope. I'm going to have to dig up my copy of Suiter's book to try to find a fault.

#35 spencerj

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Posted 29 January 2013 - 10:57 AM

What kind of cool down times were you seeing with the Mak Newts? What about the EdgeHD. I used to take mine from inside the house to outside in the winter (40-60*) temp change. It was always fine after an hour or so and ready for high magnification in about 2 hours.

Have you measured the light loss at the edge of the image in the EdgeHD?

#36 titanio

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Posted 29 January 2013 - 11:21 AM

My 6" f/5 Mak Newt has a 32% central obstruction, so I seriously doubt that the f/5.3 has a 20% obstruction. It's even difficult to find standard commercial Newtonian's with central obstructions less than 25%.


MNs designed for visual usage place focus very close to the tube wall, squeaking by with as small a (fully illuminated) secondary as possible. Placing focus so close to the OTA presents a dilemma for imaging and bino-viewing though, usually requiring a relay lens (or Barlow/Powermate etc) to sufficiently "draw out" the image enough to reach focus. To accommodate these uses, some later designs bumped focus further from the tube by reducing the distance from the primary, necessitating the use of a larger secondary, hence a larger CO.

While nice images can be attained using a MN, its greatest prowess (IMHO) is attained when optimized for visual use.

Paul

PS: I loved my (visually optimized) MN86 but, alas, eventually parted with it to make room for other equipment (it was built like a tank, and almost as pretty!)


My Mak Newt 8" f 6 has a 17% central obstruction and it weight less than 12 kg.

Toni

#37 bierbelly

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Posted 29 January 2013 - 12:46 PM

My 6" f/5 Mak Newt has a 32% central obstruction, so I seriously doubt that the f/5.3 has a 20% obstruction. It's even difficult to find standard commercial Newtonian's with central obstructions less than 25%.


MNs designed for visual usage place focus very close to the tube wall, squeaking by with as small a (fully illuminated) secondary as possible. Placing focus so close to the OTA presents a dilemma for imaging and bino-viewing though, usually requiring a relay lens (or Barlow/Powermate etc) to sufficiently "draw out" the image enough to reach focus. To accommodate these uses, some later designs bumped focus further from the tube by reducing the distance from the primary, necessitating the use of a larger secondary, hence a larger CO.

While nice images can be attained using a MN, its greatest prowess (IMHO) is attained when optimized for visual use.

Paul

PS: I loved my (visually optimized) MN86 but, alas, eventually parted with it to make room for other equipment (it was built like a tank, and almost as pretty!)


My Mak Newt 8" f 6 has a 17% central obstruction and it weight less than 12 kg.

Toni


My 8" f/4 has a 25% CO and weighs about 22lb (10 kg).

#38 TG

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Posted 29 January 2013 - 01:44 PM

My 6" f/5 Mak Newt has a 32% central obstruction, so I seriously doubt that the f/5.3 has a 20% obstruction. It's even difficult to find standard commercial Newtonian's with central obstructions less than 25%.


MNs designed for visual usage place focus very close to the tube wall, squeaking by with as small a (fully illuminated) secondary as possible. Placing focus so close to the OTA presents a dilemma for imaging and bino-viewing though, usually requiring a relay lens (or Barlow/Powermate etc) to sufficiently "draw out" the image enough to reach focus. To accommodate these uses, some later designs bumped focus further from the tube by reducing the distance from the primary, necessitating the use of a larger secondary, hence a larger CO.

While nice images can be attained using a MN, its greatest prowess (IMHO) is attained when optimized for visual use.

Paul

PS: I loved my (visually optimized) MN86 but, alas, eventually parted with it to make room for other equipment (it was built like a tank, and almost as pretty!)


My Mak Newt 8" f 6 has a 17% central obstruction and it weight less than 12 kg.

Toni


My 8" f/4 has a 25% CO and weighs about 22lb (10 kg).


Just to join the party, here's my MN-66:

Quartz primary, clear polished on the back to speed up cool down, 20% CO, 1/50 RMS , 1/10 wave certified by Intes. Mount by 1st Base Mounts, assembled and finshed by yours truly.

Unlike other MN-66s, it has a fan on the side sticking out like an ugly wart, but which also helps clearing off the boundary layer from the primary. In addition, the mirror is cored to hold it to the cell with a plug/nut.

After I almost broke my neck in the dark trying to use it on the CGE, I put it on a dob mount where it excels in both widefield (2 degrees with a 23mm Nagler clone) and planetary usage (300x on the planets and 500x on the moon). I've used it a lot more since I put it on the dob mount simply because it's always ready to go and cools down in 30min.

Tanveer.

Attached Files



#39 Paul Hyndman

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Posted 29 January 2013 - 06:00 PM

Nice set up, Tanveer!

Paul

#40 titanio

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Posted 29 January 2013 - 06:40 PM

Hi
My Mn 86 has also quartz optics :)

Posted Image

Toni

#41 Julio

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Posted 29 January 2013 - 06:51 PM

Lovely Tanveer, great handywork!

#42 Julio

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Posted 29 January 2013 - 06:55 PM

Wow que telescopio, lovely setup!

#43 titanio

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Posted 30 January 2013 - 12:29 PM

Gracias Julio

Now I have my MN86 on a very nice Losmandy GM8

Toni

#44 TG

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Posted 30 January 2013 - 01:20 PM

@Julio, @Paul: thanks! I didn't do much, just sent Mark Wagner at 1st Base Mounts and Rings the specs and he sent me a first-class CNC machine cut kit using top-notch plywood. Putting it together and finishing it took but a few days of evening work. If you need a dob mount, his shop is highly recommended.

@Titanio: You can't do better than a Wirth built tube with deluxe Intes optics. I think you'll want to hang on to that OTA for life. One question for you though: what are you doing to get your Mark V (?) to come to focus? I used to have a Siebert OCA that would allow Sibert BV's to come to focus but I sold the whole package and now have a Mark V but it won't come to focus with a regular 2" barlow. I think I need an A-P BARCON to use just the lens as an OCA.

Tanveer.

#45 Paul Hyndman

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Posted 30 January 2013 - 10:16 PM

I used to have a Siebert OCA that would allow Sibert BV's to come to focus but I sold the whole package and now have a Mark V but it won't come to focus with a regular 2" barlow. I think I need an A-P BARCON to use just the lens as an OCA.


Tanveer, I don't know about current availability, but the Denkmeier OCS did a spendid job as a low-amplification relay lens for my MN86, although there was a slight amount of field curvature at the edge and mild vignetting (most likely from the small secondary).

Here are some sample shots comparing it to a 2X Powermate. Focus was shifted outwards out from a -12mm (inside) position to a +25mm (available) position.


Posted Image

Paul

#46 maknewtnut

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Posted 30 January 2013 - 11:31 PM

I just read one fellow's negative comments about a couple of I-M MakNews he owned. Opinions can and will vary, and that's fine. IMO, most folks should be able to substantiate WHY they hold a given opinon.

In this instance, pointing out the illuminated circle size of ANY 5" f/6 Newt based design is a foray into the obvious. As another participant mentioned, this topic, as it relates to these telescopes, seems to come up on this forum with some frequency. It's noteable that in most instances, the poster also refers to illuminating their 31mm Naglers. I'm confused. Why is full illumination of ANY eyepiece with a 41mm field stop in a telescope with a 30mm secondary mirror even a topic of discussion?

I've been a long time advocate of weighing the merits of comments and reviews. One method one can utilize to separate the wheat from the chaff are common threads. One person with an axe to grind is fairly easy to spot when they complain about what almost everyone else compliments. I was taken aback about comments on cooldown with I-M MakNewts. Why? Because that's an attribute an overwhelming percentage of users have offered kudos for.

To continue along the same line with 'issues' about illuminated field size for imaging after adding a filter wheel....given the specs for backfocus, I'm confused as to why you were surprised. Perhaps others can share their successful imaging results. Names like Paul Hyndman and Dean Salman leap to mind (to name just a few) .

Most Cassegrain variants (which includes MCT's as well as SCT's) will provide you with FAR more backfocus most Newtonian based designs. Even given that, given the same simple mathematics, I wish you luck fully illuminating a 31mm Nagler with your new C8..but enjoy regardless.

I sincerely mean that last part. Enjoy John...but c'mon!

#47 jsrj98

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Posted 31 January 2013 - 02:04 AM

If I came across as severely negative against the Mak-Newts I owned that was NOT my intention. I really enjoyed them. However, from an imaging standpoint the ones I owned did have their limitations, which I well understood. For several years I happily imaged with an SX H9 using both scopes with excellent results. When I moved on to a larger chip camera their small secondary proved to be a drawback that I eventually decided I couldn't live with. Astronomy, and especially imaging, is a journey, and you often don't fully know what you are getting into when you start down a particular path.

As I mentioned in my previous post, at the time I owned them I did not also own a Nagler (all my free cash was spent on imaging equipment) so I can't comment on the view with them using those type of eyepieces. I really have no idea if the light falloff would be acceptable-- especially with a 31mm.

When I moved on to an APO refractor for imaging, I stopped taking flats because there was no need to do so-- the chip was completely illuminated. Of course, I did need to use a field flattner (there are trade offs everywhere).

I haven't imaged yet with my Edge8, I'm waiting for the dedicated reducer to be shipped-- I have no desire to image at F/10. Therefore, I have not yet measured any light fall off with the scope. I can tell you, however, that the image plane is completely flat to my eye. Even my APO had a field curvature that I could detect with a Nagler. Not so with the Edge.

Would a 6" or 7" Mak-Newt deliver a better planetary image than the Edge8? Probably. I didn't buy my first SCT for that purpose only, but as an all-around scope-- competent for both visual use and imaging. I can tell you that tonight it delivered the best view of M42 of any scope I've owned, and that includes the Mak-Newts, a customized 8" 'planetary' Newt with superb optics and a very small secondary and nice 10" Dob.

#48 roadi

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Posted 31 January 2013 - 05:41 AM

I can tell you that tonight it delivered the best view of M42 of any scope I've owned, and that includes the Mak-Newts, a customized 8" 'planetary' Newt with superb optics and a very small secondary and nice 10" Dob.


One reason for this could be you've had your best all time seeing this night! other than this just doesn't make sense.
Other reasons might be that those other " optimized ??" scopes you compared the views with, didn't really have such great optics as you say.
That said, I find it great to read so many good reviews of the new Edge HD, "Improved QC" wich might ensure future customers a certain level of quality is great!
but implying, that mass produced equipment are better than that of a niche production from companies crafting limited numbers aiming at through out quality rather than price point, is silly.

#49 maknewtnut

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Posted 31 January 2013 - 09:19 AM

One thing does appear to be sure. The Edge HD's seem to be making many folks happy, which is great. Kudos to Celestron. Enjoy!






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