New Direction Mewlon 300 to Custom Newt??

[issdaol]

Hi All,

I have had my Mewlon 300 for a number of years now and it has been an absolute outstanding scope both optically and mechanically.

However with the construction of a permanent observatory at my dark site property I am considering other options.

I am not really interested in Astrophotography and I have both TOA150 and TSA120 if I need for that purpose.

What I am thinking ..... and please tell me if I have lost my mind...... is a custom Newtonian that will provide the following general outcomes:


Optics of Higher Quality than Takahashis Mewlon 300
Wider Field Views than Mewlon 300
Excellent Mechanical Build equal to or Superior to Mewlon 300
Fixed Primary Mirror Cell
Excellent Quality Focuser with fine focus
Minimum of 14inch Mirror


I love my EM400 mount and do not wish to change from that mount so whatever alternatives I look at should be mountable on the EM400.

I would appreciate any suggestion and comments especially suggestions on current mirror makers & custom builders as I don't think I have enough time to build this myself.

Of course my Excellent Mewlon 300 will come up for sale if this project/idea can proceed as envisioned so someone after a Mewlon 300 in pristine condition should feel free to contact me via PM to discuss.

Cheers

[SpaceNoob]

I'm thinking no, Mewlon would be so much easier to look through. Not sure what a newt would give you over it other than being awkward to look through. If you were intending to use the newt for Astrophotography, that would be a completely different argument.

[glend]

A 14" newt is going to be pretty heavy, are you thinking EQ or Dob mount? It maybe hard to use with your feet on the ground if on an EQ mount/pier. So think about the usability because the easier it is to use the more it will get used.

[issdaol]

Thanks for the comments so far. Interesting things to think about.

Mount I will be using is Takahashi EM400 which already carries my 30kg + Mewlon 300 load pretty easily

Not really interested in a really large Dob as that is more hassle with ladders etc

Main outcome is to maintain or hopefully significantly improve quality of optics and mechanical components (and obviously views) and get a wider field.

In the end maybe the Mewlon 300 is still the best around compromise ?? which is why I initially went that way.

[LewisM]

Newt... you aren't young any more Phil...not so ROBUST any more (ya know I HAD to throw that in :P). For visual, it's going to be a royal PITA.

I'd stay with something catadioptric at least. The Mewlon 300 is a DAMNED fine scope. Be hard to beat. Maybe one of Intes' really large Maksutov's?

[issdaol]

Nice .... well Done !! lol

Hmmm had not really considered the Mak's before.

How do they compare in terms of Optical and Mechanical quality when up against a Mewlon 300 ??

Does a Mak offer a wider field of view?

Cheers :-)

[LewisM]

Maks are usually DEEP, not wide. High focal length.

[UniPol]

Just get an 8" Dob :thumbsup:

[ariefm71]

Keep the Mewlon...

[gregbradley]

I think your list of requirements is going to be hard put to beat the Mewlon. I have never looked through a Mewlon but I know the 300 has an outstanding reputation.

Plus Tak had or has a master mirror maker (I think his name is Rockie).

Anyway, a Newt is going to be long and the viewing spot difficult to reach easily. Perhaps those light weight Newts Paul linked to last week.I think it was Hercules Optics.

An AP 305 Maksutov may do it but they are not being made yet.

I think you are close to the visual instrument pinnacle with what you have.

Perhaps a 200mm TEC ED if you can find one. Or an APM 203mm triplet.

Greg.

[LewisM]

Though Steve has a nice RARE Tak Cat-Newt for sale: http://www.iceinspace.com.au/forum/showthread.php?t=135435

Be perfect really Phil. Best of both worlds in one scope.

Steve's good to deal with too - not that I have ever bought anything from him :lol::rofl::P:rolleyes::whistle: :face:

[issdaol]

:P You just want my M300 and will say anything to get it lol

[issdaol]

Yep dealt with Steve before and can agree on that :-)

If I was coming from a 8inch SCT or Mewlon 210 I would probably have considered that scope because it was actually one that I had long been interested in and to see an immaculate unit come up second hand is rare.

Unfortunately it was a lot of years of using other scopes, practical comparisons and testing that led me to the Mewlon 300 and I don't think I could drop back to anything smaller or lesser quality.

I have my 2 smaller refractors but I have half convinced myself I want everything that the Mewlon 300 offers but just wider field and don't want to sacrifice any quality.

[LewisM]

OK, you want BIG Newt? http://www.telescopeshercules.com/#!htn500/c1tg4

There is even a 600mm one.

It's just money, but your wallet is fairly robust (oh, stop me!)

[glend]

Assuming your willing to make the investment in another quality scope.

How about the Planewave 14" CDK, can't argue about the quality and you would get a wider field of view and a faster scope.

http://www.optcorp.com/planewave-14-cdk-telescope-introductory-price.html

[Hans Tucker]

Sorry to be blunt..but I think you are mad selling the Mewlon 300. This is one scope I would love to own...well the 300CRS.

The only suggestions as a potential replacement would be a custom scope with Royce Optics mirror. Maybe look at the Parallax Instruments range.

http://www.parallaxinstruments.com/

or

I hear Orion Optical UK make some high quality mirrors.

http://www.orionoptics.co.uk/home.html

[LewisM]

I agree Hans - absolutely nuts! The BEST of the best.

Bigger does not always equal better. QUALITY counts over quantity.

[issdaol]

The Planewave certainly seems to fit the bill but it would be interesting to see its visual performance or get feed back about its visual performance firsthand.

It seems to be more optimised as an Astrograph rather than visual platform and I wonder how the 48% Central Obstruction would affect visual use compared to the Mewlon 32% Central Obstruction??

[Kunama]

Keep the Mewlon 300 for travel and get a 24" F3.3 dob for the home obsy Phil.

Newts on Eq mounts for visual were conceived by sadists and masochists !!!

[LewisM]

Hell yes to the sadist comment.

At least you Matt at 9 ft tall can get away with it comfortably :P

[Kunama]

Only way I would want to use a Newt on Eq for visual would be with a very smooth set of rotating rings and the tube ballasted so the focuser remains at the correct angle at all times.

[Hans Tucker]

No Lewis..the best of the best is the C400 16" f/14 Classical Cassegrain :D

My dream scope.

[issdaol]

Now that is a nice piece of kit. Special build but at 75kg there goes a new mount !

Very small secondary too at 29% !

Im guessing it has an additional zero on the end before the decimal point though or getting close enough to an additional zero lol !

[ariefm71]

That plastic Telrad base seems out of place... They should made a nice aluminium version of it.

[LewisM]

Agreed. I am not a fan of plastic anything - the plastic Takahashi 1.25" diagonal annoyed my sensibilities enough to purchase the 2" Tak diagonal as well.

The 1.25" works impeccably, just... well, plastic housing is not what I want :)

Leave plastic for caps and bahtinovs.

Now Phil, you COULD buy one of the Stromlo refractors...

[gregbradley]

Even though Planewave say the CDK is also a visual instrument I found my CDK17 to not give good views. I think it shows the seeing too much. So it would really require good seeing but the scope is more optimised for imaging with the relatively larger central obstruction as opposed to a Mewlon which has a very small secondary.

Greg.

[gregbradley]

Sometimes Tak looks like they are still in the Stone Age. Can you imagine the thermal currents in that beast? The weight.

This is the age of carbon fibre with fans and thermal control for large scopes.

Greg.

[Hans Tucker]

It does have 3-4 fans behind the primary mirror. Since these are custom made scopes I would think a prospective buyer could enquire about the availability of a Carbon Fibre tube.

[LewisM]

OK Phil, I found the new scope for your property.

https://scontent-nrt1-1.xx.fbcdn.net/hphotos-xtf1/v/t1.0-9/11249407_958084697555836_4467997639 660070361_n.jpg?oh=31aae0fdd07a29a0 6f6257ed67626be7&oe=56567A7C

I am sure the ESA might sell it for a handsome fee

[issdaol]

Lewis, it would have been an option but the secondary is a bit big and the thick spiders put me off :lol:

[issdaol]

Been reviewing the options and think I will just stay with the Mewlon 300 for now considering the mounting/usability issues with a custom newt.

Any change to a new scope has to provide increased in optical performance and wider field without the prior mentioned drawbacks which looks like it will be hard to do unless I go to some sort of scope like dobsonian such as a SDM.

I don't particularly like the idea of climbing around on ladders just to get to the eyepiece !

[Rac]

The big tracking dob idea is a good one I think. IF you aren't into photography then I see no down side. Just get a good one with a good mirror set!
I would think big, no less than 24" and fast to keep it short.

[thebonz]

Why not consider the corrector for the M300. This piece of optical wizardry from takahashi will convert the scope down to f10 with much less coma delivering your wider views. The corrector works brilliantly on the m250. Cheers. John

[glend]

Not such a bad thing having to 'settle' for Mewlon 300!!:eyepop:

[issdaol]

Thanks for the suggestion.

I actually had considered this and I know another Mewlon 300 owner who did the corrector upgrade.

Reality is that visually the coma is not noticeable in the Mewlon 300 so while the corrector would provide advantage to a larger format sensor the benefit is not that big for visual.

Will get a bit wider field but again did not seem compelling enough.

I suppose I could just do it anyway for the slight visual benefits as it would not represent any drawback or loss in the investment of the scope itself.

So will ponder this again....

[issdaol]

LoL yes I can see how it would look that way .... :D

[dannat]

At Melbourne obs.,we have a 12" f7ish newt, the beauty of it is the rotating turret at the focused end, ep in wrong position, just slide it around..also useful for people of diff heights. It contains both the finder & secondary --I'm surprised you don't see more of them

[ausastronomer]

Hi Phil,

Keep in mind that Dall Kirkhams and corrected Dall Kirkhams like the Planewave and Tak Mewlons have limitations and downsides as visual instruments. A high quality newtonian, properly set up, of equal aperture is going to outperform either of these scopes as a visual telescope, in several aspects of optical performance. While you might love your Mewlon 300, a high quality 12" newtonian, which has been properly set up by someone with the required know how will outperform it in most respects as a visual telescope. There is an abundance of literature available on why this is so. It is also supported by my practical experience. The above having been said there is also a downside to newtonians. It takes a bit of learning and know how to get a large aperture newtonian to perform at its best. I have looked through dozens and dozens of large aperture newtonians that were not properly set up and badly underperforming. What is sad is that most of the scope owners thought their scope was properly set up and they just didn't know any better. If you're not experienced in setting up a large aperture newtonian it is worth spending some time with someone who is and picking their brains

Cheers,
John B

[ariefm71]

John, I think what makes Tak Cassegrains great (apart from the 1/20th wave optics) is how protected both the primary and secondary mirrors is from stray lights. If both scopes are properly set up, I still think the Tak will have an advantage over newtonian due to this, unless you observe from a very dark location.

Cheers,
Arief

[Shiraz]

why not C14 edge. lock the mirror and put on a high quality aftermarket focuser.

Surely there can be no meaningful arguments on optical quality: http://www.myastrospace.com/forums/forum/video-astrophotography-webcam/62334-more-planetary-images-than-you-can-poke-a-c14-at
http://www.airylab.fr/AirylabUS/index.php?option=com_content&view=article&id=52&Itemid=57

easy to use visual with same obstruction as Mewlon (I think). easy carry for your mount. 1.4x better light grasp and better resolution.

[ausastronomer]

Well there can be because the design paramaters which limit the capabilities of the SCT design as a visual instrument do not affect its ability as an imaging platform, nearly as much. The original poster clearly indicated he has no interest in imaging, so its a pointless excersize directing him to one of Darryl's excellent planetary images. Its a bit like pointing someone to an outstanding DSO image taken with a Ritchey Chretien and saying they make great visual DSO instruments because they take great DSO images. Truth is Ritchey Chretiens make exceptional DSO imaging platforms and very poor visual instruments.

The factors which restrict the performance of a SCT as a visual instrument are:-

Large central Obstruction (>30%)
Additional Air to Glass surfaces (Corrector plate and star diagonal)
Fast F2 primary which introduces field curvature
Narrow filed of view which limits DSO observation.
Closed tube design which inhibits thermal equilibrium of the optics
Corrector Plate which acts as a built in dew magnet.

If you think a SCT can equal a good Newtonian or refractor as a visual instrument you have found a way to defy some of the basic laws of physics.

It's worth noting that some of the factors which affect the SCT design as a visual instrument also affect the corrected Dall Kirkhams like the TAK Mewlon and the Planewave. ie large central obstruction (~30%), additional air to glass surfaces (sub aperture corrector and star diagonal), a closed back mirror cell which inhibits cooling; and a narrow FOV.

Greg Bradley who owns a 17" Planewave has already posted that it isn't a good visual platform. This is due to the reasons I stated above. While the TAK Mewlons have a smaller CO than the Planewave, they still have a 30% (or greater) CO which has a significant affect on the MTF curves.

Cheers,
John B

[ausastronomer]

Firstly that is subjective because we don't know how the optical quality is tested. Is it 1/20th wave RMS, 1/20th wave Peak to Valley, or 1/20th wave at the wavefront? However, we do know that TAK optics are excellent irrespective of the numbers, so you don't need to quote them. It's all pretty academic anyway because the skill of the observer and seeing conditions make optics better than about 1/10th wave at the wavefront superfluous. Just for the record my 14" SDM has a 1/40th wave Zambuto primary and a 1/30th wave Protostar Quartz secondary. My 10" SDM with Suchting primary has optics that match the 14".



If that's the case you have found a way to defy some of the basic laws of physics. See my previous post. The Mewlons are very good, there is no doubting that, but they still come up fractionally short of a well set up premium Newtonian due to the large central obstruction and the other factors I mentioned. They are IMO a better visual platform than an equal aperture SCT.

Cheers,
John B

[Shiraz]

Errr yes, I agree that a Dob mounted Newtonian would be best, but Phil asked for something that should be mountable on an EM400 for visual use. In my experience, that immediately rules out a big Newt - it is physically very inconvenient to use a Newt on an EQ mount and the OTA would present unacceptable wind loading.

Accepting that Phil does not sound keen on the idea of a Dob and that a visual Newt is not practical on an EM400, the only thing I could think of that would give an advantage over his existing Mewlon 300 was a C14edge, which has a fully corrected field and should provide a bit better views than the Mewlon 300 (~same obstruction, bigger aperture) and be an acceptable load on the EM400.

the links to Darryl's image and the interferometer results are not pointless - they were an attempt to pre-answer the inevitable responses that Celestron optics could not possibly be as good as Tak optics - the links show that the C14 optics more than hold their own (the C14edge tested by the French lab was significantly better than the Mewlon 300 they tested and Darryl's image was clearly produced by some near-perfect C14 optics).

[ausastronomer]

Well I have to agree. If he is hell bent on keeping the Takahashi EM400 mount then the C14 Edge HD may be his best option. A medium to large Newtonian on an equatorial mount is not fun to use in any way shape or form. Rotating tube rings help (if its a tubed scope), but it isn't how I like to observe. To be perfectly honest I think the visual astronomy world has progressed forward from using large equatorial mounts for visual astronomy, regardless of telescope design. I have observed with some of the best and most skilled visual deep sky observers in the Southern and Northern hemispheres and none of them use an equatorially mounted scope for their main observing work, and haven't done so for a couple of decades.


Knowing what I know and having used just about all of the contenders, I would be dumping the Mewlon and the EM400 mount and getting a 12" to 16"/F4 to F5 Truss Dob with Servocat and Argo Navis on it. He would probably end up with some cash back and end up with a premium visual telescope. I am not sure why Phil is scared of dobs. They have tracking and go to and all the niceties you can get on any other telescope design. With the faster optics and more modern scope designs a ladder is a thing of the past. I am only short and can observe at the zenith seated using my 14"/F4.5 SDM and stellar observing chair. That scope blows the doors off a 12" Mewlon and cost about 1/2 as much as a Mewlon 300 and EM400 mount.



Damien Peach has been demonstrating the quality of Celestron Optics as the worlds best solar system imager for at least the last 10 years, using a variety of Celestron scopes.

Cheers,
John B

[issdaol]

Thanks for all the new suggestions.

Having had multiple SCT's before and comparing them to the optical quality, mechanical and electronic quality of Mewlons I don't think I would ever go back to using an SCT.

From talking to a couple of other Mewlon 300 owners that also had 14 inch Celestron's the visually image quality does not compare despite the added aperture.

The only issue I have with Newts/Dobsonians is maintenance with collimation as well as ease of observation, as I am aware that optical quality, provided investment is made in top class mirrors, combined build quality, in the case of systems like SDM, can be achieved.

I would really need to look though one of the new breed fast SDM's to see how they compare and talk to owners about their experience with observation (standing or seated i.e. no ladders ) and maintenance.

[AlexN]

If you are worried about maintenance and collimation the worst thing you could possibly do Is buy a fast Newtonian with a truss tube that requires disassembly to transport.

As has been said. The world's best planetary images (and planetary imaging is extremely demanding of optics considering we are talking about imaging at 12 to 15 METRE focal lengths) are imaging with celestron C14's. Paul H. On these forums produced some extremely good images with his c14. Damien peach needs no introduction either.

I tend to feel a lot of people will bag out cheaper scopes in an attempt to convince themselves that purchasing that high priced astro-physics/Tak was a worth while decision.

For visual work or planetary work, a c14 is top of my wish list. That's not to say I think the Mewlon is rubbish. Just that 989.7cm2 of mirror area vs 706.8cm2... Well... Physics rarely tells lies. Larger mirror. More light. More light, more chance of seeing faint details.

I know quality of optics makes a big difference but having owned a c11 myself. I can tell you now the view through a large, high quality sct is sensational. Especially when the seeing supports the focal length.

You know if you sold the Mewlon and em 400 you could probably buy a cpc14 and a 16" dob and have the best of both worlds.

[issdaol]

I tend to feel that a lot of people, that bag out people that purchase scopes like AP or Tak, like to convince themselves that their compromise was a worthwhile decision :P :)

Seriously though, I know that SCT have improved a lot, but there are still draw backs to them and build quality and reliability is still variable and not up to what I personally want in a scope.

A extremely high quality Dob/Newt like John B has mentioned is definitely something worth considering as the only compromises then become collimation and potentially needing to use a ladder to depending if I consider one of the new fast dobs or not.

Will have to see if I can get my hands on one for a night observing and see what I think first though :)

[AlexN]

Fair enough. As is always the way, taking scopes for a test drive is the definitive answer. I do know however that a fast Newtonian will likely one serve to drive you mad. I had a 10"f/3.8 for a short while and it was superb when precisely collimated but the slightest shift and the scope was of no better quality than a cheap department store scope.

For the record too Phil, I was at no point bagging out anyone who buys pricey gear nor was I trying to come to terms with my compromises. I've never been one to compromise when I want something.. I've had Tak scopes, Ive had a TMB apo, an apm with TMB lens, had the Williams optics 110/5.6 TEC apo. I've had custom built newts for imaging, rc's, intes micro 8" mak-cass for visual work. That said I was never shy to buy a cheaper alternative ifbthat alternative could outperform the competition. That's why I bought my C11. Sure, I could have hunted about for a 12" Mewlon, or built a classical cassegrain, but after heaps of discussions and the obligatory test drive or two the C11 was the best option. And at the time the AUD was at parity with the usd so with a bit of shopping around and bargaining with a couple of shops I picked up my C11 with the dew shield,a heater strap, the 6.3 reducer and a piggyback setup for my small apo for $3600. The money saved was funnelled into a Moonlite motor focuser. The scope was a dream and all up cost me less than half the price of my other options.

[issdaol]

Sounds like you have gone through a lot of scopes :-) Astronomy seems to do that to us all lol

I had similar experiences but my last SCT was a C11 which was the best SCT OTA I had used to date. Was very nice on planets.

Then used a friends Mewlon 250 which made the C11 look very poor comparatively. Plus the outstanding build quality and secondary focuser were a dream to use.

So almost went and got a M250 until I was introduced to someone that had the Mewlon 300 which blew the doors of both of them. Especially on Planetary and Lunar visuals. So though what the hell may as well go the whole distance and get the M300.

If I could have gotten the same usability, build quality & optical quality in a cheaper alternative then certainly would have done so as I certainly don't agree with paying premium dollars for a label, but there are not many alternatives options with the same combinations.

It may be that I keep the M300 and buy a custom newt/dob with zambuto mirrors just for wide field... will have to investigate !!


Cheers

[ariefm71]

Zambuto doesn't do sub f/4 mirrors. A large SDM with Mike Lockwood mirror is in my dream list..