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AP 130 vs TEC 140 vs TOA130

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#76 SteveLD

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Posted 01 November 2010 - 11:16 PM

Hi Jim,

It's true that most premium Dobs these days are truss designs and need to be collimated regularly. The only possible exception are the Teleports which are unique in that you don't take the trusses apart when you close up the scope. They do a better job of holding collimating when you set them up and take them down. Most Dobs have full thickness mirrors which result in slow cool down, but Starmaster effectively uses thin mirrors in superb mirror cells that enables them to cool down fairly quickly.

One design that IMO has an edge over 5" APO's in terms of portability and ease of set up is the 210mm Takahashi Mewlon. It is about 27 inches long and weighs 17.6 pounds. This weight includes an outstanding 7X50 Tak finder mounted in a bracket that is welded to the optical tube assembly. This finder bracket serves as a grab handle that eases support and setup without altering the alignment of the finder one iota. The optical tube also includes a mounting plate that easily adapts to most standard mounts including Losmandy. You don't need to add tube rings or a clamshell to the Mewlon. The open tube design and removable rear mirror cell cover ensures that the scope reaches thermal equilibrium quickly. Optically the Mewlon is outstanding. It is sensitive to collimation, but once collimated, my experience is it holds collimation for long periods of time. Greater aperture, superb optics and higher focal ratio provide superior views to 5" APOs on most objects. When seeing permits, its easy to reach 400X with a 6mm eyepiece and more if the seeing is outstanding. That kind of magnification doesn't work nearly as well with shorter focal length 5" APOs. The one area where the APOs beat the Mewlon is in wide field imaging and viewing; especially from dark sites. In this respect APOs are unequaled save for much more specialized, super fast, corrected Newtonians that work best as imaging scopes. Also, inch-for-inch the APos are without peer.

Steve

#77 deprofundis

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Posted 02 November 2010 - 11:29 AM

One design that IMO has an edge over 5" APO's in terms of portability and ease of set up is the 210mm Takahashi Mewlon. It is about 27 inches long and weighs 17.6 pounds. This weight includes an outstanding 7X50 Tak finder mounted in a bracket that is welded to the optical tube assembly. This finder bracket serves as a grab handle that eases support and setup without altering the alignment of the finder one iota. The optical tube also includes a mounting plate that easily adapts to most standard mounts including Losmandy. You don't need to add tube rings or a clamshell to the Mewlon. The open tube design and removable rear mirror cell cover ensures that the scope reaches thermal equilibrium quickly.


Unless they changed the design, the Mewlon 210 doesn't have the removable rear cell cover. Only the 250 and 300 have that.

#78 jrbarnett

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Posted 02 November 2010 - 12:56 PM

I have a Mewlon 210 too. My main problem with the Mewlon is that mine does not hold collimation particularly well, and when it's even slightly miscollimated, it can't keep up with the TEC. Otherwise, it's a nice scope. Well made, cools quickly and, when collimated properly, performs extremely well. I have tried both the stock collimation screws and Bob's Knobs, and nonetheless each time I transport the scope by automobile it seems to get bumped. Mine's in a Scopeguard case, so it's not like it's rolling around in the bed of a truck or anything. :grin:

Regards,

Jim

#79 SteveLD

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Posted 02 November 2010 - 02:05 PM

I actually had a Mewlon 180 (no longer made), but it held collimation very well. I wonder if something is loose in your Mewlon? I friend of mine owns the 210 and the design seems virtually identical. Do you have a lot of mirror flop? It was minimal in my 180. It might be worth contacting Fred over at Land, Sea, and Sky/Texas Nautical (Takahashi America) to see if he has something to say about this. They do perform repairs, adjustments, cleaning, and other maintenance and provide excellent if somewhat costly service.

Steve

#80 jrbarnett

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Posted 02 November 2010 - 02:34 PM

Thanks Steve. I suspect a couple of things; one being a slightly decentered secondary and the other being something not quite mechanically right with the secondary attachment /pivot mechanism. I figured I would disassemble it here at home at some point, recenter the spider using calipers and inspect the secondary adjustment mechanism, and if I couldn't get it sorted out then send it to Art for some TLC.

Regards,

Jim






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