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Information on the Takahashi Mewlon 210 and Mewlon 250

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#576 Nippon

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Posted 26 July 2021 - 05:18 AM

I don't find my Mewlon 180 C difficult to collimate. I collimate without a diagonal and follow the instructions in the owners manual. If I'm observing on a night with good seeing and the scope is acclimated stars are textbook airy disks at high power and planet and lunar detail is excellent.  


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#577 teashea

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Posted 27 July 2021 - 08:09 PM

Hello Paw,

I have a µ210 also and have wondered the same thing as you, is my Mewlon perfectly collimated?

Teashea, who posted just above you on this thread, has discussed this issue on other posts about his Mewlon and learned from his own trail and error, that sometimes the diagonal is not perfectly  aligned perpendicularly to the light cone. It is best to collimate your Mewlon without the diagonal in place, because sometimes the diagonal does not seat perfectly.

I find where I live that atmospheric seeing can be a problem when trying to attain that ultimate perfection in collimation. Ultimately, I decided that my collimation must be pretty good, because I can split the A and B components of Xi Scorpii, which are separated by 0.76" using my 2" star diagonal inside a Moonlite focuser.  I have not tried to change the collimation of my µ210. I used to have a µ180c, but could never get the collimation right and I asked TNR, from whom I purchased it, to please check the collimation of my 180c before they shipped it to my door. It arrived mis-collimated and remained that way. Jupiter's moons were little footballs and the planet surface was blurry. I had to send it back within the return time limits, so maybe it would have eventually been fixable if I had more time available to tweak it, but I couldn't take the chance. Ed Ting had a similar problem with his µ180. 

I think that if you can split a tight double star close to the predicted Rayleigh limit, which I believe for a 210 mm scope is around 0.67 arcseconds, that your collimation would have to be excellent. 

C/S,

 

-Larry

Larry, that was someone else with the  Mewlon collimation issue.  My Mewlong 180C arrived from Japan in perfect collimation.  



#578 Sunspot

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Posted 28 July 2021 - 01:53 PM

I found this for a RA eyepiece for polar scope. probably will work with straight through finder.

 

https://www.astrosho...r-scope/p,57965

I have seen this, a company in Germany sells it, but they don't respond to emails. Now Orion Telescopes also sells it. The problem (as I see it) is the inside diameter of the part that goes onto the finder is 30mm. The outside diameter of the finder eyepiece is about 36mm. I'd need some form of adapter from 30mm id to minimum 36mm od to make it work. I was thinking maybe this company could cobble an adapter for me. I don't have experience with them. Has anyone dealt with them?

 

https://www.precisep...ain//index.html

 

Thanks

Paul Maxson



#579 Nippon

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Posted 28 July 2021 - 04:33 PM

I though there were two versions. A small and a large. As far as I can tell these are repurposed camera right angle viewers.



#580 PawPawskies

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Posted 11 August 2021 - 05:06 PM

Thanks for the input Larry and Apollo. Between post LASIK spikes and cataracts my vision does not allow me to do any fine visual observations, so I have been relying on camera work for my use and star tests.  This has not been a good summer in my area for observations so I am still waiting to move to a better site when time and weather allow. I think that the collimation is reasonable, but when I use a laser collimator there seems to be some opportunity to improve, but not clear how much of an opportunity. Just trying to focus with a computer screen seems to create more variability in results than the collimation may.  I have added an electronic focuser which seems to help a lot, and maybe more experience with the software to aid focus may give me some confidence in the collimation.



#581 nva

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Posted 24 September 2021 - 08:15 AM

I wanted to contribute to the mother thread. For Mewlon 210 probably 180 regarding the Takahashi Female Dovetail Saddle.

 

I'm not sure if anyone else feels the same way but when I mount my 210 into the universal saddle on my AZ Mount Pro the whole thing always feels a little...iffy, so I did the following.

 

If you want to use the Mewlon 210 Takahashi female dovetail saddle (https://takahashi-eu...-for-mewlon-210) the DUP7T- D Series Universal Dovetail Bar. 7″ Long, Takahashi works perfectly and the dovetail saddle slots right into the circle and is very stable so far (although the whole thing is new to me).

 

Advantages are the telescope can now sit upright on a table and would require some effort to roll over and the female saddle has security screws that work with the stock dovetail.

 

Disadvantages are its purpose built for Takahashi stuff, and the dovetail + saddle adds some weight and also moves the scope away from the mounts center of gravity a little compared to right into the saddle.


Edited by nva, 24 September 2021 - 03:53 PM.

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#582 JeremySh

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Posted 29 September 2021 - 04:08 PM

What do people recommend as widest field, low power eyepiece for the Mewlon 210? I am thinking 2-inch eyepieces.
 

I read on another thread you risk vignetting with eyepieces that have field stop more than 37mm. Is this true?



#583 rkelley8493

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Posted 29 September 2021 - 04:24 PM

What do people recommend as widest field, low power eyepiece for the Mewlon 210? I am thinking 2-inch eyepieces.
 

I read on another thread you risk vignetting with eyepieces that have field stop more than 37mm. Is this true?

22T4 Nagler.

The clear aperture of the Mu 210 is about the same clear aperture as the Baader T2 Zeiss Prism. The widest field, longest focal length I've used so far is the 22T4 Nagler, but I could probably get away with using the 21 Ethos without vignetting. I haven't tried that yet though..

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#584 Jeff Young

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Posted 29 September 2021 - 04:42 PM

I think it depends more on what your tolerance for coma is.  The outer field is going to sea-gull a bit.  (The vignetting actually helps here as it makes it less noticeable.  It's not like you put your target on the edge of the field anyway; it's just nice to have some context.)

 

I routinely use a UO 32 Mk80 with my 250.  (I'd use a 31T5 but the Mewlon is my portable rig and the UO is good enough and quite a bit smaller and lighter.)


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#585 rkelley8493

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Posted 29 September 2021 - 06:03 PM

Based on Teashea's opinion (and obvious experience smile.gif with the family of Takahashi scopes bow.gif ) I will see how the focuser goes (TSA120 although that will arrive by Christmas if I am lucky apparently).  I have been told the Mewlon 210 is 2 weeks away (5 month wait so far) and looking forward to my new arrival ... cannot wait to get this going as we head into Winter and some good viewing targets in the Southern Hemisphere).  I liked the idea of push to AltAz mounts given my mainly visual pursuits, so I invested in a Rowan AZ100 mount - not cheap but quite a robust mount with encoders and grabbed the Nexus DSC Pro with it - just need the Mewlon 210 and off we go (well the TSA120 as well as a dual mount will be nice).  Budget did not quite make the cut for a Berlebach Planet tripod to suit, but hoping to sell some gear to move towards this.  Any preferences from anyone regarding an aluminium / steel tripod vs wood?

I prefer wood tripods [i.e. Berlebach] to aluminum. They're more massive than aluminum and very sturdy [they're also better looking in my opinion].

However, I take the aluminum tripod when I travel bc I'm not scared to throw it in the bed of the truck and ride off with no worries. meditation.gif

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#586 Jeff Young

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Posted 29 September 2021 - 06:40 PM

I use an Astro-Physics pier.  A bit fiddly to assemble, but rock solid.

 

M250-on-AP600.jpg

 

 


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#587 Blueox4

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Posted 29 September 2021 - 06:49 PM

My Mu-210 arrived recently and I outfitted it with a Moonlite focuser with hi-res stepper motor and hand controller. I set it up to make sure it would balance on my mount and it does with no problem. 78A89CB7-5E02-4835-A7D7-6644CAF56E86.jpeg

stock visual back.

E6635E38-C4E5-432D-A6AC-8E0FCB844820.jpeg

weight in ounces of the Moonlite focuser with stepper motor.

91A221E0-3227-43CE-BBEA-638AC7F2676B.jpeg

weight in once’s of Feathertouch focuser and adapter for Mewlon

 

 

 

 

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Edited by Blueox4, 29 September 2021 - 06:52 PM.

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#588 btschumy

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Posted 29 September 2021 - 06:51 PM

I bought a 40 mm Pentax XW for my wide field eyepiece with the 210.  I get about 1.16 degrees with it.  There may be vignetting, but I don’t notice it.


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#589 JeremySh

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Posted 30 September 2021 - 10:39 AM

I bought a 40 mm Pentax XW for my wide field eyepiece with the 210.  I get about 1.16 degrees with it.  There may be vignetting, but I don’t notice it.

Interesting to hear that. Pentax quotes the field stop is 46.5mm. Is the 1.16deg field what you’ve actually measured?



#590 btschumy

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Posted 30 September 2021 - 12:21 PM

I have not precisely measured it, but I have estimated it.  The 1.1 degrees is very close.


Edited by btschumy, 30 September 2021 - 12:38 PM.

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#591 Reid W

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Posted 30 September 2021 - 12:32 PM

Jeremy, I use a 42mm LVW.


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#592 JeremySh

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Posted 30 September 2021 - 02:03 PM

Jeremy, I use a 42mm LVW.

THank you. That one also has a 46.5 mm field stop 



#593 Reid W

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Posted 09 October 2021 - 07:49 AM

I had an interesting "observation" last night with my 210...

 

I achieved a clean split of HR 8119 in Cepheus.  Mag 5.73 & 6.77 with 1.0" separation.

 

I was using a 2004 TV 2" Everbrite,  TV 13mm plossl and 1.25" TV 2x barlow.  About 370x.

 

After confirming, trying different eyepieces, I switched to a Tak 1.25" prism diagonal.

 

With the prism, the view was not as clean.

 

Interestingly, the Tak prism gives views as good as my standard Baader prism and those views in the Vixen doublets are cleaner than the mirror TV.

 

So I'm thinking, that the correction on the 210 is very good and the overcorrection added by a prism has a visible impact. 

 

Earlier this year I compared views in my mirror TV and AP diagonals.  I could not discern any difference.

 

Up until yesterday, I had not pushed the 210 to that point- usually conditions do not lead to such magnifications- and stability.


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#594 Deadlake

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Posted 09 October 2021 - 08:13 AM

I had an interesting "observation" last night with my 210...

 

I achieved a clean split of HR 8119 in Cepheus.  Mag 5.73 & 6.77 with 1.0" separation.

 

I was using a 2004 TV 2" Everbrite,  TV 13mm plossl and 1.25" TV 2x barlow.  About 370x.

 

After confirming, trying different eyepieces, I switched to a Tak 1.25" prism diagonal.

 

With the prism, the view was not as clean.

 

Interestingly, the Tak prism gives views as good as my standard Baader prism and those views in the Vixen doublets are cleaner than the mirror TV.

 

So I'm thinking, that the correction on the 210 is very good and the overcorrection added by a prism has a visible impact. 

 

Earlier this year I compared views in my mirror TV and AP diagonals.  I could not discern any difference.

 

Up until yesterday, I had not pushed the 210 to that point- usually conditions do not lead to such magnifications- and stability.

This is interesting as usual dogma is if a scope is less then F7 use a mirror diagonal and greater than F7 a prism.
Really depends on quality of correction of the scope, which might say a lot for some > F7 scopes....



#595 TG

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Posted 09 October 2021 - 02:09 PM

This is interesting as usual dogma is if a scope is less then F7 use a mirror diagonal and greater than F7 a prism.
Really depends on quality of correction of the scope, which might say a lot for some > F7 scopes....


It’s not dogma. I took some pains to compute the impact of a 25mm prism diagonal: see my reply a bit further down in this thread

https://www.cloudyni...or-a-reflector/

TG

#596 Deadlake

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Posted 09 October 2021 - 02:23 PM

It’s not dogma. I took some pains to compute the impact of a 25mm prism diagonal: see my reply a bit further down in this thread

https://www.cloudyni...or-a-reflector/

TG

My mis-understanding then. The u210 is F11.5. I would select a prism diagonal to use.

Ps: Excellent modelling of different prism's, any idea what Baader T2 BBHS prism glass is?


Edited by Deadlake, 09 October 2021 - 02:25 PM.


#597 TG

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Posted 09 October 2021 - 03:19 PM

My mis-understanding then. The u210 is F11.5. I would select a prism diagonal to use.

Ps: Excellent modelling of different prism's, any idea what Baader T2 BBHS prism glass is?

Thanks for the kind words. I don’t know what Baader uses but I would be surprised if it were anything other than BK7. Maybe shoot them an email?

 

TG



#598 Blueox4

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Posted 10 October 2021 - 07:27 AM

Thanks for the kind words. I don’t know what Baader uses but I would be surprised if it were anything other than BK7. Maybe shoot them an email?

 

TG

BAK4..not BAK7

 

“T-2/90 ° diagonal prism (BaK4 glass) with 35mm free aperture terminal objective side: 2 "or 1¼"”

https://www.baader-p...-part-01b).html


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#599 TG

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Posted 10 October 2021 - 12:55 PM

BAK4..not BAK7

 

“T-2/90 ° diagonal prism (BaK4 glass) with 35mm free aperture terminal objective side: 2 "or 1¼"”

https://www.baader-p...-part-01b).html

Thanks for the info. If I can locate the OSLO file, I might do a similar computation for BAK4. It's always going to be worse than BK7, in terms of polychromatic Strehl, because of its higher dispersion. In a f/12 scope there should be no cause for concern, though.

 

TG


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#600 teashea

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Posted 11 October 2021 - 08:18 PM

I had an interesting "observation" last night with my 210...

 

I achieved a clean split of HR 8119 in Cepheus.  Mag 5.73 & 6.77 with 1.0" separation.

 

I was using a 2004 TV 2" Everbrite,  TV 13mm plossl and 1.25" TV 2x barlow.  About 370x.

 

After confirming, trying different eyepieces, I switched to a Tak 1.25" prism diagonal.

 

With the prism, the view was not as clean.

 

Interestingly, the Tak prism gives views as good as my standard Baader prism and those views in the Vixen doublets are cleaner than the mirror TV.

 

So I'm thinking, that the correction on the 210 is very good and the overcorrection added by a prism has a visible impact. 

 

Earlier this year I compared views in my mirror TV and AP diagonals.  I could not discern any difference.

 

Up until yesterday, I had not pushed the 210 to that point- usually conditions do not lead to such magnifications- and stability.

that is very interesting




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