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Information on the Takahashi Mewlon 210 and Mewlon 250

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#26 TheFacelessMen

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Posted 13 November 2016 - 06:16 PM

Great thread :-)

 

Good to see some Mewlon specific threads with detailed equipment setup & use and observation experiences.

 

Would be nice to hear ongoing observation session experiences on specific targets and eyepiece combinations.

 

One quick point on the Tak Collimation scope is that although it is best used with a Centre Marked Secondary it is definitely not totally useless if the secondary does not have a centre spot.   The Tak Collimation scope slides to change focus on various points of the optical train......so at a very minimum you can use it to tell if your primary, spider and secondary housing are all properly aligned. 



#27 rolo

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Posted 13 November 2016 - 10:04 PM

I love my Mewlon 250. I use it for what it was intended, planetary excellence. I prefer the old version as I could care less for additional correcting lenses that do nothing for planetary detail. I could care less for reducers for this scope as it wasn't designed for widefield anything.

The planetary views are fantastic with refractor like contrast, and superb sharpness. I also have a C14,AP130GT and FS152 but prefer the M250 for the planets. Down here in Ga at times we get very good seeing that lets the Mewlon shine!


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#28 Tyson M

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Posted 14 November 2016 - 11:57 AM

This thread is waking my wallet tremble. 

 

Maybe I'll put off all purchases for astronomy for the next 10 years and buy a 250.....hmm


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#29 bobhen

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Posted 14 November 2016 - 12:39 PM

This thread is waking my wallet tremble. 

 

Maybe I'll put off all purchases for astronomy for the next 10 years and buy a 250.....hmm

You could do worse.

 

Bob


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#30 Tyson M

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Posted 14 November 2016 - 01:10 PM

Rolo's statement is quite interesting. Those are some fine telescopes he was comparing to. 

 

And you said you observe with the NPV night vision eyepiece with the 210. Do you think that's possible with the larger 250?

 

If they are available in Canada I was thinking that would be an amazing addition as well



#31 bobhen

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Posted 14 November 2016 - 02:39 PM

Tyson M,

 

HERE is a link to a Night Vision site that will help you with your research. Look up jdbastro he uses a 250 Mewlon with a Night Vision eyepiece and shoots video. Just a note, the live view is 2 to 4 times better than any video I've seen.

 

You can use just about any scope with NV but just like using a camera, different scopes will bring different fields of view and image scales to the party. 

 

I use my Mewlon 210 with NV for large image scale and small objects like globular clusters. I use fast refractors for wider fields and large nebula.  I have to say that NV is easy to use and a lot of fun once you get over the sticker shock.

 

Also keep in mind that Canada does not get the seeing that GA gets and for lunar/planetary a Mewlon 250 in Canada might be overkill most of the time.

 

Bob


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#32 bottlecrusher

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Posted 14 November 2016 - 02:56 PM

Does anyone know what the F ratios of the mirrors are and what the % area of the COs are on the mewlon series scopes?



#33 Tyson M

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Posted 14 November 2016 - 02:56 PM

Thanks for your input Bob! Much appreciated that link was exactly the kind of info I was looking for.

 

And yes, our seeing is typically very poor


Edited by Tyson M, 14 November 2016 - 04:17 PM.


#34 ckwastro

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Posted 14 November 2016 - 03:04 PM

Does anyone know what the F ratios of the mirrors are and what the % area of the COs are on the mewlon series scopes?

The 210 is a native f/11.5 and CO is listed as 31%.  I'll have to go back an measure mine as I thought it was 30%.  Not a big deal with only a 1% difference. However don't let it fool you.  The scope is so well-baffled that contrast is excellent (deep-sky surprised me), and it gives razor-sharp lunar & planetary images when the seeing conditions are favorable.  As I've mentioned elsewhere it is the best folded optical design I've used.



#35 dr.who

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Posted 14 November 2016 - 04:17 PM

Mewlon 210
210mm/8.27in aperture
f/11.5
32% CO
2,415mm focal length
13.4 limiting magnitude
18mm image circle
210mm back focus
Primary mirror 220mm elliptical Pyrex aluminized multi coating
Secondary mirror 65mm spherical Pyrex aluminzied multi coating
244mm/9.6in diameter
700mm/27.56in length
9 kg/19.8 lbs
7x50 finder 6.3 degree FOV
 
Mewlon 250 CRS (current production model)
f/10
250mm/9.84in aperture
28% CO
2,500mm focal length
13.8 limiting magnitude
21mm image circle
210mm back focus
Primary mirror 260mm elliptical Pyrex aluminized multi coating
Secondary mirror 72mm spherical Pyrex aluminzied multi coating
280mm/11in diameter
850mm/33.47in length
15 kg/33 lbs
7x50 finder 6.3 degree FOV with recticle illuminator
 
NOTE:  Takahashi masked off the outer 10 mm of the primary mirror in order to eliminate the coma problem that was noted in the original Dall-Kirkham design


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#36 bottlecrusher

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Posted 14 November 2016 - 04:34 PM

I know the overall focal ratio from the online specs, but do you know the F ratio of each of the two mirrors?  A Dall-Kirkham overall focal ratio should be F/R of the primary X the F/R of the secondary.  I'm guessing they are about 3 and 4, but Tak may make the primary more aggressive, but given the 30% CO I think not.  I'm considering either a 250 mm Mewlon or a CFF classical cassegrain which uses a F3 primary and F5 secondary and you end up with a CO around 25%.  



#37 TheFacelessMen

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Posted 14 November 2016 - 05:24 PM

F Ratio of the earlier non CRS version Primaries was F3 for the Mewlon 300 and F3 for the Mewlon 250......not sure about the newer CRS versions of the scopes


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#38 ckwastro

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Posted 14 November 2016 - 06:00 PM

TNR has M210 primary as f/2.9 and secondary at f/4.


Edited by ckwastro, 14 November 2016 - 06:02 PM.


#39 ckwastro

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Posted 15 November 2016 - 08:50 AM

After going over old research, reading this thread, & quite a bit of internal debate I decided to hang on to my 210 rather than move up to the 250. Now that I have the 12.5 Teeter, the 210 fits the scope progression better, and I just couldn't part with this mirror. I'm sure all of the Mewlon optics are outstanding, but this one I know for certain performs admirably, and is long paid for, so why let it go?

 

I'm going to upgrade the focuser, and probably the finder to an RA. I've decided on the Moonlite focuser this time rather than the FT. Most of my scopes always have FT, but the Moonlite is $125 less, and it's lighter weight, so I'll go this route for a change.  I thought about this years ago, but wasn't sure what I was going to do with the scope so I held off.  This seems like the right move.


Edited by ckwastro, 15 November 2016 - 10:48 AM.


#40 Daniel Mounsey

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Posted 15 November 2016 - 09:30 AM

Mewlon 210
210mm/8.27in aperture
f/11.5
32% CO
2,415mm focal length
13.4 limiting magnitude
18mm image circle
210mm back focus
Primary mirror 220mm elliptical Pyrex aluminized multi coating
Secondary mirror 65mm spherical Pyrex aluminzied multi coating
244mm/9.6in diameter
700mm/27.56in length
9 kg/19.8 lbs
7x50 finder 6.3 degree FOV
 
Mewlon 250 CRS (current production model)
f/12
250mm/9.84in aperture
28% CO
3,000mm focal length
13.8 limiting magnitude
21mm image circle
210mm back focus
Primary mirror 260mm elliptical Pyrex aluminized multi coating
Secondary mirror 72mm spherical Pyrex aluminzied multi coating
280mm/11in diameter
850mm/33.47in length
15 kg/33 lbs
7x50 finder 6.3 degree FOV with recticle illuminator
 
NOTE:  Takahashi masked off the outer 10 mm of the primary mirror in order to eliminate the coma problem that was noted in the original Dall-Kirkham design

 

 

 

Carson I think you meant to say 2500mm F10 for the corrected CRS model. 40mm image circle etc.


Edited by Daniel Mounsey, 15 November 2016 - 09:32 AM.


#41 dr.who

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Posted 15 November 2016 - 11:17 AM

After going over old research, reading this thread, & quite a bit of internal debate I decided to hang on to my 210 rather than move up to the 250. Now that I have the 12.5 Teeter, the 210 fits the scope progression better, and I just couldn't part with this mirror. I'm sure all of the Mewlon optics are outstanding, but this one I know for certain performs admirably, and is long paid for, so why let it go?

 

I'm going to upgrade the focuser, and probably the finder to an RA. I've decided on the Moonlite focuser this time rather than the FT. Most of my scopes always have FT, but the Moonlite is $125 less, and it's lighter weight, so I'll go this route for a change.  I thought about this years ago, but wasn't sure what I was going to do with the scope so I held off.  This seems like the right move.

 

Kerry

 

You can keep the excellent Mewlon finder by just adding the TE adapter I posted about above. It works really well and can also be used on a straight through polar scope if you have a EQ mount. Double duty for less than the cost of a good RACI.



#42 dr.who

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Posted 15 November 2016 - 11:18 AM

Carson I think you meant to say 2500mm F10 for the corrected CRS model. 40mm image circle etc.


You are right Daniel. I was pulling that from the Mewlon manual I found at TNR. Looks like they have the old one still up. I changed my original post.
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#43 ckwastro

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Posted 15 November 2016 - 11:30 AM

 

After going over old research, reading this thread, & quite a bit of internal debate I decided to hang on to my 210 rather than move up to the 250. Now that I have the 12.5 Teeter, the 210 fits the scope progression better, and I just couldn't part with this mirror. I'm sure all of the Mewlon optics are outstanding, but this one I know for certain performs admirably, and is long paid for, so why let it go?

 

I'm going to upgrade the focuser, and probably the finder to an RA. I've decided on the Moonlite focuser this time rather than the FT. Most of my scopes always have FT, but the Moonlite is $125 less, and it's lighter weight, so I'll go this route for a change.  I thought about this years ago, but wasn't sure what I was going to do with the scope so I held off.  This seems like the right move.

 

Kerry

 

You can keep the excellent Mewlon finder by just adding the TE adapter I posted about above. It works really well and can also be used on a straight through polar scope if you have a EQ mount. Double duty for less than the cost of a good RACI.

 

I did see your post but I have not had the best luck purchasing from overseas.  Most transactions I've attempted have been a PITA.  Is that the case here?  Did you just use a PayPal account or a credit card?  Thanks.



#44 Lola Bruce

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Posted 15 November 2016 - 12:18 PM

Carson I will now have a friend close with the same scope.

Bruce



#45 dr.who

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Posted 15 November 2016 - 07:52 PM

Cheers Bruce. Now we just need to link up for observing!

 

Kerry

 

I used a credit card to pay via PayPal. Double protection for me as a buyer. TE was really great to deal with. They sell overseas all the time.



#46 ckwastro

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Posted 15 November 2016 - 08:57 PM

Kerry

 

I used a credit card to pay via PayPal. Double protection for me as a buyer. TE was really great to deal with. They sell overseas all the time.

Thanks! 



#47 Kunama

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Posted 15 November 2016 - 09:06 PM

Bobhen, if you remove the scopes back plate/rear cell to remove the finder scope, won't you risk messing up the collimation or optical alignment?  

 

Bill

I dismantled both my Mewlon 210 and my CN-212 to clean the mirrors and after reassembly the collimation was still near perfect.  Just remember to mark the orientation so that the back plate goes exactly the same way. On the CN212 the cell could be rotated to place the Newtonian focus into a different position in relation to the finder.



#48 krakatoa1883

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Posted 16 November 2016 - 03:13 PM

The Takahashi Collimation scope DOES NOT work on the Mewlon 210. It may work on the 250. I won't know that until I get my 250 out of the box, on the bench, and get a look to see if there is actually a center spot. Supposedly there is.

I completely agree. I purchased the Taka collimator for my 210 and made the center spot by myself (it is not difficult)

secondary dot.jpg

but after some afternoons spent in trying to center the spider and to collimate the secondary following the instructions, I discovered that this procedure is all but useful and that can even lead to badly miscenter and miscollimate the tube. So, for centering the spider I removed the secondary, put a (very well) collimated laser in the eyepiece holder (provided with a self-centering 2"/1.25" adapter in order to avoid any tilting) and adjusted the four radial screws until the red dot exit the small center hole in the secondary holder (I previously removed the center nut and the threaded spacer). In doing so one should also check that the light pencil exits the primary baffle tube in center position.

For collimating the secondary my opinion is that there is no substitute to the star test or at least to an artificial star, so I don't see any reason to purchase the collimating scope or an expensive collimating tool.

Edited by krakatoa1883, 17 November 2016 - 02:08 AM.


#49 The Ardent

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Posted 17 November 2016 - 12:11 AM

Ordered Sunday and arrived Wednesday

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#50 amys

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Posted 18 November 2016 - 03:34 PM

Just placed an order for that today.  The straight-through finder on my new Mewlon 210 and the mirror shift using the stock focuser are the only 2 aspects of this scope that I don't care for.  The FeatherTouch focuser (I traded my Mak Cas adapter for the Mewlon adapter) took care of the mirror shift but using the finder scope has been a real pain in the neck.  Literally.  I don't understand why Takahashi has not provided a spot for mounting an additional finder.  




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