5" apo Vs Mewlon 180

Benjamin B · #1 15-07-2008, 11:03 PM

Hi all!

I have two scopes in mind and it´s quite difficult to decide which one to but, specially since I have never used or seen one live.

I have read about the Chinese 127 ED apo and it sure looks great. But, will it be a good scope?

I have also been looking at the Mewlon 180. The price difference is quite large, but Takahashi is always Takahashi.

The mount I am going to use is a Losmandy G11. Will the 127 ED apo tube rings fit?

Starkler (Geoff) · #2 15-07-2008, 11:24 PM

What do you want to do with it?

Visual? ap ?

Benjamin B · #3 15-07-2008, 11:49 PM

Visual and moon/sun photography. No CCD.

Ian Robinson · #4 16-07-2008, 12:58 AM

Got the money , go for the Tak Mewlon 180 .

Seems to me - it's a no brainer.

Dennis · #5 16-07-2008, 06:36 AM

Takahashi have discontinued the Mewlon 180, so I assume you will be looking for a used one?

Cheers

Dennis

Benjamin B · #6 16-07-2008, 08:06 AM

Yes, I use one.

gregbradley · #7 17-07-2008, 04:55 PM

Hi,

Firstly the term "APO" gets bandied around by scope manufacturers and has become degraded as a term.

It actually means all colours come to focus at the same or extremely closely the same point.

A Chinese ED doublet will not be able to comply with that definition. It will be sharp and a pleasant view but it will have some colour on bright objects to one degree or another.

There has been a lot of discussion about this point over the years in refractor Yahoo groups.

Generally the scale for refractors is something like this:

1. Astrophysics , TEC. Takahashi triplet (TOA or TSA series) refractors - true APOs
2. TMB Stellarvue triplets -true APOs
3. Takahashi fluorite doublets
4. Other ED doublets a fair drop down from #3.
5. Achromats.

So a Chinese ED doublet should really be called a semi-APO but of course that does not make good marketing. Not to say it wouldn't be a pleasing scope as 127mm aperture for a refractor is getting very useable.

A Mewlon though has no lens elements so there is no false colour, and the spot size is low near the centre and weakens as it goes off centre.

Below a Mewlon 250 the focus is by moving the primary mirror which is fine for visual but probably a pain for imaging (mirror shift).

I have had several Tak scopes and a mount and they were all fabulous scopes and very haveable. Whereas a Chinese scope is usually great value but a bit rough around the edges.

Greg.

Alchemy (Clive) · #8 17-07-2008, 07:38 PM

Quote:

Originally Posted by gregbradley

Hi,

Firstly the term "APO" gets bandied around by scope manufacturers and has become degraded as a term.

It actually means all colours come to focus at the same or extremely closely the same point.

A Chinese ED doublet will not be able to comply with that definition. It will be sharp and a pleasant view but it will have some colour on bright objects to one degree or another.

there are currently a few images in the deep sky version with the Chineese 127 ...... of note is the blue halos around the brighter stars, in this case the APO term really should not be used, and as greg says somewhat diminishes the term. Having said that, at 127mm that you can buy for 1200 or so dollars, the william optics 132 is 5000 and the Televue 127 is 10000 so its probably ok value for what you pay.

Kal (Andrew) · #9 17-07-2008, 11:21 PM

Isn't the Chinese 127 apo the OP is referring to an FCD1 (FPL51) triplet?

Alchemy (Clive) · #10 18-07-2008, 05:50 AM

Quote:

Originally Posted by Kal

Isn't the Chinese 127 apo the OP is referring to an FCD1 (FPL51) triplet?

no idea the one i was referring to is this http://www.iceinspace.com.au/forum/s...ad.php?t=33885
it appears to be the one a few have imported lately (note- the scope used is listed as 127mm APO), theres plenty of detail in the shot but the stars exhibit the blue halo i refferred to.

gregbradley · #11 18-07-2008, 05:09 PM

There is a bit of competition in this area.

There is a 130mm triplet I saw at Bintel that would most likely be better as it is a triplet. There are also a number of used Tak FS128 that have been selling rather cheaply on Astromart. There is also the TMB130 SS that are also good value.

But as you point out they are not AUD$1200 more like about AUD$3500 including shipping and GST form Astromart.

If you want to do visual then an Orion Optics UK Mak Cassegrain or Mewlon 210 would be the go.

Greg.

JohnH · #12 23-07-2008, 09:51 PM

Quote:

Originally Posted by Alchemy

no idea the one i was referring to is this http://www.iceinspace.com.au/forum/s...ad.php?t=33885
it appears to be the one a few have imported lately (note- the scope used is listed as 127mm APO), theres plenty of detail in the shot but the stars exhibit the blue halo i refferred to.

Humph! Call it what you like this scope is a performer - the blue halos only happen if you do not get the focus spot on. An example image here:

http://www.iceinspace.com.au/forum/a...se.php?a=44437

Or do a forum search for 127 APO and see what others are doing with this scope. I liked it so much I sold my Vixen VC200L and kept the 127 ED.

marki · #13 23-07-2008, 11:38 PM

Nice pic John. They certainly seem to be well corrected for colour if focused properly. They are a triplet aren't they?

Ciao Mark

Phil · #14 24-07-2008, 08:04 AM

I have to agree with John I have the the 127mm to and love it. This scope will be staying in the observatory next to the NP101mm. Like John says it is a performer.
Phil

Benjamin B · #15 24-07-2008, 08:16 AM

Thanks all! I think i will go for this scope.

I have only heard good thinks about this scope, so I will order one.

JohnH · #16 24-07-2008, 08:25 AM

Quote:

Originally Posted by marki

Nice pic John. They certainly seem to be well corrected for colour if focused properly. They are a triplet aren't they?

Ciao Mark

Yup it is an air spaced triplet design.

toyos · #17 24-07-2008, 09:04 AM

Even though I'm not deeply impressed by the colour correction of this 127 semi APO, but I prefer a refractor to a comparably-sized reflector of any kind. Can't match the contrast, sharpness & image crispness of a refractor plus I'm not a big fan of diffraction spikes.

It's actually quite a pain getting the focus on that 127mm ABSOLUTELY spot on to get rid of the false colour, and the focuser itself isn't very smooth. Even the el-cheapo GSO Crayford 1:10 works better.

I might sell my 127mm if you're interested since I bought it last month just out of curiosity.

h0ughy (David) · #18 24-07-2008, 09:56 AM

Quote:

Originally Posted by toyos

Even though I'm not deeply impressed by the colour correction of this 127 semi APO, but I prefer a refractor to a comparably-sized reflector of any kind. Can't match the contrast, sharpness & image crispness of a refractor plus I'm not a big fan of diffraction spikes.

It's actually quite a pain getting the focus on that 127mm ABSOLUTELY spot on to get rid of the false colour, and the focuser itself isn't very smooth. Even the el-cheapo GSO Crayford 1:10 works better.

I might sell my 127mm if you're interested since I bought it last month just out of curiosity.

i have fixed this problem by using a JMI crayford focuser with robofocus unit

- it just slips into the existing 2"

Benjamin B · #19 24-07-2008, 06:52 PM

To be honest I take it with a grain of salt when I read people that says they can see some color on bright objects. I can see that too with my TMB super apo and as well with my Takahashi. BUT this has nothing to do with the scope! Bad seeing, eyepiece, diagonal and a star/moon that is low in the sky will show some color. Color will also be seen in AP, WO, or any other expensive telescope when other factors are encounted.
The blue hallows in pictures can also be an effect of internal effects of the camera. Seen that with AP, Takahashi, TMB and other telescope. One have to be very sure that the scope is the problem. And the telescope is an apo with 3 elements/triplet objective, not a semi apo. If this is a semi apo my Takahashi and TMB super apo is also a semi apo. This is my opinion.
The lences are from Japan, not china. I have talked to people that bought this scope and have not seen any color what so ever.
I will not take any CCD or images of DSO with this scope, just the moon and sun.
I think it will be perfect for me.
About the focuser, well, I have read that the Takahashi focuser is not good! Well, in my opinion, I like the Takahashi focuser over my FT on my TMB.
The focuser can be fixed on the 127 apo if there is really any problem.
I will let you now all when my scope arrives. Thanks all!

Kal (Andrew) · #20 24-07-2008, 07:15 PM

Quote:

Originally Posted by Benjamin B

The lences are from Japan, not china. I have talked to people that bought this scope and have not seen any color what so ever.

The raw glass used as the ED element in the lens is FCD1 glass from a factory in Japan, but the lenses themselves are manufactured in China.