New Takahashi joins the fleet

[Alan White]

10 minutes ago, Mr Spock said:

Just think of it being like the JWST and you'll be fine 👍

Slightly out of context quote, sorry Michael, but

I had no idea that the Mewlon  cost so much, but with Jeremy’s link to a sports car, we’ll that makes sense 😉

This is all send with good humour and tongue in cheek.

[Alan White]

11 minutes ago, JeremyS said:

There is small shift on focus, but it’s not bad at all. Similar to my C9.25

Focus shift is perhaps just an inherent part of the design of this type of scope.

[Mr Spock]

Any design which moves the mirror for focusing is going to have shift to some degree. You can always add a focuser and fix the mirror in place.

[SthBohemia]

9 minutes ago, Mr Spock said:

Any design which moves the mirror for focusing is going to have shift to some degree. You can always add a focuser and fix the mirror in place.

^ I am surprised that a high end manufacturer, ala Takahashi does not use the standard cassegrain practice of having the mirror fixed and utilising a good quality focuser! Cost cutting measures I guess. 😞 

In actuality have been thinking of converting a Meade SCT to a fixed mirror system, only hinderance being the lathe does not have a 12" swing to 'butcher' the original endplate... Anyone got a celestron 6" SCT (orange tube only) 4 sale that I can 'convert'? 🙂 

[Stu]

1 hour ago, Mr Spock said:

The only negative is those thick vanes. Somewhat over engineered. My 12" has regular thin vanes. They work ok and I can't say I've seen any diffraction spikes worth noting.

Just think of it being like the JWST and you'll be fine 👍

You must have diffraction cane cancellation software running in your brain Michael, they are definitely there!

[Stu]

11 hours ago, JeremyS said:

Was clouded out before Saturn was sufficiently high.

Looked at few objects to get the hang of it. The most impressive was M13. With the Apollo 11 (x220) the glob filled much of the field and was scattered all over with lovely pinpoint stars, even with direct vision. M57 was a lovely green with a nice hole in the middle.

I think that’s the first time I’ve seen an Apollo 11 in the wild! Nice?

[HollyHound]

41 minutes ago, SthBohemia said:

^ I am surprised that a high end manufacturer, ala Takahashi does not use the standard cassegrain practice of having the mirror fixed and utilising a good quality focuser! Cost cutting measures I guess.

There’s a little about the Dall-Kirkham design vs Cassegrain here… http://www.scopeviews.co.uk/TakMewlon180C.htm

It does seem to be cost (it’s only been cost effective to grind hyperbolic mirrors cost effectively, quite recently) but also apparently they hold collimation a bit bette too 🤔

[HollyHound]

2 hours ago, Deadlake said:

Also how do you find BV usage, focus range makes this a little harder then the C11.

I have to swap to a much shorter optical back end when I use mine with binoviewers, but then I’m not using a GPC etc (yet).

In this configuration it does work very well indeed, especially with two Hyperion Zooms 👍

[Stu]

6 minutes ago, HollyHound said:

There’s a little about the Dall-Kirkham design vs Cassegrain here… http://www.scopeviews.co.uk/TakMewlon180C.htm

It does seem to be cost (it’s only been cost effective to grind hyperbolic mirrors cost effectively, quite recently) but also apparently they hold collimation a bit bette too 🤔

Strange if it is cost, as the primary mirror is actually 220mm to ensure no edge errors affect the image. Sure the marketing guys wanted to call it a Mewlon 220!

[HollyHound]

13 minutes ago, Stu said:

Strange if it is cost, as the primary mirror is actually 220mm to ensure no edge errors affect the image. Sure the marketing guys wanted to call it a Mewlon 220!

Yes, they definitely oversize the mirror to reduce visible aberrations… typical Takahashi, they don’t seem to ever “over claim” their specifications 👍

According to that review they finish the mirrors as a matched pair in house, so I wonder whether they literally don’t have the machinery to create hyperbolic and prefer to use their craftsman instead. But of course they have their lenses made by Canon, so that doesn’t make much sense either 🤔

One thing of note, is that Mewlons have a smaller central obstruction compared to SCT/Maks and (possibly?) Cassegrains, which does give them the exceptional contrast 😃

Edited September 3, 2022 by HollyHound

[Stu]

48 minutes ago, HollyHound said:

Yes, they definitely oversize the mirror to reduce visible aberrations… typical Takahashi, they don’t seem to ever “over claim” their specifications 👍

According to that review they finish the mirrors as a matched pair in house, so I wonder whether they literally don’t have the machinery to create hyperbolic and prefer to use their craftsman instead. But of course they have their lenses made by Canon, so that doesn’t make much sense either 🤔

One thing of note, is that Mewlons have a smaller central obstruction compared to SCT/Maks and (possibly?) Cassegrains, which does give them the exceptional contrast 😃

I think a lot of the contrast comes from the smoothness of the mirror too, cuts down on scattered light. I think my Mewlon probably showed a slightly cleaner image than my 8” f8, possibly for that reason, not sure.

[HollyHound]

6 minutes ago, Stu said:

I think a lot of the contrast comes from the smoothness of the mirror too, cuts down on scattered light. I think my Mewlon probably showed a slightly cleaner image than my 8” f8, possibly for that reason, not sure.

The ScopeView reviews seems indicates that too, so it is very likely to be a factor 👍

“I should also point out here that Takahashi finish the mirror polishing in-house and each pair is a matching set. Bench tests suggest Mewlons have excellent optics and this one certainly does, as we will see.”

[SthBohemia]

1 hour ago, Stu said:

the primary mirror is actually 220mm to ensure no edge errors affect the image.

The above has me in stitches of laughter- Turned down edge and dodgy 95% zone, tutt tutt Takahashi 🙂 In all honesty not a bad idea to use an oversized mirror for any type of Cass or for that matter Mak or SCT config.

@HollyHound making a true Cass is akin to facing a living nightmare, pure masochism. I am undertaking a 200mm newt/cass, 95% complete, final figuring of the secondary required. Testing the zones of a 60mm secondary for the hyperbola (Gaviola test) is a strain on ones sanity!

A true cass secondary is possibly larger than a Dall-Kirk because it is nigh impossible to NOT get a turned down edge when figuring the hyperbola 😞 

[Stu]

12 minutes ago, SthBohemia said:

The above has me in stitches of laughter- Turned down edge and dodgy 95% zone, tutt tutt Takahashi 🙂

Quite sure that’s not what they produce, just being ultra cautious I’m sure.

[SthBohemia]

46 minutes ago, Stu said:

just being ultra cautious I’m sure.

Just being my usual 'sarcastic' self 🙂  There are articles from Alan Macintosh and others within 'Sky and Telescope, Bulletin C, Gleanings for ATM's' and Warren Fillmore 'Construction of a Maksotov' that suggest the use of oversized mirrors. I just make 'em as the math/physics conflab is totally beyond me 😞  Anyone got a few extra brain cells 4 sale?

P.S. Regarding  the post below- Had 2 look up what MENSA is! Unless the MENSA club provides free beer and Aussie BBQ's I'm not applying!!

Edited September 3, 2022 by SthBohemia

[Stu]

2 minutes ago, SthBohemia said:

Just being my usual 'sarcastic' self 🙂  There are articles from Alan Macintosh and others within 'Sky and Telescope, Bulletin C, Gleanings for ATM's' and Warren Fillmore 'Construction of a Maksotov' that suggest the use of oversized mirrors. I just make 'em as the math/physics conflab is totally beyond me 😞  Anyone got a few extra brain cells 4 sale?

We talked about that didn’t we? 😉😉😂😂

Apparently @Mr Spock and @LukeSkywatcher are the ones over endowed with brains according to MENSA.

[Mandy D]

4 hours ago, SthBohemia said:

^ I am surprised that a high end manufacturer, ala Takahashi does not use the standard cassegrain practice of having the mirror fixed and utilising a good quality focuser! Cost cutting measures I guess. 😞 

In actuality have been thinking of converting a Meade SCT to a fixed mirror system, only hinderance being the lathe does not have a 12" swing to 'butcher' the original endplate... Anyone got a celestron 6" SCT (orange tube only) 4 sale that I can 'convert'? 🙂 

I've got a lathe with a 13"+ swing over the bed and can probably squeeze another 5" with the gap out. Do you not have a removeable gap in the bed?

[SthBohemia]

34 minutes ago, Mandy D said:

Do you not have a removeable gap in the bed?

Tis but a Myford ML-7, 7" swing thru da gap. Geez @Mandy D Whatcha turn on that monster? Propellor shafts for the Titanic? Mind is boggling at the moment- How heavy is it?

[Nicola Fletcher]

@JeremyS This is absolutely fabulous- please tell us how you get on with it!

I’d be really interested to know whether you would have this or a TSA120 if you could only have one…for visual use. I can’t afford both!

[Mandy D]

1 minute ago, SthBohemia said:

Tis but a Myford ML-7, 7" swing thru da gap. Geez @Mandy D Whatcha turn on that monster? Propellor shafts for the Titanic? Mind is boggling at the moment- How heavy is it?

It's only a Harrison M300! I believe it weighs 1650 kg. Had to get a 2 tonne fork truck in to lift it off the trailer.

[Deadlake]

11 hours ago, JeremyS said:

There is small shift on focus, but it’s not bad at all. Similar to my C9.25

Will you be keeping your C9.25?

[JeremyS]

4 minutes ago, Deadlake said:

Will you be keeping your C9.25?

Time will tell. The C9.25 is a cracking scope visually.

Need more time with the Mewlon to decide.

Another consideration is I usually have sellers remorse after trading an old friend. Which is one reason I have kept my Tak FS 102 even though I bought an FC 100DZ more recently. There are sentimental considerations too.

[Stu]

Despite the diffraction spikes, I found there was a pin point nature to the stars in the Mewlon which I had never managed to achieve with either a C8 or C925. More energy in the airy disk I assume. It was the first scope that showed me Zeta Herc, although admittedly I have subsequently seen it in my 8” f8, Heritage 150P and Vixen Fluorite, but only after I knew what to look for from the Mewlon.

[JeremyS]

Storage box arrived to allow the Mewlon to cool outside before observing 

[Stu]

1 hour ago, JeremyS said:

Storage box arrived to allow the Mewlon to cool outside before observing 

Good decision Jeremy 👍👍