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Astro Physics 130GTX - First Light


GavStar
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1 hour ago, mikeDnight said:

Hi John,

My late friend Phil was obsessed with comparing spot diagrams of various designs of telescope. He spent a lot of his time over many years designing many different kinds of telescope. From what I remember about the spot diagrams he showed me, if a telescope keeps its natural aberrations within the Airy disk, it is essentially perfect. Most telescopes come nowhere near this kind of perfection, though Apo refractors tend to be among the best. Often the aberrations between similar scopes such as the DL and DC, though being noticeably different on paper, still come close to, or within the confines of the Airy disk and so both scopes will offer essentially the same level of performance, or at least it would take a very expert eye to notice any real difference in image quality. For a 6" achromat to give a perfect image it would need to have a F ratio of around F25, yet at F15 it performs stunningly, so it illustrates how forgiving the visual view is. SCT's produce very poor spot diagrams and this is quite noticeable in the star image produced, where the star never quite seems to snap into focus, yet the SCT remains popular. As you pointed out, focal length does play a part. Short F ratio Newtonians suffer from numerous destructive aberrations outside the Airy disk, where as, long focal length Newts have very tightly constrained aberrations and deliver near perfect images. It seems to me that we're all so easily distracted by graphs, spot diagrams and Strehl that we forget the most important factor which Gavin touched on when he said he's "Loving" his AP130. ❤??

Mike

Interesting Mike and I'm sure it holds good :thumbright:

Of my 4 refractors, I'm fondest of the Vixen and the Skywatcher simply because I've owned them a long time. They and the 12" (especially that scope) are the ones that have contributed most to my enjoyment of the hobby because they have been with me longer, of course.

While the images through the Tak DL and the TMB / LZOS 130 F/9 are technically the best I've ever seen for those apertures, they have yet to become "friends" in the way the others have. These scopes will show me things that I have already seen slightly better than I have seen them before. The 12" dob is still capable of showing me new things. Gotta respect that :thumbright::grin:

None of this is surprising though - I've been in the hobby too long to nurture unrealstic expectations of kit these days :rolleyes2:

How am I going to get some new "kicks" ? - subject for another thread I think.

Sorry to rabbit on in your AP 130 thread Gavin. You have wonderful scopes mate - treasure them :grin:

 

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On 2017-5-15 at 00:29, John said:

It's funny with scopes. Last year I bought 2 "dream" scopes, the Tak FC-100DL and the TMB / LZOS 130 F/9. They are both superb instruments and undoubtely the best scopes of their respective apertures that I've ever viewed though and arguably in the top few ever made at those apertures for amateur use.

You would have thought that the old, slightly scruffy gold tubed ED120 Skywatcher would have had it's marching orders ?. But no, I keep coming back to the Skywatcher of all things. I guess that it's the whole package that is "right" with that one which includes size, weight, ease of mounting, cool down, ruggedness as well as optical ability way above it's price band. Still trying to figure it out ..... :dontknow:

 

 

Hi John,

The few reviews I've read of the first (gold) SW Ed scopes (both 100 and 120mm) seem to really rave about them. I wonder if that is because, as a crucial new product for Synta at the time they were so important and they really really tried to make them to an outstanding quality? 

Having said that, I know many with the newer versions love theirs just as much. I do think there is something quite classy about the older gold tubes though..I personally prefer them to the black diamond of the Pro Series or gloss black of the Equinox. 

Now, if they offered them in classic white with black trim, I might even become a convert! ????

Getting back to Gavsters original post, that Starfire must be a complete cracker if it is doing even slightly better than the TEC.. 

Not a bad "problem" to have, comparing two of the best fracs on the planet???.

Dave

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On 2017-5-16 at 21:17, John said:

I think the DL has a slightly tighter spot diagram, whatever that means. Probably more to do with the different focal ratio rather than differnt figuring quality though.

The official blurb at the launch said this (Google translated from the original Japanese, so blame that !):

"In recent years of refraction telescope, but Photo visual system short focus apochromat has become the mainstream, it is the emergence of these and differing length personality focus two ball fluorite apochromatic telescope FC-100DL.
FC-100DL in the FC type which arranged the street flow light lens of the name behind, worthy of long focal refraction of f / 9.0, chromatic aberration, you get high spherical aberration less contrast image. Specifically, halo is approximately 40% reduction of the g-line against FC-100D of f / 7.3 (purple), and has realized the 97.5 percent of about 4% increase in the Strehl ratio that indicates the high magnification performance. (Data calculated)
This aberration data is almost the same number as the three pieces ball apochromat, coma is coupled with stable image plane of the zero, I think that you understand that it is a telescope that has a high-eye viewing performance."

 

 

John, that does sound as though the DL is claimed to be optically "better"....as a long time fan of good long focus achros, I grew up reading that the shallower curves on longer FL objectives were/are easier to polish and figure to a high standard? Also, even on an ED "apo", longer focal lengths reduce CA even further, maybe light scatter too?

I'd LOVE to see an F11 or F12 115-125mm ED Fluorite doublet tested ?..

Two other things I still like about long achromats...you get more depth of focus, ie more range of "sweet spot", within which you can get perfect focus. This is such a boon at high powers: on my D&G 5" F15 I had a moonlight dual speed focuser, but even with the original 2.7" AP focuser I could always get a snap to focus, even up to x300 on good nights. On my FS128 the snap to focus range is much less.

The second noticeable property is that Airy disks are larger with a long focus achro, really tight, but larger, you really get the "twin bullseye's in black" effect on doubles like epsilon Lyrae.

But long, big fracs are a real pain to handle sometimes, especially when viewing near the zenith, and as you get older.. Gavin, if you find the Tec140 more of a handful than the AP130, imagine the fun and games you'd have with a 2 metre long tube!??

Dave

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8 hours ago, F15Rules said:

 

But long, big fracs are a real pain to handle sometimes, especially when viewing near the zenith, and as you get older.. Gavin, if you find the Tec140 more of a handful than the AP130, imagine the fun and games you'd have with a 2 metre long tube!??

Dave

Dave, yes I did wonder why short focal fracs are so much more popular than f9+. However even the FC100DL I have I find a bit of a handful particularly when looking near zenith. The flexibility of the 130gtx just zipping around all areas of the sky easily on the mount without having to change observing position is rather nice. ?

Edited by Gavster
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I reckon its the rise in popularity of imaging that has driven the industry to produce faster apo refractors. Thats why scopes such as the Tak FC-100 DL fluorite doublet and the TMB / LZOS 130 triplet F/9.2 are different - they are squarely aimed at the visual astronomer.

The original Tak FC100N was a F/10 fluorite doublet. Nikon and Pentax used to produce similar "slow" ED doublets some way back.

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2 minutes ago, John said:

I reckon its the rise in popularity of imaging that has driven the industry to produce faster apo refractors. Thats why scopes such as the Tak FC-100 DL fluorite doublet and the TMB / LZOS 130 triplet F/9.2 are different - they are squarely aimed at the visual astronomer.

The original Tak FC100N was a F/10 fluorite doublet. Nikon and Pentax used to produce similar "slow" ED doublets some way back.

Of course you're right John - I forgot about those imaging people!!

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12 hours ago, Gavster said:

Of course you're right John - I forgot about those imaging people!!

It's best to forget about "those imaging people!" However, they may have done visual observers a great service, by causing manufacturers to design faster, high quality optics. The comfort and greater range of usefulness of a good ED or Apochromat is godsend. I'd much rather use a tube of a metre or less than an unwieldy monster that tremors with every passing moth. With modern, well corrected eyepieces, or if preferred, a simple ortho or plossl with a barlow lens, they'll deliver both wide rich field views and razor sharp, colour free, high power views. I love em! :icon_biggrin:

 

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  • 2 months later...

So I thought I'd post a further update on this (imo amazing) scope. Due to its short length and relatively low weight it's become my most used scope. Last night I had it out side by side with my Tak FC100DF. I used the Tak on the AZ-GTi mount effectively as a large finderscope. 

I had a lot of fun comparing the images between the two (unfair on the Tak due to the difference in aperture). On objects such as M13, double cluster and M27 the AP just showed a more beautiful view with the faint stars not really visible in the Tak making a real difference to the view. By London standards the skies were very good last night. 

There is obviously a good deal of crossover between the AP130GTX and the TEC140. However, my personal preference mainly due to the lovely presentation of stars is for the AP. After a good deal of thought I've decided to move my TEC140 on. However, it's been fascinating to be able to directly compare these two scopes.

In summary, I'm still hooked and loving my AP130GTX!

Edited by GavStar
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Very interesting update Gavin :smiley:

Your description of the difference between the Tak FC 100 and the AP 130 sounds very similar to the experience I had comparing my Tak DL to my TMB / LZOS 130. Very similar superlative views just more of it with the 130 :smiley:.  Both F/9 scopes in this case.

How much does the AP 130 OTA weigh by the way ?

I imagine that the TEC 140 will move on quickly when you part with it - lots of demand for those as well !

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AP is about 8kgs compared with TEC about 9kgs so not much in it (Hmmm maybe the AP isn't particularly light) I think it's the length of the OTA which is more of a difference 72cm for AP vs 86cm for TEC.

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  • 3 years later...

A bit of thread resurrection (only 4 years 😃) but my first light comments regarding the AP130GTX focuser not being as good as a feathertouch have continued to bug me - until today!

The AP130GTX has become my favourite “all rounder” scope. Quite easy to mount, pretty light, short with a decent amount of aperture for a refractor. It can give fantastic planetary and lunar views but is also great for DSOs (with or without nv).

However the stickiness of the focuser has always been a bit of an annoyance to me and, in fact, reduced my enjoyment of this scope. 
A few weeks ago, I finally contacted Astro physics direct in the USA about it. After an exchange of emails the technical guy assured me that my focuser seemed fine. However, another employee followed up my query and said that they could provide another focuser if I wished. Since I am delighted by every other aspect of this scope, I decided to bite the bullet and purchase a new focuser. 
It arrived today and very pleasingly is buttery smooth like my feathertouches on my other scopes. It took me about 2 minutes to install it and I’m very happy. After over 4 years, finally this scope has the focuser it deserves!!! And it just shows that sometimes I need to trust my instincts that something is just not right...

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