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Explore Scientific 127mm APO...CF or AL?

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#1 MattT

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Posted 02 March 2013 - 08:40 PM

Is the tube material really the only difference between the white-tubed ES127 APO and the Carbon Fiber version? CF is not cheap to fabricate, I'm sure, but the $500 premium seems like a lot and I wonder if there's more going on. I don't want to start a rumor but the conspiracy theorist in me, based on nothing but speculation, wonders if ES might be putting their best objectives in the more expensive scopes. Not to suggest the white-tubed ES127s are lemons, but the company claims to test all the scopes at least twice, so they must know which objectives are great and which are merely good....right? Has anyone seen a pattern that might suggest this is the case?

If the tube material is the only difference, does the CF really save a full 4 pounds? That must be some pretty thick aluminum they're using in the "classic!" And does the weight difference make a significant difference in stability on a Skyview Pro / CG-5 type mount, with half-pier extension?

Also, has anyone tested these carefully to determine the true clear aperture? I have tried reading W. Rohr's scope tests and was surprised to learn that the lens cell on at least one example of the competitive 120 f7.5 ED doublet reduces the clear aperture on that scope to 118mm, and the baffling system of the 120mm Equinox (which I think is the same as the EON) reduces the clear aperture to 113mm. I haven't found such data for the ES127, or many tests for strehl ratios or etc. Sitting here waiting to move into our new house, where I'll finally have a place to setup a decent sized scope, I crave data!

#2 dr.who

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Posted 02 March 2013 - 11:27 PM

Only difference between them is the material for the tube if they are made close to each other. ES does tweak the design over time.

Carbon Fiber is expensive so it does cost more to make but there is also some "magic" with the idea of CF on the part of the AP crowd. The AP crowd drives the market and so we get CF instead of aluminum. [1]

Yes it does save close to 4 lbs. CF is surprisingly much lighter than aluminum.

Haven't done the "true aperture" test so I can't say.

[1] I had a chance to meet Scott Roberts personally and one of the questions I asked him while he was working with me on a binoviewer question was why the CF. His response was that the market was moving in that direction and they wanted to be out in front of it. It seems the AP folks like the CF and it lets the retailer charge a higher markup on the OTA because of it and the AP folks drive the market trends.

Per that same discussion all the APO parts of the ES line will be going CF.


#3 MattT

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Posted 03 March 2013 - 01:21 AM

I guess it makes sense that the CF would carry a lot of markup.

Still curious if anybody's measured the true clear aperture.

And whether the weight makes much of a real world difference...since it's in the tube it'd be near the center of gravity and I suppose have less impact than weight out at the tube ends.

#4 SeattleScott

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Posted 03 March 2013 - 01:56 AM

As a visual user the CF doesn't really matter to me other than weight. The real difference in weight can be if a tube that is 4lb lighter allows you to get by with one less counterweight. I mean if getting the CF tube meant you could get by with one 11lb counterweight instead of two, then that is a weight savings. In this case probably not, at least not unless you got a counterweight shaft extension.

#5 Arizona-Ken

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Posted 03 March 2013 - 09:41 AM

Just got an ES127 recently; the basic white tube aluminum version. I use it on a CG5 with a pier in visual mode and there is a slight shaking when focusing which dampens very quickly. I doubt it would work well for AP.

Great scope, clear crisp views, will use it for double star and planetary work as I have other larger aperture scopes for deep sky work.

I have not seen anything on strehl ratios or the like, but hey, let's not forget what it is. It is a good quality, value APO. If you're gonna get obsessed about strehl ratios you better look at TECs or Taks, APM or Williams, Astro-Techs and maybe a Stellarvue - and be prepared to cough up much more cash.

As far as the CF version getting the more "quality" optics, I see no basis for that idle speculation. If there really was a difference you bet that they would be advertising it as a "AP version" or"premium optics version" and charging accordingly.

Arizona Ken

#6 Pinbout

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Posted 03 March 2013 - 09:58 AM

From a previous thread

"By the way, Carbon fiber is not an advantage in a refractor, in fact it is a disadvantage if you will be imaging with it. As the temperature drops, the focal length of the lens shortens quite noticeably, so a thermally stable tube that does not shorten will exacerbate the defocus problem. Aluminum at least contracts enough to counteract some of the defocus.



#7 MattT

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Posted 03 March 2013 - 11:08 AM

Thanks for sharing your experience, Ken. I wouldn't expect the ES127 to keep up with one of the true premium scopes but $2-2.5k is still a chunk of change and I'd be disappointed if they were scraping the bottom of the diffraction limited criteria (1/4 wave p-v). I have owned a few scopes and can tell the difference between good and very good pretty clearly, especially in small to mid sized optics where seeing is not often limiting.

Very good vs. excellent is harder! If I had to plot "Value" on a graph with "Strehl" on one axis and "Cost" on the other, my sweet spot would probably be around .975

#8 SeattleScott

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Posted 03 March 2013 - 12:23 PM

97.5% Strehl is a high standard. You are looking at a premium vendor now. TEC I believe advertises 98-99% and that is about as good as it gets. 97.5% Strehl is reasonably obtainable for less than a small fortune in a reflector, but an APO has three curved surfaces, so getting a system strehl of 97.5% in an Apo refractor is a pretty awesome achievement.

For example, I consider Istar to be somewhat of a premium vendor (I would certainly rate them higher than Meade or Celestron but don't know how they compare optically to ES). You can buy objective lenses with a specified Strehl value from Istar's website. Most of their lenses are in the low 90's although they can hit 98% with their Apo's (for a small fortune).

#9 Mike4242

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Posted 03 March 2013 - 02:12 PM

Like you, I've been wanting one of these scopes, but don't want to pay the extra $500 for CF. However, you can't buy the white aluminum tube ones right now; apparently they're going through a redesign.

Of course, if ISTAR ever comes out with a Raycorr that I can use in my AR152 it might be a moot pint. :)

#10 George N

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Posted 03 March 2013 - 07:09 PM

Just got an ES127 recently; .......
I have not seen anything on strehl ratios or the like, but hey, let's not forget what it is. It is a good quality, value APO. ....... Arizona Ken


I don’t know if ES is still doing it, but back when I got my 127ed (I purchased Scott Roberts’ personal scope used), you could e-mail them and ask what the Chinese maker claimed for a peak-to-valley error for your particular serial number. For my scope it was 1/5th wave, peak-to-valley. ES said that they had had some 127s independently tested and a few tested not *quite* as good as the maker claimed, but others did, and “there was never a significant difference”.

I’ve had hundreds of people look thru my scope and all have been impressed. One night at the Cherry Springs Star Party a group of about 8 folks compared my ES127ed to two near-by AP 130s (on Saturn – using the same eyepiece). No one could see any difference between the three scopes. I did not personally take part in the exercise, but one guy who did is the owner of an astronomy store that sells ES products. He was happy. At least one of the AP owners was not.

Last year at CSSP a group of self-proclaimed double star “experts” (about 6 guys) showed up and wanted to see Antares in my ES127ed. After much discussion, all concluded that my scope provided the best view of the pair of any scope that they had tested so far that night. I’m not a big double star guy, but the companion was visible.

#11 MattT

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Posted 03 March 2013 - 08:33 PM

Interesting comment, George, thanks.

#12 Dan Finnerty

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Posted 04 March 2013 - 12:54 AM

I have had an ES ED127CF for a little more than a year. Regarding the CF tube, one thing I have noticed is that it dews up quickly compared to a white aluminum tube. I presume this is due to the high emissivity of the black tube. When this happens I've also noticed that the black roofs of neighbors cars likewise dew up more quickly than the light/white colored cars in the same conditions the telescope tube gets wet.

I have also heard that for CF tubes, it is more difficult to get the focuser perfectly square and centered on the tube. It is just not possible to machine the tube end and mount the focuser as precisely to the tube. I have not seen any collimation problems in use on my ES127 however, though I've not checked with a collimator.

Optically, my ES127DF is very good but definitely not perfect. I see a small amount of CA on very bright objects, the moon in particular. I see some color on the limb and also see color on the small bright peaks of mountain tops sticking up out of the dark shadows. It is enough to be noticeable and now that I have some experience, I'm finding I am not a cheap date when it comes to CA. I'd like to upgrade to a TEC 140 or equivalent premium APO. Of course I'd like to have an 8" APO permanently mounted on an AP 1600 in an observatory in dark stable cloudless skies too :). The TEC might actually happen though...

#13 MattT

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Posted 04 March 2013 - 01:26 AM

"Of course I'd like to have an 8" APO permanently mounted on an AP 1600 in an observatory in dark stable cloudless skies too..."

LOL....you and me both! I'd love a TEC-140 too, or maybe a TMB-130, but figure I should try an "entry level" ~5" apo first to see how I like handling a refractor that size.

#14 Dan Finnerty

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Posted 04 March 2013 - 02:18 AM

I have no regrets with the ES 127 APO. I did exactly the same thing, buy a good quality but affordable (by my budget anyway) moderate aperture scope. It has been great fun and a wonderful learning experience. After a year, aperture lust bit and I got a C11 Edge when Celestron had them on sale. These two make a great compination, the 5" for more casual observing (and astrophotography I hope) and the C11 for when I'm feeling more ambitions.

#15 dr.who

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Posted 04 March 2013 - 04:36 PM

As a visual user the CF doesn't really matter to me other than weight. The real difference in weight can be if a tube that is 4lb lighter allows you to get by with one less counterweight. I mean if getting the CF tube meant you could get by with one 11lb counterweight instead of two, then that is a weight savings. In this case probably not, at least not unless you got a counterweight shaft extension.


I am able to use my 127 CF on my AVX and CG5 with the 11 lbs weight all up. So it can be done. The weight is towards the end of the shaft though.

#16 dr.who

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Posted 04 March 2013 - 04:45 PM

I own the CF 127 because they are not making the aluminum one's anymore as I understand it. Occasionally you will see them "on sale" for $2,000 for what it's worth. Usually at the shows.

A word of warning for those of you who want to try AP with this. From experience you will need a good strong mount if you want to try it. Not because of weight but because the thing, due to it's size and shape, acts like a sail at times and can catch a good bit of wind.

A cheaper alternative would be a wind screen of some kind. This was my option. Cheaper to shield it from the wind than buy a CGEM DX class mount! And easier on my back! ;)

#17 dodgerm37

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Posted 04 March 2013 - 09:11 PM

The new shipment of aluminum tube ES 127's is SUPPOSED to be in this month. The G 11 mount has been waiting for the ot to arrive. The only difference I read anything about was the tube material.Sooooooo, the wait goes on! Clear skies all, Bob

#18 SeattleScott

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Posted 04 March 2013 - 11:35 PM

Good insight Dr Who about the VX mount handling the weight of the CF tube with a single counterweight. I have a 6" shaft extension already (so I can get by with just two weights for my reflector). I wonder if the new aluminum ES 127's are any lighter weight. If I could get one on my CG5 with shaft extension and one counterweight that could be an idea. With two counterweights I feel like I might as well get the reflector out. My wife asked me if I need to get one last scope before the twins arrive and drive us broke...
Kind of hate to buy a nice scope to gather dust for a couple years though.

#19 timps

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Posted 06 March 2013 - 03:24 AM

From the research I've been doing, is seems as if Takahashi have the edge with strehl of .998 and perfect colour correction. But I don't think one would notice the difference in a side by side comparison of TEC's and TAK's similar sized scopes. Please correct me if I am wrong.

#20 BenB85

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Posted 07 March 2013 - 02:38 AM

Hi

I had the aluminum white tube 127 for a short time and just received the CF. The CF was substantially better quality. Also, the coatings in the CF have a darker purplish hue compared to a greenish hue in the classic. The CF optical coatings made the glass less reflective IMHO. The dewshield is also much lighter as is the scope. If you can swing it, get the cf. The one I received has been exceptional under the stars.

#21 dr.who

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Posted 07 March 2013 - 01:07 PM

Good insight Dr Who about the VX mount handling the weight of the CF tube with a single counterweight. I have a 6" shaft extension already (so I can get by with just two weights for my reflector). I wonder if the new aluminum ES 127's are any lighter weight. If I could get one on my CG5 with shaft extension and one counterweight that could be an idea. With two counterweights I feel like I might as well get the reflector out. My wife asked me if I need to get one last scope before the twins arrive and drive us broke...
Kind of hate to buy a nice scope to gather dust for a couple years though.


Cheers. It should be able to handle it with the extension no problem.

#22 MattT

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Posted 07 March 2013 - 05:38 PM

Thanks for sharing your experience, Ben.

#23 oo_void

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Posted 07 March 2013 - 09:36 PM

Just noticed that you're in the area Matt. If the weather holds, I'll be at the SFAA public event at Land's End next weekend with my CF version if you want a first hand look at one.

Also, unless you're over in the outer East Bay area, temperature flux is minimized in our climate making the lack of expansion much less of an issue. I haven't noticed expansion issues, or lack thereof to be an issue while imaging .

Final comment, the 127 is a big scope. On my CGEM, my (heavier) counterweight is maybe and inch from the end to achieve balance. I added a Scopestuff 1lbs toe-saver to give me a little wiggle room. I really couldn't imagine the CF version on a CG5, let alone the aluminum version.

#24 MattT

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Posted 07 March 2013 - 11:14 PM

Thanks for the offer. I'm in Walnut Creek now, but know the Land's End site from my days in San Francisco, almost 20 years ago now. I won't be able to make it next weekend but hope we do meet up some time.

#25 johnnyha

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Posted 08 March 2013 - 07:13 AM

From the research I've been doing, is seems as if Takahashi have the edge with strehl of .998 and perfect colour correction. But I don't think one would notice the difference in a side by side comparison of TEC's and TAK's similar sized scopes. Please correct me if I am wrong.

The strehl ratio for Tak is the theoretical ratio for the design, not the actual strehl. They are excellent scopes but you cannot expect the strehl to be .998.

On another note, someone had mentioned how the dark CF tube attracts dew and this is true - it's why I switched from black Pelican cases to yellow, darker black colors dew up much much sooner than lighter colors.

CF is fancy, expensive, looks super cool, attracts dew because it is black, and imho unproven yet as a true upgrade for telescopes.






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