Explore Scientific 127mm APO...CF or AL?
Posted 02 March 2013 - 08:40 PM
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!
Posted 02 March 2013 - 11:27 PM
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. 
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.
 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.
Posted 03 March 2013 - 01:21 AM
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.
Posted 03 March 2013 - 01:56 AM
Posted 03 March 2013 - 09:41 AM
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.
Posted 03 March 2013 - 09:58 AM
"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.
Posted 03 March 2013 - 11:08 AM
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
Posted 03 March 2013 - 12:23 PM
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).
Posted 03 March 2013 - 02:12 PM
Of course, if ISTAR ever comes out with a Raycorr that I can use in my AR152 it might be a moot pint.
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.
Posted 04 March 2013 - 12:54 AM
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...
Posted 04 March 2013 - 01:26 AM
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.
Posted 04 March 2013 - 02:18 AM
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.
Posted 04 March 2013 - 04:45 PM
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!
Posted 04 March 2013 - 09:11 PM
Posted 04 March 2013 - 11:35 PM
Kind of hate to buy a nice scope to gather dust for a couple years though.
Posted 06 March 2013 - 03:24 AM
Posted 07 March 2013 - 02:38 AM
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.
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.
Posted 07 March 2013 - 09:36 PM
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.
Posted 07 March 2013 - 11:14 PM
Posted 08 March 2013 - 07:13 AM
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.
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.
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.