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habsburg8
scholastic sledgehammer
Reged: 07/07/05
Posts: 801
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After owning three separate Tasco #20TE 108mm f/15 refractors and four Sears 90mm #6345 refractors, I can offer this professional comparison. Both types of telescopes were made in Japan by Royal Astro Optical Industries Co. Ltd. and then exported throughout the world. In the Royal Astro catalog they are listed as Model #R-102.
(1) The basic lens cell and tube design is identical.
(2) The tube construction is much heavier than a comparable sized Unitron.
(3) The Tasco #20TE comes on a tall two-piece metal pier, while the smaller Sears #6345 has its own wooden tripod.
Advantages of the Sears 90mm over the Tasco 108mm:
(A) The objective lens forms far sharper and more perfect star images, especially at high power. The contrast is definitely superior in the Sears 90mm. This more than makes up the 18mm in aperture difference between the Sears and Tasco.
(B) It is much more portable, whether mounted on its original wooden tripod or remounted on an appropriate metal pier.
(C) The 40mm guidescope gives better images than the 50mm unit found on Tasco's #20TE.
(D) Since telescope parts from Royal Astro scopes are all interchangeable, the Sears 90mm equatorial mounting can be adapted to a variety of other products from that company.
(E) With possibly 600 used examples to choose from, the amateur astronomer and collector has a much greater opportunity of acquiring a used model.
The disadvantages of the Sears 90mm refractor compared to the Tasco 108mm are:
(A) The original wooden tripod is not adequate to support the great weight of the entire telescope assembly. It must be upgraded with either a heavier wooden tripod or a metal pier.
(B) The original cradle rings need to be upgraded with another thicker pair, such as from Parallax Instruments.
The advantages of the Tasco 108mm over the Sears 90mm are:
(A) It is a much more impressive looking telescope, suitable for a home observatory.
(B) Tasco imported and sold several different models. THE BEST ONES OPTICALLY HAVE THE LARGER SADDLES AND NOT!!! A 21... SERIAL NUMBER. THE BETTER MODELS ALSO HAVE THE ENCASED MOTOR DRIVE MECHANISM!
(C) The main tube has several sliding weights for precise balance.
Edited by habsburg8 (10/23/09 12:30 AM)
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habsburg8
scholastic sledgehammer
Reged: 07/07/05
Posts: 801
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I do not mean to belittle the great optical quality of the Tasco #20TE refractor. On good, steady nights I can see detail in and around Jupiter's Great Red Spot, while the four Galilean moons show as hard disks. However, the images in the Sears 90mm are simply BETTER.
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habsburg8
scholastic sledgehammer
Reged: 07/07/05
Posts: 801
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It should be realized that the Sears 90mm is about twice the overall size of the very common Tasco #10TE 3-inch Solarama refractor. Both the Tasco #20TE and Sears #6345 Discoverer are BIG, HEAVY telescopes.
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Max Lattanzi
sage
Reged: 06/27/07
Posts: 213
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Quote:
Advantages of the Sears 90mm over the Tasco 108mm:
(A) The objective lens forms far sharper and more perfect star images, especially at high power. The contrast is definitely superior in the Sears 90mm. This more than makes up the 18mm in aperture difference between the Sears and Tasco.
Hi John,
Thank you for this detailed analysis. Really helpful!
Though, reading your posts a question comes to my mind: are the optics in the Tasco #20TE 108 f/15 the very same used in the SYW 108 f/15...?! I thought so. But now I am wondering myself whether this is true...
The reason for asking is that, although I do not own neither a Tasco #20TE nor a Sears #6345, I do have three specimens of SYW 108/1600 (labelled Pearl, Sky-Master and Busch, respectively for the French, Italian and German market). And I own as well two Carton 90/1500.
Now, the optics of the three SYW are truly exquisite, slightly better than the Antares 105/1500 I also own (this as well is a Carton, AFAIK), than the 90/1500s (truly excellent, but not cigar), and *visually* on par with the AP Traveler and the Tak FS-102 (with Ext-Q)...
I used all of the above for one full Summer observing Jupiter, so it is not a 5 minutes impression... binoviewing at 400x with Zeiss Abbes...
If the optics were the same both in the Tasco and the SYW, this would mean that the Sears 90/1400 has better performances than all the above (including the two 4" apos), which I honestly find a bit hard to believe. From here the question.
Any insights...?!
Thanks,
Max
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mikey cee
Post Laureate
Reged: 01/18/07
Posts: 3508
Loc: bellevue ne.
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This comparison of all these scopes and the differing "opinions" is just shedding the light on comparing apples to oranges to watermelons. On any given night seeing conditions will generally favor the smaller scopes. Is a person using the same diagonal and eyepiece in each instrument? Are the tests being conducted on the same evenings in rapid fire succession. I've seen Jupiter and double stars numerous times go through turbulence changes in just a few moments. Too many variables to make blanket statements on top of the fact the word "better" can mean different things to different people. Contrast, resolution, perceived level of CA, steadiness of object and not the least of all a brighter image can affect the previous mentioned items. Now of course there are real bonafide losers....that no matter the circumstances a blind man could see the difference. But to say that one good scope model is better than the other is not a true fair and unbiased statement. There that's my  worth.  Mike
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7x35 and 10x50 sears tower binocs, 3" f/10 edmunds reflector, 2.4" f/11.7 manon refractor, 6" f/8 jaegers refractor, "The 8 Ball" 8" f/13.3 brandt refractor, 3" f/15.8 sans&streiffe refractor, 3.1" f/15 selsi refractor(towa 339), 2.4" f/15 sears refractor, selsi 30x30mm spyglass, criterion 5-draw 25x45x75x spyglass(1957), 4.25" f/14.8 tasco 20te.
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Max Lattanzi
sage
Reged: 06/27/07
Posts: 213
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Hi Mike,
I was observing for over a month with at least three scopes side-by-side each clear night for the usual Jupiter observation (2.5-3 hours).
Same bino Zeiss, same diag Zeiss, same couple of Zeiss Abbe. The apos with their own (excellent) barlow. And shifting from one scope to the other, kept side by side in an array. That's how I do it. Of course there are seeing fluctuations but, in a good night, they are very minimal. And the time (15-20 mins) you spend with each instrument - again, I am not talking of "glimpses" but the long time needed to take notes and look for details at resolution limit - nulls any fluctuation.
Then, if one has a doubt, can always shift back to the previous instrument. And, of course, the scopes are all mine so I have no temptation of bashing anyone... 
Again, I have 90mm apos and, while excellent instruments, none of them touches the SYW 108 nor the Traveler, nor the Tak. So my perplexity remains.
Cheers,
Max
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mikey cee
Post Laureate
Reged: 01/18/07
Posts: 3508
Loc: bellevue ne.
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It all boils down to luck. Either good luck or bad luck. All these lenses are made by humanoids. Your 108mm is probably like many hundreds spot on....but someone may get unlucky and get a not so spot on. Same thing can be said of the 90mm whether APO or f/15. You just can't arbitrarily say all 90mm of any one brand are better than any 108mm of another brand or vice versa. All companies even Zeiss have super runs and not so super runs. I go by what pleases me and I don't give a hoot what some optical testing lab says. Seems to me like most overkill testing is just so much hype because the eye can't perceive it. Just like an uncoated object versus a single layer versus a multicoated layer in light transmission. Optical lab tests see the difference but you as an individual only think you can. I believe it when sources say it takes 10% to 15% to see any difference at all in increased light. Mike
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7x35 and 10x50 sears tower binocs, 3" f/10 edmunds reflector, 2.4" f/11.7 manon refractor, 6" f/8 jaegers refractor, "The 8 Ball" 8" f/13.3 brandt refractor, 3" f/15.8 sans&streiffe refractor, 3.1" f/15 selsi refractor(towa 339), 2.4" f/15 sears refractor, selsi 30x30mm spyglass, criterion 5-draw 25x45x75x spyglass(1957), 4.25" f/14.8 tasco 20te.
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woodsman
Pooh-Bah
Reged: 03/12/08
Posts: 1069
Loc: Colorado Springs, CO
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I definitely agree with you Mike. On a related subject I've heard a lot back and forth on Refractors vs. SCTs, vs Maks, vs Newts. I like my C14, but I hear how cumbersome it is and that the views are mediocre on planets compared to refractors and newts, but overall it's my favorite instrument, because I like to observe deep sky objects. I observe Jupiter as well, and at lower mags it rivals my refractors, however I didn't buy it to kill planets, I use my refractors for that. I bought it as a light bucket, plus its easy to set up. Its an impressive looking scope as well. I have a harder time setting up my Sears 90mm, but I do enjoy that for planet work. I think its all in the eye of the beholder. I'd love to find an SPI refractor of large aperture though. I have a feeling there aren't very many of those around either.
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artisticwoods
C-14 Orange Tube, C-8, C-5, C-90 Astro Model, C8 Schmidt Camera 8" f1.5, C5.5 Schmidt Camera f1.65, SPI 42mm f/19 Refractor, Sears 90mm f/15.56 Ref, Sears 80mm f/15 Ref, Swift 77mm f/13 Model 831, Scope 60mm f/11.7, Sears 50mm f/12
Unitron Model 140 75mm/1200mm, Unitron model 128 60mm/900mm
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gts055
super member
Reged: 05/01/06
Posts: 158
Loc: Victoria, Australia
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I too am somewhat puzzled by Johns comments on the difference between his 108mm and 90mm telescopes. Both are relatively small apertures. In my location "seeing" begins to more noticeably affect aperture greater than 130mm. He states that all three 20TE had poorer performance than his 90mm. Hmmm, I have an SYW 108mm and it is has exceptional performance. Reading previous posts by Galakuma, he believes SYW lens sets came from Horiguchi, the same supplier to early Takahashi. Perhaps Astro 0ptical 108mm lens sets were of variable quality. For comparison my other refractors include two 102mm Unitron, 3" Unitron, Televue NP101, Tak FS128, and Astro Physics 180EDT. Yes, the SYW is an achromat and performs superbly for its type, while the two Unitron 101mm are mediocre in comparison. I also have an Astro Optical 76mm f16 with superb performance for its aperture. The 3" Unitron is similar in performance to the Astro Optical. Mark
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woodsman
Pooh-Bah
Reged: 03/12/08
Posts: 1069
Loc: Colorado Springs, CO
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Quote:
I too am somewhat puzzled by Johns comments on the difference between his 108mm and 90mm telescopes. Both are relatively small apertures. In my location "seeing" begins to more noticeably affect aperture greater than 130mm. He states that all three 20TE had poorer performance than his 90mm. Hmmm, I have an SYW 108mm and it is has exceptional performance. Reading previous posts by Galakuma, he believes SYW lens sets came from Horiguchi, the same supplier to early Takahashi. Perhaps Astro 0ptical 108mm lens sets were of variable quality. For comparison my other refractors include two 102mm Unitron, 3" Unitron, Televue NP101, Tak FS128, and Astro Physics 180EDT. Yes, the SYW is an achromat and performs superbly for its type, while the two Unitron 101mm are mediocre in comparison. I also have an Astro Optical 76mm f16 with superb performance for its aperture. The 3" Unitron is similar in performance to the Astro Optical. Mark
In a previous posting to me awhile back, John mentioned to me that he thought that the Astro Optical Lens sets for the 90mm Sears were provided by Horiguchi optical, so that might explain the quality of the 90mm. Mine is superb. I haven't had the luxury of comparing it to any other scope other than the Swift 831 which I sold recently. Optically, the Swift blew away my other scopes (Towas), but the Sears Astro Optical beat the Swift, although the comparison between a 90mm and a 76mm speaks for itself. I have nothing else to compare it to, but I know that the images in the Sears are simply amazing.
Rich
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artisticwoods
C-14 Orange Tube, C-8, C-5, C-90 Astro Model, C8 Schmidt Camera 8" f1.5, C5.5 Schmidt Camera f1.65, SPI 42mm f/19 Refractor, Sears 90mm f/15.56 Ref, Sears 80mm f/15 Ref, Swift 77mm f/13 Model 831, Scope 60mm f/11.7, Sears 50mm f/12
Unitron Model 140 75mm/1200mm, Unitron model 128 60mm/900mm
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habsburg8
scholastic sledgehammer
Reged: 07/07/05
Posts: 801
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I have personally owned over 100 vintage refractors, including 25 Unitrons of 1.6- to 5-inch aperture. I have also spent thousands of hours observing through a variety of small and large Newtonians (my current favorite is an Obsession 15-inch with a primary mirror from Nova Optical Co.). My judgment of the performance of my Sears 90mm is against all of those other telescopes, both in memory and direct comparison. Of course it does not have nearly the light-gathering power of those big Dobs, but the superb image quality and high contrast makes up for a lot of the difference in aperture.
In my collection of vintage refractors I also have a 3-inch Mayflower with optics by SYW. I consider it a superb performer for a scope of that size--star images are tack sharp and the Airy disks are textbook perfect.
My evaluations of the Tasco 108mm refractor (Model R-102 in Royal's telescope catalog) are supported in past communications with Roger Re, owner of R.V.R. Optical Co., who for many years imported and sold high-end telescopes. His opinion was that Carton scopes (AE-108) with the SYW markings were definitely optically superior to those marketed by Tasco as #20TE. I do not know where SYW acquired their lenses, but I think that the Sears 90mm f/16 objectives were custom fabricated by Royal Astro themselves. The bigger Tasco #20TE lenses definitely came from Horiguchi Optical Co.
I once had a superb Swift #831 3-inch equatorial in my collection of fine vintage telescopes. A local amateur astronomer and friend literally begged me for the chance to purchase it, so last year I agreed to let him acquire the classic scope. In side-by-side comparison tests the Sears 90mm was judged to be VERY slightly better optically, probably as a result of the larger objective diameter.
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