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Meade-Vorce "Polaris" 90mm f/10 Achromat OTA

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#76 Sky Muse

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Posted 08 October 2018 - 11:07 PM

Nice try, but if look closely you will see your example is really just a pairing of the exact same image, not a real inside and outside focus shot.

 

I have looked at every star test image I could find on the internet, but have never found "identical" in and out of focus images. The best test was of a 100mm Zeiss, but even there slight differences in the intensity and sharpness of the images were present.

 

Go to the Aberrator web site and try to find even one telescope with test identical images. You can't. Even the best telescopes show slight differences.

 

Even if your 90mm achro had the best lens ever made, the inner and outer images could not be identical due to chromatic aberration, which causes the outer diffraction rings to be different colors. If you cannot see the color differences,  you may want to be tested for color blindness.

 

Maybe we just have different understandings of what the word "identical" means. To me it is pretty much absolute, where your definition apparently allows for minor color and sharpness differences.

 

Still, you did a nice job on the telescope and I am sure it puts up some great views.

 

Fussy Steve

That's not my personal example; just something I found online.  Your guess is as good as mine as to its authenticity.

 

I was referring to the pattern only in that, nothing else; the rings, as they did appear the same on both sides of focus.  I guess you'd have to be here, eh?  Now, I don't expect this doublet to be perfect, given its mass-production, importation and second-hand pricing, so don't take it too seriously.  Star-testing is not accomplished in one sitting, as I will be testing it multiple times before me, myself and I are satisfied.


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#77 Steve Allison

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Posted 08 October 2018 - 11:26 PM

Sky Muse-

 

Yeah, I am making much ado about nothing. Too much coffee...

 

I found a Chinese sourced Celestron 80 mm, 900 mm focal length refractor tube assembly at Goodwill the other day for $9.99. Darned if it doesn't throw up great images, and with its dark blue lens coatings, bright images, too. The Chinese have come a long way with their optics.

 

I thought about getting a 90 mm like yours, but already have a 90 mm telescope that has cost me a lot in time and money.

 

If your telescope is as well-corrected spherically as my bargain basement 80 mm is, it should perform really well. And with all the modifications you have made to optimize your Meade's performance, you can be sure it is delivering everything its design has to offer.

 

Steve


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#78 tony_spina

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Posted 08 October 2018 - 11:33 PM

Thanks, Tony.  Can you guess which one I'm about to do next?  I'll give you a hint: look for it in the "Classic Telescopes" forum in future.

I'm guessing it will be the Sears 6340


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#79 Steve Allison

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Posted 08 October 2018 - 11:36 PM

Good guess. and I probably should have mentioned emotional involvement...


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#80 Sky Muse

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Posted 08 October 2018 - 11:40 PM

Sky Muse-

 

Yeah, I am making much ado about nothing. Too much coffee...

 

I found a Chinese sourced Celestron 80 mm, 900 mm focal length refractor tube assembly at Goodwill the other day for $9.99. Darned if it doesn't throw up great images, and with its dark blue lens coatings, bright images, too. The Chinese have come a long way with their optics.

 

I thought about getting a 90 mm like yours, but already have a 90 mm telescope that has cost me a lot in time and money.

 

If your telescope is as well-corrected spherically as my bargain basement 80 mm is, it should perform really well. And with all the modifications you have made to optimize your Meade's performance, you can be sure it is delivering everything its design has to offer.

 

Steve

I would be skeptical myself, if I didn't see it with my own eyes.  Before I even touched it I conducted a star-test, and despite the pinching of the doublet, and its deplorable paper spacers, I saw great promise, so I set to work...and boy, did it pay off; my personal sighting of the Trapezium attests to that.  

 

Yes, it's 2018, and perhaps not surprising that the doublets are being well-figured now.  After all, they've been out the door since 1727.

 

Would that you renovated your Goodwill find, and identically. grin.gif



#81 Sky Muse

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Posted 08 October 2018 - 11:46 PM

I'm guessing it will be the Sears 6340

No...the Sears 4-6340. lol.gif

 

With all of this newfound interest in the smaller apertures, I figured it was about time.  I do have that EQ-1 for it, after all, and a wee motor-drive.  I'm going to blacken its original .965" diagonal, as well; also, the new old-stock Parks hybrid.

 

First, however, I have to take the achromat outside and look through it, as the doublet was shuffled like a pack of cards before its arrival.  



#82 tony_spina

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Posted 09 October 2018 - 12:59 PM

My Sears 4-6340 came on an alt-az mount.   How are you planning to attach the OTA to the EQ-1 mount?

 

BTW mine gives beautiful views. Excellent optics



#83 Sky Muse

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Posted 09 October 2018 - 01:12 PM

My Sears 4-6340 came on an alt-az mount.   How are you planning to attach the OTA to the EQ-1 mount?

 

BTW mine gives beautiful views. Excellent optics

I've shared the solution with you, via PM.  Mustn't spoil the surprise. 

 

Mum's the word.



#84 Steve Allison

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Posted 09 October 2018 - 02:53 PM

I'm guessing it will be the Sears 6340

 

Good guess. and I probably should have mentioned emotional involvement...

Mine is a Sears 6345. 

 

Homer nodded.

 

Steve



#85 tony_spina

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Posted 09 October 2018 - 03:26 PM

I've shared the solution with you, via PM.  Mustn't spoil the surprise. 

 

Mum's the word.

Your secret is safe with me. Unless of course someone tortures me with a free Unitron in exchange for the knowledge I have lol.gif


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#86 Jond105

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Posted 17 February 2020 - 05:19 PM

Hate to bring up an old thread, but was wondering if you knew is that was 86.4 flange for a direct replacement focuser if someone wanted to? 



#87 Jond105

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Posted 25 February 2020 - 05:32 PM

Sorry to revive an old thread but I grabbed one of these myself from Vorce himself. Mostly thanks to this thread. Arrived today and the GSO 2” focuser was a direct fit as I had imagined. I like the blue on this. I took of the bottom vixen rail and covered the holes some vvivid wrap I had. 

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#88 Jaimo!

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Posted 25 February 2020 - 06:22 PM

Jon, what size are those rings?  I may need to pick one up for my nephew.

 

Jaimo!



#89 Jond105

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Posted 25 February 2020 - 06:42 PM

Jon, what size are those rings?  I may need to pick one up for my nephew.

 

Jaimo!

My bad these were the GSO ones

 

https://agenaastro.c...-90mm-3-54.html



#90 Jaimo!

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Posted 25 February 2020 - 11:07 PM

Thanks Jon, I think I have a set of those laying around somewhere...  but where exactly...  smiley-char145.gif


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