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Celestron C6R Lens Upgrade

Discussion in 'Telescopes and Mounts' started by Scopejunkie, Oct 22, 2018.

Celestron C6R Lens Upgrade

Started by Scopejunkie on Oct 22, 2018 at 1:50 PM

24 Replies 1974 Views 2 Likes

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  1. Scopejunkie

    Scopejunkie Well-Known Member

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    Hi All,

    Yes, I have been tinkering again. Love retirement! Anyway, working with Ales over at Istar Optical, I came up with an adapter that will allow the owners of the Celestron C6R (w/adjustable cell) the option of upgrading to an Istar 150mm F/8 R35 lens or standard Istar 150mm F/8 achromat. Got a lens not performing well? This may be an option for you. This CNC machined adapter is a composite of plastic and MDF so as to not add more weight to the front heavy C6R. The mod only requires a change of in focus position of about 3/8" and installs in about minute. The lens cell adjustability is maintained. Send me a PM if interested in the adapter.

    Hope do a lens comparison soon.

    Keith (Scopejunkie)
     

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  2. Scopejunkie

    Scopejunkie Well-Known Member

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    Walking a tightrope? Nah! Made some extension arms for the lens adapter so I could test a F/10 objective with an F/8 telescope.

    Keith (Scopejunkie)
     

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  3. Scopejunkie

    Scopejunkie Well-Known Member

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    All,

    Here is the full story: I own a Celestron C6-R refractor and I had wondered what it would be like to have an Istar R35 F/8 lens in place of the standard C6-R F/8 achromat. Without the proper information on Istar's cell design this just remained an "idea." To scratch an itch, I finally contacted Ales at Istar and he kindly sent me the Istar 150 mm lens cell information. With this information I started my design of an adapter plate so I could swap out the C6-R lens for a Istar R35 lens.

    After designing the adapter plate I asked Ales if he could send me a lens cell from one of their 150mm lenses so that after I had produced the adapter I could do a full fit check to see if what I had made worked. Ales graciously sent me an older 150mm standard F/10 achromat so I could perform my fit check since the original Istar cell design had not changed.

    Everything worked. I was a happy camper. Being the curious ATM that I am I decided to clean and check this lens for Ales and test it (yes, Ales knew what I was doing). I rigged up some extensions to extend my newly designed cell adapter from the C6-R and took a look at the night sky with the Istar F/10 lens. Using a 250 LPI etched glass ronchi grating, at only two bands, revealed that the lens had a spherical correction better than 1/8th wave looking at both sides of focus. The lens also has a good clean edge. The star test was quite good. The star test agreed well with the ronchi test. Much better than 1/6th wave overall correction (according to Suiter's book) with smooth surfaces (more like 1/7th). The lens passes the "two ring" star test.

    Even though the seeing was "average" I could easily see the small polar cap of Mars (12.4 arc sec) with full surface markings at 150x. Though this was not a "high power" night, I ran the magnification up to 375x (4mm Ortho). I was quite surprised with the results. The planet remained detailed and crisp despite the seeing effects. I did get a good view of Saturn at 150x revealing all the usual details before it sank too low. I am wondering what this lens will do on a good night! Clean split Pi Aql at 150x. Reconfirmed at 215x revealing perfectly round airy disks. Also clean split 10 Aries at 150x. You can only do this with very tight star images.

    This is without a doubt an optic that seems to "look past" the seeing allowing a lot of detail to be seen. The testing continues... After over 40 years of owning and making telescopes, I have owned only a few optics with this ability. Instead of sending this lens back, after confirming my adapter fit-up, I asked if I could buy it. It looks like Istar quality is consistent. My previous Istar 8" F/8.8 (2010) was a good lens also.

    The pics are simulations of what I was seeing at the eyepiece.

    Time to purchase some new "stuff" for a fall/winter refractor build...

    Keith (Scopejunkie)
     

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    Last edited: Oct 27, 2018
  4. Gabby76

    Gabby76 Well-Known Member

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    Very interesting adapter Kieth!
    What kind of cost are you looking at for it?
     
  5. Scopejunkie

    Scopejunkie Well-Known Member

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    $50.00

    Keith (Scopejunkie)
     
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  6. Scopejunkie

    Scopejunkie Well-Known Member

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    Well... Couldn't hold myself back. The F/10 refractor design is finished and the dust is flying. Will use some tubes I had lying around from a previous project that was never started. Since they are only 38 inches long, I will have to do some extra work to get the full length I need. The tinkering continues...
     

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  7. Scopejunkie

    Scopejunkie Well-Known Member

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    The 150mm F/10 Istar is coming together. My back hurts but I still have a smile on my face.
     

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  8. Scopejunkie

    Scopejunkie Well-Known Member

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    New countercell completed and installed. Now to make the mounts for the dew shield.
     

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    Last edited: Oct 31, 2018
  9. Scopejunkie

    Scopejunkie Well-Known Member

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    Dew shield installed. Finder next. Can't decide if I should go with a 18" dovetail with internal bracing (simple) or rings (a bit more work). :confused:
     

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  10. Scopejunkie

    Scopejunkie Well-Known Member

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    Up and operational! Testing again tonight despite the high clouds. :eek:
     

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  11. Scopejunkie

    Scopejunkie Well-Known Member

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    Baffles installed and added a new cradle/dovetail block (12" long, 3/4" thick). Scope now damps out in 1 second.
     

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  12. Gabby76

    Gabby76 Well-Known Member

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    Really nice work. I hope it gives some great views :)
     
  13. Scopejunkie

    Scopejunkie Well-Known Member

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    Thanks!!!! :cool: I have added 4 sealable vent holes in the tube just behind the objective and one below the focuser for lens cooling. Some might think that a good refractor would have no need of such things and they would be right. Yet, I have found that in severe temp swings, even a refractor can benefit from passive cooling just like a reflector. Yes, I'm a performance addict.
     

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  14. Gabby76

    Gabby76 Well-Known Member

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    I agree, I have a cat cooler that I use at times while setting up.
    Diagonals are usually set out to acclimate before the refractors go outside.
     
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  15. Scopejunkie

    Scopejunkie Well-Known Member

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    Sweet! Even though a refractor is not as badly affected as a reflector, cooling can make a subtle difference on high power observing under very good seeing conditions with large lenses. I was able to clearly confirm that this lens has a true 1/8th wave overall correction according to the star test a couple of nights ago. My 250lpi etched glass Ronchi eyepiece had killer results at a mere two bands. I had a hard time discerning any curavature in the bands on both sides of focus. That's beyond 1/8th wave spherical correction! This lens was not at this high level of performance till the lens had completely cooled. At the start it was more like 1/5 - 1/6th wave. Testing vents versus no vents tonight. And the tinkering continues...
     
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  16. Gabby76

    Gabby76 Well-Known Member

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    I recall an article by Thomas Back where he was testing a refractor and to get the numbers even better they wrapped the tube with cold towels.
    Apparently it worked. I wonder if I can find the article now?
     
  17. Scopejunkie

    Scopejunkie Well-Known Member

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    If you find it let me know. I would love to see/read it!
     
    Last edited: Nov 24, 2018
  18. Scopejunkie

    Scopejunkie Well-Known Member

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    Made a new 8" short pier to support the old Astrola mount. It's about 25lbs lighter than the Big Meade tripod it is replacing. Levelers and wheels are next. The entire mount will roll out making setup of the big refractor a breeze. Gettin' more lazy as the years go buy. :cool:
     

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  19. Gabby76

    Gabby76 Well-Known Member

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    I looked through my HD while at home but I could not find it unfortunately.

    The new mount is looking interesting :)
     
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  20. Scopejunkie

    Scopejunkie Well-Known Member

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    Here is a pic of the full pier, up and ready for the scope. Getting ready detail out the OTA. Temp and humidity between storms will dictate how soon I can get this done. Having fun. Winter fun :)
     

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