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Thread: Ethos report

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    MitchAlsup's Avatar
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    Default Ethos report



    This past weekend the telescope group was out at Ft Davis Texas on our annual pilgrimage. We suffered through 4 nights with no clouds in the sky, perfect 50dF temperatures, and some of the best skies we have seen there in a decade (it was our 25 anaversary trip).

    I took my new 21mm Ethos and 13mm Ethos and a parfocalizing kit, along with the rest of my telescope 'kit'.

    One thing that "gets" me about barrel reliefs is that no mater where the company puts them, they will always be at the wrong spot. The parfocalizing ring on the 13mm sits in the lower end of the barrel relief, making it harder to parfocalize the darned EPs. If it werent for the warning about taking them apart, I would have my machinest friend make a new set of barrels without the relief cut in them.

    The barrel on the 21mm Ethos is longer than the Tunable top on my Paracorr 1 (original non-tunable top converted to tunable top), so this EP has to be used in the #4 position, and when in this position it is parfocal with the 31mm Nagler. The 31mm Nagler is supposed to be used at #5 (lowest) but seens to operate just fine at #4. I got the 13mm parfocalized and then the set was working just fine. I did not notice any coma, but I was not looking for coma in particular.

    The 21E also caused me to push the main mirror up by about 1/8 inch in order to come to focus at the inner most position of the daw tube. At this position the width of the Tunable top is the limitation on inward focus (it bangs on the draw tube carrier of the decade old Starlights Instruments Focuser.)

    With my fast F/4 comparing a 21mm Ethos with my 20mm NT2 it is clear that Ethos is better corrected in the center of the FoV than the 20NT2. That is, I can see some residual spherical in the Nagler that was not present in the Ethos. Verys subtle but present nonetheless.

    The same thing happens with the 13E versus 13NT1: 13E perfect little pin pricks of stars, 13NT1 very slight residual spherical.

    The coating technology is clearly better than my 20 year old Naglers and the added glass is essentially invisible--that is no loss in dimmest visible stars, and no flare on bright objects. The coatings are NOT as good as what are on my (now ex) 30mm Ziess wth 86dFoV.

    All in all, I am pleased with theese EPs even after taking into account the costs. With the paracorr I get refractor-like images over most of the FoV.

    I don't really know if I can see the whole of the FoV but it was clear the the FoV IS definately wider then the Naglers how much so will be left to further experimentation.

  2. The Following 4 Users Say Thank You to MitchAlsup For This Useful Post:

    j.gardavsky (10-27-2011),Johann von Hesse (10-27-2011),OleCuss (10-27-2011),spectre180 (10-28-2011)

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    Johann von Hesse's Avatar
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    Default

    Thanks for the report on the eyepiece.
    RCP Observatory
    A Veteran of the Binoviewer Wars (2001-2003)
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    Original Mike's Avatar
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    Default

    Please forgive a dumb question. What is a parfocalizing "kit"?

    P.S. - I understand the concept of parafocal eyepieces, but it sounds like there's some hardware (i.e. your "kit") to achieve this with disparate eyepieces?
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    The parfocalizing kit in my case was a set of (Orion) 4 parfocalizing rings that go around the 2" barrel and are held in place with 3 * 2-56 set screws, the 2"+1.25" dual barrel EP was extended by a 24mm * 2" Fine tuning barrel from Baader.

    You screw in the extension barrel to the existing 2" barrel and now you have a long enough "throw" so that the barrel can be properly (and safely) grasp by the focuser tube (or Tunable Top on the Paracorr).

    First you have to find the EP that requires the most inward throw on the focuser--in my case this was with the Paracorr already in place. It turns out (as illustrated above) that the 21E required the most infocus distance. The 31NT5 focused at the same point once the tunable top was raised to the reference line in the 21E.

    For the 13E, I had to back out the set screws on the parfocal ring, slide it into the barrel, slide the barrel into the paracorr tunable top until it is focused, then carefully lock down the set screws and presto, this EP is now parfocal with the 21E adn 31NT5.

    Now one can change EPs without having to touch the focuser mechanism.

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