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Thread: A Tale of Two Plossls

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    Default A Tale of Two Plossls



    A while back I decided to invest in a good 6mm Plossl. I had owned a couple of Celestron ones in the past, one old 6mm in particular was quite well made with a brass drawtube and the writing on the housing was painted rather than silk screened. I’m fairly convinced it wasn’t made by Barsta, like most Celestron Plossls are now. I also already owned a 6mm Astro Hutech orthoscopic, but I wanted a little more field of view as an alternative to the Hutech. The 6mm would be ideal for all of the scopes I own and would get regular use.

    Both NPL's (the older Plossl now wearing the WO drawtube and with eyeguard removed)
    Pair.jpg

    My first solution was a 6mm Baader BCO as it seemed like a 50° FOV orthoscopic would be perfect for what I wanted. Unfortunately the BCO borked one night when I discovered visible, and fundamentally un-cleanable, debris had mysteriously appeared in the field of view. A replacement BCO then developed exactly the same problem. I also tried a 6mm Solomark Plossl, which was actually quite successful in my f/6.9 Newtonian. A Celestron Omni and a 6.4mm Meade were also a relatively good solution, although I replaced the Omni drawtube with a smooth chromed brass one. The eventual winner was a 6mm GSO Plossl, which had everything I wanted.

    Borked drawtube of original NPL
    Original.jpg

    Not content with this, and mainly out of curiosity, I bought a 6mm Vixen NPL. In my experience these had always been of the highest build quality. I’d owned the 6mm NPL for over six months before I discovered that the drawtube thread was borked in some way and wouldn’t readily accept any filters. I decided to cut my losses and buy another from the same retailer, which turned out to have the same fault, and so got returned. I ordered another 6mm NPL from a different retailer only to discover that it was similarly flawed. The new retailer (Telescope House) promised to find me a replacement, which was eventually delivered. Although even with this replacement some filter makes seem to have a few threading problems. Close inspection of the end of its drawtube reveals what appear like strange tooling marks. However, it is more or less usable so I kept it.

    Replacement NPL
    Replacement.jpg

    The first NPL was still a good eyepiece though so I decided to switch its drawtube for something that worked. This was partially successful. A chromed brass smooth tube did work but had no rim at the top, which the Vixen tubes do, and so it sat directly below the plastic eyeguard/top of the eyepiece. I decided this may become problematical with repeated use and in a eureka moment realised that I had a spare Williams Optics drawtube with a similar rim to the Vixen. This solution was fine when used in conjunction with a diagonal but caused in-focus problems with my 130mm Newtonian. At the time I used a Baader helical focuser threaded into the rack and pinion focuser on the scope. Amazingly, the tiny amount of extra height of the drawtube rim wouldn’t allow me to focus with the NPL.

    Original NPL with WO drawtube and Lumicon filter
    Original and Filter.jpg

    After all this, I’ve recently dug out the original 6mm NPL and reunited it with the WO drawtube. I predominantly use my 150mm Newtonian now which has a Crayford focuser. So I’ve finally sorted the original 6mm NPL! What a rigmarole lol.
    TS Optics: 150mm, f/6 Newtonian (GSO SVD series). Altair: Starwave 102ED-R. Sky-Watcher: SkyMax 102mm, SkyMax 127mm, Evostar 72ED DS Pro, Evostar 80ED DS Pro, ST80 (TS Focuser), ST102 (TS Focuser), EQ5 Deluxe, AZ5 Deluxe. Vixen: Porta II, SXG Hal-130. Orion: 90mm StarMax , ST80 (TS Focuser). Celestron: NexStar Evolution 9.25". William Optics: E-BINO-P Binoviewer. A shed load of eyepieces including: Antares, Astro Hutech, Baader, Bresser, BST, Bushnell, Celestron, Explore Scientific, GSO, Kokusai, Meade, Orion, Sky-Watcher, Solomark, SvBony, TeleVue, Vixen & one or two I'm not sure of.

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    Default Re: A Tale of Two Plossls

    Quite a journey there. Nice that you managed to sorted out, but you should not have to.

    After testing and liking 15mm NPL I wanted to try some shorter FLs, but got scared away by ultra tight (even for Plossls) ER. Vixen lists 3mm ER for 6mm NPL.
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    Default Re: A Tale of Two Plossls

    Quote Originally Posted by Bigzmey View Post
    Quite a journey there. Nice that you managed to sorted out, but you should not have to.

    After testing and liking 15mm NPL I wanted to try some shorter FLs, but got scared away by ultra tight (even for Plossls) ER. Vixen lists 3mm ER for 6mm NPL.
    Yes, it's been a bit of a journey, and the Vixen quality control was a bit of a disappointment. I can only assume it was a bad batch that for some reason affected the 6mm Plossls.

    A 3mm eye relief sounds about right. The Vixens are good in fast scopes and I have a feeling close eye relief tends to go with Plossls specifically designed for fast focal ratios. This is one of the reasons I removed the eyeguard on the 6mm.

    vixenwo1.jpg

    The upside is that the original dust cap still fits well, not always the case with all eyepieces that are de-eyeguarded.

    vixenwo2.jpg

    I had another twilight lunar session with the 102mm SkyMax, transparency wasn't good, and I think there was a lot of water vapour in the air.

    wedmoon1.png

    As it got darker I couldn't resist trying the modified Vixen. I got 216.6x on Schroter's Valley, Aristarchus and the Harbinger Mountains. I've had this quite sharp in good conditions, but it wasn't bad at all yesterday even though the conditions weren't really up to it. Theoretically 240x should be the limit for lunar viewing with the 102mm Mak (60x per inch of aperture). But nearly 217x is acceptable lol.
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    TS Optics: 150mm, f/6 Newtonian (GSO SVD series). Altair: Starwave 102ED-R. Sky-Watcher: SkyMax 102mm, SkyMax 127mm, Evostar 72ED DS Pro, Evostar 80ED DS Pro, ST80 (TS Focuser), ST102 (TS Focuser), EQ5 Deluxe, AZ5 Deluxe. Vixen: Porta II, SXG Hal-130. Orion: 90mm StarMax , ST80 (TS Focuser). Celestron: NexStar Evolution 9.25". William Optics: E-BINO-P Binoviewer. A shed load of eyepieces including: Antares, Astro Hutech, Baader, Bresser, BST, Bushnell, Celestron, Explore Scientific, GSO, Kokusai, Meade, Orion, Sky-Watcher, Solomark, SvBony, TeleVue, Vixen & one or two I'm not sure of.

 

 

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