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Thread: Pentax XW 3.5mm first impressions

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    Default Pentax XW 3.5mm first impressions



    Hello all,

    the Pentax XW 3.5mm (SMC) became the third from the Pentax XW family in my arsenal.
    Delivered in the original box on Friday by Jülich GmbH (Bonn, Germany) as a 2nd hand item,
    I am very curious how this short focus 'overkill' EP will be performing.

    The first picture is the view from above,
    Pentax XW three point five.jpg

    The second picture reveals the field lens with surprizingly large diameter, if compared with the wide and ultrawide EP designs of other manufacturers,

    Pentax XW three point five the field Smyth lens.jpg

    This may be due to the design strategy to achieve a high performance at the short focus.
    The optics design of 8 elements in 5 groups seems to follow the strategy of the Pentax XW 7mm I already have, but without the meniscus in front of the core lenses assembly, Pentax+ / smc PENTAX XO smc PENTAX XW

    The first test has been on the Leica APO Televid 82mm, offering a magnification close to 138x, 0.6mm exit pupil. The test object has been a TV antena, about 60m away. I often choose the test objects in the near field to avoid the effects of the air turbulence. The view has been sufficiently bright and sharp with enough contrast, even if such a high magnification at such a low exit pupil is more blowing up than increasing the resolution. No CA has been detected.

    More tests will follow, given the observing conditions.

    The curse of the clouds demons applies,

    The curse.jpg

    Thanks for reading,

    JG
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    Default Re: Pentax XW 3.5mm first impressions

    Hello all,

    finally I was able to test the Pentax XW 3.5mm against the Tele Vue Nagler Zoom 3mm - 6mm on the Synta 6" F/5 achromatic refractor.

    With quite a bit of luck I was able to see the transit of Europa across Jupiter, a nice smallish black spot, visibly moving away from the Jupiter rim, shortly before 23:00 local summer time.
    The identification of Europa transit is due to https://www.calsky.com/csrender.cgi?...18524858712135 , the size of the Jupiter disc has been 42.50 arcseconds.

    What I wanted to do in a short break between the clouds has been to test the Pentax XW 3.5mm against the Tele Vue Nagler Zoom 3mm - 6mm on Jupiter.

    The conditions have been good enough to magnify with the Nagler Zoom up to 250x (3mm setting), the problem has been the atmospheric haze, lowering the contrast of the view, and washing away the details in the bands.

    At 3.5mm, the both eyepieces are heads on, the view through the Pentax is as expected slightly brighter, the slightly darker view through the Nagler Zoom may have shown a little bit more contrast, otherwise there was not much to see in the both equatorial bands, and also not in the resolved bands closer the pole.

    The view through the both eyepieces reveals at 3.5mm (magnification 214x) a thin red CA fringe around the planet, and an extended faint blue hue, due to both the CA and scattering the atmospheric haze. But I did not find this amount of CA much objectionable.
    The yellow filters #8 and #12 have not improved the view.
    A substantial improvement came through the green(RGB)CCD filter, allowing to recognize 'somethings' in the bands, at least over short periods of time with better visibility.
    The both blue filters have revealed an extended blue hue due to the scattering of Jupiter's light in the atmospheric haze.

    Some sunshine between the clouds in the afternoon has also allowed to make a terrestrial test of the Pentax XW 3.5mm on the Synta 6" F/5 achromatic refractor.
    The test object has been the top of the roof on the next house, about 20m away. This way of short range terrestrial testing is not influenced by the air turbulence, or transparence.
    The performance of Pentax has been tested without filter, and then through the yellow filters #8 and #12, blue 470nm (bright), blue(RGB)CCD, and green(RGB)CCD.
    The structures on the top of the roof, including the metal parts with fine textures, have been very good resolved without any filter, and through all the filters used. The best contrast yielded the blue(RGB)CCD and the green(RGB)CCD filters, the worst contrast has yielded the 470nm bright blue filter.
    The CA without any filter has been visible, of course, making on the small high contrast textures a color noise, but not distracting from inspecting the finest textures.

    Filters used:
    yellow #8 TS color long-pass filter made in Taiwan
    yellow #12 Baader with MC color long-pass filter
    bright blue 470nm Baader with MC color band-pass filter
    blue(RGB)CCD Baader band-pass interference filter
    green(RGB)CCD Baader band-pass interference filter

    Thanks for reading,

    JG

    PS: The next test will be on the globular clusters of the season, and then on the details in the galaxies.
    It may take some time, I am not testing the optics the fast way.
    Last edited by j.gardavsky; 05-13-2017 at 10:11 PM. Reason: missing word
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    Default Re: Pentax XW 3.5mm first impressions

    I have been thinking about the 3.5 for my kit. Thank you JG.
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    Default Re: Pentax XW 3.5mm first impressions

    Excellent work, JG. Thanks much for this. Looking forward to more.
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    Default Re: Pentax XW 3.5mm first impressions

    Thanks JG! Seems like it's performing well so far!

    You were lucky to find one used. It seems the Pentax XW eyepieces don't come up that often.

    Fully clouded out here... so no first light for me yet.
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    Default Re: Pentax XW 3.5mm first impressions

    I discovered the Pentax XW's in 2009 and have slowly acquired the ones 14mm and under. They were the best eyepieces for everything, especially planets. Then the Delos came out in late 2012 and they seem to equal the XW's. Filled in the holes between the XW's so have every mm under 7 and 1/2mm's under 5. Think it is the perfect set for sneaking up to highest planetary power that the atmospheric conditions allow for any nite.
    Newtman but some refractors allowed.

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    Default Re: Pentax XW 3.5mm first impressions

    Hello TomJones,

    I have had my finger on the Delos ordering buttom, but decided to wait on the best offer for Pentax XW 3.5mm .
    Above f=10mm wide field, my peference are the Leica, Swarovski and Zeiss EPs, designed for the F/5.9 refractors,
    http://www.astronomyforum.net/member...ca-20x-ww.html
    http://www.astronomyforum.net/member...ca-20x-ww.html
    http://www.astronomyforum.net/member...506-zeiss.html

    Best,

    JG
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    Default Re: Pentax XW 3.5mm first impressions

    Hi J.G. You have posted two images of the Leica eyepiece. I was curious if your Swarovski was a duplicate focal length chosen for its different optical quality from the Leica, or if it filled in a different focal length in your fast refractor eyepiece collection?
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    Default Re: Pentax XW 3.5mm first impressions

    Thanks for the interesting report. Looking forward to performance on globular clusters.
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    Default Re: Pentax XW 3.5mm first impressions

    Quote Originally Posted by Trombatissimo View Post
    Hi J.G. You have posted two images of the Leica eyepiece. I was curious if your Swarovski was a duplicate focal length chosen for its different optical quality from the Leica, or if it filled in a different focal length in your fast refractor eyepiece collection?
    Hello Ken,

    the answer is simple: I could not resist, you know that feeling.

    The Leica spotting scope eyepieces are rated, next to the Zeiss, as the best ones (light, contrast) for the fast refractors.
    The Swarovs have some CA compensation, but they are also excellent.
    At f=10mm, the Swaro wins a margin in sharpness over the Pentax XW on the 6" F/5 Synta.

    The problem is, there must be some guys in the U.S., who have cleared from the 2nd hand markets all discontinued Leica and Zeiss EPs useable for the hoby astronomy .
    I am still on the search for Leica B32x WW f=14mm 2.3° (73° AFOV), 7 lenses inside,
    have not been fast enough with my decission.

    The Pentax XW are very good, but big and heavy,

    Pentax XW 3 5 on the 152mm Synta refractor.jpg

    making my refractor to look like a locomotive from a silent movie era.

    Thanks for asking,

    JG
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