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Jupiter in 10" Dob and focused field of view

Discussion in 'Telescopes and Mounts' started by Ed D, Mar 26, 2019.

Jupiter in 10" Dob and focused field of view

Started by Ed D on Mar 26, 2019 at 6:30 AM

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  1. Ed D

    Ed D Well-Known Member

    Jan 12, 2017
    Trophy Points:
    Sunny South Florida
    This morning I had my 10" Skywatcher strut Dob out and was observing Jupiter with it. I was using my 9mm Orion Expanse and Vixen NPL 8mm eyepieces, both of which are proven stellar performers on planets through all scopes I own and have owned.

    During the observing session I found that if the planet was outside of the central 1/3 of the field of view it would progressively get noticeably out of focus. I was not using my coma corrector . Yeah, I understand this is normal with a large, fast Newtonian. No real issue, I just simply either kept the planet in the center 1/3 of the field, or touched up the focus as needed.

    Normally, I prefer using longer focal length Plossls with a Barlow for planets and Luna. Out of curiosity, I wanted to find out how my 25mm NPL Plossl would perform when used with my 3x TV Barlow. This combination gives magnification (exit pupil) similar to what the 8mm and 9mm eyepieces were giving. Much to my surprise the planet image stayed sharp for about 85% of its travel through the field of view. I have also gotten this effect when using my binoviewer with longer focal length Plossls and Barlows. Actually, this should not have surprised me. I had simply forgotten because I haven't been observing planets for way too long, especially with this big beast.

    Just thought I would throw this out there, and hopefully get some feedback.

    Ed D

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