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  1. #1
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    Default Explore Scientific 6.7mm problem



    I bought the ES 6.7mm a few weeks ago and just recently the clouds cleared enough to give it a good look. It shows Jupiter really nicely, lots of detail. The problem is there are black "things" in the field of view when I defocus the eyepiece. They are different shapes, a couple close to the center look like bat wings. It almost looks like there is something on the lens, but there isn't. I don't see them at all when the eyepiece is focused. Today I had my 10" Skywatcher in the house playing with the collimation and I noticed those things in the view when I was trying to line up my 9x50 finder with the scope, of course I was a bit out of focus as the tree I was trying to line up on was too close.
    I don't know if there is something wrong with the ep or its normal? It doesn't really bother the viewing, but like all things I buy I will probably sell it some day and I would like to be able to tell a prospective buyer the ep is perfect....but I don't know if it really is. If this isn't normal I would try to return it. Any ideas?
    PS...I don't see this in my other eyepieces
    !6" F/3.8 under construction
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    -Brian



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  2. #2
    AustinPSD's Avatar
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    Default

    Could be any number of things ranging from simple contamination on the eyepiece lens(es) to seeing defects (floaters) in your own eye related to exit pupil and relatively high magnification.

    Try turning (rotating) the eyepiece in the focuser drawtube - if the spots move and retain their shape, the problem is most likely contamination on one or perhaps both surfaces of the lenses that make up the eyepiece - the "top", or eye lens component is one possibility vis a vis contamination on the surface of this lens element. The other is contamination on the "bottom" surface of the image forming lens element interior to the eyepiece. Less likely is contamination internal to the eyepiece itself. Unless you are relatively highly skilled, I don't recommend disassembly of the eyepiece in an attempt to clean it.

    Seeing floaters in your own eye is the next most likely cause. There isn't much you can do about this...
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  4. #3
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    Default

    I've seen those defects in a couple of eyepieces. My problem is when I turn the eyepiece in the draw tube, the specs stay in the same place. Guess I'll live with it.

    Jim
    Celestron C9.25. Atlas EQG mount. Canon 500D unmodded, Celestron ST80 guide scope, SSAG, Meade 6.3 FR, Thousand Oaks dew control with Dewnot straps. Zhumell 8/24mm Zoom, 2"Gso Superview 42mm, Meade 2"QX wide angle 30MM, Meade 1.25 EP and filter set. Tasco 10x50 Zhumell 20x80 bino and a few other odds and ends.
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  6. #4
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    Default

    What you have described is a phenomonom known as "spherical aberation of the exit pupil". It is an optical malady that causes no unshapness of the FoV.

    This was a problem with the original 13mm Nagler T1, that was cured wiht the NT2s.

    I am surprised you can see it at 6.7mm without having an absudly fast scope (F/3-ish) but daylight causes the eye's pupil to contract and makes pupil placement critical.

    Can you see it at night with fully dark adapted eyes?
    What other EPs?

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  8. #5
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    Quote Originally Posted by MitchAlsup View Post
    What you have described is a phenomonom known as "spherical aberation of the exit pupil". It is an optical malady that causes no unshapness of the FoV.

    This was a problem with the original 13mm Nagler T1, that was cured wiht the NT2s.

    I am surprised you can see it at 6.7mm without having an absudly fast scope (F/3-ish) but daylight causes the eye's pupil to contract and makes pupil placement critical.

    Can you see it at night with fully dark adapted eyes?
    What other EPs?
    Yep - relatively high mag + exit pupil defect... the Skywatcher 10" Dob is about f/4.7, not terribly fast but at 180X probably enough to surface the defect. That plus floaters evidenced at this mag are more likely than dust/surface contamination, certainly internal...
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  10. #6
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    Default

    Thanks guys. I tried rotating the ep in the drawtube and the "things" move with the rotation. I also noticed the bat wings that I had mentioned above being in the center are now at the edge. I wonder if there really is contamination in the ep and handling it has moved the loose pieces around?
    To answer a few of the other questions asked:
    I have a 10" f4.7 dob, the other eyepieces are in my signature file, 13mm Ethos, 18mm Meade. I can see these things day or night, I just have to defocus and there they are, lots of tiny ones and a couple of bigger ones.
    Thanks for the replies
    !6" F/3.8 under construction
    Night Vision moncular

    -Brian



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  11. #7
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    Default

    I played around a little more with the ES 6.7. I can see the things in the ep just held up to a light, no telescope involved. I think I'm going to RMA this one.
    !6" F/3.8 under construction
    Night Vision moncular

    -Brian



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