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Penguin eye(piece) surgery


Nyctimene

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During the last two and a half years, I've posted several experiences and observations with the Skywatcher Infinity N 76/300, a cute little scope primarily for children, but, with it's parabolic primary, well suited for rich field observing at 15x magnification with a true field of view (TFoV) of 3°30'. I modded the "Blue Penguin" last autumn by adding a Rigel Quikfinder to cure it's biggest drawback - pointing at a target. Two days ago, I inspected the 30x mag erecting eyepiece, which, in contrast to the 15x eyepiece, can only be described as an "erectile dysfunction", with a very small TFoV of just 1°19', dim views, and the hassle not only of changing the view to a Right angle - Correct image display, but doubling at the same time the magnification. At 2.00 AM, the brain goes on strike with that. As I inspected the eyepiece's front (secondary site) end, I discovered, that the retaining plastic ring was threaded and could easily be removed. Out came first a (field?) lens, followed by a small cylindric "cage", containing two prisms and a small field stop. To remove the "erectile function" contents, the cement had to be broken and another retaining clip to be taken away. I reassembled the eyepiece without the two prisms and the field stop. The result was very pleasing - a now wider TFoV of 1°36', a brighter image (larger exit pupil - still to evaluate this!)) and an astronomical correct Newtonian view. Despite the full moon and clouds, I observed some familiar objects - the Moon itself, the Double Double; Mizar and Alcor; Saturn as a tiny ellipsoid and finally M 57 as a "defocused" star. Swapping eyepieces was much easier now. Under dark skies, I'm sure, the Penguin will show many nice targets with the now comfortable 30x mag. A nice, cheap and surprisingly capable RFT, ideal for holidays or as a grab-and-go.

Attached a picture:

DSC_0023.thumb.JPG.3111beca3bfae6e6afae5bca36fe1bda.JPG

Thanks for reading

Stephan

Edited by Nyctimene
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Nice work Stephan.

I performed similar surgery on the astronomically useless 20mm Celestron Erecting Eyepiece that came with my first scope.

Having removed the prism set I noticed that although the eye lens was about 20mm diameter, the (fixed) field stop was only 12mm,                                                  presumably to match the optical path of the  Amici prisms.

I enlarged this  as much as  possible (using a small grindstone in a drill) which increased the  AFOV from about 35  to  a more respectable 50 degrees , producing a useable basic eyepiece with views similar to a Plossl.

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  • 3 weeks later...

Had fun this night with the modded 76/300 Penguin and had, under sub-average NELM 5.0 skies, a nice haul of summer globulars - M 2, 3, 5, 10, 12, 13, 14, 15, 71, 92. All were visible at mag 30x as fuzzballs, without any resolution into single stars. Some by-catch, as M 27 (bright, distinct apple-core shape), IC 4665, M 11, M 81/82, 7789, 457. With the Rigel, an easy find now, and swapping eyepieces is way more intuitively and "natural" (despite the threaded eyepieces, that work as a focuser substitute). Both eyepieces were even usable with eyeglasses. An unusual combo, with the finder being more expensive than the scope (+ additional eyepiece), but a rewarding modification. Btw., the 15x eyepiece is a must  (still available from here (of course, no affiliation etc.): www.astroshop.eu/eyepieces/skywatcher-15x-eyepiece-for-the-infinity-telescope/p,4981)

Stephan

 

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