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Low power eyepieces for new scope

Started by Inge_S, 01/15/2003 11:37AM
Posted 01/15/2003 11:37AM Opening Post
Sunday evening my astronomy club's new scope arrived, an NGT-12.5 (12.5-inch f/4.5 Newtonian). The scope lives with me, at least to begin with, and I can, of course, use my own set of eyepieces with the NGT (UO-orthos, 25mm, 12.5mm, 7mm and 5mm and a 16mm Konig, all 1.25" barrel).
Just recently I have tried some low power eyepieces (16mm, 20mm, 24mm and 28mm Celestron Erfles)with my personal 8-inch f/6, and I realise that these eyepieces provide nice views of extended objects, and work beautifully with narrowband filters. I will, however, soon have to return the Erfles to the owner, and therefore want to purchase at least one low-power wide-field eyepiece for use with the new scope. The NGT allows the use of both 1.25" and 2" eyepieces, BUT the filters I have are all 1.25". Any recommendations? I think that the focal length should be no longer than 30mm, perhaps 28mm (considering exit pupil). I would also prefer the price to be below 200$.

Posted 01/15/2003 05:01PM #1
You might also think about two of the Sky Instrument (Antares) eyepieces, the 30mm modified Erfle, 2", 72* AFOV, $130, or the 24mm Speers-Waler, 1.25", 67* AFOV, $124.

Doug Tanaka
Posted 01/16/2003 02:00AM #2
Now that I know for sure what scope you are using these in, I suspect the vignetting I experienced in my 20mm is due to use in slower systems. Does "yours" appear to be in a common 25mm ortho body with labeling imprinted into the side? Circle V on barrel. Since my lens set is akin to a Goerz ortho instead of a classic Erfle, I assume "Erfle" is more a generic WF term in this case. Goerz' mid-1920's design used a meniscus field lens and was used in binoculars. So I assume the field lens here is better suited to a fast focal ratio whereas classic Erfle's do perform well with slower f ratios. In any event, my field stop reduction is reversible and I do enjoy the orthoscopic performance, with wider than normal AFOV. Ortho's and a 32mm type I Konig in the 1.25" version satisfy me also, and I remember well the complete lack of distortion in an old common 12mm K- it's only fault was ghosts. Scope is 6" f/8 Newt. Ron
Posted 01/16/2003 10:05AM #3
I recommend a 24mm Tele Vue Panoptic or a 30mm Celestron Ultima if the Panoptic is too expensive.

Dave Mitsky

Chance favors the prepared mind.

De gustibus non est disputandum.
Posted 01/17/2003 02:55PM #4
Thank you guys for your useful comments. I will probably go for a single high-end eyepiece rather than 2 - 3 cheaper ones. Perhaps a 26mm Nagler or the 31mm (have to check if I can utilise the exit pupil). Time will show.