From: era_pul@arkimedes.ki.ericsson.se (Peter Ulfheden consultant)
Newsgroups: sci.astro
Subject: Dim Naglers (was: Russian Maksutov)
Date: 6 Oct 92 11:40:25 GMT
Organization: Ericsson Radio Sytems AB, Sweden




In-reply-to: joe@montebello.soest.hawaii.edu's message of Sat, 3 Oct 1992 10:23:25 GMT
Newsgroups: sci.astro
Subject: Dim Naglers (was:Russian Maksutov)
Distribution: 


In article <1992Oct3.102325.22361@news.Hawaii.Edu> joe@montebello.soest.hawaii.edu (Joe Dellinger) writes:
[Stuff deleted ................]

	   I'm not sure I agree wholeheartedly with him on point #1; at the
|> star party we tried both Plossls and Naglers in the 5-inch Astrophysics
|> that was there. It is true the Naglers gave a super-wide field of view
|> that was sharp ALL the way across... but it was also an image that was
|> quite noticeably _dimmer_ than the view in the Plossls (I suppose because
|> the Naglers have many more pieces of glass in them) and the view in the
|> center "sweet" part of the Plossls seemed sharper than the "equally-sharp-
|> all-the-way-across" view in the Naglers. I think both Naglers and Plossls
|> have their uses; certainly I don't agree that Naglers are in all ways
|> superior. A Plossl with a good Barlow should work quite well in a Traveler.

[Stuff deleted ................]

	/\    /\    /\/\/\/\/\/\/\.-.-.-.-.......___________
|>     /  \  /  \  /Hawaii Institute of Geophysics, Honolulu\/\/\.-.-....__
|> ___/    \/    \/Joe Dellinger, Internet: joe@montebello.soest.hawaii.edu\/\.-.__
|> ____________________________________________________
|> Objectivity is NOT an unobtainable EMPTYING OF MIND |
|> but a willingness to abandon a set of preferences   |----> Stephen J. Gould
|> WHEN the WORLD seems to work in a contrary way.     |



Now this is interesting. Naglers being dimmer. I have been discussing
this matter with the section leader of the optical section in the
Swedish Amateur Astronomical Association. He is a highly respected
and reputable telescope (and eyepiece) maker.

He claims that a negative lens, with a small diameter, in front of an
eyepiece, like in a Nagler or a plossl with barlow, reduces the
'transmssion' of light through the exit pupil. Therefore Naglers and
other eyepieces with barlows, according to him, are inferior compared
to bare plossls.

As a layman in this field I have tried to understand this but I can't
see the problem, if the diameter of the negative lens is wide enough
to grasp the light cone from the front lens/mirror of the telescope. I
have also looked in the book 'Optics Evaluation and Design' by Venroij
& Rutten (sp?) and they say nothing about this subject.

So when Joe Dellinger reports that he has seen Naglers being dimmer than
plossls I can`t keep my self from asking if the amaterur optician was right.
If any one can cast a light on this I would be more than happy.

I am currently using the 4.8, 9 and 20 mm Naglers on my 18" dobsonian.
BTW I can recommend Galaxy Optics, CO for making YOUR mirror.

Clear Skies

Peter
--

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 Peter Ulfheden              |  era_pul@ki.ericsson.se
 Amorinav. 3                 |  Phone: +46 8 751 02 15
 S-191 44 Sollentuna, SWEDEN |  Fax:   +46 8 35 04 29
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Newsgroups: sci.astro,rec.radio.amateur.misc,rec.radio.shortwave