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Re: (IAAC) FWD: What should I buy? (rich field scopes)



I agree that orthos are the ideal choice, but the larger apparent field of view provided by the
Naglers sure comes in handy if your scope is a dobsonian with no drive system.
	As far as image brightness goes, an 8 element eyepiece, assuming each coated lens element has a
transmision of 98.5%, will have a total transmission of 88.6%.  A 4 element eyepiece has a
transmision of 94%.  In a 12.5" scope used at full aperture a 5.5% reduction will probably not be
noticeable, but if an aperture stop is used it could become a problem.
Mark G. Birkmann
> I'm not sure what you mean by "wide angular ape(r)ture" (wide apparent field of
> view?), but I believe the consensus opinion is that the fewer lens elements in a
> planetary ocular the better.  Each lens element robs a little of the incident
> light.  (And a Nagler has a lot of lens elements.)  Thus 4 element orthoscopics are
> usually the eyepieces of choice for planetary observers.  (I have used the
> legendary Zeiss orthos on a few occasions.)
> 
> Did you mean a 7mm Nagler?  That would be better choice than keeping the 4.8mm,
> IMHO.  It will still produce over 300x in your scope but that will be a far more
> usable magnification than 466x!
> 
> Dave Mitsky
> ASH, DVAA

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