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