Re: (IAAC) FWD: What should I buy? (rich field scopes)
At 09:12 PM 6/15/98 -0500, you wrote:
> 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.
As you suggest, the lost light from a multielement ocular will be largely irrelevant to the view through the scope. OTOH, contrast-reducing effects such as scatter (caused by air-glass surfaces and increased by the use of coatings) and internal reflections (which, though decreased because of coatings, are still quite obvious with the Naglers), will be far more deleterious - and obviously so to the observer.
It just goes to show, everything is a compromise. I'd love to have an 80 degree field with four elements just as well corrected as a good ortho, but it won't happen until pigs fly and sustained cold weather is experienced in the infernal regions. Meantime, I'm still using orthos for some deep sky observing, as they just can't be beat when it comes to contrast.
Jeff Medkeff | Sending from under clear skies
Sierra Vista, | at Junk Bond Observatory
Arizona | Observatory Code 701