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

At 06:15 PM 6/17/98 -0400, you wrote:


>    Gee, well they weren't apparent to me or the other two observers who
>were doing comparisons with me.  The sum of our observing experience totals
>over 80 years.  I guess we still don't know how to do it right.

Gee, well, my group included observers with an aggregate experience of
about 160 years, twice yours, and they were apparent to all of us. Guess we
win....

>    The transmission of the Naglers is a few percent less - an amount not
>very noticeable to humans who sense light according to a power law.  Since
>more of the light goes where it belongs in the Nagler, the point is somewhat
>debatable anyway.

As I originally said, the point about light transmission is rather
debatable. I have not been arguing about that, this is something you are
putting in my mouth. But you are wrong on point of fact: less of the light
ends up where it should in the Nagler, in certain telescopes. 

The fact remains that Naglers are not "brighter" as you claimed, and the
perceptions that they are, are nothing more than illusory.

>    If you think that Orthos are better corrected across the field than
>Naglers, I suggest you look at the ray trace results for eyepieces in
>"Telescope Optics, Evaluation and Design" by Rutten and Van Venrooij.

I am familiar with it. The orthos are better corrected for specific
important aberrations than the Naglers, which come into play strongly when
observing small targets on axis. This fact is well known....

>I'm just getting very tired of hearing people say how terribly
>obvious their flaws are, as though Naglers are unsuitable for critical work.

Their flaws are obvious, as are the flaws in every other eyepiece design.
And in many cases, Naglers are most certainly unsuitable for critical work.
The practical difficulty of putting a hair in one to perform CM transit
timings is an example of this, but there are many other examples too.
Galilean satellite eclipse timings are biased by these (and other big)
eyepieces, and need mathematical correction; color/intensity estimates have
been shown to be practically impossible to do accurately with such
eyepieces; the list goes on.

Since all eyepiece designs are flawed, it comes down to a choice based on
application and observing needs, and in no small amount, personal
preference. Those who mindlessly defend the Nagler or any other eyepiece as
a perfect ocular sporting the best correction, the brightest images, and
the sharpest views, are simply wrong. Yes, this includes you, Sue, when you
said that Naglers were generally "sharper, brighter, and clearer" than all
other eyepieces no matter their design or number of elements. There are a
lot of variables to consider, and you don't seem willing to consider them.
Personally, I think this is related to your recent distortions of Dave
Mitsky's comments about small DSO observing - I suspect you have never met
a narrow angle eyepiece you didn't hate. Hate orthos if you want, but there
are applications for them, and in many cases they are quite superior to
Naglers.

>As for Orthos, the off-axis images go to hell in a hand-basket, 

That's why we don't use them on large targets at long (eyepiece) focal
lengths.

>and not all
>objects that profit from critical study are minute in diameter.  With Orthos
>you also have to decide whether you would rather put up with their
>astigmatism or the trade-off field distortion of the Naglers.

That's a real interesting statement. Don't you think you had better go back
to your Rutten and Van Venrooij and correct this mistake?


--
Jeff Medkeff          | Acting Assistant Coordinator
Rockland Observatory  | Association of Lunar and Planetary
Sierra Vista, Arizona | Observers, Solar Section

On the web at http://shutter.vet.ohio-state.edu/