I, too, compared a Nagler 31 to a Leitz 30mm (older silver barrel with
blue engraving, same optics as all the others). I did the comparison
using my Traveler (f/5.8), observing star fields, Jupiter, and some
daytime observing.
I purchased my Leitz 30mm eyepiece over 4 years ago, well before this
eyepiece was widely known (I believe mine is the second one imported
into
the US). It provided the widest, most comfortable field of view
of any
eyepiece I had ever used (I called it my Nagler 30mm Plus). I
was thrilled
to hear Al Nagler finally would introduce a similar eyepiece (since
the
Leitz was so expensive and hard to find). I doubt the Nagler
31 would
ever have come into existence without the presence of the Leitz 30
(until
then, who would have thought people would pay $1000 for an eyepiece...).
Well, on with my comparison.
As others have pointed out, the Nagler has a slightly larger true field.
What immediately struck me about this eyepiece (aside from the appearance
and huge size) was how sharp the image was almost to the edge.
Stars
maintained a small pinpoint character. In the Leitz, as others
have noted,
the sharpness trailed below that of the Nagler about 50% of the way
out.
Though, since I use the outer field for mainly aesthetic purposes (I
don't
concentrate on the outer edge normally), the Leitz still functioned
very
well. Nevertheless, the Nagler is significantly sharper at the
edge and
this is a real plus (though, it is evident this great edge sharpness
came
with some tradeoffs) .
On-Axis, however, I was able to detect Jupiter's bands noticeably easier
in the Leitz. The Leitz appeared to provide both a sharper and
higher
contrast view. The Nagler was no slouch, but the Leitz did do
better (and
I tried this comparison multiple times, since I did not believe the
difference at first).
Color error was pretty much similar in both, and not a problem in either.
(If you want to see an eyepiece with rainbow color, try a Kasai 30mm
88 degree eyepiece, it is no knock of of the Leitz, for sure!).
Kidney beaning was only mildly detectable in the Nagler (even in daylight),
not a problem. The Leitz effectively has none (again, to my eyes).
Both
eyepieces offer a very comfortable view. The Leitz does have
a little
larger apparent field of view (which is what these eyepieces are all
about).
The Nagler has a significant amount of distortion, which results in
a
fishbowl/dizzy feeling when panning around. I don't mind this,
but some
folks may be bothered by it. The primary downside, for me, is
the apparent
darkening of the center of the field (relative to the edge) that results.
In the Traveler from moderately light polluted skies this was very
noticeable.
The Leitz also exhibits a fair amount of distortion, though somewhat
less
than the Nagler. The darkening of the field center was less noticeable
as
a result, but still present.
A real disappointment for me with the Nagler was the reduced eye relief
over
what the TeleVue specs claim. I suspect that the relief is specified
from the
center of the eye lens, which is strongly concave as well as slightly
recessed.
This translates to eye relief of perhaps 13mm max. If you wear
glasses
for astimatism (I do), then the Nagler is unuseable (the view is way
to
restricted, why use a Nagler if you can only see half the field...).
This
is a very annoying shortcoming for me. The Leitz just works with
eyeglasses,
as it has at least 6mm more useable relief. You can make the
Nagler work
if you make a custom corrector lens (which I have done for the Leitz
for
convenience), but most folks wouldn't go to this trouble.
The other disappointment for me was the position of the eyepiece focal
plane.
It is located over 0.6" ahead of any of my other eyepieces (including
all the
other Naglers I own). This prevents this eyepiece from reaching focus
on my Obsession (not enough in-travel). This is a real shortcoming,
and
the primary reason I ended up returning my N31 (I was hoping to keep
the
Nagler and get my $$ back out of the Leitz).
I think the comparison of these two great eyepieces comes down to individual
tastes and needs. The Nagler is extremely sharp to the edge,
and if that
is your primary interest, it will likely come out as the best choice.
If you
wear glasses for astigmatism, have a strong dislike for distortion,
or must
the highest on-axis performance the Leitz would come out ahead.
Having enough in-travel to reach focus with the N31 is also a consideration.
Of course, if cost comes into play (as it does for most folks), the
Nagler
probably will be the top choice (assuming you are willing to pay $600
for
any eyepiece...). I could certainly remain happy with either
eyepiece.
For the foreseeable future, I will be hanging onto my Leitz.
Bob Luffel