First light - 13mm T6 Nagler against a 16mm T5
eye_...@arkansas.net
Eyepieces and more eyepieces... what a my gonna do!
The observing setting:
11:00 PM - 1:30 AM CST - 35.5 degrees N Latitude (Arkansas).
Nearly full moonlight ~20 degrees off away from Jupiter.
Local temperature here at 30 degrees F.
Light intermittent winds, some beautiful wave clouds and high thin
patches.
Variable seeing (mostly average) but with added short periods as VG -
EX.
Fully collimated and acclimated 17.5" f/6 Dob Newtonian.
Up and down a 6 ft. step ladder for 2 hrs. 30 minutes.
13mm Nagler T6 (205x), 16mm Nagler T5 (176x), 13.8mm SWA (193x), 12mm
Konig II (222x), and 12mm SMC-ED Ortho (222x).
The comparison briefly summarized:
I like the newest 13mm T6 Tele Vue compact "Nagler". It is a product
made in Japan vs. Taiwan were the 16mm T5 is produced. This new 13mm
may well could be the very best product namesake yet designed. It is
obvious Mr. Nagler took excellent and careful measures in doing this
one to near perfection for eye placement and use for non-eyeglass
wearers. It has a nicely placed sharp field stop with low chromatic
fringing.
The kidney bean effect in this new 13mm EP appears as not all that
intrusive or bad while under most night viewing conditions. Still it
exists in a minor way and is seen to disturb the acuity involved with
viewing the bright moon or by daylight terrestrial. The 16mm Nagler
doesn't effectively have this aberration and works much better by day.
The 16mm is probably the better model between these as used paired.
For most all other viewing (including planets) the behavior of the
13mm towards the eye is quite similar to a good larger 2" ultra-wide
super EP. There is a nice exciting "wow" image factor with this new
model. When the eye is not flooded with brighter lights, it is close
to twice as easy to hold the view as compared to the 16mm T5. Since
both are seemingly optimized (but different) designs, most of this is
probably due the larger 18mm exit aperture diameter of the 13mm model
to allow lateral eye repositioning comfort and take in the huge field.
The 16mm EP has a smaller 15mm exit aperture diameter and the eye must
be in closer and tighter to the instrument axial center and exit
pupil. There is a minor degree of blackout flutter tendency that is
often introduced by this which makes it roughly a third harder to hold
the EP for a good full field view. The 16mm has significantly less
"wow" factor involvement due its smaller to work with "peep hole".
The image in the 13mm is a bit warmer toned, than in the 16mm, where
it is closer to a more pure white.
There seems to be a very slightly greater degree of chromatic error in
the 13mm vs. the 16mm.
There is a slight bit more for pin cushion distortion in the 13mm.
The 16mm has very slightly better internal baffling but both are still
excellent.
The image contrast and color saturation in each of the two is very
similarly high.
The 16mm is brighter and seems much sharper. This is a reasonable
approximation towards fact that does take the 15% magnification
difference into consideration. For example, the 12mm Konig II seemed
sharper than the 13mm even though color saturation was lower in that
model. The 13mm T6 is still sharp but maybe not so much so as I had
initially expected.
Careful daylight resolution comparisons speak the same. My second
13mm T6 is to arrive shortly and will allow me to put them head to
head for any potentially detectable product variances. Also to pair
them experimentally in my binoviewer.
The ghost image some folks have mentioned in the T6 models is not an
issue IMHO. As example, there is a light dancer of Jupiter's likeness
seen brought to illumination left of axial center if the planet is
placed one quarter of the way from the right field stop. The 16mm T6
has a slower moving "dancer" in the same way but only about half a
bright. The 12mm Konig II has one, too, and all of these are normal
aspects and for the most part insignificant even with a powerful light
grasp scope. This is simply the nature of most wide-angle EPs.
Edge sharpness is slightly better in the 16mm. There is much more
angular magnification distortion in the 13mm (where Jupiter stretches
away from EP center point) when object is viewed near towards the
field edge.
This EP designer must have been listening to us regarding the 1.25"
barrel sleeve safety undercut. The depth of the cut is noticeably
shallower than usual (about half as deep) compared to most others
having this. The bit of barrel section as full 1.25" diameter (near
the top of barrel just under the upper body) is longer for a more
assured fit alignment when placed into a drawtube sleeve. The barrel
is also longer overall to keep fingers from contacting the R1 field
element surface.
How I'm going to decide which model to keep may hinge on the
binoviewing capacity between these two interesting choices.
Comments are welcome.
Pete Rasmussen
Jan Owen
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