I've had this ep for a while and have found that compared to the 12 Nagler
type 2 (my former most-used ep), the type 4 has:

Better contrast
Slightly brighter image
Sharper image at the edge, even in a fast scope
Better eye relief (it's very impressive to see that awesome fov without
having to stick your eyeball into the ep)
Less pincushion distortion (although that never bothered me in the t2)
Less ghosting
Dramatic reduction in flare

The flare (my definition) in the t2 is very easy to see. Put a bright object
(Venus) just outside of the fov, shut off the drive, and let the object
drift into view. In my Zeiss Abbe orthos, you see nothing until the object
actually peeks into view. In the 12 t2, you can see a flare across the fov
before the object appears--you can "see it coming." In the t4, there is a
dramatic reduction in this, not quite to the point of the Zeiss.

The kidney beaning reported by some wasn't evident to me, but it was never a
problem to me in the older Naglers, either. There seems to be an individual
difference in sensitivity to this.

The "Instadjust" initially seemed too loose to me, but I like it a lot more
after using it a while. When I first started observing with it, if I bumped
it with my eyebrow, it would slide down to the next click (I was used to the
very firm sliding eyeguard on the Zeiss Abbe orthos). I called TeleVue to
discuss it and was put through immediately to Al Nagler. He said they
deliberately set the eyeguard to require only a small amount of force to
move it. This way, it could be easily adjusted to suit different observers
without having to use enough force to move a well-balanced scope.

I asked if the coatings were different, as they have a different hue, and if
that was the reason for the improvement in contrast and reduced flare. Al
said that the improvement in those was due to both newer, better glass and
newer, better coatings. He said the improvement in ghosting is due to the
different shape of the eye lens.

Al also recommended that even experienced folks use the included pupil
guide; it should give even better contrast.

Overall, I was most impressed with two things: 1) The new Nagler type 4
beats the type 2 in every way. 2) It's gratifying to buy a new design
eyepiece, call the company to discuss my impressions, and be able to talk
with the man who designed it. Kudos to Al Nagler and TeleVue. I can't wait
for the 17 and the 22!

Paul Gustafson

Scopes used: AP 105 Traveler EDF, AP 155 EDFS, Celestron C-11, 10" f/4 dob
(not mine).