Left to right: 7mm Nagler t1, Pentax XL 40, TV 35 Panoptic, TV 20mm Plossl
For many of us, a Rodenstock or a Nagler 31 is a little outside our ballpark. Faced with the reality of limited
funds, we find there are many remaining choices, but two of the undisputed best commonly available eyepieces in
this FL are the Pentax XL 40 and the TV 35 Panoptic. Both are wonderful wide field eyepieces, and both are heavy
hitters on the pocketbook.
First the stats:
||Pentax 40mm XL
||5 Elements in 5 groups
||1deg 18min 50x
||1 deg 11 min 57x
||2 deg 5 min 31 x
||1deg 54 min 36x
|Tele Vue Pronto
||5 deg 28 min 12x
||5 deg 14x
Pentax uses their trademark SMC coatings on all optical surfaces. It should be noted that while not huge players
in the astronomy market, professional photographers have long been enamored of the SMC coatings found on the better
Pentax lenses. Pentax coatings are very warm, and the lens surfaces are extremely transparent, with little coloration
due to the SMC coatings - a slight yellow green is all.
The Pan has the traditional blue green coatings commonly seen on TV products.
As I pass light through the lenses and inspect the output on white paper, I see that the Panoptic seems to have
a slightly higher transmission rate, and a whiter image. The light from the Pentax seems to have a slightly yellowish
The XL, while actually taller (with the higher shield on), is a much lighter eyepiece.If you have to worry about
balance in your scope, that may be a factor. The Panoptic on the other hand, feels short and squat, sort of like
a hand grenade. It's heavy.
The TeleVue has the traditional soft flexible rubber eyecup, while the XL has a fixed hard eyecup.It is supplied
w/ two different eyecups, one for use w/ glasses, one for use without. While I typically prefer the soft rubber
eyecups, I have to say the XL eyecup actually worked better.If the height is an issue, you can screw the Pentax
eyecup slightly up or down to accurately adjust for your eye. The Panoptic has noticeably more eye relief, although
both should be sufficient for use w/ glasses.
Both 2-inch eyepieces are threaded for filters.
The following observations were done at night on a TeleVue Pronto:
The Pentax gives wonderful wide field views, with stars sharp across 98-99% of the field.Only the very outer
trace showed a very, very slight astigmatism - to be honest, my eye shows more defects with this FL than the eyepiece
does.Perhaps the exit pupil is actually too large.Its field is extremely flat and gives no detectible pincushion
when panning.It is an extremely comfortable eyepiece to view through. I could not get any kidney bean effect no
matter how I tried. I could get a blackout, but it was only when I moved my eye far off axis. Because of the short
FL of the scope and because of my semi-rural skies, sky background was a dark purple instead of the velvet black
we associate w/ truly dark skies. This is a great finder eyepiece, and works very well to showcase extremely large
objects. Contrast is acceptable without being exceptional. This is perhaps to be expected of a 40mm eyepiece. I
like this eyepiece. There is little to no lateral color, but again with eyepieces in this FL, I would expect that.I
felt like I was looking through the porthole of a spaceship. It had a nice wide and sharp field, and the view was
correct, but lacked an intimacy that I have seen with eyepieces in smaller focal lengths. Views are somewhat dimmer
than I expected, perhaps because of all the air surfaces in the 5 element groups.
The Panoptic also gives fantastic wide views. Because the exit pupil is smaller, my slight astigmatism is less
of a factor. In the Pronto, stars are sharp across the entire field of view. The field is flat, with far less pincushion
than I had been led to believe from the reports scattered across the Internet. Actually, it was only noticeable
because I looked for it; I would not have noticed it otherwise. The Pan is not as tolerant as the XL is as far
as blackouts are concerned; eye placement is more critical. Because the eyecup does not extend, it can be difficult
to keep your eye in the proper position, which may lead to some slight kidney beaning. Please note that this does
not mean that the Pan is difficult to view through, only that it is not quite as comfortable as the Pentax .On
the other hand, there was noticeably more contrast in the Panoptic.
The true FOV seemed much smaller, until I did a few careful measurements. I found that while the true field
of view of the XL specs out larger, the actual FOV of the Panoptic was nearly as large. I did not think there would
be as large a difference between 65 deg and 68 deg as there was. I must admit, the apparent field of view in the
Panoptic was larger than I expected. There is defiantly more of a WOW! feeling with the Panoptic (more intimate).
Although the 40 takes in slightly more sky, images are larger in the 35, and the sky background is noticeably darker.
I could constantly acquire slightly fainter stars in the Panoptic. Once I knew they were there, I could usually
see them by averted vision in the XL, but I needed the Panoptic to spot them the first time. Star colors seemed
slightly stronger in the Panoptic as well. Images were also slightly sharper both on and off axis.
Before I close, take notice of how often I use the word slight. The two are that close. Before I started this
review, for some reason (probably based on the cost - we always assume that more expensive means better) I assumed
that the Panoptic would be a much better eyepiece. I was surprised to find how little the Pentax actually gave
up to it. The XL is lighter, has less pincushion and a larger TFOV. On the other hand, images possessed more contrast
in the Panoptic. Skies were darker and images larger. I was able to consistently detect fainter stars with the
35. I also found the exit pupil to be closer to my optimum with the Pan, but that is a personal thing.
They are both fantastic eyepieces. In the end, it largely comes down to personal preference. This is a tougher
call than I had expected, but for me, the Panoptic pulls slightly ahead, unless the difference in cost is a factor.I
did wind up selling the XL, and I am sure that the new owner will be very happy with it.