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The 31mm Nagler, when Bigger is Better

Posted by Ralph Aguirre   06/24/2005 00:00:AM

The 31mm Nagler, when Bigger is Better

The mammoth 31mm Nagler from Televue “must” be included in every serious visual astronomers eyepiece collection. I’ve lived with this eyepiece now for nearly 3 years, using it in the 4 telescopes I currently own, consisting of my TV-85, 4” F/8 Takahashi FS-102 Apo, 6” F/8 Meade AR-6 Achromatic and my C14. The performance in every scope is exactly what you would expect from the price of admission to own what I think is the all time premiere deep space eyepiece on the market today. This eyepiece must have been quite a challenge for Al to develop, coming out 20 years after the original Nagler line up.


Removing the eyepiece from its box shows that even the packaging was a well thought out idea. The custom foam lining inside the box, similar to the 41 Panoptic, protects this eyepiece as well as you would hope any scope to be protected when delivered. I’m surprised scope guard hasn’t released a small case just for this eyepiece, or at least a custom case for 5 or 6 of the largest 2” eyepieces Televue now offers, since a full collection of the 2” Naglers with the 41 Panoptic can easily cost more than the scopes they are used in.

Physical Size and Weight:

One has to be ready for the physical size and weight of this behemoth, especially in the smaller telescopes before you can look past its size, and appreciate the incredible advantage this eyepiece offers to any scope it’s used in.

In my 6” Meade AR-6 for example, this eyepiece with my 2” Everbrite diagonal was just too much weight for the stock focuser. The focuser became extremely loose and wobbly regardless of how much I attempted to tighten up the focusing mechanism. Fortunately, these Chinese made Achros are excellent scopes optically, and when matched with the finest eyepieces on the market, they give simply stunning views of space. My AR-6 performed so well with the large Naglers, I decided to purchase an excellent aftermarket Moonlight crayford focuser for the OTA. Now the mechanical qualities of my 6” scope match the optics perfectly, and the scope performs flawlessly with these large heavy high performance eyepieces. Some have questioned as to why I use eyepieces that cost more than an entire OTA as is the case with my 6” Meade, but one view under dark skies with the 31 Nagler quickly changes that questioning completely.

Balancing your scope:

You soon appreciate the meaning of a balanced telescope when using this eyepiece, and pay special attention when removing it from your diagonal. The shift in balance after removing it will send any scope into a violent nosedive if you’re not ready. I always keep one hand on my scope when removing the 31 Nagler, and have another eyepiece handy, to prevent this from happening. I usually find myself rebalancing my telescope, by either shifting the OTA on its mount, or repositioning a counterweight, or both, after adding or removing this eyepiece from my telescopes.

Daytime Orange Perimeter Glow:

As some have mentioned, during daytime viewing, and even while solar viewing with a white filter, you will notice a dull orange ring around the perimeter of the field of view. I noticed this several times while planet hunting in the daytime, and also while solar viewing with my 6” Meade refractor. Although this can be rather annoying to some, my focus is on the objects I’m viewing when I use my equipment, and not on insignificant anomalies around the perimeter of the field of view. During the many daytime outreach programs I’ve attended with the 31 Nagler inserted into my scopes, no one has ever mentioned the orange perimeter ring. It only shows up during daytime viewing, and never is an issue once the skies turn dark.

Viewing with a TV-85:

With a 0.63 focal reducer installed in straight through viewing with my TV-85 and the 31 Nagler, I can capture the entire belt and sword of the constellation Orion in one impressive field of view, offering more field of view than even the impressive 41 Panoptic and actually, more than some wide field binoculars. The field of view remains flat and perfectly sharp when used this way. Even without the reducer, The North America Nebula and Pelican are both clearly seen under dark skies using the combo of the 31 Nagler, TV-85 and OIII Filter. The entire structure of the Veil Nebula is also captured in one field of view. Star patterns are always flat across the entire field, as well as tack sharp pinpoint stars at the extreme edges when using the big 31 Nagler.

This is always the first eyepiece I start with, in any scope I use, because it’s an excellent wide field eyepiece while also providing enough magnification for hunting down objects using star hopping techniques. I’m not a “GoTo” astronomer, and appreciate the “hunt” sometimes as much or more, as the “kill.” Armed with this eyepiece under dark skies and a good star chart, there’s not an object I can’t find if my scopes are capable of resolving them. Time and patience are the key, on the dimmest objects.

Viewing with a Takahashi FS-102:

This is the premier eyepiece for viewing the entire Pleiades in my 4” Tak FS-102, as well as the entire Andromeda Galaxy. It’s excellent for viewing large areas of the sky in one field of view, such as viewing the Eagle and Lagoon Nebulas together, or viewing the many galaxies over Sagittarius and around Virgo. It is also the choice eyepiece for finding and viewing the Rosetta nebula in my 4” scope under dark skies. The views using a 31 Nagler at the double cluster in Perseus with a 2x Powermate or Big Barlow will leave you walking back again and again for a second and third look. Suddenly you get the urge to go higher in power wanting to see more of what you may have never seen before. The rich black skies formed with the fluorite glass of the Takahashi, and the 31 Nagler make the Double Cluster one of the most spectacular opens clusters to view, bringing you back to that object many times in a single night. I prefer viewing with the 31 Nagler and a Powermate, vs. using a 16mm Nagler, for that slight edge in clarity the 2” combination offers.

Viewing with a 6” F/8 Refractor:

In my 6” F/8 refractor, and the 31 Nagler, the entire Markarians chain is visible in one field of view, with enough resolution with the 6” scope under dark skies to make out the entire collection of galaxies easily. This is also one of my favorite eyepieces for viewing solar and lunar eclipses in my smaller refractors, since it offers an entire view of the sun or moon in one field of view with enough space around those objects to show them floating in space.

Panning the skies for the Leo triplets, the Draco triplets, seeing the owl nebula and M108 side by side, viewing M81/M82, and the many deep space combinations viewable in one field of view are a pleasure with this eyepiece in my 6” refractor on my G11. It also makes for an excellent comet-chasing eyepiece, in the 3 refractors mentioned above.

Viewing with a C14:

Having convinced everyone that the 31Nagler is an excellent eyepiece for refractors of all sizes, it also works beautifully in Schmidt Cassagrains. The biggest Nagler seems perfectly matched when mounted in the back of my C14. No other eyepiece brings out the phenomenal spiral structure of M51 and its companion better than this eyepiece.

Under Mag. 6+ skies, especially during June and July when M51 is at its zenith, the wispy spirals look similar to long exposure CCD imaging, but with a much more pleasing 3 dimensional appearance. You can see through the galaxies and see stars and dark space behind and around the spiraling arms of these double whirlpools.

M13 is also another object, which clearly excels in my C14 with this eyepiece. The view is pulled back enough that you can see the tiny galaxies of IC4617 and NGC 6207 in the same field of view, but M13 has to be at one edge of the eyepiece to capture all three at one time. You can literally see down to the core of this globular, and identify the tiny individual central stars, stars that I’ve never seen captured in any CCD imaging. Only the 26 Nagler in my opinion can out perform the 31 Nagler on M13, because it seems to frame just that object so perfectly in the field of view.

After the initial “Oh My God” you hear from someone looking at M13, they begin talking about the details they can see with this eyepiece, keeping their face glued to the scope. People tend to look hypnotized when they finally pull themselves away from the eyepiece, and begin looking at the eyepiece and scope, asking questions about the scope and eyepiece that gave them such an incredible view. At star parties, you find even the most critical observers coming back for more deep space viewing, once they’ve had an opportunity to view with a 31mm Nagler in a 6” refractor, or a C14.

Appreciation of the design intent:

This is a deep space observer’s treasure in their collection of eyepieces. To truly appreciate the vision that must have gone into its design, the observer should sit comfortably in a chair in front of the many wonderful deep space objects they can view while using this eyepiece, and spend 10 minutes to half an hour or more just viewing each individual object, and let your eyes and mind open up to the beauty of our universe and appreciate the space walk you experience, when viewing with this eyepiece. You literally have to move your eye around the entire eyepiece, to see everything offered to you. You can’t possibly see the details in M13, or the Swan or Orion Nebula, or the many open clusters, unless you spend time just placing your eyes over this eyepiece, and absorbing every photon of light that comes from relaxing over this eyepiece for extended periods of time sitting in a comfortable chair.

This is not a planetary eyepiece, mostly because the 31mm focal length is really too long to capture the details in Jupiter or Saturn for example, that a 26mm or 22mm Nagler or shorter focal length eyepiece can bring out. The shorter focal length eyepieces may appear to offer more contrast, but this is only because wide field eyepieces have so much light to gather compared to shorter focal lengths. Compare this eyepiece to other 31mm designs, and you’ll see how the newer 6 elements perform with its 4 exotic glass types to enhance contras, while offering razor sharp star patterns across the entire 82 degrees of apparent field of view. The 31mm Nagler was designed as a wide field deep space no nonsense eyepiece. The huge amount of clear glass in this design makes that instantly apparent.

Using the C14 with a focal reducer with the 31 Nagler:
With my 0.63 focal reducer inserted behind my C14 with the 31 Nagler, there’s enough field of view to see the Leo triplets, M81/M82 and many of the open clusters, which would otherwise not be possible to see at one time, because of the longer F/11 focal length of my C14. There is an almost undetectable amount of vignetting when using this eyepiece in this way, and the benefits of capturing more field of view with 14” of aperture clearly outweighs the ever so slight amount of vignetting I get. When I absolutely have to get the most field of view out of my C14, and the 41 Panoptic still doesn’t give me enough, I turn to my Meade 0.63 focal reducer and my 31mm Nagler.

Using the 2” Powermates or Big Barlows:

This eyepiece also does exactly what you would expect it to do, when inserted into a 2x big Barlow, and both 2x and 4x Powermate, which multiplies its magnification without any trace of degradation in performance. I generally prefer to use 2” eyepieces with Powermates or Barlows to achieve higher power, than to use the shorter focal length 1.25” eyepieces. This eyepiece stands so high in a big barlow or Powermate, one has to make sure the diagonal is secured in the focuser before using this combination, otherwise the entire combo may roll downward.

Why use 2” Eyepieces:

As an example of why I prefer the 2” eyepieces to the 1.25” ones, squint your eyes a little, and look around at your surroundings. Now open your eyes fully and look around yourself again. You still see everything around you, but everything is just a bit clearer, and a bit sharper. When your trying to observe every last bit of details on an object, the larger 2” eyepieces just cant be beat.


In the world of eyepieces, the 31 Nagler stands alone as a Gargantuan against others. In my opinion it’s the benchmark to which all other wide field deep space eyepieces must be judged against. Some may snicker at the cost, but very few will deny the incredible views it delivers in any telescope its used in.

From my first peek through my 60mm Tasco refractor at the moon at age 10, astronomy is the one pleasure in life I’ve never walked away from. The eyepiece is half your optical system, and over the years, I’ve learned to appreciate the benefits and value from what a high quality eyepiece can do to escalate the performance of any telescope from just an average viewing instrument, to a supremely rewarding optical research system.

Only the 20mm Type 2 Nagler, and new 41 Panoptic, and quite possibly the 26 Nagler, can stand beside the 31mm Nagler Type 5, as probably the most impressive quartet of deep space eyepieces to ever be offered to the amateur market.

However if I had to use just one eyepiece, the 31 Nagler would be the one.

Click here for more about this subject. -Ed.