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Four 40mm Widefield Eyepieces Compared

Posted by Charles Zdeb   01/15/2008 12:21PM

Four 40mm Widefield Eyepieces Compared
If you don’t have a big widefield eyepiece of around 30-40mm focal length, you need one. Really. These eyepieces serve up the biggest piece of the sky you can fit into your eye at one time More technically, a 2 inch eyepiece of about 40mm focal length and around 60-70 degrees apparent field of view has the widest field stop possible in the 2 inch format, which gives you the widest true field of view (TFOV) you can get from the typical telescope. By comparison, any 1.25” eyepiece feels like you’re looking at the sky through a peephole. That big picture view makes these eyepieces incredibly handy for finding objects. It’s also a great tool for sweeping large chunks of sky like the summer Milky Way, or to view large objects like the Pleiades or the Andromeda Galaxy.

Unfortunately, being convinced that having one of these eyepieces is a good idea and being able to afford the super eyepieces that offer both big fields of view and beautiful pinpoint stars edge-to-edge are two different things. Those super eyepieces have super price tags. Since I’m most frequently a lunar and planetary observer (thanks, light pollution), I spend most of my eyepiece money on mid- and high-power eyepieces because they’re the ones I use the most. I wanted a big low-power widefield without spending too much. There are modestly-priced 40mm widefields out there, but there were few reviews on them and almost no comparisons between them. Are the lower-end eyepieces “bags o’blobs”, or would they work acceptably well in my scopes? Are any of them performance standouts? To answer my questions, I obtained four of the more economical and commonly available eyepieces in that range and compared them side-by-side:

From left to right in both pictures, they are:

Orion 40mm Optiluxe – 62 degree apparent field of view, no longer sold new but available used. Was also apparently sold under another name.

BW Optik 30mm – 80 degree apparent field gives it a true field competitive with the others, despite the shorter focal length. Available under other names.

Orion Q70 38mm – 70 degree apparent field, recently introduced, and also apparently available under other names.

TMB/Burgess Paragon SW40mm – 70 degree apparent field, also recently introduced, and about twice the price of the above eyepieces (but less than some other well-known eyepieces). What does the higher price buy?

Eyepiece preferences, like preferences in shoes, pizza, and movie stars, are notoriously subjective. Some people don’t mind being close in and personal with an eyepiece; others need enough eye relief to use glasses or just hate having eyelashes constantly smearing the lens. Different people seem to have different sensitivity to aberrations. For example, some hardly notice pincushion distortion, for others it can induce motion sickness. Individual eyes can vary quite a bit, too. I’m old enough to recall that my first widefield eyepiece was a 25mm Ortho. Don’t laugh, it had a wide field compared to the two Ramsden eyepieces that made up the rest of my set in those days. Aside from remembrances of obsolete eyepieces, age means my eyes no longer have as much accommodation (the ability to adjust eye focus) as a younger person does. So, relative to a younger person, my eyes don’t compensate as much for defocus due to field curvature and therefore make me less tolerant of it. Even sky conditions can make a distinct difference. A moonlit or light-polluted sky tends to hide the light spread out of a star image by aberrations and make the stars look more pin-pointy. Additionally, each type of scope has its own inherent aberrations and focal plane curvature which interact differently with any given eyepiece, not to mention the powerful effect of the focal ratio and exit pupil on eyepiece performance.

My goal with this comparison was not to do a rigorous quantitative test (Eyepiece A has 7.42 metric bucketloads of brightness and 12.37 cubic quartiles of contrast), but to compare the quality of the view in the eyepieces relative to each other (in this scope, the view in Eyepiece A is better than Eyepiece B). I was looking to see which eyepiece had the widest field of pinpoint stars and least obnoxious aberrations, what was the faintest star or nebulosity I could see, the true field of view, and how comfortable the eyepiece was in use.

My method of comparison was to view a given object and star field (the Dumbbell and the Ring were favorites), swap the eyepieces back and forth repeatedly, and take notes. Over a series of nights, I used a 4 inch f/5 achromat, an 8 inch f/6 Newtonian, and a 6 inch f/12 Mak-Cass. Each eyepiece was compared to each of the others in the same scope, each scope on more than one night, all eyepieces under the same conditions. I did not compare them on planets or the Moon because these eyepieces are not the tools for those objects, any more than a 4mm Ortho would be the right eyepiece for the Veil Nebula. The results are listed below for each scope, with the eyepieces listed in order of preference for use in that scope:

4 inch f/5 Achromatic Refractor

1) Paragon 40mm – Inner 3/4 of the field looks pretty good, only the about the last quarter starts looking ugly with stars stretched into little lines and with some defocus. Definitely have to fold down the rather-stiff eyecup to see the whole field with glasses on. This and the Q70 are tied for the biggest TFOV (well over five degrees in this scope!), but their margin over the other two eyepieces (about a half-degree) isn’t all that noticeable in practice. Yes, I know the exit pupil was way too big in this scope, but did I mention the TFOV was over five degrees?

2) Q70 38mm – Inner 2/3 of the field is good, after which the stars start to bloat from defocus and astigmatism. The Q70 is the most comfortable to view through, but do need to fold down the eyecup (much thinner and easier to fold down than the Paragon) to use glasses. The Q70 consistently sees slightly fainter stars than the Paragon (in the central fov), maybe due to the slightly shorter focal length.

3) Optiluxe 40mm – Rather similar to the Paragon in the way the stars look, but only in the inner 2/3 of the field, and gets quite noticeably aberrated (mostly astigmatism) near the edge of the field. The eye relief is very comfortable for use with glasses, but it’s mildly prone to blackout. This and the BW-Optik have just about identical TFOV, which is maybe 10% less than the Paragon and Q70. Again, it really isn’t very noticeable. Both the Optiluxe and Paragon are dead-even in seeing faint stars.

4) BW-Optik 30mm – This eyepiece would not be my choice with a fast scope, only the inner half of the field is even mildly aberration-free. The outer half is pretty bad, like looking into a whirlpool. However, due to the higher magnification, it’s clearly the champ for seeing fainter stars in the inner part of the field. Eye relief is good, but the metal shoulder of the eyepiece is a lens scratching hazard if you wear glasses while observing.

8 inch f/6 Newtonian Reflector

1) Paragon – Good out to maybe the last fifth of the field, some astigmatism and some mildly bloaty-looking stars visible out there, but the inner field looks pretty tight. The over two degree TFOV I get with these eyepieces in this scope (on a Dob mount) is pretty spectacular and makes finding objects vastly easier than with 1.25 inch eyepieces.

2) BW-Optik – Oddly, while this one has obviously visible star distortions in the outer half of the field and the smallest clean field, the higher magnification shows more detail in the objects and makes me pay less attention to how bad the outer field looks (especially comparing on galaxies). The very wide apparent field (80 degrees) allows you to find things, even though they’re not very pretty near the field stop, and then get a better look at them in the center of the field. The main aberration with this scope seems to be field curvature because I can roll the focus and get sharp focus any place in the field, just not the whole field at the same time. If the deciding factor is visible aberrations, the BW-Optik is in last place; but how much detail you can see in the center of the field pushed this eyepiece a few places up. The outer field in the BW-Optik is un-good in all the scopes, but doesn’t bother me as much in the Newtonian.

3) Q70 – Inner 2/3 of the field are good, it again sees a little deeper than the Paragon (nothing like as deep as the BW-Optik), but the outer third of the field has bloaty stars that stretch and defocus. Doesn’t seem happy in a Newtonian. It only beats out the Optiluxe because of more comfortable eye placement and a wider true field.

4) Optiluxe – The inner 3/4 of the field is good, looks very similar to the Paragon, but the outer fourth of the field has distinct astigmatism and defocus. This eyepiece has a cleaner-looking field in the Newtonian than either the BW-Optik or the Q70, but I find I slightly prefer using those in this scope. Life isn’t fair.

6 inch f/12 Maksutov-Cassegrain

1) Q70 – Ahh, this is the way this eyepiece was meant to be used. About 4/5 of the field looks quite fine. I really only see aberrations out near the edge, and only when I look for them (or have a bright star out there). Very comfortable in use, as always. Instead of precisely positioning your eye over an optical instrument, it’s more like looking out a porthole.

2) Paragon –Narrowly behind the Q70 because it’s a little less comfortable for eye placement and because it doesn’t see quite as deep (very small difference). But the field is good almost to the edge.

3) Optiluxe – The view again very much resembles the Paragon, but with a smaller true field of view and somewhat more visible aberrations in the outer 1/5 of the field. A very nice view all the same.

4) BW-Optik – The stars turn into little lines in the outer third of the field, but only mildly compared to what it did at shorter f ratios, not all that noticeable. As before, the view in the center is better because of the higher magnification.

Overall notes:

I really didn’t see any differences in contrast or brightness between the eyepieces that weren’t in line with the magnification differences, nor vignetting, or more than very minor amounts of distortion. Of course, at the very low magnifications resulting from these eyepieces, any faults in the telescopes were also well-hidden (at 13X, the f/5 achromat looks like an apo). I was a little disappointed that all the eyepieces still showed noticeable aberrations at f/12 in the well-corrected Mak, I’d hoped that at least one would be near-perfect. Bear in mind that I was deliberately looking for trouble- most of the time in normal use your eye is looking at the center of the field and peripheral vision isn’t very sensitive to the aberrations.


The Paragon 40mm is the winner when it comes to having the biggest field of pin-pointiest stars, the least visible aberrations, and is tied with the Q70 for largest true field of view. Open clusters, here we come. It’s also quite light weight, with only the Optiluxe being lighter. However, while it is better, it’s only a little better than the Q70 or Optiluxe, and is less comfortable to use. Admittedly, that’s a bit like saying one easy chair is less comfortable than another, they’re all good. But the real clincher is that the Paragon costs two to three times as much as the other eyepieces here. That mild performance edge could be hard to justify on a tight budget or in a slower f ratio scope.

The Optiluxe 40mm has about a ten percent smaller field than the Paragon or Q70, and is a little more prone to aberrations in the outer field. If it had that bigger true field of view, it would be hard to tell from the Paragon. It is easily the smallest and lightest of these eyepieces and the only one really comfortable for use with glasses. You can turn down the eyecups on the Paragon and the Q70 to make them more glasses-friendly, but you could tear or lose the eyecup in the process. If you always use glasses at the scope and/or have scope balancing issues, the Optiluxe would be my first choice.

The Q70 38mm nips closely at the Paragon’s heels performance-wise, especially at slower f ratios, and consistently sees just slightly deeper. Plus it’s the most comfortable eyepiece of the bunch, that “porthole” experience I mentioned. On the unhappy side, it’s the heaviest eyepiece here by a good margin (weight is roughly double that of the lightweight Optiluxe), so weight/balance could be an issue for some scopes. But if weight isn’t an issue and you have an f/10 or slower scope, the Q70 probably offers the most performance bang for the buck.

The BW-Optik 30mm brings up the tail end of the group performance-wise and is nearly as heavy the Q70. But if you use a slower scope and can’t or don’t want to spend more, the BW-Optik is a very useable eyepiece. Maybe the best way to think of it is as a replacement for a low-power 1.25 inch eyepiece: it has a huge true field of view that dwarfs anything from a 1.25 inch eyepiece and is great for finding objects or as a star party eyepiece. Since it costs roughly the same as a good 1.25 inch Plossl, that’s probably a fair comparison (unlike comparing it with the Paragon).

Given the chance, I would choose an eyepiece with the Paragon’s TFOV and field correction, with the eye relief, size, and light weight of the Optiluxe, and the excellent comfort of the Q70, all at the price of the BW-Optik. Unfortunately, that choice isn’t on the menu. As with all astro equipment, you have to look at the strong and weak points of what is available, evaluate it against what is important to you, and choose accordingly. Then, in six months, go to Astromart and see if you can do better ;-)