Evaluating the Pentax
XL series eyepieces, and the Meade Superwides!
(CLICK
HERE FOR GENERAL EYEPIECE REVIEW INCLUDING ULTRAWIDES)
While I am no expert in evaluating eyepieces for planetary use, I have become quite proficient in comparing the various premium wide-field eyepieces on the market, particularly from Televue (Naglers, Panoptics) Meade (superwides), and now the Pentax XLs. As I haven't yet written up the Meade superwides, I'll start with them, then go to the XLs in the article below. Note. . . that I do not have any experience with the Meade Ultrawides, which is why they are not here on the web page. Enjoy and happy wide field viewing!
********The MEADE Superwides***********
The Meade Superwide eyepieces are simply put, fantastic, for the price. They feature about the same apparent field size (about 67 deg.) as the Panoptics, and the Pentax XLs, but are not as sharp near the edge as either of the other two. In addition, unlike the Televue Panoptics, you cannot simply send them in for repair, should you scratch the eyepiece. However, they are the least expensive of the group. The eyecups on all units are very thin and easy to flip up or down, and adequately shelter you from extraneous light.
the 13.8mm Superwide.. Eye relief is short, about 10mm. Views are extremely crisp on planets, and the wide field is comfortable, completely fitting into view without having to move your eye around like you would in a Nagler eyepiece. On some scopes, the edge of field is somewhat out of focus. The eyepiece is quite small. Glasses will not work well with this eyepiece, but at this focal length, astigmatism is often not a problem, as the exit pupil is small, and astigmatism is less aggravated in most people. (My astigmatism kicks in on an f/10 scope at about 15 or 20mm eps)
The 18mm Superwide.. Eye relief is comfortable, and people with glasses should just be able to make it, around 16m, or 18mm or so. Planetary views are extremely crisp, and the edge of field is a bit out of focus mostly in fast scopes. The eyepiece is rather small, and is probably one of the reasons Televue put out the 19mm Panoptic. The 18mm is one of the best possible eyepieces to use in a binoviewer because of it's easy of viewing, comfortable eye relief, and small size.
The 24.5mm Superwide.. I have had this eyepiece for some time, and know it inside/out. It has recently been improved somewhat, it's overall size is about the same, but be careful if you are matching this eyepiece to be used in a binoviewer. This eyepiece performs well, but is not as crisp towards the edge, by a large margin, as the Televue panoptic 22/27 or the Pentax XL 21 on fast scopes. In addition, despite darkening of the interior at the factory, there is a bit more false brightness at the edge of the field, and not quite as distinct a field stop (the sudden ending of the field, which would be good). This eyepiece is medium sized, and still fits well in binoviewers. It is just beginning to feel a bit heavy, but really not bad at all, and has great eye relief, around 20m or more.
The 32mm and 40mmSuperwides.. These huge eyepieces were a bit of a disappointment for me. The good thing..both had a very nice eye relief.. not too close, not too far.. which is not the HUGE (too huge) eye relief that some eps have at this focal length, and start showing blackout areas partially due to the over-relief. (some people call it the Kidney bean effect, but I think it is similar, not exactly the same.. see my Nagler article for the 13mm kidney bean explanation) The bad thing.. the performance on SCTs and fast scopes. The edges showed significant out-of-focus images, really bad "sea-gulls", which is corrected much more for in the Pentax XL, and Panoptic line. (especially the Panoptics) The flip side of this though, is that these eps are a bit less expensive than the 35mm panoptic, and also..they do not exhibit as much of the "pin-cushion" distortion that the Panoptics do while panning the scope. (Panoptics tend to show a bent field which is noticeable while moving the scope, a by-product of the excellent edge correction, and a big problem on scopes that lend themselves to panning, like Dobs)
****************The PENTAX XL series.*******************
These eyepieces are now readily available in the United States. Orion Telescope carries them, along with other dealers such as Stew Squires, who is a frequent contributor on the Internet newsgroup:
sci.astro.amateur
Except for the 28mm, they all offer 65 deg apparent field of views. Only the 40mm is a 2" eyepiece. All of them have the same odd eyecup which works like an upside down funnel, where you have to place your eye down into (as your eye bulges a bit), rather than a cup that comes up around your eye. It is certainly unique.
At the lower end, the short focal length eyepieces are perhaps the most incredible eyepieces on the market, period. The reason is because somehow..they manage to retain the full eye relief, and feel of the longer focal length eps. On the high end.. the longer ones fall just short of Panoptic performance, particularly up at 40mm.
First of all, I have to say that these are huge, mostly 1.25" eyepieces. the eyecup is very fat, and is something you look down into, kind of like looking into the bottom of a funnel, which is upside down. The advantage to this is that it actually works, even though it looks at first glance like there is no eyecup at all..and also that you can screw the cup up and down to fit your SPECIFICALLY needed eye relief. Since there is abundant (had to be 20mm or more) eye relief on all units, you can view with glasses easily. The only problem is you cannot instantly "switch" to the proper relief for glasses, and the proper relief w/o glasses. That is, you have to take the time to screw that upside down funnel-like eyecup down, screw it up, and screw it down again. On the other hand, you can adjust this directly. The VIXEN LANTHANUM eyepieces have renowned, long enough eye relief..but it is a bit difficult to get it right with glasses on, as you need to fold down the eyecup on the Vixen, and then you end up "searching" for the best place to view, kind of a similar problem to standard 32 and 40mm plossls. However, even though there is ample relief on the Pentax XL series, you can fiddle and find the right spot with or without glasses. (but as mentioned, you can't switch easily between the two)
While I was able to get these to work in a binoviewer, some people's eyes will be too close together, and these are all pretty heavy, so they aren't really great for that use.
Specifically..
The 5mm, 7mm, 10.5mm Pentax XLs.. Vary
in length, and a bit in weight, all around a hefty 13 oz. They have sharp
to the edge apparent field of views. These are the most comfortable eyepieces
to use, at this focal length, of anything that I have tried, for those
who wear glasses.
I haven't tried the 14mm XL, but I understand it is similar.
The 21mm Pentax XL is much the same as above, but here there is some competition. The 19mm Panoptic is just as sharp, if not sharper towards the edge, and is much smaller and lighter, and can be used easily in binoviewers. Also, the 18mm Meade Superwide, and the 19mm panoptic, both have adequate eye relief.
The 28m Pentax XL is only a 55 apparent FOV eyepiece, so I didn't try it, The 40mm Pentax XL is a 2" eyepiece, and although similar to the others, is not as sharp at the edge of field. It has the same eye relief characteristics, and eyecup type. It seemed to view sharper at the edges than the 40mm Superwide, but not as sharp as the 35mm Panoptic. This mostly on fast scopes.
Overall, a perfect wide-field collection
would probably be something like this:
35mm Panoptic
19mm Panoptic (or 18mm Superwide)
10.5mm Pentax XL
5.2mm Pentax XL
The question will come up as to whether or not you should buy a Nagler compared to the 5-20mm eyepieces above, and that is definitely a contender if you do not need to wear glasses. Also, If using a binoviewer, the Nagler apparent field size (see the Nagler article, 82 deg. app. field) is overkill, you can only take in around 70 degrees. Also..of all these eyepieces, you need to consider their size and weight for binoviewers. (see the binoviewer article)
Please note that I am sure that I unintentinoally mis-stated some point of fact in the article above, much of this was written from relocation, and should be taken as a starting point for more research, rather than a final view.
Speaking of which.. enjoy the views!