Pentax SMC-XL 40mm


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Pentax SMC-XL 40mm
This lens is actually pretty good but at lower f ratios it's not very
sharp at the edges. I use it on my 155mm f/7 refractor. With a 2X
Barlow it's awesome and is every bit as good as my 22mm Panoptic.

Overall Rating: 7
Weight: 3 (Unreliable Vote)
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Pentax SMC-XL 40mm
Great Eyepiece with good eye relief. I use it for finding objects with my telescope

Overall Rating: 9
Weight: 4 (Unreliable Vote)
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Link to this vote: http://excelsis.com/1.0/displayvote.php?voteid=42987


Pentax SMC-XL 40mm
Excellent finder eyepece for fast dobs, light weight, great trasmission.
Lack of distortion a real plus for panning around. Amazing with a 2X barlow,
with only drawback being lack of range in eye position.

Overall Rating: 9
Weight: 5 (Veritable Vote)
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Pentax SMC-XL 40mm
There's a comment by one of the reviewers that this eyepiece is not sharp all the way to the edges. This is true, but is a phenomena of other 40mm eyepieces as well. If you want to scan the skies as you move the scope around, this is a superb eyepiece.

Overall Rating: 10
Weight: 4 (Unreliable Vote)
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Link to this vote: http://excelsis.com/1.0/displayvote.php?voteid=42991


Pentax SMC-XL 40mm
I use this eyepiece with my F/4.5 10 inch dob. The wide field views are staggering! Despite the high exit pupil with my scope (near 9mm), I do not much notice the "wasted" 2 inches in effective aperture. As long as I keep my glasses on, the near edge performance is almost as good as the performance of my Panoptic 22. Without my glasses, my own mild astigmatism kicks in, increasing the distortion near the edge of field. The nearly 2.3 degree real field of view dwarfts the real field of my Panoptic 22 at 1.3 degrees. I did not notice any problem with blackouts either. The magnification, (using my F/4.5 10 inch dob) is sufficient for locating most deep sky objects easily. Small planetaries and faint galaxies can be a bit tough though. The Ring nebula is easily visible using the 40. Even M101 popped right out at me. This eyepiece is large (about the size of Nagler Type 4), but feels a bit lighter than the Nagler. The 10 rating is based upon the price to performance ratio. When compared to the cost of a Panoptic 35 or Nagler 31, it would seem to be a real bargain.

Overall Rating: 10
Weight: 5 (Veritable Vote)
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Pentax SMC-XL 40mm
I have used this eyepiece on my 20", 10" & 8" newts. All of these scopes are F5.2 - F5.6. The stars are not perfect at the edge, but I prefer this eyepiece over the Panoptic 35mm because there is no noticable distortion as in the Panoptic. It is great to pan around with this eyepiece. I think one of the greatest strengths is the fact that the actual field of view it gives within my telescopes affords me the opportunity to utilize them as finders and look for my target at low power.

My Home Page

Overall Rating: 9
Weight: 7 (
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Pentax SMC-XL 40mm
This eyepiece gives such a huge true field of view that it is hard to beat. I get pinpoint stars right to the edge if I take time to carefully collimate my telescope.

Overall Rating: 9
Weight: 3 (Unreliable Vote)
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Pentax SMC-XL 40mm
Great Eyepiece! The maximum FOV I can totally use with no eye movement. Razor sharp images up to the edges. Very comortable to look through. I use it with a 10" f/6.

Overall Rating: 10
Weight: 3 (Unreliable Vote)
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Pentax SMC-XL 40mm
A nice, big, heavy 2" bug-eyed eyepiece that shows large chunks of sky. For some reason this eyepiece does not have an adjustable eyecup like all other Pentax XLs. Instead, it comes with two interchangeable fixed eyecups -- one for eyeglass wearers and one for non-wearers. Works fine, but less elegant than the eyecups on the other Pentax XLs.

Overall Rating: 9
Weight: 6 (Veritable Vote)
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Pentax SMC-XL 40mm
I have a 14.5" Dobsonian. I bought this wide angle eyepiece because I could not bring my Tele Vue Nagler 31mm to focus in the telescope. The Pentax 40mm has very soft focus at the field of view's margin. By "soft focus" I mean that the edge of the field is blurry, out of focus. The margin is also quite wide, 20% of the image is affected. The contrast is weak, with poor definition throughout. By lowering my truss tubes 1/4" I was able to use the Nagler 31. What a difference! It was the poor performance of the Pentax 40mm that motivated me to modify the telescope to accomodate the Nagler. By comparison the Nagler shows crisp images that are clear to the edge and with high contrast and sharp definition. Looking at the Orion Nebula with the Pentax shows a gray cardboard-colored cloud. Truly nebulous. With the Nagler you see curdling and subtle variations in the structure of the nebula. I returned the Pentax to the retailer. It gets a 5 because it is half the price of the Nagler, half the weight, and it delivers half the performance.

Overall Rating: 5
Weight: 5 (Veritable Vote)
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Pentax SMC-XL 40mm
I purchased the 40mm Pentax XL to be my extra low power eyepiece on my 12.5" f/5 reflector equipped with the original Paracorr coma corrector. The 40mm Pentax without the Paracorr resulted in very poor images off axis, largely due to curvature of the focal plane. I then tried it with the Paracorr but was unable to obtain sharp images across the field. I cannot understand how others can describe the field as razor sharp on a fast reflector. It definitely is not. I ended up returning the eyepiece for a refund. It will probably work much better at f/10 or so.

Overall Rating: 3
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Pentax SMC-XL 40mm
I give this eyepiece a 9. It is the most comfortable eyepiece I have ever used. I have a f15 mak, but still have edge problems with this one, but it is slight. The exit pupil on my scope is less than 3mm, so it is a perfect fit. Beware fast scope owners, large exit pupil, and edge distortion may plauge you. Try before you buy.

Overall Rating: 9
Weight: 3 (Unreliable Vote)
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Pentax SMC-XL 40mm
I bought the 40mm Pentax XL used. All my other eyepieces are Panoptics and Naglers, so I thought the Pentax would not impress me. Well, I was definitely wrong.

On a f/10 SCT, I noticed no secondary color off-axis and exceptional sharpness. Almost as sharp as the Panoptic (extreme sharpness), but a little less. Compared to a 35mm Panoptic, the Pentax did not exhibit any field curvature (try panning the sky with a Panoptic and you may end up sea sick!) The apparent field of view was more than adequate unless you are a Nagler diehard. The actual field of view is wide, and without the field curvature, makes for the ideal EP for searching deep sky objects.

This EP not only excels at sky views, it can also be used as a terrestrial EP. Hey, everyone can use at least one awesome EP for viewing birds, frogs and other interesting things when the sky is cloudy. A definite keeper.

Overall Rating: 10
Weight: 4 (Unreliable Vote)
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Pentax SMC-XL 40mm
This is my first "real premium" eyepiece. My 2nd one is an MK70 25mm. Use it on my C-9.25 SCT w/ 2" visual back and 2" everbright diagonal. There is field curvature, even at F/10, but it's minor. I got rid of my F/6.3 corrector - it didn't flatten the field IMO, with other eyepieces. Curvature is only noticable if you use it for daytime terrestrial viewing. This is my low power deep-sky eyepiece for nebulas (1.1 degrees FOV). Very comfortable, good eye relief, very sharp. LOTS OF GLASS. On the heavy side. I'd give it a 9.5 out of 10.

Overall Rating: No Vote
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Pentax SMC-XL 40mm
Images in the center are sharp and have excellent contrast. However, even though I have a long focal length telescope (Celestron 11" f/10)there is very bad curvature at the edges, performance that is quite inconsistent with the price of this supposedly premium eyepiece. I returned it.

Robert S.

Overall Rating: 6
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Pentax SMC-XL 40mm
Well, I own this eyepiece for about 4 months now.
I wanted some thing that will give my TV-102 APO
refractor its maximum 3 degree FOV. The choice
came down to the 40mm Pentax XL and the Tele Vue
35mm PanOptic. From my research, it appears that
the TV is better, but it gave me only 2.7 degree
FOV; so I went with the Pentax. If there were
a 40mm PanOptic, I'd gone with it instead ;-).

I have to say that this eyepiece helped me nail
the dimly lit Veil Nebula and the Helix Nebula.
It helped me as a finder to locate teeny (6")
or dim (13 magnitude) planetary nebula. It is
very bright and contrast. It is also sharp, BUT
only out to about 75%-80% of the FOV. Then, the
stars begin to look like comet and it get worse
at the edge of the FOV. The stars also lost some
focus at the edge when compared to the center.
But in defense of this eyepiece, the FOV is huge
and the glass is large; so I guess it's hard to
be perfect in all category. In practice, I could
not "see" the entire FOV all at once anyway. What
I mean by this is that I tend to concentrate in
the central area and move my eyes around the FOV
instead. So it isn't as bad as you may tend to
believe.

One of the reason I also decided against the
PanOptic is the "sea sick" effect I read about
when panning the sky in several places. Not
wanting to throw up all over my beloved TV-102,
the Pentax does not exhibit this effect. I also
view houses and walls in the day light - no
pincushion or barrel distortion even near the
edge that I can see. The view is bright, sharp
and contrasty. The other reason I went with the
Pentax is because of its weight. It balances quite
nicely with my other TV Radian eyepieces.

Panning the Milky way with this eyepiece is an
experience no binocular could offer, IMHO. Tons
teeny pin-point stars, bright round stars,
colorful stars everywhere, not to mention
occasionally running into DSO.

Some the object that really need this sort of wide
view are the Veil, Helix, M45, M31. I've seen M31
and M45 before through my Celestron Ultima (1.7 deg
FOV). I only yawned at the view until I looked through
the Pentax: WOWWWWW! These objects simply can't be
appreciated with such narrow FOV!

Lastly, there's no ghosting or reflection that I
can detect.

Recommended, but if there were a 40mm PanOptic ... ;-).

PS: One more negative, the darn rubber eyecup. I can't
see the whole FOV with glasses on. So I have to use the
plastic eyecup instead. But now the lens cap won't fit
on it. Nothing detrimental, but definitely an annoyance
:-(. Pentax, please give me the TV InstaAdjust ;-).

Overall Rating: 8
Weight: 4 (Unreliable Vote)
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Pentax SMC-XL 40mm
In a fast refractor (didn't try it in anything else), the performance is poor at the edge of the field of view, negating its slightly larger fov over the 35 Panoptic. The 35 Pan is sharp to the edge and is a better eyepiece for this type of scope. If the slight pincushion at the edge of the 35 Pan bothers you (I don't even notice it), the 31 Nagler is an even better choice.

Overall Rating: 5
Weight: 1 (Unreliable Vote)
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Pentax SMC-XL 40mm
Some people report good edge performance in very fast systems because of exit pupil vignetting. Their systems are being effectively "stopped down" to a slower f ratio, thus improving the EP's edge performance.

Meanwhile this EP is a really superb performer on slower systems. There is some field curvature, but the effect will be more pronounced on SCT's because they have rather strong inherent field curvature of their own.

Put it this way: every extreme wide field/low power EP that can beat the XL40 is far, far more expensive, whereas these are available for about $230.

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Pentax SMC-XL 40mm
In an f/9 refractor:

Significant field curvature. The extent to which this bothers you will depend in part on how strong your eye's ability to compensate focus is. It doesn't bother me much.

Surprisingly at f/9, there is pretty noticeable astigmatism at the edge of the field. However, it is only at the extreme edge. I'd guess that this EP won't do all that well in fast systems.

Basically I'm satisfied with it. Not even a 31 Nagler can provide this wide a field; I don't see a field stop in it so it must be pretty much the widest field you can get with a 2" focuser. I find it very useful as a finder EP and for panning around in star fields. Note that it is alot cheaper than a 31 Nagler. If you have a fast system, however, the 35 Panoptic might be a better bet. TFOV is smaller in the Panoptic, but, heck, you have a fast system anyway.

Best thing is to try out the Pentax before buying it so you can see how much of an issue the curvature of field is for you. For some people it is probably no big deal.

Comfort and ease of use are wonderful, like the rest of the XL line. No blackouts, eye placement is not critical.

Overall Rating: 8
Weight: 1 (Unreliable Vote)
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Pentax SMC-XL 40mm
I have used one of these in a 8" f10 sct, a 5" f10 sct and a 70mm f6.8 pronto. I must admit I am stunned when individuals talk about field curvature, coma and astigmatism in this ep. I see very little field curvature (I must admit there is more at f6.8 than at f10 tho), a very, very slight amount of coma and as far as the astigmatism, I think there is more in my eyes than in the EP (and I don't wear glasses). At 2/3 the price of the panoptic 35, and about 1/3 the price of the nagler 31, there is no other eyepiece that I have seen that comes close to the performance offered by the Pentax for the price. It is a supurb finder ep in my pronto, offering a fantastic 5.25 deg field of view. Its also a wonderful viewing EP in my 8" and 5" SCT's. If you have the bucks, you can go for the Nagler 31. If you have to live in the real world (like most of us), buy the Pentax 40, and you will have enough money left over to buy two more premium EP in shorter FL's - and get 3 ep's for the cost of the Nagler.

Bottom line? Its a beautiful ep, its no panoptic or nagler, but its the next best thing.

Overall Rating: 8
Weight: 1 (Unreliable Vote)
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