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9mm Pentax SMC Ortho vs. 9mm University Optics Ortho



I've seen a number of reviews lauding University Optics orthoscopic eyepieces and claiming that they have nearly the performance of the highest quality Zeiss and Pentax orthos. That sounded intriguing, so when I recently had a UO 9mm ortho and a Pentax 9mm SMC ortho in my eyepiece case at the same time, I thought it would be a great opportunity to compare them head-to-head.

The Pentax came to me as part of a set. It is no longer manufactured (why, Pentax, why?) and somewhat hard to find. Its prorated individual cost was $170. The UO ortho is available but in such demand that University Optics was out of stock when I tried to order one directly from them. This sample was purchased used for $48 and it was in excellent, like-new condition. The new price is $55.95. The price differential needs to be kept in mind with these eyepieces. One would expect the Pentax to be something special (although there are plenty of poor-performing $170 eyepieces out there); the question is, how well can the UO keep up?

The comparison took place in a Chicago suburb on a couple of nights of relatively good seeing. The scope used was a 76mm f6.6 Borg apochromatic refractor, 1/7-1/8 wave, 97.5% Strehl ratio. The moon was just beyond half-moon phase and an easy target, as were Jupiter and Saturn. M42 was a poor target in these viewing conditions, but interesting as part of an eyepiece test.

At the dining room table

The two eyepieces are different sizes. The UO fits 1.25" focusers, while the .965" Pentax requires an adapter. Not a big deal, but if most of the eyepieces you use are 1.25", you might want to buy the same number of adapters as you have .965" eyepieces so you don't have to juggle adapters when you switch eyepieces out in the field. They're both in the lightweight category, but the Pentax, as you'd expect, is lighter.

The UO has two end caps, while the Pentax came with a cap just for the top. Neither of them has an eyeguard to keep out extraneous light, but the eye is positioned close enough to them that this is somewhat less of a problem than it might be if they had longer eye relief. The UO has the classic ortho black truncated metal cone on top of a chrome cylinder, and the Pentax has a flat black rubber ring encasing a black metal housing on top of a chrome cylinder. The rubber ring on the Pentax reflects less light near the eye lens than the black metal does on the UO.

Perceived quality is high for both of them, although higher for the Pentax. Exterior finishes were perfect on both. Looking inside the barrel, the Pentax has tiny ridges and is uniformly painted flat black everywhere. The UO also has painted ridges, but the paint adhered to them poorly, leaving some parts of the chrome interior showing through. Rubbing my finger gently on the inside of the barrel did not remove any paint, however.

The lens coatings for the Pentax were a deep blue-green and reflected very little light, while the UO coatings were purple and reflected quite a lot. The field lenses and eye lenses appeared to be the same size on each. Looking inside the eyepieces, the field stops were sharp in both. Holding them up to a bright window, there was no reflected light off the interior of the barrels of either, surprisingly so for the UO given its poor interior paint job. Looking through the eyepieces at an illuminated blank wall (again with no telescope involved), the Pentax was brighter, transmitting noticeably more light than the UO ortho.

The 9mm eyepiece focal length would give me 55x with the 500mm focal length Borg, and with both orthos' 42-degree apparent fields of view I could look at roughly a 0.75-degree piece of the sky, or one-and-a-half moon widths. When I finally got outside, the amount of sky actually covered appeared to be about the same for each.

In the parking lot behind my building

This isn't my favorite site for observing, but I was doing a comparison on mostly bright objects rather than trying to maximize the visual experience. Still, all you Arizona desert observers, imagine this: a city apartment parking lot surrounded by buildings, with safety lights illuminating most of the lot, and a few shadowed areas where a desperate astronomer might set up a scope. Not exactly ideal, except that it's right outside my back door.

Thankfully, the Borg is well-baffled and could be positioned in relation to the lights so that there were minimal internal reflections to contend with. Also, I can shield my eyes in such a way that the surrounding light is not very intrusive while viewing. Dark adaptation is out of the question, of course, but it's not as bad for the moon and planets as it could be.

Eye relief

There was no significant difference in eye relief, which would be rated at something like 7 to 8mm for a 9mm ortho. This was comfortable, but probably would not work well with glasses.

Chromatic aberration

First up, the moon. The limb on both eyepieces was sharp, even at the edge of the field. The terminator was color-free, shadows were color-free, everything was color-free - except one thing. The Pentax showed the slightest bit of a light green edge on the limb of the moon. This was quite a surprise, but it was there every time I went looking for it. I did not see it on Jupiter or on bright stars. The limb of the moon was sharp and color-free in the UO ortho. However, Jupiter showed also showed a slight bit of color (red on one edge of the planet, blue on the other) near the field stop with the UO ortho.

Sharpness

Both eyepieces were sharp on-axis, but the Pentax was sharper in resolving lunar and planetary detail and provided me with my first experience of the "snap-to" focus that I've read about in reviews of high-quality equipment. When you reach the point of ideal focus, even with the scope shaking a bit as you focus it, you know it immediately: the image is just right there. Quite amazing.

Which is not to say that the on-axis focus with the UO was anything remotely like unacceptable. To put it in perspective, I pulled out a 12.5mm Ultima for comparison, and although the focal lengths were different and made sharpness hard to judge, I thought that the UO was maybe a bit sharper than this well-regarded eyepiece.

Specifically, both orthos were able to resolve five craters in Clavius, but they were easier to see with the Pentax. Fine detail on the moon's surface was also easier to see. Several times I would find something at the edge of resolution with the Pentax and then try to see it with the UO ortho. Although most of these threshold targets could still be resolved, none of them were as clear. The two dark bands visible on Jupiter were just slightly sharper as well and Jupiter's moons were tighter points of light in the Pentax.

Off-axis, again there was not much to choose between them. There was minimal sharpness drop-off at the edge of the field of view. The advantage the Pentax started with was maintained, but the UO did not fall farther behind off-axis than it was on-axis.

Brightness and Contrast

Again, the Pentax maintained the brightness advantage it had established in my dining room. On M42, the nebulosity was brighter and more extended and began to reveal the shape I can see in my 10" dob as well as start to reveal some interesting irregularities in surface brightness, and the background was slightly darker. Background darkness was also examined against the field stop in two situations: when viewing a dark patch of sky, and with Jupiter centered in the view. In both cases, the sky was slightly darker in the Pentax.

Planetary detail contrast was also somewhat better in the Pentax, with bands on Jupiter not only sharper but darker as well. However, at this power in this scope, under these viewing conditions, planetary details were hard to distinguish with either eyepiece.

Faint star resolution was better in the Pentax as well. Examining the trapezium in M42, four stars were clearer and steadier in the Pentax. More telling was looking at the faint companion of Polaris. In the Pentax, it was not an easy target in these conditions but it was steady and clear with direct vision. In the UO, I never saw it, even after persistent looking with averted vision and knowing exactly where to look.

Besides the difference in light throughput, the other reason that this occurred is probably that bright object "scatter" was greater in the UO. Jupiter and the moon both cast noticeably more glare over their surroundings. Both also had some minor ghosting on nearby bright objects, with somewhat more being evident with the UO.

Other musings

Taking price into account in the comparison is very difficult. When is it worth spending three times as much for an eyepiece? That's pretty much a choice reflecting your personal priorities and interests. Just in terms of the equipment, it might be fairer to do a comparison of UO orthos and Pocono Optics orthos, and throw in some similarly priced Ultimas and plossls for good measure.

Summary

As expected, the 9mm Pentax won in the performance category. As I wrote a friend shortly after making the test, I think I'm "spoiled." It will be hard to go back to eyepieces and equipment with less than this level of exquisite performance. But there's more than one price to pay if the cost of expensive eyepieces limits the other equipment you can afford and enjoy using.

On the other hand, the 9mm UO ortho kept up pretty well. It's a fine eyepiece and deserves respect for what it can reveal of the sky. It also won, hands down, the "value for your money" competition. And you can actually telephone University Optics and buy it! This is not just planet Earth, but the real world as well. You can order three UO orthos for the price of one Pentax, assuming you can find a Pentax at all.

The bottom line: if the University Optics coatings were better, I'd start collecting a set. And if I didn't already have the Pentax orthos, I'd get a set of UO orthos anyway, even with the coatings the way they are.


Update 4-12-01: 5mm Pentax and UO ortho comparison

Much of the above review implies a comparison across the entire lines of UO and Pentax orthos. When I had a chance to compare a 5mm Pentax ortho with a 5mm UO ortho, I thought I would see if some of my conclusions held true at a different focal length.

The Pentax 5mm again had better light throughput and contrast on fine lunar and planetary detail. It was perhaps very slightly sharper on-axis, and noticeably sharper at the edge of the field. The 5mm UO ortho showed slightly more edge of field deterioration than did the 9mm UO.

As for color, both showed improvement. The Pentax's slight green edge on the limb of the moon was less prominent at 5mm than at 9mm, and the UO also showed less edge color at this focal length.

However, on ease of use, the UO won handily with significantly better usable eye relief. The UO eye lens is at the top of a truncated cone, while the Pentax eye lens is slightly recessed. At this short focal length, it's easier to see and hold the entire field of view in the UO. I'd expect a similar advantage at 6mm and particularly 4mm (3.8mm for the Pentax XP ortho).

Finally, the UO again easily won the "real world availability" and "value for your money" awards. There have been a number of mildly frantic requests to pay extraordinary amounts of money for the 5mm Pentax ortho on various classified ad services, not entirely motivated, I expect, by the pure and noble desire for better eyepiece performance. (At least, my own ad wasn't!) But if you're not looking through ANY 5mm ortho while you wait for the Pentax 5mm to show up, you're losing an opportunity to enjoy another fine UO eyepiece.



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