I've been using Brandon eyepieces and University Optics orthos side by side
for the last two months. Thought you might like to know the results. I'm
working up some charts for a webpage about this comparison.
 

MEET THE EYEPIECES

Both eyepiece lines are 1 1/4 inch barrel, four-element eyepieces that are
pitched straight at the planetary observer. The Brandon line has long been
considered a premium eyepiece, while the UO orthos have born the 'budget'
label for many years. Some published data for both are included below:
 

Vernonscope Brandon

FL          Eye Rel.  Apparent Field    Price*

32           30 mm         45           149.00
24           18 mm         45           149.00
16           10 mm         45           149.00
12            9 mm         45           149.00
8                          45           149.00

* Dealer price as of Mar 22, 1999
 
 

University Optics Abbe Ortho

FL          Eye Rel.  Apparent Field    Price*

25            ?          42-45           55.95
18            ?          42-45           55.95
12.5          ?          42-45           55.95
9             ?          42-45           55.95
7             ?          42-45           57.95
6             ?          42-45           57.95
5             ?          42-45           57.95
4             ?          42-45           59.95

* Direct price as of last UO catalog, ca. December 1998
 
 

My University Optics orthos come either from my own collection, or from the
collections of several astronomy club buddies. I started my own UO ortho
acquisitions to fill some holes in my focal length selections when I
procured a short focal ratio telescope. All were acquired direct from UO in
the last 1.5 years. The entire Brandon set was loaned to me for the last
couple months by Glen Sanner, also of the local astronomy club. They were
acquired some five or so years ago. They were essentially unused, as Glenn
is a (quite well known) deep sky observer who prefers wider angle eyepieces
for use with his large Dobsonian. Prior to testing, all the eyepieces were
professionally cleaned.

I'm still the only one I know with a 6mm UO Ortho. Does anyone here have one?
 

THE FIELD TESTS

The field tests of these eyepieces were mostly done using a 10" f/4.5
reflector, which is my preferred observing instrument; a 4.5" f/7
reflector, which is my primary solar and portable instrument; and a C-14
(14" f/10) Schmidt-Cassegrain.

My subjective impressions were at first that the Brandons were beating the
UO orthos hands down. However, as I used them more often, and especially as
I encountered several nights of good seeing, I began to suspect that the
eyepieces were more closely matched than I had at first thought. This
prompted some bench testing, about which more will be related shortly.

My subjective impressions were most strongly oriented toward two issues:
focal length, and eye relief. The Brandon eyepieces are very much multiple
of two oriented in their focal lengths - with 8, 16, and 32 millimeter and
12, 24 millimeter oculars. Thus the magnification selectability of the line
is rather crude, especially at the high power end which peters off rather
abruptly at 8mm. Because of the focal length availability, 2x barlows are
nearly useless in this eyepiece line.

The UO line is similar only in the longer focal lengths, with the shorter
eyepieces not having multiple of two companions in the higher focal
lengths. This results in the ability to more finely select the desired
magnification without introducing the additional machinations of a barlow
lens. If a 2x barlow is used, it is less redundant than in the Brandon line.

The Brandon eye relief was horrible. As a NON-glasses wearing observer, I
found the 8mm Brandon eye relief intolerably bad. In fact, it served as my
introduction to what it must mean to be an eyeglasses wearer, constantly
concerned with eye relief. While I measured the 8mm Brandon eye relief to
be a bit over 6mm, the eye lens of the Brandon eyepieces are mounted at the
bottom of a well (I suppose one could generously call it an 'eyecup') that
is very nearly 1/4 inch deep. It was impossible for me to see the entire
field of the Brandon 8 at the same time, even by removing the rubber eye
guard and pressing my face strongly against the eyepiece (which of course
shook the mount badly). The 12mm Brandon was little better. I could see the
entire field when my face was very snug against the eyecup, again strongly
enough so that it induced unwanted mounting motion. The longer focal length
Brandons were found to be tolerable in eye relief, with generous enough
clearances that I had no problems seeing the entire field with the rest of
them. However, it did not escape my notice that with my sunglasses on (for
solar observing with a solar filter), I could not see the entire field of
even the 32mm Brandon eyepiece.

Without this deep well at the bottom of which is the eye lens, the Brandon
eye relief would have been fine for me. The point of the exercise here is
to state that the published tables of eye relief on the Brandon line of
eyepieces does not reflect the observer's actually usable eye relief.

The UO Orthos also sport rather short eye relief. However, instead of
mounting the eye lens in the bottom of an indentation in the the eyepiece,
the eye lens is mounted at the top of a cone. This results in a great deal
more effective eye relief than one enjoys with a Brandon. My measured eye
relief of the 25mm UO was ~18mm, identical to that of the 24mm Brandon. My
measured eye relief of the 9mm UO was ~7mm, which is more or less equal to
that of the 8mm Brandon. However, due to the more advantageous mounting
position of the eye lens, it seemed as though the UO orthos had much more
generous eye relief. I was able to see the full field of all UO orthos
without touching the eyepiece, though the 4mm was a close run thing and I
was prone to bumping it (though I felt this was a good compromise for twice
the magnification, as the alternative was the nearly unusable Brandon 8mm
with a 2x barlow).
 

Figure 1: Eye Lens Positions (fixed-width font, please)
                                      __   __
          |\          /|            /         \
          | \___  ___/ |           /           \
          |            |          |             |
          |            |          |             |
          |            |          |             |
          |            |          |             |
          |            |          |             |
          |            |          |             |
              Brandon             University Ortho

In addition to the observations about eye relief, I noted a discrepancy in
claimed apparent fields of view. First, longer focal length Brandons had
larger apparent fields than shorter focal length Brandons, though all are
said to be 45 degree fields in the literature. Based on drift testing (both
are distortionless designs), the 32mm Brandon had an apparent field of 45.8
degrees while the 8mm had an apparent field of 41.2 degrees. This is not
unreasonable as far as adherence to the published specifications goes.

The University orthos claim a 42 to 45 degree field, which led me to expect
a more or less random scatter in field sizes through the line. This was not
the case, however. The apparent field sizes were 46.1 degrees for the 25mm
and 42.2 degrees for the 4mm, with a nearly linear progression from big
field to little field.

In this matter, both eyepiece lines performed about the same - apparent
fields of view are small by modern standards, and get smaller with shorter
eyepiece focal length. Both companies do about equally well or equally
poorly in advertizing their specifications, though the University
specifications at least lead one to expect some variation from eyepiece to
eyepiece.

Both eyepieces sport the somewhat troublesome 'eyeball glint', that is, the
reflection of the telescopic image off the eye's cornea, which is in turn
reflected back into the eye by the eye lens, where it is seen as a small
ghost that rocks back and forth across the eye lens as the observer's head
is moved. To evaluate this eyeball glint, some Meade Super Plossls were
procured for comparison purposes (Plossl eyepieces are generally notorious
for having the worst eyeball glint unless the coatings are excellent). Both
the Brandon and the University eyepiece glints were found to be
subjectively not as big or bright as with the plossls, and in blind testing
I could not tell the difference between the Brandons and Universities on
the basis of this glint.

It was noted that the Brandons are not threaded for standard filter
threads. Adaptor rings were used to mount standard filters into the Brandon
line, which were not needed for the University oculars. These adaptor rings
kept inadvertently coming off with the filters until I made them behave
with a product known as Lok-Tite.

The Brandons are "parfocal" while the University orthos are not. In
practice, as it seems with all parfocal eyepieces, the Brandons are only
nearly parfocal, requiring fine focusing whenever switching eyepieces. The
University orthos require focuser in travel in shorter focal lengths, with
the amount of focuser travel between the 25mm and the 4mm orthos being a
fairly hefty 1.4 inches. In practice, I did not find either the Brandon
near-parfocality, or the University non-parfocality, to be especially
advantageous.

Finally, it must be mentioned that at least a few of the Brandons have an
optical element much closer to the focal plane than the University orthos.
Small bits of dust that accumulated on the field lens were much more easily
seen against, e.g. the moon, than they were on the orthos.
 

THE ROAD TO THE BENCH TESTS

With regard to eyepiece focal length, I was delighted to find that stamped
focal lengths were in all cases very close to the actual. I used an
Ottway's Scaleometer in the workshop of a friend to measure the exit pupils
of these eyepieces on an optical bench with an objective of known focal
length. The true focal lengths of all the oculars were within .2mm of the
stamped focal length. I was surprised by this result, as the popular wisdom
as I was growing up seemed to be that there was a good deal of scatter here.

During use in the field, I noted that each eyepiece was about the same in
scattered light properties. Since I use reflecting telescopes, which in
Arizona get dirty quickly, I took the opportunity of using a small APO (6")
that is strapped onto the back of a locally available big dob. I still
could discern no clear difference in the scattered light in each eyepiece.
This helped lead to the idea of bench testing.

Another in use consideration involved the perceived sharpness of the image.
Both sets of eyepieces were again subjectively not easy to distinguish,
with the exception of the 16mm Brandon. This eyepiece impressed me as being
exceptional, and subjectively better than either the 18mm or 12.5mm
University. Paradoxically, I at first preferred the Brandons on the basis
of sharpness, during some nights of ill seeing. Later, however, I could
distinguish no real difference in apparent sharpness regardless of the
seeing conditions. This experience continues to puzzle me, but I am
suspicious that I was comparing lower-power Brandons to higher power Orthos
at first. After the first week or so, I consciously tried to mix things up
a bit.

The final consideration was the most demanding, and entailed the perception
of resolution of the eyepieces. Exhaustive (and exhausting) testing on
dozens of double stars impressed me strongly with the certain knowledge
that I have absolutely no interest whatever in observing double stars, and
that I would learn nothing about the relative merits of the eyepieces
chasing that goose. It was left to post-opposition Jupiter and Saturn, both
already less than favorably placed, and pre-opposition Mars, also less than
favorable, along with the sun and moon, to decide the question. After a
while, I threw up my hands in despair. Subjectively, I could tell no
difference, and often got confused about whether a Brandon or a University
were in the focuser at any given time. This also helped inspire a bench test.

The bench testing involved a return, after hours, to the optical bench of a
friend who runs a small military and government optical lab on the grounds
of the nearby Army base. I was inspired along these lines by some metrics
that we use in minor planet astrometry and photometry. In these
disciplines, the full width, half-maximum (FWHM) size of a star image must
be known for various calculations. The FWHM is a term that crops up over
and over again in astronomy, and in the case of star image sizes it is
roughly analogous to the optical term 'encircled energy ratio' - which in
turn can be predicted by the modulation transfer function. The main
difference is that a measured FWHM star image size in the field is largely
a measure of seeing conditions, and not of optical quality. Seeing is of
course not an influence in a temperature controlled lab. The other relevant
measurement are background values. In photometry, the background value of
light in the field is used to calibrate the measured brightness values of
the photometric targets. In the field, background levels indicate scattered
light, atmospheric dispersion, stars below the s/n discernibility limits,
and other terms.

In this test, a 60mm four element objective was placed at one end of the
bench, 'aimed at' an artificial star projected at infinity onto something
much like a Telrad window sitting just a few feet in front of the
objective. A rather intimidatingly large CCD camera was used to image this
artificial star both at the prime focus position and using each eyepiece at
a carefully controlled eyepiece projection distance. The FWHM of the star
image was measured at each iteration, as was the field brightness at 5, 10,
and 20 star image diameters from the star in the image plane. The star
images were of course larger with higher magnifications, so the results
were corrected by dividing the measured size by the scale magnification of
the projection system. The artificial star was on axis in all cases. Five
iterations for each eyepiece were done.

The results were interesting. There was no statistically significant
difference in the corrected star image sizes with any of the eyepieces
used. The plot was almost vertical, with the 32mm Brandon offering a mean
corrected size of 2.13 seconds, the 4mm University offering a size of 2.15
seconds, and the eyepieces in between situated very close to that very
narrow plunging line. At prime focus, the artificial star image was 1.95
seconds across as sampled across 8 pixels FWHM (i.e., well oversampled) and
reduced using Gaussian methods. I concluded that no eyepiece had an edge
when it came to the FWHM of star images. They all seemed to smear out the
light by a very modest amount, almost equally and certainly in a linear
manner based on focal length. I interpreted this to mean that neither
eyepiece has an edge in resolution. The color of light used was red (on the
orange, rather than near-IR, side of the spectrum).

The field background results were also interesting. All eyepieces
preferentially scattered light close to the star image, with the highest
counts at five diameters. All of the Brandons offered essentially identical
results - 10^16 electrons at five diameters, 10^14 electrons at ten, and
10^13 electrons at twenty (these electron counts come from a different kind
of animal than astronomical CCDs, so one should not expect to see analogous
results expressed in equations of real photometric scatter). These scatter
results are typical of the effects of antireflection coatings, which tend
to keep scatter close to its source rather than flinging it far afield.

The University orthos were not significantly different. The results for the
Brandons can be used to express the scatter characteristics of the
University eyepieces as well, with the exception that certain University
eyepieces (12.5, 9, and 6mm) showed less scatter (10^11 electrons) at the
20 diameters position. It was felt that this measurement was real
(indicating less scatter) and not noise, but that the difference between
10^11 and 10^13 was well below the limits of visual discernability on
astronomical targets.
 

THE CONCLUSIONS

The conclusions are simply that these eyepieces tie in both objective
tests. There were no significant differences in bench measurements in two
important tests of quality. The first is that of resolution, as measured by
the eyepiece induced bloating of the star image. The second is of scattered
light, as measured by light levels at spatial locations in the field that
approximate the extent of a small planetary image. From an objective
standpoint, the tests done would suggest that if both the Brandons and the
University orthos used were of representative quality, neither is optically
superior. There are limits to this test, specifically limits as to the
ability to discern if either eyepiece breaks down preferentially at certain
spatial frequencies. But considering the subjective impressions and double
star tests, and the difficulty of making an eyepiece aberration that whacks
just a small chord of spatial frequencies from an MTF, this is a remote
possibility at best.

>From a usability standpoint, the University eyepieces had a non-trivial
edge in effective eye relief even for non-glasses wearers, because of much
better engineering of the eyepiece barrel. Eyeglasses wearers should
probably not pursue Brandons considering that they annoyed me, a
non-glasses wearer, so badly. A few other trivial usability edges went to
the University line as well, such as the lack of adaptor rings for filters.
 

FINAL THOUGHTS

The University Optics literature makes some outrageous claims about the UO
Abbe Orthos. If one wants, we are told, the "sharpest view of a planet or
lunar mountain range, then you need the University Abbe Orthoscopic". This
is clearly bunk, like all marketing prose, about all astronomical
equipment, ever penned. The Brandons clearly perform very much like the UO
Orthos, so one would expect to see just as well with a set of those.

The only interesting difference here involves price. The old mantra about
getting what you pay for is in some ways suspended in this case. There is
obviously no clear performance advantage to induce one to buy a Brandon at
the quoted price, when two University orthos and then some could be had for
the same amount of money. I discovered when I first started my consulting
practice that if I did not quote outrageous per-hour rates to prospective
clients, I got no respect and little business simply because clients didn't
believe I was running with the 'big boys,' as one of them put it. A similar
situation probably exists with the University orthos.

Until University jacks the price of these orthos up to 3x its current level
and changes their name to the Ernst-Abbe Super-Clariton eyepiece, they
probably won't get the respect their performance deserves. This situation
calls to mind a late 1970's advertizement which referred to the Clave
plossl as the "ultimate ego trip" eyepiece. A well made plossl is indeed
nice, and the Claves of the time were indeed well made. Until the
University eyepieces have similarly aggressive marketing and inflated
prices, they won't do as well.

This state of affairs is, of course, not necessarily a bad thing for those
currently looking for a good planetary eyepiece. Science has yet to find
that the physical laws which describe our universe suspend themselves in
favor of those pursuing an ego trip, whether through Clave eyepieces or
otherwise. So buy whatever you want.
 

--
Jeff Medkeff          | Acting Assistant Coordinator
Rockland Observatory  | Association of Lunar and Planetary
Hereford, Arizona     | Observers, Solar Section