From: bunner@vms.macc.wisc.edu (Dana A. Bunner)
Subject: More on Binoculars
Organization:  University of Wisconsin Academic Computing Center
Date: 28 DEC 92 14:35:03    

I just finished a rather extensive comparison of binoculars and thought
some of this group would find it interesting.

I am fortunate to live near a rather large birding/astronomical binocular
shop.  In fact they were consulted by Astronomy Magazine on their recent
binocular Buyer's Guide article.

My prime objective was to purchase a second pair of binoculars to 
supplement my compact 7x21 sports glasses and to serve as a good all-purpose
lightweight astronomical and wildlife glass.  Also with nature having blessed
me with eyes requiring 6.25 diopter corrective lenses, I desired enough
eye relief to use them with eyeglasses, as well as enough focus correction
to use them naked eye.  This is a rather difficult combination.

First, I quickly found that vendor advertised eye relief figures are not
reliable.  My local store performs their own tests to determine actual
eye relief performance.  Eyepiece design enters into this measurement.
In many designs the eyepiece does approach the claimed figure if measured
from the back of the eyepiece glass to the focused image.  However several
eyepieces are recessed into their eyepiece "frames," which do not allow the
front surface of eyeglasses to get closer than 4-8mm of the lense.  Thus
reducing the effective eye relief for eyeglass wearers.  A good example 
of this design is the Celestron Ultima 8x56.  A very nice binocular with
an advertised eye relief of 21mm.  However actual in-store testing revealed
that the image was focused just 11mm back of partial hard plastic, non-
rolled down eyepiece cup.  Some other results are shown below:

Model               Advertised ER     Measured ER
Fujicon 8x40 BFL          19               17
Celestron 7x42 Ultima     23               19
Zeiss 7x42 B/GA T Dialyt  19               18
Pentax 7x35 PCF           14                9
Nikon 8x30E Criterion     13               13
Swift 8x25 Micron         13               11
Pentax 8x24 UCF           13                8
Bausch & Lomb 7x26 Custom 16               15
Celestron 10x50 Pro       13               10
Celestron 10x50 Ultima    19               17
Pentax 7x50 PCF           20               10
Minolta 7x50 Standard     18               16
Fujicon 7x50 FMT-SX       23               20

As the typical recommended eye relief is 15mm for eyeglass wearers,
a few of these discrepancies can make a big difference.

Another interesting discovery was comparing the highly rated Carton
Adlerblicks to Celestron Ultimas.  If one covered the nameplates, it
was impossible to tell them apart.  Store personal said the same was
true when they were disassembled.  The parts are interchangable.  
Selected models of the Swift Ultra Light series are also identical 
except they have replaced the "leatherette" covering of the Carton's
and Celestron's with a light rubber coating.  In store testing of the
8x42 Ultima, Adlerblick, and Swift was unable to detect any difference
in eye relief, image brightness, or field of view.

Several low-end binoculars were also near-identical, for example the 
7x35 models of the Minolta EZ, Swift All-Sports, and Bausch & Lomb
Legacy's were the same except for the Minolta's using plastic hinges.

As to finding models which could achieve a naked eye sharp focus at
infinity for my defective eyes, I met much failure.  Out of all of the
7x50's tested, only the Minolta 7x50XL came close and it wasn't 100%
sharp.  None of the 8x56's were successful (I was considering the 8x56
Celestron Ultimas before testing them but they failed both the effective
eye-relief and unaided focus tests).  The inexpensive 7x35's from Swift
& crew were able to focus however with an effective eye relief of just
7mm, they were unusable.  Also these extra-wide angle (578ft @ 1000 yds)
designs had severe edge sharpness problems on starfields.

In the end, I decided on a pair of the Celestron/Carton/Swift 7x42
models.  All had fully multicoated glass surfaces (tested by shining
a strong light into each end and observing the color of the reflections.
No white reflections could be found.  All are very light, weighing in at
20-21 ounces.  But I had to go through 6 pairs to find a Celestron which
gave me a sharp naked-eye focus, the rest were just off ... usable for
birding but not for astronomical purposes.  I would've seriously 
considered popping for the extra $40 for the Ultima 7x50's if I could
have found any which focused w/o eyeglasses.  And might have been 
tempted by the heavier Celestron Pro 7x50's for less money if not for
the same focusing problem.  A couple of nice looking Miradors and
Swifts (non-Ultra Lites) came up short with non-coated inner surfaces.
The Orion 8x56 Mini-Giants were attractive at $129 but are heavy and
untested on naked eye focus and claimed eye relief of 18mm.  Plus the
recent negative sci.astro review didn't generate enthusiam.

This model has a 6mm exit pupil image and with the superb coatings, 
transmits more light than many cheaper and heavier 7x50's.  Last night
being a great night for viewing (and having a wind chill reading of 
better than 20 degrees ... very rare for Wisconsin this time of year)
I took them out for about 90 minutes.  They were wonderful, vastly 
better than my old 7x21 compacts.  I was able to easily observe several
Messier objects, including M36, M37, and M38 in Auriga, objects my
compacts could not detect.  Certainly they are not the match of a 10x70
but then again they are 1/3 the weight and great for hikes.  When used
with my Coulter 13.1" and Telrad, they were a perfect compliment to 
locate objects, cutting down my search time by several minutes per object.
Also the edge to edge sharpness was quite good, far better than the $75
wide angle pairs.  The field of view of 368 ft @ 1000 yards gives nice
images of constellations, the 10x50 models with 263' FOV cut off some of
my favorite views.

At $180 they seem to be a good value.  If I had another $200 lying 
around I would've seriously considered the Celestron 6.5x44 ED model.
It was beautiful, great sharpness, bright images, excellent color.
A little heavier at 26 ounces but with a slightly wider field.  A near
perfect (IMHO) all-around design.  With a cresent moon shining on snow,
I was stunned by the image brightness, I watched a rabbit in my 
neighbors yard and could see more detail than I ever thought possible.

Now I can start saving for some 15x80's!

Dana Bunner
Newsgroups: sci.astro