>Subject: RE: [OM] Olympus Binoculars
>I purchased a pair of Olympus EXPS 7x50 binoculars (for astronomical
>observations, primarily) about two weeks ago. . . the salesman didn't
hesitate
>to recommended the Olympus over the Pentax, claiming that the Olympus' optics
>were "superior". Well, since I already knew from the Olympus web site that
>this model employs BaK4 glass in the porro prisms. . . but one characteristic
>that's quite evident is a fall-off in image quality towards the very edge of
>the field of view. I find this not to be too much of a problem, however, as
>I generally have the object of interest centred, where it appears nice and
>sharp! I've never used the Adlerblick or Celestron binox you mention. Do
>they also exhibit image quality fall-off towards the edge of the FOV? Are
they
>in the same price range as the Olympus model? --Roger Davies,Lisbon, Portugal
Roger, thanks for the post. I think your underlying question is, "Are
these good binoculars?" Probably so. They do use BAK-4 prism glass, which
is state-of-the-art. The criteria I use for testing binocs are, after
finding a suitably bright surrounding: 1) hold the binocs at arm's length
and look at/through the eyepieces. Do you see a "square within a circle"?
Is there a shadow-like attenuation in the shape of a square or diamond,
imposing on the edges of the circle of light? If so, not good. If just a
round circle, then good. 2) Let light stream through the objectives and
place a card near the eyepieces. How large a circle of light is projected
onto the card? Big = good for brightness, up to 7mm, after which bigger
is not better. (This is actually controlled by magnification and
objective size, and a 7x50 binoc should give a 7mm diameter "exit pupil."
3) Look through the binoculars backward. Are there obstructions in the
lightway? A "flattened circle"? (While you're there, look for prism chips
on used binocs.) I look for minimal or no circle flattening. 4) Looking
through the binocs the correct way again, how far away from my eyes can I
hold the binoculars and still get a full field of view? (Eye relief).
Typically, quality binoculars offer longish eye relief (but not always).
Cheapo binoculars, on the other hand, almost ALWAYS require pressing your
eyeballs up against the eyepieces. 5) The last test is the most rigorous:
on a clear night, gaze at a starfield. At what point do the stars get
perceptibly "blobby"? 1/3 from the middle? 2/3 from the middle? Just at
the edge of the field? This is really a test you must do via comparison,
although you can get a sense of it in the daytime, too, by looking at a
target with fine detail and moving the target to the edge of the viewing
field. Get a good pair of binoculars for comparison (Fujinons are often
ranked at the top and represent for many the 'holy grail' of binoculars;
personally I think the Celestrons with ED glass are great, too; there's a
lot of hype from the Rolls Royce crowd about Leitz and Zeiss but most of
them are roof-prism designs (straight barrel) and, honestly, the porro
prism design (bent barrel) has the optical edge. My binocs are
Adlerblicks, which are touted by astro-heads as competitive with Fujinon
without the weight and the $$, at a minor debit in image quality.) As you
have guessed, it's common to see image falloff in binocs, and the
majority exhibit some. You'll have to get a "sense" for it by comparing
with other binocs, but when you have, I'd like to hear another report on
what you think about the quality of your Olympus binocs. Well, I can feel
the list police ready to write me up an "off-topic" ticket, so I'll sign
off. But in closing, if you are one of those who believe that
"subjectivity is good and good for you," please ignore ALL of the methods
above. Instead, cradle you binoculars, become one with them, and ask
yourself, "Do I like how these binoculars make me feel?" Let me know what
happens. --Kelton
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|