by Gordon on Mon Jul 10, 2006 6:07 pm
Just be sure to stay away from Trashco, err I mean Tasco binoculars which are
pretty crappy. You are going to be limited to what the store has for sale so the
best thing is to try them all for image quality, how wide the field of view is
and how good the focusing mechanism is.
When you look into them you want a wide field - known as the apparent field. ie,
when you look into the eyepiece does it give the impression of looking down a
narrow cardboard tube? - 25 or 30 deg eyepieces will look like this. Most decent
binos will have 50 or even up to 65 deg eyepieces, this makes them much easier
to use, especially at higher magnifications such as 10 or 12X. You can work out
what the apparent field is - for 10X binoculars the apparent field is 10X the
true field, so 10X50s with a true (claimed anyway) field of 5 degrees have 50
deg eyepieces. A 6.5 deg field will be 65 deg eyepieces.
Wider eyepieces generally have more aberrations around the edges- you will
pretty much always see some blue fringing due to chromatic aberration near the
edges, along with flying seagulls... look at a point source of light and you
will see what I mean- astigmatism and spherical aberration spread out the light.
You want binoculars that have nice sharp images with no colour in the centre of
the field of view- that's where you generally look, the outer areas are useful
when trying to locate things, especially if they are moving like flying birds.
Even expensive brands wont be sharp around the edge, so its a matter of
comparing brands to see which looks best.
Looking at a grid of some sort will show how much distortion there is as you
sweep across it- all binoculars will have some, but try to get some without too
much.
Also, check for focus- can you get a nice crisp image or does it always look a
bit blurry? Does the adjuster on one of hte eyepieces have enough range to accommodate differences
between your eyes? Is the view contrasty or is there a slight haziness? Are the lenses multi-coated?
Does the focus mechanism work smoothly? Some lower power binoculars dont allow focus adjustment,
they rely on your eyes to change focus, but you wont get as large a focus range
with these.
If the binoculars are going to get a fair amount of use its worth paying a bit
more for quality.
That said most Nikon or Pentax are good, but there are plenty of others around
too. Try an astronomical shop as well as camera shops to increase the potential
range of brands to compare.
Gordon
D70, D200, CP5700