OH, SAY, CAN YOU SEE?
Light-gathering ability is critical for a boater. When I purchased my first set of high-quality binoculars many years
ago, I was amazed at what I could see out in the ocean at
night with starlight providing the only ambient light. It was
very different from the cheap sets I’d used before. The size
of the objective lens is important for this, but there’s more
involved. Color differentiation and sharpness are also concerns. We want not only to see that buoy at night but also
to hopefully determine its color and shape. Many factors
contribute to enhanced night vision, including quality of the
glass in the objective and eyepiece lens, quality and type
of prisms used (we’ll get to prisms below), and lens coatings. The light transmission as well as color differentiation
can be objectively measured by the manufacturer as the
beam exits the eyepiece, and the makers of more expensive
binoculars strive to excel here as well as with other issues.
PHOTO: MEL NEALE
Although the subject of lens coatings seems somewhat
esoteric, it’s not just smoke and mirrors. Coatings can do
things such as reduce internal glare and light loss, which
can yield better light transmission and brighter images.
Coatings may also reduce internal fogging, helpful even if
the binoculars are nitrogen filled. There are different levels
FEBRUARY | MARCH 2012
of lens coatings, ranging from coated to fully coated, multicoated, and fully multicoated, the latter being the best. It
means multiple coatings are on each lens.
Quality manufacturers go to great lengths to develop
and apply proprietary coatings. One example would be
what Fujinon refers to as its patented EBC (electronic beam
coating). This is another reason why I wouldn’t buy cheap
binoculars. Resolution and contrast are important on the
water. Poor quality here could make you miss a distant buoy
or mistake its shape.
PORRO OR ROOF: A PRISM PRIMER
Prism lenses are internal and sometimes called mirrors,
although that term doesn’t fully describe what they do.
They reflect the image and, if made with high-quality glass,
can help reduce internal light scattering and enhance the
view in other ways. Binoculars typically used on boats have
objective lenses at a wider distance apart than the eyepiece
lenses. Many prefer this arrangement because they feel it
gives the effect of more depth. This type of construction
uses Porro prisms, which are rated BK- 7 or BAK- 4. Generally
the BAK- 4 prism has better glass and produces a better
image. Binoculars with straight-line tubes (the objective