| What are Optics?
by Tom Hall
The classic text "OPTICS" by Vasco Ronchi, an
Italian researcher, describes the complex relationships between the
eye, perception, and optical equipment. Having some understanding of
these concepts that Ronchi describes will aid in your search for
optical equipment. By experimenting with the optical equipment you
are considering, you will feel comfortable in eliminating those
binoculars or spotting scopes that will not work for you. This
experimentation will leave you with a few finalists to consider as
your ideal binocular or spotting scope.
Optics are the mechanical means by which we
collect light information from an object, and vision can be
considered the gathering of this information through the eye and
it's processing by the brain. We have three aspects to our search
for the ideal "image"- the object, the eye, and the brain- physics,
physiology and psychology! The binocular or spotting scope is only
one third of this equation, collecting and magnifying the light from
an object and "feeding" it to your eye. Find what works with your
particular situation and remember that no one reacts to optics in
quite the same way. The following are questions about relevant
optical terms as well as some definitions and guidelines gleaned
from years of collecting feedback on variables in optical design.
Let's see if we can narrow your choices.
QUESTIONS TO ASK WHEN CONSIDERING OPTICS
1. What is your primary application?
a. What distances will you most likely want to view to?
Will you be looking at butterflies at 5 feet,
watching birds at 30 yards, or looking at whales at distances of a
half-mile or more? Identifying your primary application will
illuminate the need for either a spotting scope or a binocular. This
decision is essentially between magnification performance and
portability. Hand-held binoculars will top out in magnification at
10x or 12x. Beyond that magnification, binoculars become difficult
to hand hold and should be mounted on a tripod to steady the image.
Low power magnifications (6x, 7x, or 8x) will maximize the field of
view that you see. This can be more critical for those "up close"
situations under canopy looking for warblers, or for theater use to
see more of the stage. Can you use binoculars of 6x to 10x
magnification to view an object at a half-mile or more? Certainly,
but you won't be reading the ship names out at sea, or see much
detail on the peregrine atop the cellular tower 500 yards away.
These two examples would be cases for the extra range of a spotting
scope, giving 15x to 60x magnification or even more.
b. When you will be using these optics (time of
day) and how dark does it get?
If you plan to be out at dawn or under heavy
canopy in dense woods, you should consider a binocular that has 30mm
of aperture or more to perform well in these low-light conditions.
Here is a situation where you have to tradeoff: weight and size for
brightness and low-light performance. Larger aperture binoculars
will perform better in low light, but will weigh a lot more. Also,
know that magnification will work against you for brightness in
lower light conditions (see exit pupil). I like a number of the
8x30s or 8x32s that are currently on the market as a minimum for a
good low light glass. Also, this size of binocular will often
deliver wider fields of view for following fast moving targets.
2. Would you prefer to keep your eyeglasses on
when using the binocular or spotting scope?
Statistically, over 50% of the adult population
wears some sort of eye correction. There are several factors to
consider in matching your correction to your optical equipment. If
you only need correction for near- or far-sightedness, you need not
worry, as binoculars and spotting scopes will generally have enough
range to correct your vision without having to use your eyeglasses.
However, if you have astigmatism, (a warping of the eye's cornea)
you will get your best results by leaving your glasses on. Also,
many people prefer the obvious convenience of leaving their glasses
on at all times and will want to find optics that allow them to do
just that. The specification to look for here is called eye relief
and we have a very complete description if you click on the link.
3. How much weight are you willing to carry
around for your application?
The lightest full-size binoculars weigh 20 oz.
Some of the German or Japanese high-end binoculars will weigh 28 oz.
and more. As I mentioned under "How Dark Does It Get When I Use
These" you are going to have to balance performance under low light
performance vs. weight and size. You can get compact binoculars that
weigh less than 8 oz. that perform well in normal lighting
conditions.
4. Will you be using your optical equipment in
any-and-all weather conditions?
Waterproofing. You can't tell if a binocular or
spotting scope is waterproof by just looking at it, you will need to
check the specifications because everything that makes a binocular
or spotting scope waterproof happens "under the hood". Rubber
armoring alone is no indication of any weatherproofing.
If the equipment is not waterproof, it may get
water inside the optical equipment causing droplets or a fog to
condense on the inside lenses. This effectively degrades or
completely blocks the optical image and introduces mold and mildew
spores to the interior of the equipment. You can get the water out
at some point but the mold and mildew is there to stay. Mildew will
etch minerals from the surface of the glass lenses and prisms,
rendering the equipment permanently flawed. The trick is to choose a
piece that will prevent water intrusion with seals. This is usually
accomplished with rubber O-rings sealing the moving parts of the
focus mechanisms (many individual focus binoculars have sealed,
threaded eyepieces). Spotting scopes have to seal the focus, front
objective, and the eyepiece mount - if the eyepiece is removable
there is usually an optical flat in the body of the scope where the
eyepiece threads or bayonets on to prevent dust and water
intrusion.
Here is my thumbnail guide to waterproofing
definitions:
Weather Resistant, Weather Proof, or Shower proof-
means that the manufacturer feels that the equipment will withstand
the occasional shower or spray but does not mean that it will
withstand submersion or continued use in wet conditions. If the
equipment fogs internally the manufacturer may not repair the piece
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Waterproof- means the manufacturer will guarantee
against water intrusion under most circumstances - rain or even
brief submersion. Some will even specify a depth underwater that the
equipment will withstand (usually no more than a depth of 15 feet).
You can generally expect that the manufacturer will back up the
warranty and make repairs for free if the equipment fogs
internally.
Nitrogen Purged or Dry Nitrogen Purged- is not
specifically a quality that seals the equipment against water
getting in. It is meant to "charge" the interior of the piece with
nitrogen gas that has no moisture in it during the assembly process.
This will deny mold or mildew an oxygen environment to start up in,
and start the equipment out with no water vapor in the interior of
the piece. The equipment still has to be sealed correctly with
O-rings or threaded focusers to prevent water intrusion.
5. What are the benefits of spending more money
on optical equipment?
What do you get as you step up in price? Within
the past 5 years or so there has been a dramatic improvement in the
optical quality of equipment in the $50 to $150 price range. It is
possible to get very respectable performance in binoculars at this
price range. It is even possible to get some measure of weather
resistance. But you generally do get what you pay for as you go up
in price, starting with weatherproofing and body integrity. Most of
the mid- price range binoculars ($250 to $500) will feature the roof
prism body style with higher quality coatings and full
waterproofing. Stepping beyond the $500 range will give you even
more expensive glass types used in the equipment with more durable
body construction.
What do the more expensive glass types bring to
your optics? The idea behind ED (extra low dispersion), HD (high
definition or high density) glasses and fluorite lens elements is to
minimize or eliminate chromatic aberrations: the natural dispersion
of different wavelengths of light passing through the optical
system.
6. Is it possible to get everything you want
with one "ideal" piece of equipment?
In optics, the name of the game is trade-offs. As
you increase magnification you will decrease the field of view and
brightness under low light. As you increase brightness, you will
also increase the size and weight. There is no single optic that
will be a perfect fit for all situations. Think again of how and
where you wish to do your viewing and choose the one that will work
best for those situations. As your viewing needs change or expand,
your optical needs will also change. |
