Thursday, February 16, 2006

Do you need glasses?

Yes, yes you do.

Even if you have perfect vision, you still need glasses; by which I mean you need a good set of binoculars. Or at least you do if you do any boating, hiking, camping, hunting, fishing, shooting, flying... I could go on.

A 7x50 marine binocular is the basic all purpose set of field glasses that everyone should have. Fancy addon features like range finders, compases and the like can be nice (especially on the water), but they may detract from the ruggedness and light transmissivity of the glasses.

Binoculars, aka field glasses are there to let you see detail at a distance, to spot relatively small objects at a distance, and in general to make that far away world a little bit close to your eyes; especially in the dark, or at twilight time, when your eyes are confused and inefficient.

A good set of 7x50s can actually see better than you can. The light gathering and transmissivity of a decent pair of binocs can actually give you BETTER vision (light gathering and contrast) than with the naked eye, never mind the magnification. In fact a good pair of 10x70s can make a medium moon look like an overcast day. That may not sound impressive at first, but it's pretty startling when you try it out the first time. Some of the giant spotter glasses (like the 20x120) can take a full moon night, and make it damn near as bright as the morning.

Now, as to picking out glasses, how do you choose? There are literally thousands of models out there, with a bunch of different specifications, brands, and price points.

First things first, general quality. If you are looking for an all around set of glasses, you want to go for decent quality. A set of compacts you can fold up and stick in your coat pocket are fine for $30 but dont expect them to be a decent pair of primary field glasses. Expect to pay $200 to $500 for a good pair of 7x50's for example, from a reputable brand; and from $500 up to about $1500 for a premium brand.

The brands I generally look at in the "reasonable" price range include Bushnell, Steiner, Nikon, Pentax, Fujinon, Zhumell, and Bausch and Lomb. There are others, notably from scope manufacturers and camera manufacturers, but that list right there covers the majority of the field. Oh, and several of these manufacturers has a lower end economy orented line that I would stay away from, some under their own name (Bushnell), and some under another trade name (Bosch and Lomb)

The "premium" brands include Swarovski, Zeiss, Leica, Newcon, Oberwork, and Kowa, among others.

Honestly, unlike rifle scopes or spotting scopes, where high end glass can be worth every penny; in this case you don't necessarily get what you pay for.

What I mean by that is, I don't think you get much value for money by going to the premium brands, unless you are buying very high magnification glasses, you're using your binocs in extremely low light conditions; or unless you require a specialty feature like image stabilization (which reduces the visible shaking in the image from hand held glasses at high magnification).

There is definitely a difference in optical clarity between the low end (which I wouldn't even consider) and the middle, and the middle and high end... I just dont think the 10% extra clarity from a Leica makes it worth three to five times the cost of a Steiner.

The important considerations, other than overal quality of the optics and contruction, are the objective lens size, the magnification, and the field of view.

When I talk about a 7x50 pair of binoculars, what I am saying is that the magnification is 7 power, and the objective lens is 50mm across. If You see 7-24x56 it means that the optics will zoom from 7 all the way to 24 power, and have a 56mm objective lens.

Why is the objective size important? Well, two reasons. The first is, the larger the objective size, the more light is gathered by it (as I described above). The second is related to that, because the larger the objective, the large the exit pupil size will be for a given magnification.

Whats that? Well the exit pupil is the diameter of the light that is being projected onto your eye by the glasses.

In full darkness, a young eye will dilate up to about 7mm, to take in more light from the surroundings. With optics, the wider the exit pupil, the more light YOUR pupil can gather, to form a clearer brighter image. In an ideal world, you want to use all 7mm if you can.

To figure the exit pupil diameter, you divide the size of the objective lens in millimeters by the magnification power. So a 7x50 would have an exit pupil diameter of 7.14 millimeters; which is just about the most your eye can use.

All that said, most of your binoculars use if you're an "average" person will be in the day time. It's important to note that in broad daylight your pupils normal at rest state is around 2-3mm, and in bright light your pupils will be at their smallest. Also note that as your eyes get older, the lose flexibility and dont dilate as widely, so that by the time you are in your fifties, the average puil dilation is down to around 5mm.

Given those factors, although I don't generally recommend that your primary glasses have anything less than a 5mm exit pupil at max magnification, even down to a 2-3mm pupil will still transmit useful amounts of light in the day time.

Now, the other import specification to look at is the field of view (FOV). This is generally given either in degrees, or in feet at 1000 yards. 1 degree is 60 minutes of angle, or just under 5 feet at 100 yards, 50 feet at 1000 yards etc (actually it's about 48 feet, but estimating to 50 is usually sufficient)... You can find binoculars with fields of vew as narrow as 2 degrees, or as wide as 18 degrees, but the normal range is from 4-8 degrees. Anything more than 8 degrees is considerd a wide field binocular, and you will pay a bit more for them.

Generally speaking the higher the power, the narrower the field of view, though this can be compensated for with different optical configurations. Also generally speaking a wider field of view is an advantage, because it lets you glass more area, faster, without scanning as much; thus you are less likely to miss something completley when you are moving relatively quickly. Now, here's the thing though; field of view is important, but WIDE field of view isn't necessarily better. In some situations a narower field is an advantage. Picking out a small object at great distances can be quite difficult with a wide field of view; and if you already know where to scan, a narrower field of view helps you focus in on difficult to spot objects. You have to make a more careful search, but you get better results, and will see more detail. Basically you need to pick your FOV based on your needs.

Okay, so what do you buy?

Well, About the best binocs out there are MilSurp 10x70, 15x80, and 20x120 "BigEye" marine spotting glasses. They were made on contract spec by various manufacturers, including Swarovski, Zeiss, Leica, Leitz, Newcon, Steiner, Fujinon, and Nikon. Technically speaking I dont think the navy officially remaindered any of them, but you can find them on the MilSurp market for a fairly high, but not ridiculous price. Unfortunately they are quite heavy (the 120mms are only tripod mounted), so they aren't exactly ideal for field use; but if you have to glass long open spaces (prairie, long mountain views, or water) in the dark; they are indispensible.

Realistically thoguh, most of us don't need that kind of light gathering, most of the time; and a tripod mounted glass isn't exactly usful while hiking; so as I said above, a compromise is in order. The 7x50 is generally the best all around compromise position between cost, size, power, ruggedness, weight etc... I also recommend you chose a 7x50 marine, whether you are boating or not, because they are generally more rugged, and almost always more waterproof than other glasses.

Grab yourself a 7x50 from a reputable, medium grade brand and you won't be sorry. I have a pair of Steiner 7x50 marine glasses somewhere, but I can't find them. I may have lost them when my storage unit went bye-bye; in which case I'll be replacing them, probably with the same make and model.

Oh and while you're at it, a half decent pair of compact field glasses, and a very decent compact monocular are also things I recommend anyone carry out in the field at all times. I have both, they only weigh a few ounces each, they ride in a vest pocket and on a lanyard around my neck, and they instantly give me a quick up close view.

You obviously can't get the quality and light gathering of larger glasses, but my bushnell 8x25 compacts are just fine for a well lit day. They fold, and they have a 7 degree FOV so I can spot distant objects fairly quickly. If you ARE hunting or tracking at twilight, you can get compact glasses with a 5mm exit pupil; and there are compacts with up to an 18 degree FOV. My monocular is also an 8x25, but it is very small, and it has a narrower field of view, basically acting as a mini spotting scope.

Add in a set of 10x70's for your house, car, or boat; and your field glass needs are pretty well covered.

Of coures then we get into rifle scopes, and spotting scopes; and thats a whole nother post... hell it's a whole nother BOOK.