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Thursday, April 24, 2014

Scoping out paradise

Ed Stephens Jr.

There’s no use being in paradise if you don’t bother to look at it. Sometimes the best way to look is with binoculars: boat-spotting, beach-bumming, Kingfisher bird watching, whatever. Binocs are just an occasional purchase for the average household, mine included. Well, for us, it’s that time again, so here I go.

The market has changed since I last looked at it. But the optical basics haven’t, so I haven’t seen any reason to abandon my trusty old binoc benchmarks. Hey, it’s good timing: If you’re playing Santa next month, you might want to heed this gig.

My goal was to see if I could find anything good for under $99. I’m talking casual, fair-weather use, for both bright and dark conditions.

But having a tight budget doesn’t mean we should be sloppy about things. To the contrary, we should be informed and calculating. So let’s start on an analytical footing.

Here’s the basic deal: Binoculars are specified with two numbers. The first is the magnification. The second is the diameter of the objective lens in millimeters; this is the lens that is on the far side of the binocs from your eyes, typically the “big end” of the binocs.

Thus, an “8x40” pair of binoculars has a magnification of eight times, and has objective lens diameters of 40mm.

Now, here’s the secret sauce: When you divide the last number by the first, you get the size of the exit pupil (the light that reaches your eyes). This corresponds to the light-gathering ability of the binocs. Bigger is better. The darker the conditions, the more this matters.

So a pair of 8x40 binocs will have an exit pupil of 5mm (40mm divided by eight).

How that plays out depends on how wide your pupils get in the dark. Endless discussions are held over this stuff, including the physiology of eyes as we age. Well, enter my first old benchmark, which you can take or leave: Any exit pupil over 7mm doesn’t seem to offer much, if any, additional benefit, but anything under 5mm is too dicey because it’s weak in non-bright conditions.

So my sweet spot is 5mm to 7mm for exit pupils, and within this range, the higher the better.

For the technically-minded, I’ll note there is a “relative brightness” factor that is a squared function of the diameter. This makes sense if you think about it, since we’re talking about circles of light here, hence surface area. So you can’t just linearly interpolate between 5mm and 7mm to get a feel for this side of things.

As for magnification, the market offers anything you can imagine. Actually, it gets downright wacky. I’ll note another personal benchmark, which you can also take or leave as you see fit: Seven to 10 power seems like a sweet spot. Any lower than that lacks punch, but anything over 10 times can be hard to hold steady.

You’ll note that we are in the range of tradeoffs. For a given size of objective lens, if you gain magnification, you lose exit pupil size. Meanwhile, the bigger you make the objective lenses, the bigger and heavier the binocs are; once you get over two pounds (32 oz) or so, the weight becomes a real factor for extended holding. There is no free lunch.

For my shopping I tried a bunch of brands. Wow; so many The Nikon Action series emerged as the best bet.

Within the Nikon Action line, I tried three popular sizes: 8x40, 7x50, and 10x50. The price range was about $70 to $95, depending on model, vendor, shipping details, availability, and so on.

My pick for general duty? 8x40. It’s great for daylight, and OK for dusk or dark.

These 8x40 glasses are wide-angle, which is nice, but anything outside the center half of the field strikes me as distorted. The stuff in the center area, however, is nice and clear. They hold their focus well, and at 27oz they are light enough to be user-friendly.

Incidentally, at night, these little guys could clearly show at least three of Jupiter’s four Galilean moons in a clear sky. (I don’t know if the fourth was in a visible position that night.) Andromeda galaxy and the Orion nebula also showed very well.

Drifting away from the “general” use context, I’ll add a footnote for my fellow space cadets:

I hefted the larger 7x50 and 10x50 models toward the night sky. Results? Very nice. Those larger 50mm lenses offer a lot more area to gather the scant light, but they add almost a half-pound of weight. My wife liked the 10x50 so much she immediately claimed it.

In summary, for those on a beachcomber’s budget, I found that there is some good stuff to be had for under $99. Mission accomplished!

Visit Ed Stephens Jr. at EdStephensJr.com. His column runs every Friday.

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