25 meters and a number plate? Sounds quite familiar. I've been promoting the following for many years.
Also, and more importantly, do you know Rafael Chamon of Madrid? He's a bino guy--and the only person I've seen on the Internet with a clue about true collimation. He has not answered my email lately, and I'm worried about him.
Cheers,
Bill :hi:
*****
7 "I WANT AN 'AUTO-FOCUS' BINOCULAR; MY BROTHER HAS ONE”
The Fallacy: This represents a great advance in modern optics.
The Fact: There are no non-electronic auto-focus binoculars on the market.
Despite what you have read, been told, or think you have experienced for yourself, there are no non-electronic “auto-focus” binoculars . . . period!
“But how can that be; I saw it myself?”
Focusing a traditional film camera for a distance from 5- to 500 feet, you might turn the lens half a turn. Focusing from 500 feet to 5,000,000,000 miles, however, may require only a 1/16th of a turn. The reason? Depth of field.
To illustrate: hold your hand one foot in front of your face and concentrate until you can see the swirls in your fingertips. Then, while keeping your fingers sharply focused, try to look at a wall or some object one foot farther away. Oops! It can’t be done. We can’t focus on two objects simultaneously—separated, in our line of sight, by only a foot—at close range.
Next, look at trees or buildings a mile or more distant. Notice that although some of those trees or buildings may be separated by more than 200 feet, along your line-of-sight, they’re all in sharp focus. Distance and depth of field make the difference.
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Photo, Illustration, or Comment 2 photos illustrating the last two concepts
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Most handheld binoculars of moderate power, when focused for a distance of 80 yards or so, will provide reasonably good imagery up close (~40 feet) and at infinity. They must, however, be refocused if they’re to provide optimum clarity at either extreme. Yes, so focused, you will be able to see the trees on the horizon and the license plate on the car across the street—possibly making you believe you have an “auto-focusing” binocular. However, if you want to see the leaves on those trees or the dirt specks on the license plate, you must refocus.
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Photo, Illustration, or Comment Photo Illustrating Depth of Field
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Some companies market binoculars that don’t have a focus mechanism, supporting the notion that no focusing is required. The real magic here is in the ad campaign and not the binocular. These instruments force the user's eyes to adapt to their fixed-focus setting. This can lead to eyestrain, headaches, and less than crisp imagery at all distances.
Furthermore, without the ability to focus, there is no way to compensate for the observer’s different dioptric strengths, and few are the people with perfectly matched dioptric strengths. There is a three-diopter difference in mine. Do you know your settings?
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Photo, Illustration, or Comment Illustration of how eye muscles work and that eyes are rarely perfectly matched
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For a time, Celestron marketed a line of fixed-focus binoculars—which the others should more correctly be called—but they had the integrity to market them as "fixed-focus" instruments and nothing more. In that case, the responsibility for buying an acceptable product falls entirely on the consumer.
On a number of occasions, people have assured me they could see just as good, or “better,” with a fixed-focus product as they could with any “so-called quality binocular” made. If they were happy, I must be happy for them. Still, their assertion relates more to what they don’t understand or appreciate about what a binocular should do for them than actual empirical performance. Even so, let’s try to understand why they feel this way, without throwing Uncle Ernie under the bus.
A person might grab his binocular to see who it was that just drove slowly past his house. He doesn’t notice that the burgundy car looks purple (with a yellow/green fringe on the right side), that the image starts getting soft 1/3 of the way off-axis, or that the binocular is out of collimation and he has to use the limits of his spatial accommodation to achieve an acceptable image.
That poor quality binocular told him what he wanted to know; his needs were met. Would he have noticed the difference had he been using a Swarovski or Leica? Probably not. Physics never takes a back seat to opinion. But, it’s opinion—not physics—that make cash registers ring!
