Based on over five years of intensive testing of optics for birders, and extensive conversations with others involved in the same endeavor, I can make this statement:
There is often, too often, a noticeable, visible, variation in optical quality between supposedly identical units of the same make and model of binoculars or spotting scopes. Sometimes, especially in less expensive models, the variation in quality between individual units of the same model can be more pronounced than the variation in quality between the best examples of two different models! What is more, in my experience, variation in quality between supposedly identical units exists at every price point. It is certainly more prevalent in the lower price ranges, but there is some variation even in the most expensive, and supposedly the best, most uniform, optics.
I ran the gist of this argument by a cross-section of the manufacturers for response (for direct quotations and digests see the next issue), and some of them actually admitted the truth of it‹always, of course, with the proviso that the variation was in someone else's line, not their own.
Should a certain amount of unit to unit variation surprise us? No. Not if you think about it.
Think of the number of precision parts in the average binoculars or spotting scope (20 in the simplest, 2 to 3 times that number in the more complex designs). Think of the number of glass, metal, and plastic surfaces that must be critically shaped, molded, or cut and polished. Think of the number of elements that must be perfectly aligned in three dimensional space. Think of the potential for error.
Then consider this: each individual piece is manufactured to a certain tolerance (a range of acceptable values) set by the designers so that variation in any one element will not degrade the performance of the system below an acceptable level. In most units, the variations in tolerance for each element average out to produce optical quality in the whole system that is very close to what the designers intended. In a certain percentage of units, however, the tolerances may all be on the small side of average, and the unit may well perform significantly better than its average siblings. Unfortunately, the opposite is equally true. If you get a unit where all the tolerances are on the wide side, the net result will be performance that is at the bottom range of what the designers would accept, or, in a worse case, visibly below the performance the designers intended.
Should a certain amount of unit to unit variation concern us?
It concerns me, since I can not be sure that the unit I am testing is a fair representation of the average performance of the design. Worse, I can not be sure that the unit I test and the unit you buy will have the same optical quality.
In the lower price ranges, say anything below $300, unit to unit variation is a real concern. At those prices, manufacturers are pushing the limits of what can reasonably be done. They have to allow more variation. Some units, while they might meet the manufacturer's acceptable performance limits for the product, do not meet mine. Some units, of otherwise very fine products, I would not want to own!
Even in the highest priced binoculars, where stricter quality control measures should insure that no individual unit ever falls below the design goals for the model (no lemons!‹that is part of what you are paying for when you pay $1000 for binoculars or a scope), I am convinced that there will be still be individual units which push the upper limits of the design's possibilities (cherries!)‹and I am convinced that you can see the difference between, say, a cherry Leica (or Zeiss, or Swarovski, or Swift, or Nikon, or Celestron, or any other brand you can name) and an average unit of the same model.
I know that many optical designers would not agree.
To quote the people at Leica: "The optical and mechanical parts are designed in such a way to ensure that tolerances remain within limits that do not have any influence on the functions of the finished system (e.g. parameters influencing image quality are designed so that deviations are below the resolving power of the human eye)."
What The Eye Can See...
It is that last part about "deviations are below the resolving power of the human eye" that I would take issue with. As far as I know, we are still working with theoretical resolution limits for the human eye, based on purely physical factors. No statistical study, based on actual human eyes, has ever been done, and, if it has, certainly no study that included the factor of trained verses untrained eyes. (Such a study would be next to impossible to design and implement, and of little actual value in establishing true limits for the eye's resolution anyway.) In fact, no one knows just what any individual human eye is or isn't capable of seeing, and no one knows how sensitive the trained human eye might be to variations in image detail, contrast, color fidelity, etc. What we see is not solely the result of physical factors. The image we see is built up in the brain from data supplied by the eye over time. With binoculars, it is built up from data supplied by two different eyes, from two slightly different angles, over time. A lot of image processing goes on in the brain that, I am convinced, extracts more information from the data than physical factors would suggest it could contain. Training the brain, by repeatedly demanding close analysis of the image, only increases its processing capabilities. In my own experience, because I know what I am looking for, I can detect very subtle defiances in optical quality. I can certainly identify a cherry when I see (or rather, "see through") one.
What Are We Paying For?
Now, it would be nice to think that cherry performance is what we are paying for when we buy $1000 optics. It is not. What we are paying for is, dare we say it, average superior performance‹within acceptable limits for a superior product. We may get better than average superior performance, but that is, as they say, the luck of the draw. Chances are that we will get average superior performance. We may, indeed, by the luck of the draw, get below average superior performance, but, at that price point, it should still be superior performance.
If you pay $1000 and get a unit that does not give you clearly superior performance, then something is seriously wrong, and you have legitimate reason to complain.
If, on the other hand, you pay $1000 for optics that are clearly superior, and then find that your friend or acquittance has an identical unit that is even better‹ well‹may it never happen to you!
Let The Buyer Be Aware
If you are shopping for binoculars in the $200-$300 price range, more care is required. The best way would be to find a cooperative local dealer who would let you compare several units of the same model and take the one that looked best to you. You should expect to pay for that privilege‹certainly by paying the slightly higher price your local dealer may charge when compared to mail order, and perhaps even a bit over for the time and effort expended by the sales staff. If you were convinced you got the best example of your chosen optics available at that particular store, wouldn't that be worth an extra $20 to you? If you buy mail order, check your purchase carefully when it arrives. Put it through the Consumer Tests below. If you are suspicious, do not, I repeat Do Not, take it to your local dealer to compare it to his off the shelf unit, unless you are ready to buy his, and compensate him for his time and effort, if the local example is clearly superior to the one you got through the mail. If you can borrow an identical unit from a friend for comparison, well and good. Then you would have clear basis for returning the mail order optics. Most mail order dealers accept returns.
Defective Merchandise
None of this is meant to address obviously defective merchandise. An occasional lemon is apt to slip through even the tightest quality control. Then too, even if every unit left the factory in perfect order, that is no guarantee that your particular unit will reach you in the same condition. Optics are often shipped half way around the world by, as the saying goes, common carrier. They often arrive at your home or the local dealer via UPS. The box may pass through 50 pairs of hands between the time it leaves the factory and the time you open it. It is not unreasonable to expect that a certain percentage of optics are going to be dropped somewhere along the way; stacked three tiers too high; stored at too high or two low a temperature for too long; bounced off a bulkhead; left vibrating for fifteen minutes on a fork lift while the driver gets coffee; generally shaken, rattled, and rolled until something gives inside. There is no doubt that most of the unit to unit variation I have seen can be attributed to optics that are slightly out of wack‹a single element has become decentered in its mount, the prisms have slipped, the body has gotten twisted somehow so that everything isn't lined up just exactly right.
There is simply no way that binoculars designed to sell for under $100 can be designed to be as durable or as shock resistant as $250, or $1000, binoculars. You have to expect that a higher percentage of the less expensive binoculars will reach the consumer (you) in worse shape than they left the factory. Therefore, what was said about shopping locally for $200 binoculars above goes double for $100 binoculars. Examine inexpensive binoculars carefully before you take them home. If at all possible, look at more than one sample of the model you are buying. Test $100 mail order binoculars thoroughly before you decide to keep them.
Always, always carefully check the alignment of any new binoculars (see the Test Your Own article in the next issue). In the past 4 years I have seen binoculars at every price point, including the $1000 roof prisms, come out of the box misaligned badly enough so that I would not want to use them.
Trust Your Instincts!
Finally, trust your instincts. Vision is our primary sense‹our primary way of gathering information about the world around us. We are very sensitive to abnormalities in our visual data. When something is wrong with what we are seeing, we may not be able to say what it is, but we do know that something is wrong! This sense of visual rightness extends to our use of optics. If the optics are distorting, degrading, or otherwise introducing an abnormal amount of abnormality into the visual data stream, we will know. It may be no more than a nagging feeling of wrongness‹a suspicion‹or even a simple reluctance to use the optics in question. Trust your instinct. If, after a few weeks of use, you feel that something is not right with your new optics, and, once aware of that feeling you can't convince yourself otherwise, then chances are there really is something wrong. Have them checked by a more knowledgeable person. Run them through the tests in the Test Your Own piece in the next issue. Borrow another supposedly identical unit and compare the two critically. If you can identify the problem, fine, seek recourse from the store or the manufacturer. If you can't identify the problem, and you still are not happy with the optics, try a letter describing your experience directed to Customer Service at the manufacturer. Ask if they would have the optics checked out for you.
Good Will
I know, or have dealt with, a lot of people in the optics industry. My overall impression is that they are people of good will, doing their best to provide a quality product at a reasonable price, while making enough money to pay a living wage to everyone involved and to make a reasonable return to their investors. That is not an easy task. Most of them are as frustrated with quality control issues as any consumer, and many of them more frustrated. Take that into account when dealing with them‹especially the good will part. Approach what you see as quality control problems with assumption that you are dealing with people of good will. Try to avoid an adversarial relationship. You want to own a quality product, the best binoculars or spotting scope your money can buy. They want exactly the same thing, and in addition, they want to be the ones to make and sell it to you, and to a lot of people you might know. You are all on the same side. Remember that!
In addition to seeking response to the general quality control issue, I also asked the manufacturers to outline the recourse a consumer has when they are dissatisfied with a product. Responses, or a digest there-of, will appear in the next issue of BVD.
Unit to unit variation, whether caused by a fortuitous alignment of tolerances or by obvious defects in optical alignment, is, as far as I am concerned, a fact. It is there, and it is something that we must deal with as consumers. Arm yourself with awareness and some basic skills. With good will on all sides and some patience, there is no reason not to end up with the better view we all desire.