Nice article, but variation in optical quality is very well known inside the industry. This applies to everything from telescopes, microscopes, camera lenses, etc. One of the very few areas where you have little to no variation in a final product is military optics. To paraphrase what I was once told "Do you want to find out that the optics in that nuke carrying Tomahawk are only 98% perfect?"
However to get to that 100% "perfect" rate of installed optics in military hardware, the intentional "spoilage" rates can be very high. From blocks of raw glass to the final product before cylinders of glass are even cut, to the final assembled product, you might have a spoilage rate of over 90%.
When you buy a premium lens from Canon, Zeiss, or whomever, what you are paying for - or supposed to be paying for - is a product that will have performance in specified range. for example, I would of loved to see lensrentals do a similar article on cheaper lenses. For example, while they are well praised today, I remember when the Nikon Series E lenses first came out ( yeah, I know, dating myself here
), there were some real dogs. Not any specific lens, but for example, my old 50mm Series E is not that good, although many people praise it. I later bought a good, used, plain old 50mm F1.4 Nikkor and what a difference in sharpness. However my old 135mm Series E is an amazingly good lens.
So the more you pay, it's not always a lens that performs that much better, although it may and should be, but rather you are paying for the fact somebody before you did some serious quality control (at least we hope).
One other issue I remember is getting what you pay for. I remember talking to a telescope manufacturer over 20 yers ago, and he told me how only certain brands of eyepieces were exactly as they were labeled. for example, if you bought his brand - at least according to him, and the eyepiece was labeled "10mm), then is was always 10mm, right on. Other brands might be 11mm in reality, but labeled 10mm, and others still may be very inconsistant, one run all being around 9.7mm, and another run all being 10.7mm, etc.
this came to light when binoviewers in telescopes became very popular - oh about ten years ago. At that time, people found out the hard way that you needed premium quality eyepieces because many of the less expensive brands were not useable because even though they were labeled one thing, they might be another.
Often makes me wonder on some the cheaper camera brands and lenses, especially in the past if a lens say 135mm, is it really exactly 135mm, or something else? Case in point, up here in Canada those Samyang 8mm fisheye lenses are sold by Henry's under the Opteka brand, but they are labeled 6.5mm, not 8mm. At least the one I own says 6.5mm. So which one is right. In any case, at least for that particular lens, I am very happy with it. But still, makes me wonder some days...
