Good morning, William Markey;
Minolta lenses. Let's hit the ROKKOR versus the ROKKOR-X bit first:
There is no real difference in the Minolta ROKKOR and ROKKOR-X lenses. They were both made on the same production line using the same parts. The only real difference is that the ROKKOR-X versions were supposed to receive some extra quality control checking to qualify for the "M Tag Warranty Program" in North America; the USA and Canada. The "-X" was to indicate "Export." This was done at the request of the Minolta-USA people in Ramsey, New Jersey. You might notice that there are very few ROKKOR-X lenses available in Europe and other locations. As the USA market was a large part of the total sales for Minolta, this was not an unreasonable thing. You might also notice that in the 1980's, the -X was dropped from the ROKKOR lenses.
The original Minolta manual focus SLR lens mount was first called the SR mount. Mechanically, it never really changed as far as mounting a lens goes. The only thing was, first, the addition of the Meter Coupling (MC) tab system to link the aperture to the TTL light metering system with the SR-T series. Second, later they added the second tab to indicate the lens minimum aperture (f/16, f/22, f/32) to the TTL light meter system, and it is called the MD tab or MD lens, and it is used with the bodies that had a full Program Mode or automatic mode of operation, such as the X-700. Actually, you can use any SR lens with the X-700 in the program mode if you fudge a little. It is amazing what the X-700 "final exposure check" just before the shutter is released will do.
One difference between the MC and the MD lenses is the lens aperture leaves. The MD leaf is a bit lighter than the equivalent MC leaf. This is to help with the electro-mechanical system stopping down the lens to the taking aperture in the minimum time with minimum bounce. This is very beneficial with the X-700 TTL light metering system and its "final exposure check." The advantage probably will show up mainly when you are stopping down to f/11 or smaller from wide open.
All of the Minolta SR lenses were anti-reflection coated, most of them at least double coated. As I recall (almost 50 year old memory here), the original Minolta SR lenses introduced at the time of the SR-2 may have been single coated, but by the early 1960's, they were at least double coated, so they could qualify as "multi coated." Minolta had a very vigorous development program for lens coatings. They also improved the lens coatings when they felt there was merit in doing so, and did not wait until a "model year end" or change to improve the coatings on the lenses in production. The MC lenses are indeed also Multi Coated, but so were the SR. The MD lenses coatings are even better. As mentioned, their development program in lens coatings was aggressive. They did good work.
Optically, once we get to the late 1960's, the prime lens design methods were pretty mature. In the single focal length lenses, you will not really find a major improvement in lens design as shown on the negative from the late 1960's to the late 1980's. Incremental improvements, yes, but no major strides forward. Yes, there are real improvements in the anti-reflection coatings, as mentioned earlier.
The question of the Celtic lens series has come up. Optically, these lenses were actually pretty good, in many cases being slightly simpler and older lens designs, but with more modern refractive index glass and, again, the improved lens coatings. They also did use more plastic in the barrels to achieve lighter weight and lower manufacturing costs. Those developments in the use of plastics may have been a proving ground for developments in Minolta lenses later.
Yes, this brings us now to the topic of the "build quality" of the ROKKOR lenses and the addition of plastics in the MD series of lenses. Yes, the use of plastic in the MD lenses is controversial, but those lenses are lighter in weight, and they were able to hold down the cost of the lenses. Again, this work with various high density polymer plastics seems to be another element in the development of lighter weight components and lighter lenses.
Having reached the end of the Minolta manual focusing lenses at this point, we can now look at what they did with the technology they developed. The coming Minolta "A" mount for the Automatic Focusing Maxxum/Dynax/Alpha camera bodies did require lenses that had very light weight components to allow the control systems to quickly move the lens elements to the point of best focus. The apertures also had to be light weight to allow the rapid closing and re-opening of the lens. This also reduced the amount of power required of the battery system in the camera body. There are some very good reasons for the development of these lighter weight components that many may call the "cheapening" or "lowering of the build quality" because they used high density plastics. That lighter weight meant that they could build a system that would respond in a time period acceptable to the person whose finger was on the shutter release button. Was this a compromise? Perhaps it depends on what you prefer to emphasize. If speed of focus is not a problem, then perhaps it was. If recognizing that an automatic focusing system with a battery of a finite capacity powering that system was in use, then it begins to make some sense.
If we look at the use of computers in lens design, the major steps forward have been in the design of very good zoom lenses. Many zoom lenses today are the equal of the prime lenses of the 1970's in the quality of the image on the negative, but it did take 25 years or so to catch up.
While I have focused on Minolta mainly here, these comments actually apply to lens technology across the entire industry. Where one manufacturer came up with a technique that improved a quality, the other manufacturers did determine how that technique was done, and implemented it or something very much like it in their own lenses. We are the ones who have benefited with the lenses available to us today.
