Oh boy. We pick apart your quotes to Ken Rockwell, you find someone else to quote. Funny thing is I don't think you ever really read what is said, you just yank parts out and go to it. So here we go again....
I say the average beginner asking about lenses on this forum has very little interest in edge sharpness for example nor will they or their audience ever care.
I agree, but for the millionth time, to which you never respond, this thread is not about beginners, it is about someone who is getting paid "MAJOR money" to shoot a wedding.
Please understand that.
Same with the flaw called "good" bokeh
Again with the bokeh is a flaw comments. Where, exactly where, does it say that it is a flaw?
I am going to over simplify this so hopefully it will make sense to you. If you want the real story, go take some physics classes.
In order to get an image on the focal plane (sensor or film), light passes through some kind of hole (as in a pinhole camera) and creates an inverted image on the opposite side of the hole. This works pretty well and gets pretty much everything in focus at once. There are however a couple of problems.
1) Since the hole is very small, very long exposures are required.
2) To change the image (get an object larger or smaller on the film or sensor) you have to move the hole forward or backwards by quite a large distance.
3) Controlling the image can be very difficult since you can not use too wide an angle and still have room for a shutter, film transport (or digital equipment), etc.
To solve these problems lenses were introduced. Unfortunately, even though the lenses fixed all of the above problems (much larger hole so faster exposures, 300mm lenses can be 5" long instead of 12", wide angle lenses are very possible) now we have a new problem, focusing.
For this next part, I am going to ignore convergance, divergance, difraction, and some other problems with light traveling through several glass elements, coatings, bouncing around in tubes, etc, even though they have tangable and real effects, they are not needed to understand where this is going.
The reason focusing is an issue is that as light travels through different parts of the glass it actually travels different distances and that has to be corrected. That is not an issue when you are talking about a pinhole that might be 1mm or less. It is a huge issue when you are talking about 30mm or more.The better corrected, the better the lens, the more expensive the lens.
Now an object at one distance will be different than an object at another distance. Think of it like a building in the distance. Although you can see the top and bottom of the 100 story building, the light traveling from the top takes a much longer path to get to you than the light traveling from the bottom. You can place a coke bottle on the table in front of you and although it appears the same size as the building in the distance, it is much closer so the light from the top of the bottle and light from the bottom of the bottle are much closer to the same length than it is for the building.
So in order to get the benefits, you have to deal with only some things being in focus. This is OK because that is how we precieve things anyway. Our brains relate to this very well so it is a non-issue. Images with close and distant objects all in focus at the same time seem disturbing, too busy and surreal anyway as a general rule.
So, if only certain things can be in focus at one time, other things must be out of focus. This is understood, it is part of physics, it is not a flaw, it is a design decision based on what we want to achieve.
The visual qualities or attibutes of the areas that are not in focus is called bokeh. Yes, this area is caused by a misalignment of the lenses in relation to the area in question, but it is not a flaw, it is by design, it is intentional. It can be controlled and achieved in different ways, one of which is spherical abberation. You can increase or decrease spherical abberations in the in-focus area, out-of-focus area, both or neither, and you can do it partially, totally, or not at all.
Now lenses can be taylored to specific uses, and to specific attributes. Some lenses are taylored so that the bokeh is considered more pleasing. If you think lens manufacturer's ignore bokeh why did Nikon produce two DC lenses (DC stands for Defocus Control, they allow user modification of the area that is not in focus, in other words change the bokeh)? Why does Nikon also produce the 85mm 1.4 which is specifically sold and marketed as a portrait lens know for it's outstanding bokeh?
Get it?
Allan
I'm on an international photography forum and I am having to explain the basics of photography to someone, arg! I'm going to bed.