My word... What a hornet's nest I've stepped into here.
The 'difference' between refraction and reflection is ... drum beat ... the CRITCAL angle!!! If anyone doesn't understand this ... a study of Snell's law is in order. (BTW - I was NOT disagreeing with your statement).
I will make my statement again: An optical system (lens, if you will), CAN be improved by the addition of a supplementary lens. Perhaps the Hubble was not the best example - but it certainly WAS an example of improvement ... not "perfection", but it was IMPROVED.
I do NOT want this to degrade to a "Win- Lose" argument (if it has not already). I am trying to stay on-track, with what little I know about lens design and production. If anyone chooses to use bellows, extension tubes,`Proxar' supplementary lenses, saran wrap or Mel's Mystery Smoke - that is fine with me.
Now ... backing up a little...
The first step in the design of every camera lens is to define the desired properties. A list of design parameters will be established: Field and format; focal length; maximum and minimum field distance; resolution (MTF, now); acceptable aperture range; size and mechanical considerations - and a HOST of others.
The design is done to satisfy these parameters - and for ALL intents and purposes, the lens manufacturers DO. The Zeiss design crew certainly DOES - it will be rare day in a frozen hell when they slip so far as to condone a whole line of supplementary lenses, such as Proxars, and not know what effect their use has on the performance of their lenses.
We are discussing the use of lenses beyond their original design parameters - through the use of either supplementary lenses, OR extension tubes / bellows. Supplementary lenses "change" focal length to something other than required in the original design specifications; tubes situate the lens further from the film plane than originally intended. In either case, the performance of the lens is affected.
That effect will be difficult - in my book, too difficult to be of ANY value - to determine without a critical analysis of the lens design: it certainly cannot be left to a blanket, "All close up lenses WRECK the overall optical system - lens or mirror ... or whatever ... performance".
This might be of interest - from Lens Testing 101: In examining a lens for resoultion on an optical bench, what media is used as a focal plane?
BTW - Introducing another element to convert a single element to a cemented (n.b. "cemented - together) pair WILL reduce the amount of light transimitted - with *no* additional relfective surfaces - see "T" stops.
The 'difference' between refraction and reflection is ... drum beat ... the CRITCAL angle!!! If anyone doesn't understand this ... a study of Snell's law is in order. (BTW - I was NOT disagreeing with your statement).
I will make my statement again: An optical system (lens, if you will), CAN be improved by the addition of a supplementary lens. Perhaps the Hubble was not the best example - but it certainly WAS an example of improvement ... not "perfection", but it was IMPROVED.
I do NOT want this to degrade to a "Win- Lose" argument (if it has not already). I am trying to stay on-track, with what little I know about lens design and production. If anyone chooses to use bellows, extension tubes,`Proxar' supplementary lenses, saran wrap or Mel's Mystery Smoke - that is fine with me.
Now ... backing up a little...
The first step in the design of every camera lens is to define the desired properties. A list of design parameters will be established: Field and format; focal length; maximum and minimum field distance; resolution (MTF, now); acceptable aperture range; size and mechanical considerations - and a HOST of others.
The design is done to satisfy these parameters - and for ALL intents and purposes, the lens manufacturers DO. The Zeiss design crew certainly DOES - it will be rare day in a frozen hell when they slip so far as to condone a whole line of supplementary lenses, such as Proxars, and not know what effect their use has on the performance of their lenses.
We are discussing the use of lenses beyond their original design parameters - through the use of either supplementary lenses, OR extension tubes / bellows. Supplementary lenses "change" focal length to something other than required in the original design specifications; tubes situate the lens further from the film plane than originally intended. In either case, the performance of the lens is affected.
That effect will be difficult - in my book, too difficult to be of ANY value - to determine without a critical analysis of the lens design: it certainly cannot be left to a blanket, "All close up lenses WRECK the overall optical system - lens or mirror ... or whatever ... performance".
This might be of interest - from Lens Testing 101: In examining a lens for resoultion on an optical bench, what media is used as a focal plane?
BTW - Introducing another element to convert a single element to a cemented (n.b. "cemented - together) pair WILL reduce the amount of light transimitted - with *no* additional relfective surfaces - see "T" stops.