The last couple of days I spent some time wading through the confusing Pentax lens naming conventions. Found some interesting information and also some misinformation (event though I am sure it was well intended). A google search revealed much information, some very detailed but difficult to follow. I found mosphotos.com the easiest to follow:
Pentax K-Mount Lenses Explained: The differences between various Pentax lens series
Some web sites claim that the old film lenses are not as sharp as the digital lenses because digital sensors require a sharper image. I found this view not to match with line pairs testing and it seems as if some fine grain films may still outperform the mainstream digital sensors.
From the many sources I concluded (rightly or wrongly) that the digital lenses have a coating on the rear elements to minimize/eliminate back scatter reflection of light bouncing off the sensor. I did an experiment and applied a DIY anti glare treatment on my 2x converter, and low and behold the light transmission seemed better, by about 1 stop compared with my 1.4x converter. The difference was even noticeable in the view finder, even though any backscatter from the sensor was obviously not at play when I saw the difference in the view finder. It did not change the perceivable sharpness however.
Anybody else with similar experience? If confirmed, this will bring a new dimension to my old film lenses and they will all undergo some "treatment" on the rear element :-) No pun intended...
Theuns
Have fun!!!
Originally posted by tdvanniekerk 
Post #1 by Dlanor Sekao
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