Archived posting to the Leica Users Group, 1997/06/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I have a 112mm filter for the Leitz 280mm/2.8 APO-TELYT that Leitz calls a lens protector rather than an ultra violet filter. They also say that all Leitz post-war glass absorbs ultra violet rays so calling a filter UV would seem redundant. Has anyone ever been sun-burned in an auto - through the glass. Doesnt all glass absorb UV rays? My eye-glasses are specially coated to absorb UV since they are plastic and not glass. I would be interested in all comments. Marvin Moss - ---------- From: owner-leica-users@mejac.palo-alto.ca.us on behalf of Jim Brick Sent: Friday, June 13, 1997 11:33 PM To: leica-users@mejac.palo-alto.ca.us Subject: Re: Noncoated filter At 07:46 PM 6/13/97 -0700, you wrote: >I already understand the physics of lens coatings. I was only asking for an >explanation as to why you believe that "The first surface is indeed the >most >important". I believe the opposite is true. The first surface benefits the >LEAST from lens coatings. This may expalin why as Mark pointed out some >lenses have all surfaces EXCEPT the first surface coated. > >So why do modern lenses and filters have coatings on the front surface? >There are 2 reasons: > 1. If a filter is added to a lens, or if filters are stacked, then the >first surface is no longer the first surface. > 2. Less importantly there will be light reflected from a surface other >than the first surface traveling towards the first surface (away from the >camera). Lens coating on the first surface will minimize the amount of this >light reflected back towards the film by the first surface. > I was very tired last night and couldn't sit, write, & think. It may not be any better tonite. The HIGHEST INTENSITY of light hits the first surface. An uncoated first surface will not only reflect approximately 4% of this light away, but when the 96% hits the next glass-air surface, it will reflect some light back toward the first surface, which in turn, being uncoated, will reflect more of this stray light toward the film than if the first surface is coated. Causing flare. I guess I am trying to think about this as the first surface is where the most light intensity is, therefore bigger portions of everything good and bad happens. As the light progresses through the elements and aperture, it's less intense possibly causing less trouble. As always, I could be wrong and if so, I am more than willing to learn. Jim