Archived posting to the Leica Users Group, 2000/06/29
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Since this thread started back a while ago, I started to notice glass, in its many incarnations, and it seems that ALL glass has bubbles in it to some degree- I have seen it in window glass, bottles, glasses (drinking type) and just about any place you look. Exceptions seem to be the float type plate glass, and perhaps it is raise to a high enough temperature that it becomes fluid enough that bubbles can escape. Optical glass, however, is not made in huge batched, but in relatively small quantities, and according to the Brittannica, is cooked for a fairly long time to make sure it is thoroughly homogenous, and then it is cooled slowly so as to minimize areas of stress within the glass. The bubbles pretty much should not effect the image as they only occlude the rays passing through that point, and being optically dense, would not scatter light to contribute to flare. The area they occlude would be insignificant in calculating open aperture- unless they were so many that they blocked a statistically significant amount of light. For all practical purposes, small bubbles, or even small specks of dust will mot harm the image; it would take something like a smear of grease or fingerprint oil- or someother diffuse obstruction to introduce the flare and loss of detail. For me, it has become less important to get every little tiny speck of dust off the lens, as it intrudes on my looking for interesting subjuects! So- quit looking so much into the front of your cameras looking for fly spots and dingleberries- and spend more time looking through the viewfinder!! :o) Dan - ----- Original Message ----- From: Jim Brick <jimbrick@photoaccess.com> To: <leica-users@mejac.palo-alto.ca.us>; <leica-users@mejac.palo-alto.ca.us> Sent: Thursday, June 29, 2000 1:49 PM Subject: [Leica] Re: impurities in lens > At 01:04 PM 6/29/00 -0700, Chris Lee wrote: > > > >How can a bubble in a lens improve image quality? > > > >Regards, > > > >Chris Lee > > It cannot. > > The best glass available for lens making used to produce bubbles when > cooling, or something to that effect. It was therefore said that the best > glass had bubbles. So if your lens had a bubble, it was high grade optical > glass. > > Jim