Re: [Leica] Re: impurities in lens

[Chris Lee <chrislee@mac.com>]

Hi Dan,

Thanks for sharing the information.

It's not so much the effect of these bubbles/dust specks on optical
performance that concerned me. I was just wondering why they should be there
considering the relative high price of Leica lenses.

I have many Zeiss lenses. 4 for the G system, and 3 for the 645 system. The
lenses for the G system exhibit the same bubbles/dust specks as the Leica
lenses. However, the 645 lenses are completely free of these things, and the
glass looks as crystal clear as one can imagine. Perhaps the higher price of
the 645 lenses allows Zeiss/Kyocera to institute higher QC standards then
what they have for the G lenses. But aren't Leica lenses nearly as expensive
or perhaps more so than the 645 lenses?

Regards,   

Chris

> 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