At 5:32 AM +0000 7/8/03, olympus-digest wrote:
>Date: Tue, 8 Jul 2003 10:28:37 +0800
>From: "C.H.Ling-Accura" <chling@xxxxxxxxxxxxx>
>Subject: RE: [OM] True, or just BS? (Effect of lost lens coating)
>
>I also believe lossing of coating on back or front element will cause
>similar effect but may be in most case you will only get a small area
>coating off so with same area on front and rear element the effect on front
>lens will be less as the front glass is much larger.
>
>On the other hand I can't agree with the flare and ghosts, if you wear
>glasses you will know, a non coated glasses will have very high flare and
>ghosts in severe backlight situation and it is only one element, right? Ok,
>today most glasses are coated and you will not notice this.
I have coated eyeglass lenses for just that reason, but there is a difference
-- eyeglasses are not long, with multiple lens surfaces and baffles, all in a
black tube. Too style-challenged.
Joe
> > -----Original Message-----
> >
> > There are long answers, but here's the short answer.
> >
> > Front surface: Light never enters the lens, so cannot cause
> > flare or ghosts. Only a slight loss of light, 4% at worst. This
> > 4 0s the per-surface reflection from uncoated glass. This is
> > log2(1-0.04)= 0.06 stop, which is a negligable loss.
> >
> > Rear surface: Up to 40f the light coming out of the lens (on
> > its way to the film) is instead reflected back into the lens,
> > where it bounces around causing flare and ghosts. However, most
> > modern lenses have very good internal baffles, and the coatings
> > of internal len surfaces will have survived, so most of this
> > reflected light is simply absorbed.
> >
> > So, I bet that loss of either front or back or both coatings
> > makes little difference in practice in that one will get ghosts
> > in situations where one would already get ghosts, and flare isn't
> > likely to be much worse.
> >
> > Joe Gwinn
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