Archived posting to the Leica Users Group, 2003/05/07

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Subject: RE: [Leica] Re: Re: optics for digital
From: "Austin Franklin" <darkroom@ix.netcom.com>
Date: Thu, 8 May 2003 02:09:10 -0400

Hi Jerry,

Actually I don't know squat about the Rolleiflex Optical Glass Film Plane in
the Rolleiflex F or the Tele Rollei, and they really don't have much to do
with this subject as far as I know.  The only reason I know squat about
anti-aliasing filters in front of CCD sensors is I've designed digital image
capture devices, and had to specify the frequencies of the filters, and test
different filters.

The anti-aliasing filters used in front of CCD sensors are typically simply
diffusers of some kind, made via one of many different techniques.  The ones
I am familiar with for high resolution digital imaging sensors can use
lithium niobate, which, from my understanding, is a very small crystalline
structure that is very uniform and can be controlled such that the amount of
diffusion is easily controlled.  You might want to ask Richard Knoppow, or
some physicist who specializes in optical materials, they might be more
helpful.

Austin


> -----Original Message-----
> From: owner-leica-users@mejac.palo-alto.ca.us
> [mailto:owner-leica-users@mejac.palo-alto.ca.us]On Behalf Of Jerry
> Lehrer
> Sent: Thursday, May 08, 2003 1:42 AM
> To: leica-users@mejac.palo-alto.ca.us
> Subject: Re: [Leica] Re: Re: optics for digital
>
>
> Jim
>
> Ah yes!  Since Austin is intimately familiar with the Optical Glass
> Film Plane in the Rolleiflex F and Tele Rollei, maybe he can tell us
> how the glass will affect the MTF of the lenses image.
>
> Jerry
>
> Jim Brick wrote:
>
> > At 07:57 PM 5/7/2003 -0700, Jerry Lehrer wrote:
> >
> > >Jim
> > >
> > >Congratulations!   You did it again, without resorting to mysticism.
> > >
> > >I wondered why there were different requirements for digital vs.
> > >film lenses.  Now what does a low pass cut-off filter look like?
> > >
> > >Jerry
> >
> > They look like clear class, no density, no color. But they
> somehow reduce
> > the MTF frequency that it will pass.
> >
> > Perhaps Austin knows how it works... ?
> >
> > Jim

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