[opendtv] Re: Image quality
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 10 Nov 2005 20:52:08 -0500
Mark -
I'm afraid I am not familiar with that formula and don't understand it.
Could you give some typical numbers?
For instance I'd think lamda would be a very small number as the
wavelength of visible light.
- Tom
Mark Schubin wrote:
>>"high quality out of focus picture" does seem humorously
>>oxymoronic to me.
>
>
> Indeed! But it might be worthwhile for HDTV shooters to consider lens
> diffraction and other optical foibles that can degrade images.
>
> Here is the formula for monochromatic diffraction-limited modulation transfer
> function:
>
> MTF = 1-(1.22*f*lamda*lp/mm)
>
> where f is the numerical aperture,
> lamda is the wavelength of light, and
> lp/mm is the number of line pairs per millimeter (nominally the number of
> lighter and darker points per scanning line divided by two divided the width
> of the imager)
>
> Because it is a "one-minus" equation, the only way to get 100% MTF is to have
> either zero input frequency (the whole screen is one shade) or a zero
> numerical aperture (the lens is infinitely large).
>
> We do a lot of dancing around about 1920 x 1080 when it's becoming less and
> less likely (with smaller and smaller imagers) that there will be any
> significant energy at the high end of that.
>
> TTFN,
> Mark
>
>
>
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