Re: ATM "Diffraction Limited" a definition

[PFAFF2@delphi.com (Robert C. Pfaff)]

>> From:          Andy Hochstetler <andyhoc@mindspring.com>
>> To:            "'ATM List'" <atm@shore.net>
>> Subject:       Re: ATM "Diffraction Limited" a definition
>> Date:          Mon, 17 Feb 1997 17:58:09 -0000
>> Reply-to:      Andy Hochstetler <andyhoc@mindspring.com>
>
>
>> I wanted to better understand this topic, so...out of sheer curiosity, I 
>> looked up the term diffraction limited in the McGraw-Hill Dictionary Of 
>> Scientific and Technical Terms, 5th ed.
>> 
>> It gives the following definition:
>> 
>> "Capable of producing images whose separations are as small as the 
>> theoretical limit imposed by diffraction effects."
>> 
><analysis of size of Airy disk snipped>
>
>Andy,
>
>As your analysis showed, a clear round aperture with perfect
>transmission characteristics gives a diffraction spot and a series of
>rings whose size is related to the wavelength of light divided by the
>diameter of the aperture.   Thus for a given wavelength, the diameter
>of the spot and rings decreases with increasing aperture.  For any
>size perfect round aperture, 84% of the light will be in that
>central spot and the rest will be in the rings. 
>

>Good Observing,
>Alan
>

I am not sure if I understood what you are saying but my understanding
is the the diameter of the diffraction spot decreases with decreasing
f ratio. That means a 2" f4 mirror and a 100" f4 mirror will
have the same size diffraction spot. The 100" mirror will have much
greater resolving power because of greater focal length.
More focal lenght gives more magnification at the same f ratio
enabling you to separate the spots. 

Bob Pfaff